AD8145WYCPZ-R7 [ADI]

High Speed, Triple Differential Receiver with Comparators; 高速,三路差分接收器与比较
AD8145WYCPZ-R7
型号: AD8145WYCPZ-R7
厂家: ADI    ADI
描述:

High Speed, Triple Differential Receiver with Comparators
高速,三路差分接收器与比较

文件: 总24页 (文件大小:464K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
High Speed, Triple Differential Receiver  
with Comparators  
AD8145  
FUNCTIONAL BLOCK DIAGRAM  
FEATURES  
High speed: 500 MHz, 2000 V/μs @ G = 1, VOUT = 2 V p-p  
0.1 dB flatness out to 75 MHz  
32  
31  
30  
29  
28  
27  
26  
25  
High CMRR: 69 dB @ 10 MHz  
C
High differential input impedance: 1 MΩ  
Wide input common-mode range: 3.5 V ( 5 V supplies)  
On-chip, gain setting resistors can be configured for gain of 1 or 2  
Fast settling: 15 ns to 0.1% @ 2 V p-p  
Low input referred noise: 13 nV/√Hz  
Disable feature  
1
2
3
4
5
6
7
8
R
R
24  
23  
22  
21  
20  
19  
18  
17  
GND  
REF_G  
GAIN_G  
IN+_G  
GND  
OUT_B  
OUT_G  
OUT_R  
+
C
R
R
+
Small packaging: 32-lead, 5 mm × 5 mm LFCSP  
AEC-Q10 qualified (AD8145W)  
IN–_G  
V
S+  
AD8145  
REF_R  
GAIN_R  
GND  
+
COMPB_IN+  
COMPB_IN–  
GND  
C
R
B
APPLICATIONS  
A
R
RGB video receivers  
YPbPr video receivers  
9
10  
11  
12  
13  
14  
15  
16  
Keyboard, video, mouse (KVM)  
Unshielded twisted pair (UTP) receivers  
Automotive driver assistance (AD8145W)  
Automotive Infotainment (AD8145W)  
Figure 1.  
GENERAL DESCRIPTION  
The AD8145 is a triple, low cost, differential-to-single-ended  
receiver specifically designed for receiving red-green-blue (RGB)  
video signals over twisted pair cable or differential printed circuit  
board (PCB) traces. It can also be used to receive any type of  
analog signal or high speed data transmission. Two auxiliary  
comparators with hysteresis are provided that can be used to  
decode video sync signals, which are encoded on the received  
common-mode voltages, to receive digital signals or as general-  
purpose comparators. The AD8145 can be used in conjunction  
with the AD8133 or AD8134 triple differential drivers to provide a  
complete low cost solution for RGB over Category 5 UTP cable  
applications, including KVM.  
The AD8145 can be configured for a differential-to-single-ended  
gain of 1 or 2 by connecting the GAIN_x pin of each channel to  
its respective output (G = 1) or connecting it to a reference voltage  
(G = 2), which is normally grounded.  
A REF_x input is provided on each channel that allows designers to  
level shift the output signals.  
The AD8145W is the automotive grade version that is qualified  
per the AEC-Q100 for use in automotive applications. See the  
Automotive Products section for more details.  
The AD8145 is available in a 5 mm × 5 mm, 32-lead LFCSP and  
is rated to work over the extended industrial temperature range  
of −40°C to +105°C.  
The excellent common-mode rejection (69 dB @ 10 MHz) of  
the AD8145 allows for the use of low cost, unshielded twisted  
pair cables in noisy environments.  
Rev. A  
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  
www.analog.com  
Fax: 781.461.3113 ©2006–2010 Analog Devices, Inc. All rights reserved.  
 
 
AD8145  
TABLE OF CONTENTS  
Features .............................................................................................. 1  
Overview ..................................................................................... 15  
Basic Closed-Loop Gain Configurations ................................ 15  
Terminating the Input................................................................ 16  
Input Clamping........................................................................... 17  
PCB Layout Considerations...................................................... 18  
Driving a Capacitive Load......................................................... 19  
Power-Down ............................................................................... 19  
Automotive Products................................................................. 19  
Comparators ............................................................................... 19  
Sync Pulse Extraction Using Comparators............................. 20  
Outline Dimensions....................................................................... 21  
Ordering Guide .......................................................................... 21  
Applications....................................................................................... 1  
Functional Block Diagram .............................................................. 1  
General Description......................................................................... 1  
Revision History ............................................................................... 2  
Specifications..................................................................................... 3  
Absolute Maximum Ratings............................................................ 7  
Thermal Resistance ...................................................................... 7  
Maximum Power Dissipation ..................................................... 7  
ESD Caution.................................................................................. 7  
Pin Configuration and Function Description .............................. 8  
Typical Performance Characteristics ............................................. 9  
Theory of Operation ...................................................................... 14  
Applications Information .............................................................. 15  
REVISION HISTORY  
1/10—Rev. 0 to Rev. A  
Changes to Features Section, Applications Section, and General  
Description Section.......................................................................... 1  
Changes to Table 1............................................................................ 3  
Changes to Table 2............................................................................ 5  
Added Automotive Products Section .......................................... 19  
Added Exposed Paddle Notation to Outline Dimensions ........ 21  
Changes to Ordering Guide .......................................................... 21  
10/06—Revision 0: Initial Version  
Rev. A | Page 2 of 24  
 
