AD603SQ/883B2 [ADI]

Low Noise, 90 MHz Variable Gain Amplifier; 低噪声, 90 MHz可变增益放大器
AD603SQ/883B2
型号: AD603SQ/883B2
厂家: ADI    ADI
描述:

Low Noise, 90 MHz Variable Gain Amplifier
低噪声, 90 MHz可变增益放大器

模拟IC 信号电路 放大器
文件: 总24页 (文件大小:556K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
Low Noise, 90 MHz  
Variable Gain Amplifier  
AD603  
The decibel gain is linear in dB, accurately calibrated, and stable  
over temperature and supply. The gain is controlled at a high  
impedance (50 MΩ), low bias (200 nA) differential input; the  
scaling is 25 mV/dB, requiring a gain control voltage of only  
1 V to span the central 40 dB of the gain range. An overrange  
and underrange of 1 dB is provided whatever the selected range.  
The gain control response time is less than 1 μs for a 40 dB change.  
FEATURES  
Linear-in-dB gain control  
Pin-programmable gain ranges  
−11 dB to +31 dB with 90 MHz bandwidth  
9 dB to 51 dB with 9 MHz bandwidth  
Any intermediate range, for example −1 dB to +41 dB  
with 30 MHz bandwidth  
Bandwidth independent of variable gain  
1.3 nV/√Hz input noise spectral density  
0.5 dB typical gain accuracy  
The differential gain control interface allows the use of either  
differential or single-ended positive or negative control voltages.  
Several of these amplifiers may be cascaded and their gain  
control gains offset to optimize the system SNR.  
The AD603 can drive a load impedance as low as 100 Ω with  
low distortion. For a 500 Ω load in shunt with 5 pF, the total  
harmonic distortion for a 1 V sinusoidal output at 10 MHz is  
typically −60 dBc. The peak specified output is 2.5 V minimum  
into a 500 Ω load.  
APPLICATIONS  
RF/IF AGC amplifiers  
Video gain controls  
A/D range extensions  
Signal measurements  
The AD603 uses a patented proprietary circuit topology—the  
X-AMP®. The X-AMP comprises a variable attenuator of 0 dB  
to −42.14 dB followed by a fixed-gain amplifier. Because of the  
attenuator, the amplifier never has to cope with large inputs and  
can use negative feedback to define its (fixed) gain and dynamic  
performance. The attenuator has an input resistance of 100 Ω,  
laser trimmed to 3ꢀ, and comprises a 7-stage R-2R ladder  
network, resulting in an attenuation between tap points of  
6.021 dB. A proprietary interpolation technique provides a  
continuous gain control function that is linear in dB.  
GENERAL DESCRIPTION  
The AD603 is a low noise, voltage-controlled amplifier for use  
in RF and IF AGC systems. It provides accurate, pin-selectable  
gains of −11 dB to +31 dB with a bandwidth of 90 MHz or +9 dB to  
51+ dB with a bandwidth of 9 MHz. Any intermediate gain  
range may be arranged using one external resistor. The input  
referred noise spectral density is only 1.3 nV/√Hz, and power  
consumption is 125 mW at the recommended 5 V supplies.  
The AD603 is specified for operation from −40°C to +85°C.  
FUNCTIONAL BLOCK DIAGRAM  
8
6
1
2
VPOS  
VNEG  
GPOS  
GNEG  
SCALING  
REFERENCE  
PRECISION PASSIVE  
INPUT ATTENUATOR  
FIXED-GAIN  
AMPLIFIER  
7
5
VOUT  
FDBK  
V
G
6.44k*  
GAIN-  
AD603  
CONTROL  
INTERFACE  
694*  
20*  
0dB  
–6.02dB –12.04dB –18.06dB –24.08dB –30.1dB –36.12dB –42.14dB  
3
4
VINP  
R
R
R
R
R
R
R
2R  
2R  
2R  
2R  
2R  
2R  
R
COMM  
R-2R LADDER NETWORK  
*NOMINAL VALUES.  
Figure 1.  
Rev. H  
Information furnished by Analog Devices is believed to be accurate and reliable. However, no  
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other  
rights of third parties that may result from its use. Specifications subject to change without notice. No  
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.  
Trademarks and registeredtrademarks arethe property of their respective owners.  
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.  
Tel: 781.329.4700  
Fax: 781.461.3113  
www.analog.com  
©2007 Analog Devices, Inc. All rights reserved.  
 
AD603  
TABLE OF CONTENTS  
Features .............................................................................................. 1  
Programming the Fixed-Gain Amplifier Using  
Pin Strapping............................................................................... 12  
Applications....................................................................................... 1  
General Description......................................................................... 1  
Functional Block Diagram .............................................................. 1  
Revision History ............................................................................... 2  
Specifications..................................................................................... 3  
Absolute Maximum Ratings............................................................ 4  
ESD Caution.................................................................................. 4  
Pin Configurations and Function Descriptions ........................... 5  
Typical Performance Characteristics ............................................. 6  
Theory of Operation ...................................................................... 11  
Noise Performance ..................................................................... 11  
The Gain Control Interface....................................................... 12  
Using the AD603 in Cascade ........................................................ 14  
Sequential Mode (Optimal SNR)............................................. 14  
Parallel Mode (Simplest Gain Control Interface) .................. 16  
Low Gain Ripple Mode (Minimum Gain Error) ................... 16  
Applications Information.............................................................. 17  
A Low Noise AGC Amplifier.................................................... 17  
Caution ........................................................................................ 18  
Evaluation Board ............................................................................ 19  
Outline Dimensions....................................................................... 21  
Ordering Guide .......................................................................... 21  
REVISION HISTORY  
5/07—Rev. G to Rev. H  
4/04—Rev. E to Rev. F  
Changes to Layout ...........................................................................14  
Changes to Layout ...........................................................................15  
Changes to Layout ...........................................................................16  
Inserted Evaluation Board Section, and Figure 48 to  
Figure 51 ...........................................................................................19  
Inserted Figure 52 and Table 4.......................................................20  
Changes to Ordering Guide ...........................................................21  
Changes to Specifications.................................................................2  
Changes to Ordering Guide.............................................................3  
8/03—Rev. D to Rev E  
Updated Format.................................................................. Universal  
Changes to Specifications.................................................................2  
Changes to TPCs 2, 3, 4....................................................................4  
Changes to Sequential Mode (Optimal S/N Ratio) section.........9  
Change to Figure 8 ..........................................................................10  
Updated Outline Dimensions........................................................14  
3/05—Rev. F to Rev. G  
Updated Format.................................................................. Universal  
Change to Features ............................................................................1  
Changes to General Description .....................................................1  
Change to Figure 1 ............................................................................1  
Changes to Specifications.................................................................3  
New Figure 4 and Renumbering Subsequent Figures...................6  
Change to Figure 10 ..........................................................................7  
Change to Figure 23 ..........................................................................9  
Change to Figure 29 ........................................................................12  
Updated Outline Dimensions........................................................20  
Rev. H | Page 2 of 24  
 
