LT6600CS8-10 [Linear]
Very Low Noise, Differential Amplifier and 10MHz Lowpass Filter; 非常低噪声，差分放大器和10MHz的低通滤波器
| 型号： | LT6600CS8-10 |
| 厂家： | 
Linear |
| 描述： | Very Low Noise, Differential Amplifier and 10MHz Lowpass Filter |
| 文件： | 总12页 (文件大小：223K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT6600-10
Very Low Noise, Differential
Amplifier and 10MHz Lowpass Filter
U
FEATURES
DESCRIPTIO
■
Programmable Differential Gain via Two External
The LT®6600-10 combines a fully differential amplifier
with a 4th order 10MHz lowpass filter approximating a
Chebyshev frequency response. Most differential amplifi-
ers require many precision external components to tailor
gain and bandwidth. In contrast, with the LT6600-10, two
externalresistorsprogramdifferentialgain, andthefilter’s
10MHzcutofffrequencyandpassbandrippleareinternally
set. The LT6600-10 also provides the necessary level
shifting to set its output common mode voltage to accom-
modate the reference voltage requirements of A/Ds.
Resistors
■
Adjustable Output Common Mode Voltage
■
Operates and Specified with 3V, 5V, ±5V Supplies
■
0.5dB Ripple 4th Order Lowpass Filter with 10MHz
Cutoff
■
82dB S/N with 3V Supply and 2VP-P Output
■
Low Distortion, 2VP-P, 800Ω Load
1MHz: 88dBc 2nd, 97dBc 3rd
5MHz: 74dBc 2nd, 77dBc 3rd
■
Fully Differential Inputs and Outputs
Using a proprietary internal architecture, the LT6600-10
integrates an antialiasing filter and a differential amplifier/
driver without compromising distortion or low noise
performance. At unity gain the measured in band
signal-to-noise ratio is an impressive 82dB. At higher
gains the input referred noise decreases so the part can
process smaller input differential signals without signifi-
cantly degrading the output signal-to-noise ratio.
■
SO-8 Package
■
Compatible with Popular Differential Amplifier
Pinouts
U
APPLICATIO S
■
High Speed ADC Antialiasing and DAC Smoothing in
Networking or Cellular Base Station Applications
The LT6600-10 also features low voltage operation. The
differential design provides outstanding performance for
a2VP-P signallevelwhilethepartoperateswithasingle3V
supply.
■
High Speed Test and Measurement Equipment
■
Medical Imaging
■
Drop-in Replacement for Differential Amplifiers
, LTC and LT are registered trademarks of Linear Technology Corporation.
For similar devices with other cutoff frequencies, refer to
the LT6600-20 and LT6600-2.5.
U
TYPICAL APPLICATIO
An 8192 Point FFT Spectrum
0
INPUT IS A 4.7MHz SINEWAVE
–10
LT6600-10
5V
2V
SAMPLE
P-P
f
= 66MHz
–20
–30
0.1µF
5V
R
402Ω
IN
–40
–50
–60
–70
3
+
1
7
2
8
V
49.9Ω
49.9Ω
–
4
+
+
V
MID
A
18pF
D
LTC1748
IN
OUT
–
V
0.01µF
OCM
–
–
5
V
+
–80
–90
–100
–110
IN
V
V
CM
R
6
IN
402Ω
1µF
GAIN = 402Ω/R
IN
6600 TA01a
0
4
8
12 16 20 24 28 32
FREQUENCY (MHz)
6600 TA01b
6600f
1
LT6600-10
W W U W
U
W
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ABSOLUTE AXI U RATI GS
(Note 1)
PACKAGE/ORDER I FOR ATIO
Total Supply Voltage................................................ 11V
Operating Temperature Range (Note 6) ...–40°C to 85°C
Specified Temperature Range (Note 7)....–40°C to 85°C
Junction Temperature........................................... 150°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
TOP VIEW
NUMBER
–
+
IN
1
2
3
4
8
7
6
5
IN
LT6600CS8-10
LT6600IS8-10
V
V
V
OCM
MID
–
+
V
+
–
OUT
OUT
S8 PART MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
660010
600I10
TJMAX = 150°C, θJA = 100°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V– = 0V), RIN = 402Ω, and RLOAD = 1k.