AD8145  
SPECIFICATIONS  
TA = 25°C, VS = 5 V, REF_x = 0 V, RL = 150 Ω, CL = 2 pF, G = 1, TMIN to TMAX = −40°C to +105°C, unless otherwise noted.  
Table 1.  
Parameter  
Conditions  
Min  
Typ  
Max  
Unit  
DYNAMIC PERFORMANCE  
−3 dB Bandwidth  
VOUT = 0.2 V p-p  
VOUT = 2 V p-p  
530  
500  
200  
200  
75  
100  
2100  
2100  
15  
MHz  
MHz  
MHz  
MHz  
MHz  
MHz  
V/μs  
V/μs  
ns  
VOUT = 0.2 V p-p, G = 2  
VOUT = 2 V p-p, G = 2  
VOUT = 2 V p-p  
VOUT = 2 V p-p, G = 2  
VOUT = 2 V p-p  
Bandwidth for 0.1 dB Flatness  
Slew Rate  
VOUT = 2 V p-p, G = 2  
VOUT = 2 V p-p, 0.1%  
Settling Time  
Output Overdrive Recovery  
NOISE/DISTORTION  
Second Harmonic  
Third Harmonic  
Crosstalk  
Input Voltage Noise (RTI)  
Differential Gain Error  
Differential Phase Error  
INPUT CHARACTERISTICS  
Common-Mode Rejection  
20  
ns  
VOUT = 2 V p-p, 1 MHz  
VOUT = 2 V p-p, 1 MHz  
VOUT = 2 V p-p, 10 MHz  
f ≥ 10 kHz  
NTSC, 200 IRE, RL ≥ 150 Ω  
NTSC, 200 IRE, RL ≥ 150 Ω  
−67  
−88  
−62  
13  
0.25  
0.1  
dBc  
dBc  
dB  
nV/√Hz  
%
Degrees  
DC, VCM = −2 V to +2 V  
AD8145W only, TMIN to TMAX  
VCM = 1 V p-p, f = 10 MHz  
VCM = 1 V p-p, f = 100 MHz  
V+IN − V−IN = 0 V  
81  
78  
90  
dB  
dB  
dB  
dB  
V
69  
41  
3.5  
2.5  
1
1.3  
1
2
Common-Mode Voltage Range  
Differential Operating Range  
Resistance  
V
Differential  
Common mode  
Differential  
MΩ  
MΩ  
pF  
pF  
Capacitance  
Common mode  
DC PERFORMANCE  
Closed-Loop Gain  
DC, G = 2  
AD8145W only, TMIN to TMAX  
G = 2  
AD8145W only, TMIN to TMAX  
TMIN to TMAX  
1.955  
1.930  
−17.5  
−25  
1.985  
+7.0  
2.020  
2.030  
+1.0  
V/V  
V/V  
mV  
mV  
μV/°C  
μA  
μA  
nA/°C  
nA  
Output Offset Voltage  
+8.0  
Output Offset Voltage Drift  
Input Bias Current (+IN, −IN)  
−18  
−3.4  
−6  
−7  
−0.9  
−0.5  
AD8145W only, TMIN to TMAX  
TMIN to TMAX (+IN, −IN)  
Input Bias Current Drift  
Input Offset Current  
25  
−65  
−400  
−650  
+300  
+650  
AD8145W only, TMIN to TMAX  
nA  
OUTPUT PERFORMANCE  
Voltage Swing  
−3.64  
−3.45  
+3.55  
+3.35  
V
V
mA  
mA  
AD8145W only, TMIN to TMAX  
Short to GND, source/sink  
Output Current  
Short-Circuit Current  
50  
+195/−230  
Rev. A | Page 3 of 24  
 
 
AD8145  
Parameter  
Conditions  
Min  
Typ  
Max  
Unit  
COMPARATOR PERFORMANCE  
VOH  
RL = 1 kΩ  
AD8145W only, TMIN to TMAX  
RL = 1 kΩ  
3.205  
2.950  
3.310  
0.390  
V
V
V
V
VOL  
0.420  
0.440  
AD8145W only, TMIN to TMAX  
Input Offset Voltage  
Hysteresis Width  
Input Bias Current  
Propagation Delay, tPLH  
Propagation Delay, tPHL  
Rise Time  
2.5  
18  
1.5  
6
6
6
mV  
mV  
μA  
ns  
ns  
ns  
ns  
10% to 90%  
10% to 90%  
Fall Time  
2
POWER-DOWN PERFORMANCE  
Power-Down VIH  
Power-Down VIL  
Power-Down IIH  
Power-Down IIL  
VS+ − 1.65  
VS+ − 2.65  
0.5  
−250  
1
V
V
μA  
μA  
μs  
Power-Down Assert Time  
POWER SUPPLY  
Operating Range  
4.5  
11  
V
Quiescent Current, Positive Supply  
48.5  
16  
57.5  
70  
19.5  
25  
mA  
mA  
mA  
mA  
mA  
mA  
mA  
mA  
dB  
AD8145W only, TMIN to TMAX  
Disabled  
AD8145W only, TMIN to TMAX  
Quiescent Current, Negative Supply  
−52  
−65  
−13.9  
−20  
−43.5  
−11  
−79  
−68  
AD8145W only, TMIN to TMAX  
Disabled  
AD8145W only, TMIN to TMAX  
DC  
AD8145W only, TMIN to TMAX  
DC  
AD8145W only, TMIN to TMAX  
PSRR, Positive Supply  
PSRR, Negative Supply  
−70  
−66  
−57  
−54  
dB  
dB  
dB  
Rev. A | Page 4 of 24  
AD8145  
TA = 25°C, VS = 2.5 V, REF_x = 0 V, RL = 1 kΩ, CL = 2 pF, G = 1, TMIN to TMAX = −40°C to +105°C, unless otherwise noted.  
Table 2.  
Parameter  
Conditions  
Min  
Typ  
Max  
Unit  
DYNAMIC PERFORMANCE  
−3 dB Bandwidth  
VOUT = 0.2 V p-p  
VOUT = 2 V p-p  
450  
425  
180  
180  
53  
100  
2000  
2000  
16  
MHz  
MHz  
MHz  
MHz  
MHz  
MHz  
V/μs  
V/μs  
ns  
VOUT = 0.2 V p-p, G = 2, RL = 150 Ω  
VOUT = 2 V p-p, G = 2, RL = 150 Ω  
VOUT = 2 V p-p  
VOUT = 2 V p-p, G = 2, RL = 150 Ω  
VOUT = 2 V p-p  
Bandwidth for 0.1 dB Flatness  
Slew Rate  
VOUT = 2 V p-p, G = 2, RL = 150 Ω  
VOUT = 2 V p-p, 0.1%  
Settling Time  
Output Overdrive Recovery  
NOISE/DISTORTION  
Second Harmonic  
Third Harmonic  
Crosstalk  
Input Voltage Noise (RTI)  
INPUT CHARACTERISTICS  
Common-Mode Rejection  
10  
ns  
VOUT = 1 V p-p, 1 MHz  
VOUT = 1 V p-p, 1 MHz  
VOUT = 1 V p-p, 10 MHz  
f ≥ 10 kHz  
−71  
−76  
−62  
13  
dBc  
dBc  
dB  
nV/√Hz  
DC, VCM = −1 V to +1 V  
AD8145W only, TMIN to TMAX  
VCM = 1 V p-p, f = 10 MHz  
VCM = 1 V p-p, f = 100 MHz  
V+IN − V−IN = 0 V  
78  
75  
86  
dB  
dB  
dB  
dB  
V
72  
43  
1.25  
1.6  
1
1.3  
1
2
Common-Mode Voltage Range  
Differential Operating Range  
Resistance  
V
Differential  
Common mode  
Differential  
MΩ  
MΩ  
pF  
pF  
Capacitance  
Common mode  
DC PERFORMANCE  
Closed-Loop Gain  
DC, G = 2  
AD8145W only, TMIN to TMAX  
G = 2  
AD8145W only, TMIN to TMAX  
TMIN to TMAX  
1.960  
1.930  
−13.5  
−18  
1.985  
−4.5  
2.016  
2.030  
+2  
V/V  
V/V  
mV  
mV  
μV/°C  
μA  
μA  
nA/°C  
nA  
Output Offset Voltage  
+8  
Output Offset Voltage Drift  
Input Bias Current (+IN, −IN)  
−18  
−3.5  
−6  
−7  
−0.9  
−0.5  
AD8145W only, TMIN to TMAX  
TMIN to TMAX (+IN, −IN)  
Input Bias Current Drift  
Input Offset Current  
25  
−60  
−400  
−650  
+300  
+650  
AD8145W only, TMIN to TMAX  
nA  
OUTPUT PERFORMANCE  
Voltage Swing  
RL = 150 Ω  
AD8145W only, TMIN to TMAX  
−1.35  
−1.20  
+1.3  
+1.15  
V
V
Output Current  
25  
mA  
mA  
Short-Circuit Current  
POWER-DOWN PERFORMANCE  
Power-Down VIH  
Power-Down VIL  
Power-Down IIH  
Short to GND, source/sink  
+100/−100  
VS+ − 1.5  
VS+ − 2.5  
0.25  
50  
1
V
V
μA  
μA  
μs  
Power-Down IIL  
Power-Down Assert Time  
Rev. A | Page 5 of 24  
AD8145  
Parameter  
Conditions  
Min  
Typ  
Max  
Unit  
POWER SUPPLY  
Operating Range  
Quiescent Current, Positive Supply  
4.5  
11  
47  
57  
16  
21  
V
40  
mA  
mA  
mA  
mA  
mA  
mA  
mA  
mA  
dB  
AD8145W only, TMIN to TMAX  
Disabled  
AD8145W only, TMIN to TMAX  
13.5  
−36  
−10  
−83  
−67  
Quiescent Current, Negative Supply  
−43.5  
−54  
−12.5  
−17  
AD8145W only, TMIN to TMAX  
Disabled  
AD8145W only, TMIN to TMAX  
DC  
AD8145W only, TMIN to TMAX  
DC  
AD8145W only, TMIN to TMAX  
PSRR, Positive Supply  
PSRR, Negative Supply  
−73  
−68  
−62  
−59  
dB  
dB  
dB  
Rev. A | Page 6 of 24  
AD8145  
ABSOLUTE MAXIMUM RATINGS  
MAXIMUM POWER DISSIPATION  
Table 3.  
The maximum safe power dissipation in the AD8145 package is  
limited by the associated rise in junction temperature (TJ) on  
the die. At approximately 150°C, which is the glass transition  
temperature, the plastic changes its properties. Even temporarily  
exceeding this temperature limit can change the stresses that the  
package exerts on the die, permanently shifting the parametric  
performance of the AD8145. Exceeding a junction temperature  
of 150°C for an extended period can result in changes in the  
silicon devices, potentially causing failure.  
Parameter  
Rating  
Supply Voltage  
Power Dissipation  
Storage Temperature Range  
Operating Temperature Range  
Lead Temperature (Soldering, 10 sec)  
Junction Temperature  
12 V  
See Figure 2  
−65°C to +125°C  
−40°C to +105°C  
300°C  
150°C  
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.  
The power dissipated in the package (PD) is the sum of the  
quiescent power dissipation and the power dissipated in the  
package due to the load drive for all outputs. The quiescent  
power is the voltage between the supply pins (VS) times the  
quiescent current (IS). The power dissipated due to the load  
drive depends on the particular application. For each output, the  
power due to load drive is calculated by multiplying the load  
current by the associated voltage drop across the device. The  
power dissipated due to all of the loads is equal to the sum of  
the power dissipation due to each individual load. RMS voltages  
and currents must be used in these calculations.  
THERMAL RESISTANCE  
θJA is specified for the worst-case conditions, that is, θJA is  
specified for a device soldered in the circuit board with its  
exposed paddle soldered to a pad on the PCB surface, which is  
thermally connected to a copper plane.  
Airflow increases heat dissipation, effectively reducing θJA. In  
addition, more metal directly in contact with the package leads  
from metal traces, through-holes, ground, and power planes  
reduces the θJA. The exposed paddle on the underside of the  
package must be soldered to a pad on the PCB surface, which is  
thermally connected to a copper plane to achieve the specified θJA.  
Table 4. Thermal Resistance  
Package Type  
θJA  
θJC  
Unit  
5 mm × 5 mm, 32-Lead LFCSP  
47  
8.5  
°C/W  
4.5  
4.0  
3.5  
3.0  
2.5  
2.0  
1.5  
1.0  
0.5  
0
Figure 2 shows the maximum safe power dissipation in the  
package vs. the ambient temperature for the 32-lead LFCSP  
(47°C/W) on a JEDEC standard 4-layer board with the underside  
paddle soldered to a pad, which is thermally connected to a  
PCB plane.  
ESD CAUTION  
–40  
–20  
0
20  
40  
60  
80  
100  
AMBIENT TEMPERATURE (°C)  
Figure 2. Maximum Power Dissipation vs. Temperature for a 4-Layer Board  
Rev. A | Page 7 of 24  
 