AD603  
SPECIFICATIONS  
@ TA = 25°C, VS = 5 V, 500 mV ≤ VG ≤ +500 mV, GNEG = 0 V, 10 dB to +30 dB gain range, RL = 500 Ω, and CL = 5 pF, unless  
otherwise noted.  
Table 1.  
Parameter  
Conditions  
Min  
Typ  
Max  
Unit  
INPUT CHARACTERISTICS  
Input Resistance  
Input Capacitance  
Input Noise Spectral Density1  
Noise Figure  
1 dB Compression Point  
Peak Input Voltage  
Pin 3 to Pin 4  
97  
100  
2
1.3  
8.8  
−11  
1.4  
103  
Ω
pF  
nV/√Hz  
dB  
dBm  
V
Input short-circuited  
f = 10 MHz, gain = maximum, RS = 10 Ω  
f = 10 MHz, gain = maximum, RS = 10 Ω  
2
OUTPUT CHARACTERISTICS  
−3 dB Bandwidth  
Slew Rate  
Peak Output2  
VOUT = 100 mV rms  
RL ≥ 500 Ω  
RL ≥ 500 Ω  
90  
275  
3.0  
2
MHz  
V/μs  
V
2.5  
Output Impedance  
f ≤ 10 MHz  
Ω
Output Short-Circuit Current  
Group Delay Change vs. Gain  
Group Delay Change vs. Frequency  
Differential Gain  
50  
2
2
0.2  
0.2  
−60  
15  
mA  
ns  
ns  
f = 3 MHz; full gain range  
VG = 0 V; f = 1 MHz to 10 MHz  
%
Differential Phase  
Degree  
dBc  
dBm  
Total Harmonic Distortion  
Third-Order Intercept  
ACCURACY  
f = 10 MHz, VOUT = 1 V rms  
f = 40 MHz, gain = maximum, RS = 50 Ω  
Gain Accuracy, f = 100 kHz; Gain (dB) = (40 VG + 10) dB  
TMIN to TMAX  
Gain, f = 10.7 MHz  
−500 mV ≤ VG ≤ +500 mV  
−1  
−1.5  
0.5  
+1  
+1.5  
−8.0  
dB  
dB  
dB  
VG = -0.5 V  
VG = 0.0 V  
VG = 0.5 V  
VG = 0 V  
−10.3 −9.0  
+9.5  
+29.3 +30.3 +31.3 dB  
−20  
−30  
−20  
−30  
+10.5 +11.5 dB  
Output Offset Voltage3  
TMIN to TMAX  
Output Offset Variation vs. VG  
TMIN to TMAX  
+20  
+30  
+20  
+30  
mV  
mV  
mV  
mV  
−500 mV ≤ VG ≤ +500 mV  
GAIN CONTROL INTERFACE  
Gain Scaling Factor  
TMIN to TMAX  
100 kHz  
39.4  
38  
38.7  
−1.2  
40  
40.6  
42  
39.9  
+2.0  
dB/V  
dB/V  
dB/V  
V
nA  
nA  
10.7 MHz  
39.3  
GNEG, GPOS Voltage Range4  
Input Bias Current  
Input Offset Current  
Differential Input Resistance  
Response Rate  
200  
10  
50  
Pin 1 to Pin 2  
Full 40 dB gain change  
MΩ  
dB/μs  
80  
POWER SUPPLY  
Specified Operating Range  
Quiescent Current  
TMIN to TMAX  
4.75  
6.3  
17  
20  
V
mA  
mA  
12.5  
1 Typical open or short-circuited input; noise is lower when system is set to maximum gain and input is short-circuited. This figure includes the effects of both voltage  
and current noise sources.  
2 Using resistive loads of 500 Ω or greater or with the addition of a 1 kΩ pull-down resistor when driving lower loads.  
3 The dc gain of the main amplifier in the AD603 is ×35.7; therefore, an input offset of 100 μV becomes a 3.57 mV output offset.  
4 GNEG and GPOS, gain control, and voltage range are guaranteed to be within the range of −VS + 4.2 V to +VS − 3.4 V over the full temperature range of −40°C to +85°C.  
Rev. H | Page 3 of 24  
 
 
AD603  
ABSOLUTE MAXIMUM RATINGS  
Table 2.  
Parameter  
Rating  
Table 3. Thermal Characteristics  
Supply Voltage VS  
Internal Voltage VINP (Pin 3)  
7.5 V  
Package Type  
θJA  
θJC  
33  
15  
Unit  
°C/W  
°C/W  
2 V Continuous  
VS for 10 ms  
VS  
8-Lead SOIC  
8-Lead CERDIP  
155  
140  
GPOS, GNEG (Pin 1 and Pin2)  
Internal Power Dissipation  
Operating Temperature Range  
AD603A  
400 mW  
ESD CAUTION  
−40°C to +85°C  
−55°C to +125°C  
−65°C to +150°C  
300°C  
AD603S  
Storage Temperature Range  
Lead Temperature (Soldering, 60 sec)  
Stresses above those listed under Absolute Maximum Ratings  
may cause permanent damage to the device. This is a stress  
rating only; functional operation of the device at these or any  
other conditions above those indicated in the operational  
section of this specification is not implied. Exposure to absolute  
maximum rating conditions for extended periods may affect  
device reliability.  
Rev. H | Page 4 of 24  
 
AD603  
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS  
GPOS  
GNEG  
VINP  
1
2
3
4
8
7
6
5
VPOS  
VOUT  
VNEG  
FDBK  
GPOS  
GNEG  
VINP  
1
2
3
4
8
7
6
5
VPOS  
VOUT  
VNEG  
FDBK  
AD603  
AD603  
TOP VIEW  
(Not to Scale)  
TOP VIEW  
(Not to Scale)  
COMM  
COMM  
Figure 2. 8-Lead SOIC Pin Configuration  
Figure 3. 8-Lead CERDIP Pin Configuration  
Table 4. Pin Function Descriptions  
Pin No.  
Mnemonic  
Description  
1
2
3
4
5
6
7
8
GPOS  
GNEG  
VINP  
COMM  
FDBK  
VNEG  
Gain Control Input High (Positive Voltage Increases Gain).  
Gain Control Input Low (Negative Voltage Increases Gain).  
Amplifier Input.  
Amplifier Ground.  
Connection to Feedback Network.  
Negative Supply Input.  
VOUT  
VPOS  
Amplifier Output.  
Positive Supply Input.  
Rev. H | Page 5 of 24  
 
AD603  
TYPICAL PERFORMANCE CHARACTERISTICS  
@ TA = 25°C, VS = 5 V, 500 mV ≤ VG ≤ +500 mV, GNEG = 0 V, 10 dB to +30 dB gain range, RL = 500 Ω, and CL = 5 pF, unless  
otherwise noted.  
40  
30  
20  
10  
0
4
225  
180  
135  
90  
3
2
1
GAIN  
0
45  
–1  
–2  
–3  
–4  
–5  
–6  
0
10.7MHz  
PHASE  
–45  
–90  
–135  
–180  
–225  
100kHz  
–10  
–0.6  
–0.4  
–0.2  
0
0.2  
0.4  
0.6  
100k  
1M  
10M  
FREQUENCY (Hz)  
100M  
V
(V)  
G
Figure 4. Gain vs. VG at 100 kHz and 10.7 MHz  
Figure 7. Frequency and Phase Response vs. Gain  
(Gain = 10 dB, PIN = −30 dBm)  
2.5  
2.0  
4
3
225  
180  
135  
90  
45MHz  
2
1.5  
1
GAIN  
1.0  
70MHz  
0
45  
10.7MHz  
0.5  
–1  
–2  
–3  
–4  
–5  
–6  
0
PHASE  
–45  
–90  
–135  
–180  
–225  
0
455kHz  
–0.5  
–1.0  
–1.5  
70MHz  
–0.5 –0.4 –0.3 –0.2 –0.1  
0
0.1  
0.2  
0.3  
0.4  
0.5  
100k  
1M  
10M  
100M  
GAIN VOLTAGE (V)  
FREQUENCY (Hz)  
Figure 5. Gain Error vs. Gain Control Voltage at 455 kHz,  
10.7 MHz, 45 MHz, 70 MHz  
Figure 8. Frequency and Phase Response vs. Gain  
(Gain = 30 dB, PIN = −30 dBm)  
4
3
7.6  
7.4  
7.2  
7.0  
6.8  
6.6  
6.4  
225  
180  
135  
90  
2
1
GAIN  
0
45  
–1  
–2  
–3  
–4  
–5  
–6  
0
PHASE  
–45  
–90  
–135  
–180  
–225  
100k  
1M  
10M  
100M  
–0.6  
–0.4  
–0.2  
0
0.2  
0.4  
0.6  
FREQUENCY (Hz)  
GAIN CONTROL VOLTAGE (V)  
Figure 6. Frequency and Phase Response vs. Gain  
(Gain = −10 dB, PIN = −30 dBm)  
Figure 9. Group Delay vs. Gain Control Voltage  
Rev. H | Page 6 of 24  
 
 
AD603  
–1.0  
–1.2  
–1.4  
–1.6  
–1.8  
–2.0  
–2.2  
–2.4  
–2.6  
–2.8  
–3.0  
–3.2  
–3.4  
0.1µF  
+5V  
8
HP3326A  
DUAL-  
CHANNEL  
SYNTHESIZER  
3
4
HP3585A  
SPECTRUM  
ANALYZER  
5
7
2
10×  
PROBE  
AD603  
100  
1
511Ω  
6
0.1µF  
–5V  
DATEL  
DVC 8500  
0
50  
100  
200  
500  
1000  
2000  
LOAD RESISTANCE ()  
Figure 10. Third-Order Intermodulation Distortion Test Setup  
Figure 13. Typical Output Voltage Swing vs. Load Resistance  
(Negative Output Swing Limits First)  
102  
10dB/DIV  
100  
98  
96  
94  
100k  
1M  
10M  
FREQUENCY (Hz)  
100M  
Figure 11. Third-Order Intermodulation Distortion at 455 kHz  
(10× Probe Used to HP3585A Spectrum Analyzer, Gain = 0 dB, PIN = 0 dBm)  
Figure 14. Input Impedance vs. Frequency (Gain = −10 dB)  
102  
100  
98  
10dB/DIV  
96  
94  
100k  
1M  
10M  
FREQUENCY (Hz)  
100M  
Figure 12. Third-Order Intermodulation Distortion at 10.7 MHz  
(10× Probe Used to HP3585A Spectrum Analyzer, Gain = 0 dB, PIN = 0 dBm)  
Figure 15. Input Impedance vs. Frequency (Gain = 10 dB)  
Rev. H | Page 7 of 24  
AD603  
3V  
102  
INPUT GND  
100MV/DIV  
100  
98  
1V  
OUTPUT GND  
1V/DIV  
96  
94  
–2V  
–49ns  
100k  
1M  
10M  
FREQUENCY (Hz)  
100M  
50ns  
451ns  
Figure 19. Output Stage Overload Recovery Time  
(Input Is 500 ns Period, 50% Duty-Cycle Square Wave,  
Figure 16. Input Impedance vs. Frequency (Gain = 30 dB)  
Output Is Captured Using Tektronix 11402 Digitizing Oscilloscope)  
3.5V  
INPUT  
500mV/DIV  
1V  
GND  
GND  
100  
90  
500mV  
OUTPUT  
500mV/DIV  
10  
0%  
–1.5V  
–44ns  
200ns  
1V  
50ns  
456ns  
Figure 20. Transient Response, G = 0 dB  
(Input Is 500 ns Period, 50% Duty-Cycle Square Wave,  
Output Is Captured Using Tektronix 11402 Digitizing Oscilloscope)  
Figure 17. Gain Control Channel Response Time  
3.5V  
4.5V  
INPUT GND  
1V/DIV  
INPUT GND  
100mV/DIV  
500mV  
500mV  
OUTPUT GND  
500mV/DIV  
OUTPUT GND  
500mV/DIV  
–1.5V  
–44ns  
–500mV  
50ns  
456ns  
–49ns  
50ns  
451ns  
Figure 21. Transient Response, G = 20 dB  
(Input Is 500 ns Period, 50% Duty-Cycle Square Wave,  
Output Is Captured Using Tektronix 11402 Digitizing Oscilloscope)  
Figure 18. Input Stage Overload Recovery Time  
(Input Is 500 ns Period, 50% Duty-Cycle Square Wave,  
Output Is Captured Using Tektronix 11402 Digitizing Oscilloscope)  
Rev. H | Page 8 of 24  
AD603  
21  
19  
17  
15  
13  
11  
9
T
R
= 25°C  
= 50  
A
10MHz  
S
0
–10  
–20  
–30  
–40  
–50  
–60  
TEST SETUP FIGURE 23  
20MHz  
7
5
30  
100k  
1M  
10M  
FREQUENCY (Hz)  
100M  
31  
32  
33  
34  
35  
36  
37  
38  
39  
40  
GAIN (dB)  
Figure 22. PSRR vs. Frequency  
Figure 25. Noise Figure in 0 dB/40 dB Mode  
(Worst Case Is Negative Supply PSRR, Shown Here)  
0
–5  
T
= 25°C  
A
TEST SETUP FIGURE 23  
0.1µF  
+5V  
8
–10  
–15  
–20  
–25  
HP3326A  
DUAL-  
CHANNEL  
SYNTHESIZER  
3
4
HP3585A  
SPECTRUM  
ANALYZER  
5
7
2
50  
AD603  
100Ω  
1
6
0.1µF  
–5V  
DATEL  
DVC 8500  
10  
30  
50  
70  
INPUT FREQUENCY (MHz)  
Figure 23. Test Setup Used for: Noise Figure, Third-Order Intercept, and  
1 dB Compression Point Measurements  
Figure 26. 1 dB Compression Point, −10 dB/+30 dB Mode, Gain = 30 dB  
23  
20  
T
R
= 25°C  
= 50V  
T
= 25°C  
A
A
TEST SETUP FIGURE 23  
S
21  
19  
17  
15  
13  
11  
9
70MHz  
TEST SETUP FIGURE 23  
18  
16  
14  
12  
10  
0
30MHz  
50MHz  
40MHz  
30MHz  
10MHz  
70MHz  
7
5
20  
21  
22  
23  
24  
25  
26  
27  
28  
29  
30  
–20  
–10  
INPUT LEVEL (dBm)  
0
GAIN (dB)  
Figure 24. Noise Figure in −10 dB/+30 dB Mode  
Figure 27. Third-Order Intercept −10 dB/+30 dB Mode, Gain = 10 dB  
Rev. H | Page 9 of 24  
AD603  
20  
18  
16  
14  
12  
10  
T
= 25°C  
= 50Ω  
A
R
R
R
S
= 50Ω  
IN  
= 100Ω  
L
TEST SETUP FIGURE 23  
30MHz  
40MHz  
70MHz  
8
–40  
–30  
INPUT LEVEL (dBm)  
–20  
Figure 28. Third-Order Intercept −10 dB/+30 dB Mode, Gain = 30 dB  
Rev. H | Page 10 of 24  
AD603  
THEORY OF OPERATION  
The AD603 comprises a fixed-gain amplifier, preceded by a  
broadband passive attenuator of 0 dB to 42.14 dB, having a gain  
control scaling factor of 40 dB per volt. The fixed gain is laser-  
trimmed in two ranges, to either 31.07 dB (×35.8) or 50 dB  
(×358), or it may be set to any range in between using one  
external resistor between Pin 5 and Pin 7. Somewhat higher  
gain can be obtained by connecting the resistor from Pin 5 to  
common, but the increase in output offset voltage limits the  
maximum gain to about 60 dB. For any given range, the  
bandwidth is independent of the voltage-controlled gain. This  
system provides an underrange and overrange of 1.07 dB in all  
cases; for example, the overall gain is −11.07 dB to +31.07 dB in  
the maximum bandwidth mode (Pin 5 and Pin 7 strapped).  
The gain is at all times very exactly determined, and a linear-in-  
dB relationship is automatically guaranteed by the exponential  
nature of the attenuation in the ladder network (the X-AMP  
principle). In practice, the gain deviates slightly from the ideal  
law, by about 0.2 dB peak (see, for example, Figure 5).  
NOISE PERFORMANCE  
An important advantage of the X-AMP is its superior noise  
performance. The nominal resistance seen at inner tap points is  
41.7 Ω (one third of 125 Ω), which exhibits a Johnson noise  
spectral density (NSD) of 0.83 nV/√Hz (that is, √4kTR) at 27°C,  
which is a large fraction of the total input noise. The first stage  
of the amplifier contributes a further 1 nV/√Hz, for a total input  
noise of 1.3 nV/√Hz. It is apparent that it is essential to use a  
low resistance in the ladder network to achieve the very low  
specified noise level. The source impedance of the signal  
forms a voltage divider with the 100 Ω input resistance of the  
AD603. In some applications, the resulting attenuation may  
be unacceptable, requiring the use of an external buffer or  
preamplifier to match a high impedance source to the low  
impedance AD603.  
This X-AMP structure has many advantages over former  
methods of gain control based on nonlinear elements. Most  
importantly, the fixed-gain amplifier can use negative feedback  
to increase its accuracy. Because large inputs are first attenuated,  
the amplifier input is always small. For example, to deliver a  
1 V output in the −1 dB/+41 dB mode (that is, using a fixed  
amplifier gain of 41.07 dB), its input is only 8.84 mV; therefore,  
the distortion can be very low. Equally important, the small-  
signal gain and phase response, and thus the pulse response, are  
essentially independent of gain.  
The noise at maximum gain (that is, at the 0 dB tap) depends on  
whether the input is short-circuited or open-circuited. When  
short-circuited, the minimum NSD of slightly over 1 nV/√Hz is  
achieved. When open-circuited, the resistance of 100 Ω looking  
into the first tap generates 1.29 nV/√Hz, so the noise increases  
to 1.63 nV/√Hz. (This last calculation would be important if the  
AD603 were preceded by, for example, a 900 Ω resistor to allow  
operation from inputs up to 10 V rms.) As the selected tap  
moves away from the input, the dependence of the noise on  
source impedance quickly diminishes.  
Figure 29 is a simplified schematic. The input attenuator is a  
7-section R-2R ladder network, using untrimmed resistors of  
nominally R = 62.5 Ω, which results in a characteristic resistance of  
125 Ω 20ꢀ. A shunt resistor is included at the input and laser  
trimmed to establish a more exact input resistance of 100 Ω 3ꢀ,  
which ensures accurate operation (gain and HP corner frequency)  
when used in conjunction with external resistors or capacitors.  
The nominal maximum signal at input VINP is 1 V rms  
( 1.4 V peak) when using the recommended 5 V supplies,  
although operation to 2 V peak is permissible with some  
increase in HF distortion and feedthrough. Pin 4 (COMM)  
must be connected directly to the input ground; significant  
impedance in this connection reduces the gain accuracy.  
Apart from the small variations just discussed, the signal-to-  
noise (SNR) at the output is essentially independent of the  
attenuator setting. For example, on the −11 dB/+31 dB range,  
the fixed gain of ×35.8 raises the output NSD to 46.5 nV/√Hz.  
Therefore, for the maximum undistorted output of 1 V rms and  
a 1 MHz bandwidth, the output SNR would be 86.6 dB, that is,  
20 log(1 V/46.5 μV).  
The signal applied at the input of the ladder network is attenuated  
by 6.02 dB by each section; therefore, the attenuation to each of  
the taps is progressively 0 dB, 6.02 dB, 12.04 dB, 18.06 dB,  
24.08 dB, 30.1 dB, 36.12 dB, and 42.14 dB. A unique circuit  
technique is employed to interpolate between these tap points,  
indicated by the slider in Figure 29, thus providing continuous  
attenuation from 0 dB to 42.14 dB. It helps in understanding the  
AD603 to think in terms of a mechanical means for moving this  
slider from left to right; in fact, its position is controlled by the  
voltage between Pin 1 and Pin 2. The details of the gain control  
interface are in the The Gain Control Interface section.  
Rev. H | Page 11 of 24  
 