 
 
AD8145  
PIN CONFIGURATION AND FUNCTION DESCRIPTION  
GND  
REF_G  
GAIN_G  
IN+_G  
1
2
3
4
5
6
7
8
24 GND  
PIN 1  
INDICATOR  
23 OUT_B  
22 OUT_G  
21 OUT_R  
AD8145  
IN–_G  
20 V  
S+  
TOP VIEW  
REF_R  
GAIN_R  
GND  
19 COMPB_IN+  
18 COMPB_IN–  
17 GND  
(Not to Scale)  
NOTES  
1. EXPOSED PAD ON UNDERSIDE OF DEVICE  
MUST BE CONNECTED TO GROUND.  
Figure 3. Pin Configuration  
Table 5. Pin Function Descriptions  
Pin No.  
Mnemonic  
Description  
1, 8, 9, 16, 17, 24, 25, 32  
2
GND  
REF_G  
Signal Ground and Thermal Plane Connection. (See the Absolute Maximum Ratings section.)  
Reference Input, Green Channel.  
3
4
5
GAIN_G  
IN+_G  
IN−_G  
Gain Connection, Green Channel.  
Noninverting Input, Green Channel.  
Inverting Input, Green Channel.  
6
REF_R  
Reference Input, Red Channel.  
7
10  
11  
GAIN_R  
IN+_R  
IN−_R  
Gain Connection, Red Channel.  
Noninverting Input, Red Channel.  
Inverting Input, Red Channel.  
12  
13  
14  
COMPA_IN+  
COMPA_IN−  
COMPA_OUT  
Positive Input, Comparator A.  
Negative Input, Comparator A.  
Output, Comparator A.  
15  
COMPB_OUT Output, Comparator B.  
18  
19  
20  
COMPB_IN−  
COMPB_IN+  
VS+  
Negative Input, Comparator B.  
Positive Input, Comparator B.  
Positive Power Supply.  
21  
22  
23  
26  
OUT_R  
OUT_G  
OUT_B  
VS−  
Output, Red Channel.  
Output, Green Channel.  
Output, Blue Channel.  
Negative Power Supply.  
27  
DIS/PD  
REF_B  
GAIN_B  
IN+_B  
IN−_B  
GND  
Disable/Power Down.  
28  
29  
30  
31  
Reference Input, Blue Channel.  
Gain Connection, Blue Channel.  
Noninverting Input, Blue Channel.  
Inverting Input, Blue Channel.  
Signal Ground and Thermal Plane Connection.  
Exposed Underside Pad  
Rev. A | Page 8 of 24  
 