AD603  
8
6
1
2
VPOS  
VNEG  
GPOS  
GNEG  
SCALING  
REFERENCE  
PRECISION PASSIVE  
INPUT ATTENUATOR  
FIXED-GAIN  
AMPLIFIER  
7
5
VOUT  
FDBK  
V
G
6.44k*  
GAIN-  
AD603  
CONTROL  
INTERFACE  
694*  
20*  
0dB  
–6.02dB –12.04dB –18.06dB –24.08dB –30.1dB –36.12dB –42.14dB  
3
4
VINP  
R
R
R
R
R
R
R
2R  
2R  
2R  
2R  
2R  
2R  
R
COMM  
R-2R LADDER NETWORK  
*NOMINAL VALUES.  
Figure 29. Simplified Block Diagram  
For example, if the gain is to be controlled by a DAC providing  
a positive-only, ground-referenced output, the gain control low  
(GNEG) pin should be biased to a fixed offset of 500 mV to set  
the gain to −10 dB when gain control high (GPOS) is at zero,  
and to 30 dB when at 1.00 V.  
THE GAIN CONTROL INTERFACE  
The attenuation is controlled through a differential, high  
impedance (50 MΩ) input, with a scaling factor that is laser-  
trimmed to 40 dB per volt, that is, 25 mV/dB. An internal band  
gap reference ensures stability of the scaling with respect to  
supply and temperature variations.  
It is a simple matter to include a voltage divider to achieve other  
scaling factors. When using an 8-bit DAC having an FS output  
of 2.55 V (10 mV/bit), a divider ratio of 2 (generating 5 mV/bit)  
results in a gain-setting resolution of 0.2 dB/bit. The use of such  
offsets is valuable when two AD603s are cascaded, when  
various options exist for optimizing the signal-to-noise profile,  
as is shown in the Sequential Mode (Optimal SNR) section,  
When the differential input voltage VG = 0 V, the attenuator  
slider is centered, providing an attenuation of 21.07 dB. For the  
maximum bandwidth range, this results in an overall gain of  
10 dB (= −21.07 dB + 31.07 dB). When the control input is  
−500 mV, the gain is lowered by +20 dB (= 0.500 V × 40 dB/V)  
to −10 dB; when set to +500 mV, the gain is increased by  
+20 dB to +30 dB. When this interface is overdriven in either  
direction, the gain approaches either −11.07 dB (= − 42.14 dB +  
+31.07 dB) or 31.07 dB (= 0 + 31.07 dB), respectively. The only  
constraint on the gain control voltage is that it be kept within  
the common-mode range (−1.2 V to +2.0 V assuming +5 V  
supplies) of the gain control interface.  
PROGRAMMING THE FIXED-GAIN AMPLIFIER  
USING PIN STRAPPING  
Access to the feedback network is provided at Pin 5 (FDBK).  
The user may program the gain of the output amplifier of the  
AD603 using this pin, as shown in Figure 30, Figure 31, and  
Figure 32. There are three modes: in the default mode, FDBK  
is unconnected, providing the range +9 dB/+51 dB; when VOUT  
and FDBK are shorted, the gain is lowered to −11 dB/+31 dB;  
and, when an external resistor is placed between VOUT and  
FDBK, any intermediate gain can be achieved, for example,  
−1 dB/+41 dB. Figure 33 shows the nominal maximum gain vs.  
external resistor for this mode.  
The basic gain of the AD603 can therefore be calculated by  
Gain (dB) = 40 VG +10  
(1)  
where VG is in volts. When Pin 5 and Pin 7 are strapped (see the  
Programming the Fixed-Gain Amplifier Using Pin Strapping  
section), the gain becomes  
Gain (dB) = 40 VG + 20 for 0 to +40 dB  
1
2
3
4
8
7
6
5
VC1  
GPOS VPOS  
AD603  
VPOS  
and  
VC2  
GNEG VOUT  
VOUT  
Gain (dB) = 40 VG + 30 for +10 to +50 dB  
(2)  
The high impedance gain control input ensures minimal  
loading when driving many amplifiers in multiple channel  
or cascaded applications. The differential capability provides  
flexibility in choosing the appropriate signal levels and  
polarities for various control schemes.  
VIN  
VINP  
VNEG  
VNEG  
COMM FDBK  
Figure 30. −10 dB to +30 dB; 90 MHz Bandwidth  
Rev. H | Page 12 of 24  
 