AD8145  
TYPICAL PERFORMANCE CHARACTERISTICS  
Unless otherwise noted, G = 1, RL = 150 Ω, CL = 2 pF, REF_x = midsupply, VS = 5 V, TA = 25°C. Refer to the circuit in Figure 35.  
3
2
3
2
+5V  
±5V  
+5V  
±5V  
1
1
0
0
–1  
–2  
–3  
–4  
–5  
–6  
–7  
–1  
–2  
–3  
–4  
–5  
–6  
–7  
V
= 2V p-p  
V
= 0.2V p-p  
OUT  
OUT  
1
10  
100  
1000  
1
10  
100  
1000  
FREQUENCY (MHz)  
FREQUENCY (MHz)  
Figure 4. Small Signal Frequency Response at Various Power Supplies, G = 1  
Figure 7. Large Signal Frequency Response at Various Power Supplies, G = 1  
9
8
7
6
5
4
3
9
8
7
6
5
4
3
+5V ±5V  
+5V  
±5V  
2
1
2
1
0
0
V
= 0.2V p-p  
V
= 2V p-p  
OUT  
OUT  
–1  
–1  
1
10  
100  
1000  
1
10  
100  
1000  
FREQUENCY (MHz)  
FREQUENCY (MHz)  
Figure 5. Small Signal Frequency Response at Various Power Supplies, G = 2  
Figure 8. Large Signal Frequency Response at Various Power Supplies, G = 2  
3
2
3
2
1
0
1
0
–1  
–1  
–2  
–3  
–4  
–5  
–6  
–7  
G = 2, C = 10 + 2pF, R  
SNUB  
= 20  
= 20Ω  
L
= 20Ω  
= 20Ω  
SNUB  
G = 2, C = 0 + 2pF, R  
= 0Ω  
L
SNUB  
= 0Ω  
–2  
–3  
–4  
–5  
–6  
–7  
G = 1, C = 10 + 2pF, R  
L
SNUB  
G = 1, C = 0 + 2pF, R  
= 0Ω  
L
SNUB  
G = 1, C = 0 + 2pF, R  
= 0Ω  
L
SNUB  
V
= 2V p-p  
V
= 0.2V p-p  
OUT  
OUT  
1
10  
100  
1000  
1
10  
100  
1000  
FREQUENCY (MHz)  
FREQUENCY (MHz)  
Figure 6. Small Signal Frequency Response at Various Gains  
and 10 pF Capacitive Load Buffered by 20 Ω Resistor  
Figure 9. Large Signal Frequency Response at Various Gains  
and 10 pF Capacitive Load Buffered by 20 Ω Resistor  
Rev. A | Page 9 of 24  
 
AD8145  
3
3
2
2
1
1
G = 1  
G = 1  
0
0
–1  
–2  
–3  
–4  
–5  
–1  
–2  
–3  
–4  
–5  
–6  
–7  
G = 2  
G = 2  
–6  
V
–7  
1
= 0.2V p-p  
V
= 2V p-p  
OUT  
OUT  
10  
100  
1000  
1
10  
100  
1000  
FREQUENCY (MHz)  
FREQUENCY (MHz)  
Figure 13. Large Signal Frequency Response at Various Gains  
Figure 10. Small Signal Frequency Response at Various Gains  
1000  
0.5  
G = 1, V = +5V  
S
0.4  
0.3  
G = 1, V = ±5V  
S
0.2  
0.1  
100  
0
G = 2, V = +5V  
S
–0.1  
–0.2  
–0.3  
–0.4  
–0.5  
G = 2, V = ±5V  
S
V
= 2V p-p  
OUT  
10  
0.01  
0.1  
1
10  
100  
1000  
10000 100000  
1
10  
100  
1000  
FREQUENCY (kHz)  
FREQUENCY (MHz)  
Figure 14. Input Referred Voltage Noise vs. Frequency  
Figure 11. 0.1 dB Flatness for Various Power Supplies and Gains  
110  
100  
90  
4
3
2
1
0
R
= OPEN CIRCUIT  
L
G = 1  
= ±5V  
V
S
80  
V
= +5V  
S
70  
60  
50  
40  
30  
20  
10  
V
= ±5V  
S
–1  
–2  
–3  
–4  
0.1  
1
10  
FREQUENCY (MHz)  
100  
1000  
–5  
–4  
–3  
–2  
–1  
0
1
2
3
4
5
DIFFERENTIAL INPUT VOLTAGE (V)  
Figure 12. Common-Mode Rejection vs. Frequency at Various Supplies  
Figure 15. Differential Input Operating Range  
Rev. A | Page 10 of 24  
AD8145  
150  
100  
50  
1.5  
1.0  
BLACK = +5V  
GRAY = ±5V  
BLACK = +5V  
GRAY = ±5V  
0.5  
0
0
–50  
–100  
–150  
–0.5  
–1.0  
–1.5  
V
= 2V p-p  
20  
V
= 0.2V p-p  
OUT  
OUT  
0
10  
20  
30  
40  
50  
60  
70  
80  
90  
100  
0
10  
30  
40  
50  
60  
70  
80  
90  
100  
TIME (ns)  
TIME (ns)  
Figure 16. Small Signal Transient Response at Various Power Supplies, G = 1  
Figure 19. Large Signal Transient Response at Various Power Supplies, G = 1  
150  
100  
1.5  
1.0  
BLACK = +5V  
GRAY = ±5V  
BLACK = +5V  
GRAY = ±5V  
50  
0
0.5  
0
–50  
–100  
–0.5  
–1.0  
V
= 2V p-p  
20  
V
= 0.2V p-p  
20  
OUT  
OUT  
–150  
–1.5  
0
10  
30  
40  
50  
60  
70  
80  
90  
100  
0
10  
30  
40  
50  
60  
70  
80  
90  
100  
TIME (ns)  
TIME (ns)  
Figure 17. Small Signal Transient Response at Various Power Supplies, G = 2  
Figure 20. Large Signal Transient Response at Various Power Supplies, G = 2  
150  
1.5  
G = 1, C = 0 + 2pF, R  
SNUB  
= 0  
= 20Ω  
G = 1, C = 0 + 2pF, R  
SNUB  
= 0Ω  
= 20Ω  
L
L
G = 1, C = 10 + 2pF, R  
G = 1, C = 10 + 2pF, R  
L
SNUB  
L
SNUB  
100  
50  
1.0  
0.5  
V = 2V p-p  
OUT  
V
= 0.2V p-p  
OUT  
0
0
–50  
–100  
–150  
–0.5  
–1.0  
–1.5  
G = 2, C = 0 + 2pF, R  
L
= 0Ω  
G = 2, C = 0 + 2pF, R  
L
= 0Ω  
SNUB  
SNUB  
G = 2, C = 10 + 2pF, R  
= 20Ω  
G = 2, C = 10 + 2pF, R  
= 20Ω  
L
SNUB  
L
SNUB  
0
10  
20  
30  
40  
50  
60  
70  
80  
90  
100  
0
10  
20  
30  
40  
50  
60  
70  
80  
90  
100  
TIME (ns)  
TIME (ns)  
Figure 18. Small Signal Transient Response at Various Gains  
and 10 pF Capacitive Load Buffered by 20 Ω Resistor  
Figure 21. Large Signal Transient Response at Various Gains  
and 10 pF Capacitive Load Buffered by 20 Ω Resistor  
Rev. A | Page 11 of 24  
AD8145  
2.0  
0.5  
4500  
4000  
3500  
3000  
2500  
2000  
1500  
1000  
500  
POSITIVE  
SLEW RATE  
1.6  
0.4  
OUTPUT  
INPUT  
1.2  
0.3  
0.8  
0.4  
0.2  
NEGATIVE  
SLEW RATE  
0.1  
ERROR  
0
0
–0.4  
–0.8  
–1.2  
–1.6  
–2.0  
–0.1  
–0.2  
–0.3  
–0.4  
–0.5  
0
0
5
10  
15  
20  
25  
TIME (ns)  
30  
35  
40  
45  
50  
0
0.5  
1.0  
1.5  
2.0  
2.5  
3.0  
3.5  
4.0  
4.5  
5.0  
OUTPUT VOLTAGE (V p-p)  
Figure 22. Settling Time  
Figure 25. Slew Rate vs. Output Voltage Swing  
–50  
–55  
–60  
–65  
–70  
–75  
–80  
–50  
–60  
V
= +5V  
S
–70  
–80  
V
= ±5V  
S
V
= ±5V  
= +5V  
S
–90  
–100  
–110  
–120  
V
S
V
= 2V p-p  
V
= 2V p-p  
OUT  
OUT  
0.1  
1
10  
FREQUENCY (MHz)  
100  
0.1  
1
10  
FREQUENCY (MHz)  
100  
Figure 26. Third Harmonic Distortion vs. Frequency and Power Supplies,  
OUT = 2 V p-p, G = 1  
Figure 23. Second Harmonic Distortion vs. Frequency and Power Supplies,  
VOUT = 2 V p-p, G = 1  
V
–50  
–50  
–60  
V
= 2V p-p  
OUT  
–55  
–60  
–65  
–70  
–75  
–80  
V
= +5V  
S
–70  
V
= ±5V  
S
–80  
–90  
V
V
= ±5V  
= +5V  
S
S
–100  
–110  
–120  
V
= 2V p-p  
OUT  
0.1  
1
10  
FREQUENCY (MHz)  
100  
0.1  
1
10  
FREQUENCY (MHz)  
100  
Figure 24. Second Harmonic Distortion vs. Frequency and Power Supplies,  
OUT = 2 V p-p, G = 2  
Figure 27. Third Harmonic Distortion vs. Frequency and Power Supplies,  
OUT = 2 V p-p, G = 2  
V
V
Rev. A | Page 12 of 24  
AD8145  
65  
60  
55  
50  
45  
40  
35  
30  
25  
20  
15  
5
4
R
= OPEN CIRCUIT  
L
3
I
(±5V)  
CC  
2
I
(±5V)  
1
EE  
0
–1  
–2  
–3  
–4  
–5  
+5V OUTPUT  
I
(±2.5V)  
EE  
+5V 2 × V  
IN  
I
(±2.5V)  
20  
±5V OUTPUT  
CC  
±5V 2 × V  
IN  
G = 2  
50  
–60  
–40  
–20  
0
40  
60  
80  
100  
120  
0
100 150 200 250 300 350 400 450 500  
TIME (ns)  
TEMPERATURE (°C)  
Figure 28. Power Supply Current vs. Temperature  
Figure 31. Output Overdrive Recovery  
10  
0
10  
0
–10  
–20  
–30  
–40  
–50  
–60  
–70  
–80  
–90  
–10  
–20  
–30  
–40  
–50  
–60  
–70  
–80  
–90  
BLACK = ±2.5V  
GRAY = ±5V  
BLACK = +5V  
GRAY = ±5V  
0.01  
0.1  
1
10  
100  
1000  
0.01  
0.1  
1
10  
100  
1000  
FREQUENCY (MHz)  
FREQUENCY (MHz)  
Figure 32. Negative Power Supply Rejection Ratio (PSRR) vs. Frequency  
Figure 29. Positive Power Supply Rejection Ratio (PSRR) vs. Frequency  
3.5  
3.0  
2.5  
2.0  
1.5  
1.0  
0.5  
0
–15  
–10  
–5  
0
5
10  
15  
V
(mV)  
IN  
Figure 30. Comparator Hysteresis  
Rev. A | Page 13 of 24  
AD8145  
THEORY OF OPERATION  
The AD8145 amplifiers use an architecture called active feedback,  
which differs from that of conventional op amps. The most  
obvious differentiating feature is the presence of two separate  
pairs of differential inputs compared to a conventional op amp’s  
single pair. Typically, for the active feedback architecture, one of  
these input pairs is driven by a differential input signal while  
the other is used for the feedback. This active stage in the feedback  
path is where the term active feedback is derived. The AD8145  
has an internal feedback resistor from each amplifier output to  
the negative input of its feedback input stage. This limits the  
possible closed-loop gain configurations for the AD8145.  
The two differential input stages of the AD8145 are each  
transconductance stages that are well matched. These stages  
convert the respective differential input voltages to internal  
currents. The currents are then summed and converted to a  
voltage, which is buffered to drive the output. The compensation  
capacitor is included in the summing circuit. When the feedback  
path is closed around the part, the output drives the feedback  
input to the voltage that causes the internal currents to sum to  
zero. This occurs when the two differential inputs are equal and  
opposite; that is, their algebraic sum is zero.  
In a closed-loop application, a conventional op amp has its  
differential input voltage driven to near zero under non-  
transient conditions. The AD8145 generally has differential  
input voltages at each of its input pairs, even under equilibrium  
conditions. As a practical consideration, it is necessary to limit  
the differential input voltage internally with a clamp circuit.  
Therefore, the input dynamic ranges are limited to approximately  
2.5 V (see the Specifications section for more details). For this  
reason, it is not recommended to reverse the input and feedback  
stages of the AD8145, even though some normal functionality  
may be observed under some conditions.  
The active feedback architecture offers several advantages over a  
conventional op amp in several types of applications. Among  
these are excellent common-mode rejection, wide input common-  
mode range, and a pair of inputs that are high impedance and  
completely balanced in a typical application. In addition, while  
an external feedback network establishes the gain response as in a  
conventional op amp, its separate path makes it entirely independent  
of the signal input. This eliminates any interaction between the  
feedback and input circuits, which traditionally causes problems  
with CMRR in conventional differential-input op amp circuits.  
Another advantage of active feedback is the ability to change the  
polarity of the gain merely by switching the differential inputs.  
A high input impedance inverting amplifier can therefore be  
made. Besides high input impedance, a unity-gain inverter with  
the AD8145 has a noise gain of unity, producing lower output  
noise and higher bandwidth than op amps that have noise gain  
equal to 2 for a unity-gain inverter.  
Rev. A | Page 14 of 24  
 