 
 
 
 
AD603  
Optionally, when a resistor is placed from FDBK to COMM,  
1
2
3
4
8
7
6
5
VC1  
VC2  
GPOS VPOS  
VPOS  
VNEG  
higher gains can be achieved. This fourth mode is of limited  
value because of the low bandwidth and the elevated output  
offsets; it is thus not included in Figure 30, Figure 31, or  
Figure 32.  
AD603  
GNEG VOUT  
VOUT  
VIN  
VINP  
VNEG  
2.15k  
The gain of this amplifier in the first two modes is set by the  
ratio of on-chip laser-trimmed resistors. While the ratio of these  
resistors is very accurate, the absolute value of these resistors  
can vary by as much as 20ꢀ. Therefore, when an external  
resistor is connected in parallel with the nominal 6.44 kΩ 20ꢀ  
internal resistor, the overall gain accuracy is somewhat poorer.  
The worst-case error occurs at about 2 kΩ (see Figure 34).  
1.2  
COMM FDBK  
5.6pF  
Figure 31. 0 dB to 40 dB; 30 MHz Bandwidth  
1
2
3
4
8
7
6
5
VC1  
VC2  
GPOS VPOS  
VPOS  
AD603  
GNEG VOUT  
VOUT  
–1:VdB (OUT) – (–1):VdB (O  
)
REF  
VIN  
VINP  
VNEG  
VNEG  
18pF  
1.0  
0.8  
COMM FDBK  
0.6  
0.4  
Figure 32. 10 dB to 50 dB; 9 MHz to Set Gain  
0.2  
52  
50  
48  
46  
44  
42  
40  
38  
36  
34  
32  
30  
0
–1:VdB (OUT)  
–0.2  
–0.4  
–0.6  
–0.8  
–1.0  
VdB (OUT)  
VdB (OUT) – VdB (O  
)
REF  
–2:VdB (OUT)  
10  
100  
1k  
10k  
100k  
1M  
R
()  
EXT  
Figure 34. Worst-Case Gain Error, Assuming Internal Resistors Have a  
Maximum Tolerance of −20% (Top Curve) or = 20% (Bottom Curve)  
While the gain bandwidth product of the fixed-gain amplifier is  
about 4 GHz, the actual bandwidth is not exactly related to the  
maximum gain. This is because there is a slight enhancing of  
the ac response magnitude on the maximum bandwidth range,  
due to higher order poles in the open-loop gain function; this  
mild peaking is not present on the higher gain ranges. Figure 30,  
Figure 31, and Figure 32 show how an optional capacitor may  
be added to extend the frequency response in high gain modes.  
10  
100  
1k  
10k  
100k  
1M  
R
()  
EXT  
Figure 33. Gain vs. REXT, Showing Worst-Case Limits Assuming Internal  
Resistors Have a Maximum Tolerance of 20%  
Rev. H | Page 13 of 24  
 
 
 
 
AD603  
USING THE AD603 IN CASCADE  
Two or more AD603s can be connected in series to achieve  
higher gain. Invariably, ac coupling must be used to prevent the  
dc offset voltage at the output of each amplifier from overloading  
the following amplifier at maximum gain. The required high-  
pass coupling network is usually just a capacitor, chosen to set  
the desired corner frequency in conjunction with the well-  
defined 100 Ω input resistance of the following amplifier.  
Figure 35 shows the SNR over a gain range of −22 dB to +62 dB,  
assuming an output of 1 V rms and a 1 MHz bandwidth. Figure 36,  
Figure 37, and Figure 38 show the general connections to  
accomplish this. Here, both the positive gain control inputs  
(GPOS) are driven in parallel by a positive-only, ground-referenced  
source with a range of 0 V to 2 V, while the negative gain  
control inputs (GNEG) are biased by stable voltages to provide  
the needed gain offsets. These voltages may be provided by  
resistive dividers operating from a common voltage reference.  
90  
For two AD603s, the total gain control range becomes 84 dB  
(2 × 42.14 dB); the overall −3 dB bandwidth of cascaded stages  
is somewhat reduced. Depending on the pin strapping, the gain  
and bandwidth for two cascaded amplifiers can range from  
−22 dB to +62 dB (with a bandwidth of about 70 MHz) to  
+22 dB to +102 dB (with a bandwidth of about 6 MHz).  
85  
80  
75  
70  
65  
60  
55  
50  
There are several ways of connecting the gain control inputs  
in cascaded operation. The choice depends on whether it is  
important to achieve the highest possible instantaneous signal-  
to-noise ratio (ISNR), or, alternatively, to minimize the ripple  
in the gain error. The following examples feature the AD603  
programmed for maximum bandwidth; the explanations apply  
to other gain/bandwidth combinations with appropriate  
changes to the arrangements for setting the maximum gain.  
–0.2  
0.2  
0.6  
1.0  
(V)  
1.4  
1.8  
2.2  
SEQUENTIAL MODE (OPTIMAL SNR)  
V
C
Figure 35. SNR vs. Control Voltage, Sequential Control (1 MHz Bandwidth)  
In the sequential mode of operation, the ISNR is maintained at  
its highest level for as much of the gain control range as possible.  
A1  
A2  
–40.00dB  
–51.07dB  
–8.93dB  
–42.14dB  
INPUT  
–42.14dB  
31.07dB  
31.07dB  
OUTPUT  
–20dB  
0dB  
GPOS  
GNEG  
GPOS  
GNEG  
V
V
G2  
G1  
V
= 0.473V  
V
= 1.526V  
O2  
O1  
V
= 0V  
C
Figure 36. AD603 Gain Control Input Calculations for Sequential Control Operation VC = 0 V  
0dB  
–11.07dB  
31.07dB  
0dB  
–42.14dB  
GPOS GNEG  
INPUT  
0dB  
OUTPUT  
20dB  
31.07dB  
31.07dB  
GPOS  
GNEG  
V
V
G2  
G1  
V
= 0.473V  
V
= 1.526V  
O2  
O1  
V
= 1.0V  
C
Figure 37. AD603 Gain Control Calculations for Sequential Control Operation VC = 1.0 V  
0dB  
–28.93dB  
31.07dB  
0dB  
–2.14dB  
GPOS GNEG  
INPUT  
0dB  
31.07dB  
31.07dB  
OUTPUT  
60dB  
GPOS  
GNEG  
V
V
G2  
G1  
V
= 0.473V  
V
= 1.526V  
O2  
O1  
V
= 2.0V  
C
Figure 38. AD603 Gain Control Input Calculations for Sequential Operation VC = 2.0 V  
Rev. H | Page 14 of 24  
 