AD8145  
APPLICATIONS INFORMATION  
+5V  
OVERVIEW  
The AD8145 contains three independent active feedback amplifiers  
that can be effectively applied as differential line receivers for  
red-green-blue (RGB) signals or component video signals, such  
as YPbPr, transmitted over UTP cable. The AD8145 also contains  
two general-purpose comparators with hysteresis that can be  
used to receive digital signals or to extract video synchronization  
pulses from received common-mode signals that contain  
encoded synchronization signals.  
0.01µF  
V
IN  
OUT  
V
REF  
OUT  
V
REF  
R
The comparators, which receive power from the positive supply, are  
referenced to GND and require greater than 4.5 V on the positive  
supply for proper operation. If the comparators are not used,  
then a split 2.5 V can be used with the amplifiers operating  
normally.  
R
C
GAIN  
0.01µF  
–5V  
The AD8145 includes a power-down feature that can be asserted to  
reduce the supply current when a particular device is not in use.  
Figure 33. Basic Gain = 1 Circuit: VOUT = VIN + VREF  
The gain equation for the circuit in Figure 33 is  
OUT = VIN + VREF  
BASIC CLOSED-LOOP GAIN CONFIGURATIONS  
V
(1)  
Each amplifier in the AD8145 comprises two transconductance  
amplifiers—one for the input signal and one for negative feedback.  
Note that the closed-loop gain of the amplifier used in the signal  
path is defined as the single-ended output voltage of the amplifier  
divided by its differential input voltage. Therefore, each amplifier  
in the AD8145 provides differential-to-single-ended gain.  
Additionally, the amplifier used for feedback has two high  
impedance inputs—the feedback input, where the negative  
feedback is applied, and the REF input, that can be used as  
an independent single-ended input to apply a dc offset to the  
output signal.  
In this configuration, the voltage applied to the REF pin appears  
at the output with a gain of 1.  
Figure 34 illustrates one way to operate an AD8145 amplifier  
with a gain of 2.  
+5V  
0.01µF  
V
IN  
REF  
The AD8145 contains on-chip feedback networks between each  
amplifier output and its respective feedback input. The closed-  
loop gain of the amplifier is set to 1 by connecting the amplifier  
output directly to its respective GAIN_x pin. Doing this places  
the on-chip resistors and capacitor in parallel across the amplifier  
output and feedback pin. The small feedback capacitor mitigates  
the effects of the summing-node capacitance, which is most  
problematic in the unity gain case. Closed-loop gain of an  
amplifier is set to 2 by connecting the respective GAIN_x pin  
to a reference voltage, often directly to ground. In Figure 1,  
R = 350 ꢀ and C = 2 pF.  
V
OUT  
V
REF  
C
R
GAIN  
R
0.01µF  
–5V  
Figure 34. Basic Gain = 2 Circuit: VOUT = 2(VIN + VREF  
)
The gain equation for the circuit in Figure 34 is  
OUT = 2(VIN + VREF  
V
)
(2)  
Some basic gain configurations implemented with an AD8145  
amplifier are shown in Figure 33 through Figure 36.  
Rev. A | Page 15 of 24  
 
 
 
AD8145  
To achieve unity gain from VREF to VOUT in this configuration,  
divide VREF by the same factor used in the feedback loop; the  
divider resistors, RD, need not be the same values used in the  
internal feedback loop. Figure 35 illustrates this approach.  
+5V  
TERMINATING THE INPUT  
One of the key benefits of the active feedback architecture is the  
separation that exists between the differential input signal and  
the feedback network. Because of this separation, the differential  
input maintains its high CMRR and provides high differential  
and common-mode input impedances, making line termination  
a simple task.  
0.01µF  
Most applications that use the AD8145 involve transmitting broad-  
band video signals over 100 Ω UTP cables and use dc-coupled  
terminations. The two most common types of dc-coupled  
terminations are differential and common-mode. Differential  
termination of 100 Ω UTP cables is implemented by simply  
connecting a 100 Ω resistor across the amplifier input, as shown  
in Figure 37.  
V
IN  
R
REF  
D
V
OUT  
R
D
V
REF  
C
R
GAIN  
R
+5V  
0.01µF  
–5V  
0.01µF  
Figure 35. Basic Gain Circuit: VOUT = 2VIN + VREF  
100  
UTP  
The gain equation for the circuit in Figure 35 is  
OUT = 2VIN + VREF  
V
100Ω  
IN  
OUT  
V
(3)  
V
REF  
OUT  
Another configuration that provides the same gain equation as  
Equation 3 is shown in Figure 36. In this configuration, it is  
important to keep the source resistance of VREF much smaller  
than 350 ꢀ to avoid gain errors.  
R
R
C
+5V  
GAIN  
0.01µF  
0.01µF  
–5V  
V
IN  
Figure 37. Differential-Mode Termination with G = 1  
REF  
V
OUT  
Some applications require common-mode terminations for  
common-mode currents generated at the transmitter. In these  
cases, the 100 Ω termination resistor is split into two 50 Ω  
resistors. The required common-mode termination voltage is  
applied at the tap between the two resistors. In many of these  
applications, the common-mode tap is connected to ground  
(VTERM (CM) = 0). This scheme is illustrated in Figure 38.  
+5V  
C
R
R
GAIN  
V
REF  
0.01µF  
–5V  
Figure 36. Basic Gain Circuit: VOUT = 2VIN + VREF  
For stability reasons, the inductance of the trace connected to  
the REF_x pin must be kept to less than 10 nH. The typical  
inductance of 50 Ω traces on the outer layers of the FR-4 boards  
is 7 nH/in, and on the inner layers, it is typically 9 nH/in. Vias  
must be accounted for as well. The inductance of a typical via in  
a 0.062-inch board is 1.5 nH. If longer traces are required, a 200 Ω  
resistor should be placed in series with the trace to reduce the  
Q-factor of the inductance.  
0.01µF  
50Ω  
100Ω  
UTP  
V
IN  
50Ω  
OUT  
V
REF  
V
(CM)  
OUT  
TERM  
R
In many dual-supply applications, VREF can be directly connected to  
ground right at the device.  
R
C
GAIN  
0.01µF  
–5V  
Figure 38. Common-Mode Termination with G = 1  
Rev. A | Page 16 of 24  
 
 
 
 
 