 
 
 
 
 
AD603  
The gains are offset (Figure 39) such that the gain of A2 is  
increased only after the gain of A1 has reached its maximum  
value. Note that for a differential input of –600 mV or less, the  
gain of a single amplifier (A1 or A2) is at its minimum value of  
−11.07 dB; for a differential input of 600 mV or more, the gain  
is at its maximum value of 31.07 dB. Control inputs beyond  
these limits do not affect the gain and can be tolerated without  
damage or foldover in the response. This is an important aspect  
of the gain control response of the AD603. (See the Specifications  
section for more details on the allowable voltage range.) The  
gain is now  
Figure 41 is a plot of the SNR of the cascaded amplifiers vs. the  
control voltage. Figure 42 is a plot of the gain error of the  
cascaded stages vs. the control voltages.  
70  
60  
COMBINED  
50  
40  
A1  
30  
20  
10  
0
Gain (dB) = 40 VG + GO  
where:  
(3)  
A2  
–10  
VG is the applied control voltage.  
–20  
GO is determined by the gain range chosen.  
–30  
–0.2  
0.2  
0.6  
1.0  
(V)  
1.4  
1.8  
2.0  
In the explanatory notes that follow, it is assumed that  
the maximum bandwidth connections are used, for which  
GO is −20 dB.  
V
C
Figure 40. Plot of Separate and Overall Gains in Sequential Control  
90  
+31.07dB  
80  
70  
60  
50  
40  
30  
20  
10  
+31.07dB  
+28.96dB  
+10dB  
*
A1  
A2  
*
–11.07dB  
–8.93dB  
–11.07dB  
0.473  
1.526  
GAIN  
0
–20  
0.5  
0
1.0  
20  
1.50  
40  
2.0  
60  
V (V)  
C
62.14  
–22.14  
(dB)  
*GAIN OFFSET OF 1.07dB, OR 26.75mV.  
Figure 39. Explanation of Offset Calibration for Sequential Control  
–0.2  
0.2  
0.6  
1.0  
(V)  
1.4  
1.8  
2.0  
With reference to Figure 36, Figure 37, and Figure 38, note that  
V
C
VG1 refers to the differential gain control input to A1, and VG2  
Figure 41. SNR for Cascaded Stages—Sequential Control  
refers to the differential gain control input to A2. When VG is  
0 V, VG1 = −473 mV and thus the gain of A1 is −8.93 dB (recall  
that the gain of each individual amplifier in the maximum  
bandwidth mode is –10 dB for VG = −500 mV and 10 dB for VG  
= 0 V); meanwhile, VG2 = −1.908 V so the gain of A2 is pinned  
at −11.07 dB. The overall gain is therefore –20 dB (see Figure 36).  
2.0  
1.5  
1.0  
0.5  
When VG = 1.00 V, VG1 = 1.00 V − 0.473 V = 0.526 V, which sets  
the gain of A1 to nearly its maximum value of +31.07 dB, while  
0
–0.5  
–1.0  
–1.5  
–2.0  
VG2 = 1.00 V − 1.526 V = 0.526 V, which sets the gain of A2 to  
nearly its minimum value of −11.07 dB. Close analysis shows  
that the degree to which neither AD603 is completely pushed to  
its maximum nor minimum gain exactly cancels in the overall  
gain, which is now 20 dB (see Figure 37).  
–0.2  
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2  
(V)  
When VG = 2.0 V, the gain of A1 is pinned at 31.07 dB and that  
of A2 is near its maximum value of 28.93 dB, resulting in an  
overall gain of 60 dB (see Figure 38). This mode of operation is  
further clarified in Figure 40, which is a plot of the separate  
gains of A1 and A2 and the overall gain vs. the control voltage.  
V
C
Figure 42. Gain Error for Cascaded Stages–Sequential Control  
Rev. H | Page 15 of 24  
 
 
 
 
AD603  
PARALLEL MODE (SIMPLEST GAIN CONTROL  
INTERFACE)  
LOW GAIN RIPPLE MODE (MINIMUM GAIN ERROR)  
As can be seen in Figure 42 and Figure 43, the error in the gain  
is periodic, that is, it shows a small ripple. (Note that there is  
also a variation in the output offset voltage, which is due to the  
gain interpolation, but this is not exact in amplitude.) By  
offsetting the gains of A1 and A2 by half the period of the ripple,  
In this mode, the gain control of voltage is applied to both  
inputs in parallel: the GPOS pins of both A1 and A2 are  
connected to the control voltage and the GNEW inputs are  
grounded. The gain scaling is then doubled to 80 dB/V,  
requiring only a 1.00 V change for an 80 dB change of gain  
that is, by 3 dB, the residual gain errors of the two amplifiers  
can be made to cancel. Figure 45 shows much lower gain ripple  
when configured in this manner. Figure 46 plots the ISNR as a  
function of gain; it is very similar to that in the parallel mode.  
Gain = (dB) = 80 VG + GO  
(4)  
where, as before, GO depends on the range selected; for example,  
in the maximum bandwidth mode, GO is 20 dB. Alternatively,  
the GNEG pins may be connected to an offset voltage of  
0.500 V, in which case GO is −20 dB.  
3.0  
2.5  
2.0  
1.5  
The amplitude of the gain ripple in this case is also doubled, as  
shown in Figure 43, while the ISNR at the output of A2 now  
decreases linearly as the gain increases, as shown in Figure 44.  
2.0  
1.0  
0.5  
0
–0.5  
–1.0  
–1.5  
–2.0  
–2.5  
–3.0  
1.5  
1.0  
0.5  
0
–0.1  
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1  
(V)  
V
C
–0.5  
–1.0  
–1.5  
–2.0  
Figure 45. Gain Error for Cascaded Stages—Low Ripple Mode  
90  
85  
80  
75  
–0.2  
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2  
(V)  
V
C
Figure 43. Gain Error for Cascaded Stages—Parallel Control  
70  
65  
90  
85  
80  
75  
70  
65  
60  
55  
50  
60  
55  
50  
–0.2  
0
0.2  
0.4  
0.6  
0.8  
1.0  
1.2  
V
(V)  
C
Figure 46. ISNR vs. Control Voltage—Low Ripple Mode  
–0.2  
0
0.2  
0.4  
0.6  
(V)  
0.8  
1.0  
1.2  
V
C
Figure 44. ISNR for Cascaded Stages—Parallel Control  
Rev. H | Page 16 of 24  
 
 
 
 
 
AD603  
APPLICATIONS INFORMATION  
The circuit operates as follows:  
A LOW NOISE AGC AMPLIFIER  
Figure 47 shows the ease with which the AD603 can be  
connected as an AGC amplifier. The circuit illustrates many of  
the points previously discussed: it uses few parts, has linear-in-  
dB gain, operates from a single supply, uses two cascaded amplifiers  
in sequential gain mode for maximum SNR, and an external  
resistor programs each gain of the amplifier. It also uses a  
simple temperature-compensated detector.  
A1 and A2 are cascaded.  
Capacitor C1 and the 100 Ω of resistance at the input of A1  
form a time constant of 10 μs.  
C2 blocks the small dc offset voltage at the output of A1  
(which might otherwise saturate A2 at its maximum gain)  
and introduces a high-pass corner at about 16 kHz,  
eliminating low frequency noise.  
The circuit operates from a single 10 V supply. Resistors R1, R2,  
R3, and R4 bias the common pins of A1 and A2 at 5 V. The  
common pin is a low impedance point and must have a low  
impedance path to ground, provided here by the 100 μF tantalum  
capacitors and the 0.1 μF ceramic capacitors.  
A half-wave detector is used, based on Q1 and R8. The current  
into capacitor, CAV, is the difference between the collector  
current of Q2 (biased to be 300 μA at 300 K, 27°C) and the  
collector current of Q1, which increases with the amplitude  
of the output signal.  
The cascaded amplifiers operate in sequential gain. Here, the  
offset voltage between Pin 2 (GNEG) of A1 and A2 is 1.05 V  
(42.14 dB × 25 mV/dB), provided by a voltage divider consisting of  
Resistors R5, R6, and R7. Using standard values, the offset is not  
exact, but it is not critical for this application.  
The automatic gain control voltage, VAGC, is the time integral  
of this error current. For VAGC (and thus the gain) to remain  
insensitive to short-term amplitude fluctuations in the output  
signal, the rectified current in Q1 must, on average, exactly  
balance the current in Q2. If the output of A2 is too small to  
do this, VAGC increases, causing the gain to increase until Q1  
conducts sufficiently.  
The gain of both A1 and A2 is programmed by Resistors R13  
and R14, respectively, to be about 42 dB; therefore, the maximum  
gain of the circuit is twice that, or 84 dB. The gain control range  
can be shifted up by as much as 20 dB by appropriate choices of  
R13 and R14.  
Consider the case where R8 is zero and the output voltage VOUT  
is a square wave at, for example, 455 kHz, which is well above  
the corner frequency of the control loop.  
10V  
C11  
0.1µF  
R9  
1.54kΩ  
R10  
1.24kΩ  
THIS CAPACITOR SETS  
AGC TIME CONSTANT  
C7  
0.1µF  
Q2  
2N3906  
V
AGC  
10V  
C8  
R11  
3.83kΩ  
0.1µF  
R13  
2.49kΩ  
10V  
8
C1  
0.1µF  
C
AV  
0.1µF  
8
Q1  
2N3904  
5V  
R14  
2.49kΩ  
C2  
0.1µF  
6
3
4
J1  
C9  
0.1µF  
1
5
2
R12  
4.99kΩ  
RT  
A1  
R8  
806Ω  
10V  
6
7
3
4
100Ω  
AD603  
5
2
A2  
AD603  
10V  
7
J2  
R1  
2.49kΩ  
1
C10  
0.1µF  
R3  
2.49kΩ  
2
+
1
C3  
100µF  
C4  
0.1µF  
R2  
2.49kΩ  
2
+
C5  
100µF  
C6  
0.1µF  
R4  
2.49kΩ  
AGC LINE  
1V OFFSET FOR  
SEQUENTIAL GAIN  
R5  
5.49kΩ  
R7  
3.48kΩ  
10V  
R6  
5.5V  
6.5V  
1.05kΩ  
1
2
RT PROVIDES A 50INPUT IMPEDANCE.  
C3 AND C5 ARE TANTALUM.  
Figure 47. A Low Noise AGC Amplifier  
Rev. H | Page 17 of 24  
 
 
AD603  
During the time VOUT is negative with respect to the base  
voltage of Q1, Q1 conducts; when VOUT is positive, it is cut off.  
Because the average collector current of Q1 is forced to be  
300 μA, and the square wave has a duty cycle of 1:1, Q1s  
collector current when conducting must be 600 μA. With R8  
omitted, the peak amplitude of VOUT is forced to be just the VBE  
of Q1 at 600 μA, typically about 700 mV, or 2 VBE peak-to-peak.  
This voltage, the amplitude at which the output stabilizes, has a  
strong negative temperature coefficient (TC), typically −1.7 mV/°C.  
Although this may not be troublesome in some applications, the  
correct value of R8 renders the output stable with temperature.  
This resistor also serves to lower the peak current in Q1 when  
more typical signals (usually sinusoidal) are involved, and the  
1.8 kHz LP filter it forms with CAV helps to minimize distortion  
due to ripple in VAGC. Note that the output amplitude under sine  
wave conditions is higher than for a square wave because the  
average value of the current for an ideal rectifier is 0.637 times  
as large, causing the output amplitude to be 1.88 (= 1.2/0.637) V,  
or 1.33 V rms. In practice, the somewhat nonideal rectifier  
results in the sine-wave output being regulated to about  
1.4 V rms, or 3.6 V p-p.  
The bandwidth of the circuit exceeds 40 MHz. At 10.7 MHz, the  
AGC threshold is 100 μV (−67 dBm) and its maximum gain is  
83 dB (20 log 1.4 V/100 μV). The circuit holds its output at  
1.4 V rms for inputs as low as −67 dBm to +15 dBm (82 dB),  
where the input signal exceeds the maximum input rating of the  
AD603. For a 30 dBm input at 10.7 MHz, the second harmonic  
is 34 dB down from the fundamental, and the third harmonic is  
35 dB down from the fundamental.  
To understand this, note that the current in Q2 is made to be  
proportional to absolute temperature (PTAT). For the moment,  
continue to assume that the signal is a square wave.  
When Q1 is conducting, VOUT is now the sum of VBE and a  
voltage that is PTAT and that can be chosen to have an equal  
but opposite TC to that of the VBE. This is actually nothing more  
than an application of the band gap voltage reference principle.  
When R8 is chosen such that the sum of the voltage across it  
and the VBE of Q1 is close to the band gap voltage of about 1.2 V,  
CAUTION  
Careful component selection, circuit layout, power supply  
decoupling, and shielding are needed to minimize the susceptibility  
of the AD603 to interference from signals such as those from  
radio and TV stations. In bench evaluation, it is recommended  
to place all of the components into a shielded box and use  
feedthrough decoupling networks for the supply voltage. Circuit  
layout and construction are also critical because stray capacitances  
and lead inductances can form resonant circuits and are a  
potential source of circuit peaking, oscillation, or both.  
VOUT is stable over a wide range of temperatures, provided, of  
course, that Q1 and Q2 share the same thermal environment.  
Because the average emitter current is 600 μA during each half  
cycle of the square wave, a resistor of 833 Ω adds a PTAT  
voltage of 500 mV at 300 K, increasing by 1.66 mV/°C. In  
practice, the optimum value depends on the type of transistor  
used and, to a lesser extent, on the waveform for which the  
temperature stability is to be optimized; for the inexpensive  
2N3904/2N3906 pair and sine wave signals, the recommended  
value is 806 Ω.  
Rev. H | Page 18 of 24  
 