AD8145  
A simple way to implement a clamp is to use a number of diodes in  
series. The resultant clamping voltage is then the sum of the  
clamping voltages of individual diodes.  
INPUT CLAMPING  
The differential input that is assigned to receive the input signal  
includes clamping diodes that limit the differential input swing  
to approximately 5.5 V p-p at 25°C. Because of this, the input  
and feedback stages should never be interchanged.  
A 1N4448 diode has a forward voltage of approximately 0.70 V  
to 0.75 V at typical current levels that are seen when it is being  
used as a clamp, and 2 pF maximum capacitance at 0 V bias.  
(The capacitance of a diode decreases as its reverse-bias voltage  
is increased.) The series connection of two 1N4448 diodes,  
therefore, has a clamping voltage of 1.4 V to 1.5 V. Figure 40  
shows how to limit the differential input voltage applied to an  
AD8145 amplifier to ±1.4 V to ±1.5 V (2.8 V p-p to 3.0 V p-p).  
Note that the capacitance of the two series diodes is half that of  
one diode. Different numbers of series diodes can be used to  
obtain different clamping voltages.  
The supply current drawn by the AD8145 has a strong dependence  
on the input signal magnitude because the input transconductance  
stages operate with differential input signals that can be up to a  
few volts peak-to-peak. This behavior is distinctly different  
from that of traditional op amps, where the differential input  
signal is driven to essentially 0 V by negative feedback.  
For most applications, including receiving RGB video signals,  
the input signal magnitudes encountered are well within the  
safe operating limits of the AD8145 over its full power supply  
and operating temperature ranges. In some extreme applications  
where large differential and/or common-mode voltages are  
encountered, external clamping may be necessary. External  
common-mode clamping is also sometimes required when an  
unpowered AD8145 receives a signal from an active driver. In  
this case, external diodes are required when the current drawn  
by the internal ESD diodes cannot be kept to less than 5 mA.  
RT is the differential termination resistor, and the series  
resistances, RS, limit the current into the diodes. The series  
resistors should be highly matched in value to preserve high  
frequency CMRR.  
+5V  
POSITIVE CLAMP  
NEGATIVE CLAMP  
0.01µF  
+
R
S
Figure 39 shows a general approach to external differential-mode  
clamping.  
V
IN  
R
T
R
OUT  
S
+5V  
V
REF  
POSITIVE CLAMP NEGATIVE CLAMP  
OUT  
+
0.01µF  
R
S
R
V
IN  
R
T
R
C
OUT  
GAIN  
R
S
V
REF  
OUT  
0.01µF  
–5V  
R
Figure 40. Using Two 1N4448 Diodes in Series as a Clamp  
R
C
Many other nonlinear devices can be used as clamps. The best  
choice for a particular application depends upon the desired  
clamping voltage, response time, parasitic capacitance, and  
other factors.  
GAIN  
0.01µF  
–5V  
Figure 39. Differential-Mode Clamping with G = 1  
When using external differential-mode clamping, it is important  
to ensure that the series resistors (RS), the sum of the parasitic  
capacitance of the clamping devices, and the input capacitance  
of the AD8145 are small enough to preserve the desired signal  
bandwidth.  
The positive and negative clamps are nonlinear devices that exhibit  
very low impedance when the voltage across them reaches a  
critical threshold (clamping voltage), thereby limiting the voltage  
across the AD8145 input. The positive clamp has a positive  
threshold, and the negative clamp has a negative threshold.  
A diode is a simple example of such a clamp. Schottky diodes  
generally have lower clamping voltages than typical signal diodes.  
The clamping voltage should be larger than the largest expected  
signal amplitude, with enough margin to ensure that the received  
signal passes without being distorted.  
Rev. A | Page 17 of 24  
 
 
 
AD8145  
Figure 41 shows a specific example of external common-mode  
clamping.  
not required. In these cases, small series resistors should be used to  
buffer the capacitance presented by the load.  
V+  
2
Broadband power supply decoupling networks should be placed  
as close as possible to the supply pins. Small surface-mount ceramic  
capacitors are recommended for these networks, and tantalum  
capacitors are recommended for bulk supply decoupling.  
+5V  
3
+
R
S
0.01µF  
1
V–  
HBAT-540C  
Minimizing Parasitic Feedback Reactances  
V
R
T
IN  
Parasitic trace capacitance and inductance are both reduced in  
the unity-gain configuration when the feedback trace that connects  
the OUT_x pin to the GAIN_x pin is reduced in length. Removing  
the copper from the planes below the trace reduces trace capacitance,  
but increases trace inductance, because the loop area formed by  
the trace and ground plane is increased. A reasonable compromise  
that works well is to void all copper directly under the feedback  
trace and component pads with margins on each side approximately  
equal to one trace width. Combining this technique with minimizing  
trace length is effective in keeping parasitic trace reactance in  
the unity-gain feedback loop to a minimum.  
V+  
2
OUT  
V
REF  
OUT  
R
S
3
R
1
V–  
HBAT-540C  
R
C
GAIN  
0.01µF  
–5V  
Figure 41. External Common-Mode Clamping  
Maximizing Heat Removal  
A square array of thermal vias works well to connect the exposed  
paddle to internal ground planes. The vias should be placed  
inside the PCB pad that is soldered to the exposed paddle and  
should connect to all ground planes.  
The series resistances, RS, limit the current in each leg, and the  
Schottky diodes limit the voltages on each input to approximately  
0.3 V to 0.4 V over the positive power supply, V+, and to 0.3 V  
to 0.4 V below the negative power supply, V−. The required  
signal bandwidth, the line impedance, and the effective  
differential capacitance due to the AD8145 inputs and the  
diodes determine the maximum RS value.  
The AD8145 includes ground connections on its corner pins.  
These pins can be used to provide additional heat removal from  
the AD8145 by connecting them between the PCB pad that is  
soldered to the exposed paddle and a ground plane on the  
component side of the board. This layout technique lowers the  
overall package thermal resistance. Use of this technique is not  
required, but it does result in a lower junction temperature. Designs  
must often conform to Design for Manufacturing (DFM) rules  
that stipulate how to lay out PCBs in such a way as to facilitate  
the manufacturing process. Some of these rules require thermal  
relief on pads that connect to planes, and the rules may limit the  
extent to which this technique can be used.  
As with the differential clamp, the series resistors should be  
highly matched in value to preserve high frequency CMRR.  
PCB LAYOUT CONSIDERATIONS  
The two most important issues with regard to PCB layout are  
minimizing parasitic signal trace reactances in the feedback  
network and providing sufficient thermal relief.  
Excessive parasitic reactances in the feedback network cause  
excessive peaking in the frequency response of the amplifier  
and excessive overshoot in its step response due to a reduction  
in phase margin. Oscillation occurs when these parasitic  
reactances are increased to a critical point where the phase margin  
is reduced to zero. Minimizing these reactances is important to  
obtain optimal performance from the AD8145. General high  
speed layout practices should be adhered to when applying the  
AD8145. Controlled impedance transmission lines are required  
for incoming and outgoing signals, referenced to a ground plane.  
Typically, the input signals are received over 100 Ω differential  
transmission lines. A 100 Ω differential transmission line is readily  
realized on the PCB using two well-matched, closely-spaced,  
50 Ω single-ended traces that are coupled through the ground  
plane. The traces that carry the single-ended output signals are  
most often 75 Ω for video signals. Output signal connections  
should include series termination resistors that are matched to  
the impedance of the line they are driving. When driving high  
impedance loads over very short traces, impedance matching is  
Rev. A | Page 18 of 24  
 