AD603  
EVALUATION BOARD  
The evaluation board of the AD603 enables simple bench-top  
experimenting to be performed with easy control of the  
AD603. Built-in flexibility allows convenient configuration to  
accommodate most operating configurations. Figure 48 is a  
photograph of the AD603 evaluation board.  
The output is also ac-coupled and includes a 453 Ω series  
resistor. The gain of the AD603 is adjusted by connecting a  
voltage source between the GNEG and GPOS test loops. A 0 Ω  
resistor, R5, is provided, permitting ground reference of the  
differential gain control inputs. For other gain configurations, a  
signal generator may be connected to the test loops, or the  
GNEG and/or GPOS pins may be biased. Either pin may be  
driven to either polarity within the common-mode limits of  
−1.2 V to +2.0 V; therefore, to invert the gain slope, simply  
consider the GPOS as the reference and drive the GNEG pin  
positively with respect to GPOS.  
The AD603 includes built-in gain resistors selectable at the  
FDBK pin. The board is shipped with the gain at minimum,  
with a 0 Ω resistor installed in R3. For maximum gain, simply  
remove R3. Because of the architecture of the AD603, the  
bandwidth decreases by 10, but the gain range remains at 40 dB.  
Intermediate gain values may be selected by installing a resistor  
between the VOUT and FDBK pins.  
Figure 48. AD603 Evaluation Board  
Any dual-polarity power supply capable of providing 20 mA is  
all that is required, in addition to whatever test equipment the  
user wishes to perform the intended tests.  
Figure 50, Figure 51, and Figure 52 show the component and  
circuit side copper patterns and silkscreen. A bill of materials is  
shown in Table 5.  
Referring to the schematic in Figure 49, the input to the VGA is  
single-ended, ac-coupled, and terminated in 50 Ω to accommodate  
most commonly available signal generators.  
V+  
V–  
G1 G2 GND G3 G4  
C7  
10µF  
25V  
C8  
10µF  
25V  
+
+
V+  
V–  
V+  
V+  
R7  
GPOS  
C1  
0.1µF  
R1  
C2  
0.1µF  
VO  
R6  
R5  
0  
R4  
453Ω  
AD603  
GNEG  
1
2
3
4
8
7
6
5
VOUT  
GPOS  
GNEG  
VINP  
VPOS  
VOUT  
VNEG  
FDBK  
C6  
C4  
W1  
0.1µF  
C5  
0.1µF  
Figure 50. Component Side Copper  
R3  
0Ω  
VIN  
COMM  
V–  
C9  
C3  
0.1µF  
R2  
100Ω  
W2  
Figure 49. Schematic of the AD603 Evaluation Board  
Figure 51. Circuit Side Copper  
Rev. H | Page 19 of 24  
 
 
 
 
 
AD603  
G1  
G4  
V+  
V–  
+
GND  
R7  
VO  
GPOS  
+
C2  
GNEG  
VIN  
C3  
R4  
DUT  
C5  
W1  
VOUT  
Pb  
RoHS  
G2  
G3  
AD603ARZ  
EVALUATION BOARD  
Figure 52. Component Side Silk Screen  
Table 5. Bill of Materials  
Qty Name Description  
Reference Designator  
Manufacturer  
KEMET  
Nichicon  
Mfg Part Number  
C0603C104K4RACTU  
F931E106MCC  
5
2
1
5
3
1
2
1
1
1
2
2
Capacitors  
Capacitors  
IC  
Test Loops  
Test Loops  
Resistor  
Resistors  
Resistor  
Test Loop  
Test Loop  
Connectors  
Headers  
0.1 μF, 16 V, 0603, X7R  
10 μF, 25 V, C size tantalum  
Variable gain amplifier  
0.125diameter, black  
0.125diameter, purple  
100 Ω, 1%, 1/16 W, 0603  
0 Ω, 5%, 1/10 W, 0603  
453 Ω, 1/16 W, 1%, 0603  
0.125diameter, red  
0.125diameter, green  
SMA female PC mount, RA  
2-pin 025" sq., 0.1" spacing  
Not inserted  
C1, C2, C3, C5, C6  
C7, C8  
DUT  
G1, G2, G3, G4, GND  
GNEG, GPOS, VO  
R2  
R3, R5  
R4  
+5V  
−5 V  
VIN, VOUT  
W1, W2  
C4, C9, R1, R6, R7  
Analog Devices, Inc. AD603ARZ  
Components Corp.  
Components Corp.  
Panasonic  
Panasonic  
Panasonic  
Components Corp.  
Components Corp.  
Amphenol  
TP-104-01-00  
TP-104-01-07  
ERJ-3EKF1000V  
ERJ-2GE0R00X  
ERJ-3EKF4530V  
TP-104-01-02  
TP-104-01-05  
901-143-6RFX  
22-11-2032  
Molex  
Rev. H | Page 20 of 24  
 
 
AD603  
OUTLINE DIMENSIONS  
0.005 (0.13)  
MIN  
0.055 (1.40)  
MAX  
8
5
0.310 (7.87)  
0.220 (5.59)  
1
4
0.100 (2.54) BSC  
0.405 (10.29) MAX  
0.320 (8.13)  
0.290 (7.37)  
0.060 (1.52)  
0.015 (0.38)  
0.200 (5.08)  
MAX  
0.150 (3.81)  
MIN  
0.200 (5.08)  
0.125 (3.18)  
0.015 (0.38)  
0.008 (0.20)  
SEATING  
PLANE  
0.023 (0.58)  
0.014 (0.36)  
15°  
0°  
0.070 (1.78)  
0.030 (0.76)  
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS  
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR  
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.  
Figure 53. 8-Lead Ceramic Dual In-Line Package [CERDIP]  
(Q-8)  
Dimensions shown in inches and (millimeters)  
5.00 (0.1968)  
4.80 (0.1890)  
8
1
5
4
6.20 (0.2441)  
5.80 (0.2284)  
4.00 (0.1574)  
3.80 (0.1497)  
0.50 (0.0196)  
0.25 (0.0099)  
1.27 (0.0500)  
BSC  
45°  
1.75 (0.0688)  
1.35 (0.0532)  
0.25 (0.0098)  
0.10 (0.0040)  
8°  
0°  
0.51 (0.0201)  
0.31 (0.0122)  
COPLANARITY  
0.10  
1.27 (0.0500)  
0.40 (0.0157)  
0.25 (0.0098)  
0.17 (0.0067)  
SEATING  
PLANE  
COMPLIANT TO JEDEC STANDARDS MS-012-AA  
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS  
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR  
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.  
Figure 54. 8-Lead Standard Small Outline Package [SOIC-N]  
Narrow Body (R-8)  
Dimensions shown in millimeters and (inches)  
ORDERING GUIDE  
Model  
AD603AR  
AD603AR-REEL  
AD603AR-REEL7  
AD603ARZ1  
AD603ARZ-REEL1  
AD603ARZ-REEL71  
AD603AQ  
Temperature Range  
−40°C to +85°C  
−40°C to +85°C  
−40°C to +85°C  
−40°C to +85°C  
−40°C to +85°C  
−40°C to +85°C  
−40°C to +85°C  
−55°C to +125°C  
Package Description  
8-Lead SOIC  
8-Lead SOIC, 13" Reel  
8-Lead SOIC, 7" Reel  
8-Lead SOIC  
8-Lead SOIC, 13" Reel  
8-Lead SOIC, 7" Reel  
8-Lead CERDIP  
Package Option  
R-8  
R-8  
R-8  
R-8  
R-8  
R-8  
Q-8  
Q-8  
AD603SQ/883B2  
AD603-EVALZ1  
AD603ACHIPS  
8-Lead CERDIP  
Evaluation Board  
DIE  
1 Z = RoHS Compliant Part.  
2 Refer to AD603 Military data sheet. Also available as 5962-9457203MPA.  
Rev. H | Page 21 of 24  
 
 
AD603  
NOTES  
Rev. H | Page 22 of 24  
AD603  
NOTES  
Rev. H | Page 23 of 24  
AD603  
NOTES  
©2007 Analog Devices, Inc. All rights reserved. Trademarks and  
registered trademarks are the property of their respective owners.  
C00539-0-5/07(H)  
Rev. H | Page 24 of 24  
 

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