 
AD8145  
DRIVING A CAPACITIVE LOAD  
POWER-DOWN  
The AD8145 typically drives either high impedance loads over  
short PCB traces, such as crosspoint switch inputs, or doubly  
terminated coaxial cables. A gain of 1 is commonly used in  
the high impedance case because a 6 dB transmission line  
termination loss is not incurred. A gain of 2 is required when  
driving cables to compensate for the 6 dB termination loss.  
The power-down feature can be used to reduce power consumption  
when a particular device is not in use and does not place the output  
in a high-Z state when asserted. The power-down feature is  
asserted when the voltage applied to the power-down pin drops  
to approximately 2 V below the positive supply. The AD8145 is  
enabled by pulling the power-down pin to the positive supply.  
In all cases, the output must drive the parasitic capacitance of  
the feedback loop, conservatively estimated to be 1 pF, in addition  
to the capacitance presented by the actual load. When driving a  
high impedance input, it is recommended that a small series  
resistor be used to buffer the input capacitance of the device  
being driven. Clearly, the resistor value must be small enough to  
preserve the required bandwidth. In the ideal doubly terminated  
cable case, the AD8145 output sees a purely resistive load. In  
reality, there is some residual capacitance, which is buffered by  
the series termination resistor. Figure 42 illustrates the high  
impedance case, and Figure 43 illustrates the cable driving case.  
+5V  
AUTOMOTIVE PRODUCTS  
The AD8145W product is qualified per the AEC-Q100 for use  
in automotive applications. This model meets stringent automotive  
performance and quality requirements and offers the same  
functionalities as the commercial and industrial grade devices but  
operates over a temperature range of −40°C to +105°C. For more  
information, contact your local Analog Devices, Inc., sales  
representative.  
COMPARATORS  
In addition to general-purpose applications, the two on-chip  
comparators can be used to decode video sync pulses from the  
received common-mode voltages or to receive differential digital  
information. Built-in hysteresis helps to eliminate false triggers  
from noise.  
0.01µF  
V
IN  
The comparator outputs are designed to drive source-terminated  
transmission lines. The source termination technique uses a resistor  
in-series with each comparator output such that the sum of the  
comparator source resistance (≈20 ꢀ) and the series resistor  
equals the transmission line characteristic impedance. The load  
end of the transmission line is high impedance. When the signal  
is launched into the source termination, its initial value is one-  
half of its source value because its amplitude is divided-by-2 by  
the voltage divider formed by the source termination and the  
transmission line. At the load, the signal experiences nearly  
100% positive reflection due to the high impedance load and  
is restored to nearly its full value. This technique is commonly  
used in PCB layouts that involve high speed digital logic.  
R
OUT  
S
REF  
C
IN  
V
REF  
R
R
C
GAIN  
0.01µF  
–5V  
Figure 42. Buffering the Input Capacitance of a High-Z Load with G = 1  
An internal linear voltage regulator derives power for the  
comparators from the positive supply; therefore, the AD8145  
must always have a minimum positive supply voltage of 4.5 V.  
+5V  
0.01µF  
V
IN  
R
OUT  
S
REF  
C
R
S
L
V
REF  
C
R
GAIN  
R
0.01µF  
–5V  
Figure 43. Driving a Doubly Terminated Cable with G = 2  
Rev. A | Page 19 of 24  
 
 
 
 
AD8145  
The AD8134 encoding equations are given in Equation 4,  
Equation 5, and Equation 6.  
SYNC PULSE EXTRACTION USING COMPARATORS  
The AD8145 is particularly useful in KVM applications. KVM  
networks transmit and receive computer video signals that typically  
comprise red, green, and blue (RGB) video signals and separate  
horizontal and vertical sync signals. Because the sync signals are  
separate and not embedded in the color signals, it is advantageous  
to transmit them using a simple scheme that encodes them among  
the three common-mode voltages of the RGB signals. The AD8134  
triple differential driver is a natural complement to the AD8145  
and performs the sync pulse encoding with the necessary  
circuitry on-chip.  
K
2
Red VCM  
=
[
V H  
]
(4)  
(5)  
(6)  
K
2
Green VCM  
=
[
2 V  
]
K
2
Blue VCM  
where:  
=
[
V + H  
]
Red VCM, Green VCM, and Blue VCM are the transmitted common-  
mode voltages of the respective color signals.  
K is an adjustable gain constant that is set by the AD8134.  
V and H are the vertical and horizontal sync pulses, defined  
with a weight of −1 when the pulses are in their low states and a  
weight of +1 when they are in their high states.  
The AD8134 data sheet contains further details regarding the  
encoding scheme. Figure 44 illustrates how the AD8145 comparators  
can be used to extract the horizontal and vertical sync pulses that  
are encoded on the RGB common-mode voltages by the AD8134.  
50Ω  
RED CMV  
RECEIVED  
RED VIDEO  
R
S
HSYNC  
50Ω  
1kΩ  
47pF  
47pF  
50Ω  
GREEN CMV  
475Ω  
RECEIVED  
GREEN VIDEO  
R
S
VSYNC  
50Ω  
1kΩ  
50Ω  
BLUE CMV  
RECEIVED  
BLUE VIDEO  
50Ω  
Figure 44. Extracting Sync Signals from Received Common-Mode Signal  
Rev. A | Page 20 of 24  
 
 
AD8145  
OUTLINE DIMENSIONS  
5.00  
BSC SQ  
0.60 MAX  
0.60 MAX  
PIN 1  
INDICATOR  
25  
24  
32  
1
PIN 1  
INDICATOR  
0.50  
BSC  
EXPOSED  
PAD  
(BOTTOM VIEW)  
3.45  
3.30 SQ  
3.15  
TOP  
VIEW  
4.75  
BSC SQ  
0.50  
0.40  
0.30  
17  
16  
8
9
0.25 MIN  
0.80 MAX  
0.65 TYP  
3.50 REF  
12° MAX  
FOR PROPER CONNECTION OF  
THE EXPOSED PAD, REFER TO  
THE PIN CONFIGURATION AND  
FUNCTION DESCRIPTIONS  
0.05 MAX  
0.02 NOM  
COPLANARITY  
1.00  
0.85  
0.80  
0.30  
0.23  
0.18  
SECTION OF THIS DATA SHEET.  
0.08  
0.20 REF  
SEATING  
PLANE  
COMPLIANT TO JEDEC STANDARDS MO-220-VHHD-2  
Figure 45. 32-Lead Lead Frame Chip Scale Package [LFCSP_VQ]  
5 mm × 5 mm Body, Very Thin Quad  
(CP-32-3)  
Dimensions shown in millimeters  
ORDERING GUIDE  
Model1  
AD8145YCPZ-R2  
AD8145YCPZ-RL  
AD8145YCPZ-R7  
AD8145WYCPZ-R72  
Temperature Range  
−40°C to +105°C  
−40°C to +105°C  
−40°C to +105°C  
−40°C to +105°C  
Package Description  
Package Option  
32-Lead Lead Frame Chip Scale Package [LFCSP_VQ]  
32-Lead Lead Frame Chip Scale Package [LFCSP_VQ]  
32-Lead Lead Frame Chip Scale Package [LFCSP_VQ]  
32-Lead Lead Frame Chip Scale Package [LFCSP_VQ]  
CP-32-3  
CP-32-3  
CP-32-3  
CP-32-3  
1 Z = RoHS Compliant Part.  
2 W = automotive qualified product.  
Rev. A | Page 21 of 24  
 
AD8145  
NOTES  
Rev. A | Page 22 of 24  
AD8145  
NOTES  
Rev. A | Page 23 of 24  
AD8145  
NOTES  
©2006–2010 Analog Devices, Inc. All rights reserved. Trademarks and  
registered trademarks are the property of their respective owners.  
D06307-0-1/10(A)  
Rev. A | Page 24 of 24  

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