PARAMETER
Filter Gain, V = 3V
CONDITIONS
= 2V , f = DC to 260kHz
MIN
– 0.4
– 0.1
– 0.4
– 0.3
–0.2
TYP
0
MAX
0.5
0.1
0.3
1
UNITS
dB
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
S
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
P-P IN
= 2V , f = 1MHz (Gain Relative to 260kHz)
●
●
●
●
●
●
0
dB
P-P IN
= 2V , f = 5MHz (Gain Relative to 260kHz)
– 0.1
0.1
0.3
– 28
– 44
0
dB
P-P IN
= 2V , f = 8MHz (Gain Relative to 260kHz)
dB
P-P IN
= 2V , f = 10MHz (Gain Relative to 260kHz)
1.7
– 25
dB
P-P IN
= 2V , f = 30MHz (Gain Relative to 260kHz)
dB
P-P IN
= 2V , f = 50MHz (Gain Relative to 260kHz)
dB
P-P IN
Filter Gain, V = 5V
= 2V , f = DC to 260kHz
–0.5
– 0.1
– 0.4
– 0.4
– 0.3
0.5
0.1
0.3
0.9
1.4
–25
dB
S
P-P IN
= 2V , f = 1MHz (Gain Relative to 260kHz)
●
●
●
●
●
●
0
dB
P-P IN
= 2V , f = 5MHz (Gain Relative to 260kHz)
–0.1
0.1
0.2
–28
–44
–0.1
12
dB
P-P IN
= 2V , f = 8MHz (Gain Relative to 260kHz)
dB
P-P IN
= 2V , f = 10MHz (Gain Relative to 260kHz)
dB
P-P IN
= 2V , f = 30MHz (Gain Relative to 260kHz)
dB
P-P IN
= 2V , f = 50MHz (Gain Relative to 260kHz)
dB
P-P IN
Filter Gain, V = ±5V
= 2V , f = DC to 260kHz
–0.6
11.4
0.4
dB
S
P-P IN
Filter Gain, R = 100Ω, V = 3V, 5V, ±5V
= 2V , f = DC to 260kHz
12.6
dB
IN
S
P-P IN
Filter Gain Temperature Coefficient (Note 2)
f
= 260kHz, V = 2V
P-P
780
56
ppm/C
IN
IN
Noise
Noise BW = 10kHz to 10MHz, R = 402Ω
µV
RMS
IN
Distortion (Note 4)
1MHz, 2V , R = 800Ω
2nd Harmonic
3rd Harmonic
88
97
dBc
dBc
P-P
L
5MHz, 2V , R = 800Ω
2nd Harmonic
3rd Harmonic
74
77
dBc
dBc
P-P
L
Differential Output Swing
Input Bias Current
Measured Between Pins 4 and 5
Pin 7 Shorted to Pin 2
V = 5V
V = 3V
S
●
●
3.85
3.85
5.0
4.9
V
V
S
P-P DIFF
P-P DIFF
Average of Pin 1 and Pin 8
●
– 85
–40
µA
6600f
2
LT6600-10
ELECTRICAL CHARACTERISTICS
The ● denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V– = 0V), RIN = 402Ω, and RLOAD = 1k.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Referred Differential Offset
R
IN
= 402Ω
V = 3V
●
●
●
5
10
8
20
30
35
mV
mV
mV
S
V = 5V
S
V = ±5V
S
R
IN
= 100Ω
V = 3V
●
●
●
5
5
5
13
22
30
mV
mV
mV
S
V = 5V
S
V = ±5V
S
Differential Offset Drift
10
µV/°C
Input Common Mode Voltage (Note 3)
Differential Input = 500mV
,
V = 3V
●
●
●
0.0
0.0
–2.5
1.5
3.0
1.0
V
V
V
P-P
S
R
IN
= 100Ω
V = 5V
S
V = ±5V
S
Output Common Mode Voltage (Note 5)
Differential Output = 2V
Pin 7 at Midsupply
,
V = 3V
●
●
●
1.0
1.5
–1.0
1.5
3.0
2.0
V
V
V
P-P
S
V = 5V
S
V = ±5V
S
Output Common Mode Offset
(with respect to Pin 2)
V = 3V
●
●
●
–35
–40
–55
5
0
–5
40
40
35
mV
mV
mV
S
V = 5V
S
V = ±5V
S
Common Mode Rejection Ratio
61
dB
Voltage at V
(Pin 7)
V = 5
V = 3
S
●
●
2.46
4.3
2.51
1.5
2.55
7.7
V
V
MID
S
V
V
Input Resistance
Bias Current
5.5
kΩ
MID
V
= V = V /2
V = 5V
●
●
–15
–10
–3
–3
µA
µA
OCM
OCM
MID
S
S
V = 3V
S
Power Supply Current
V = 3V, V = 5
35
39
43
46
mA
mA
mA
S
S
V = 3V, V = 5
●
●
S
S
V = ±5V
S
36
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: This is the temperature coefficient of the internal feedback
Note 5: Output common mode voltage is the average of the voltages at
Pins 4 and 5. The output common mode voltage is equal to the voltage
applied to Pin 2.
resistors assuming a temperature independent external resistor (R ).
Note 3: The input common mode voltage is the average of the voltages
Note 6: The LT6600C is guaranteed functional over the operating
temperature range –40°C to 85°C.
IN
applied to the external resistors (R ). Specification guaranteed for
Note 7: The LT6600C is guaranteed to meet 0°C to 70°C specifications and
is designed, characterized and expected to meet the extended temperature
limits, but is not tested at –40°C and 85°C. The LT6600I is guaranteed to
meet specified performance from –40°C to 85°C.
IN
R
IN
≥ 100Ω.
Note 4: Distortion is measured differentially using a differential stimulus,
The input common mode voltage, the voltage at Pin 2, and the voltage at
Pin 7 are equal to one half of the total power supply voltage.
6600f
3
LT6600-10
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Amplitude Response
Passband Gain and Group Delay
1
60
55
50
45
40
35
30
25
20
15
10
10
V
= 5V
S
0
–1
–2
–3
–4
–5
–6
–7
–8
–9
GAIN = 1
0
–10
–20
–30
–40
–50
–60
–70
–80
V
= 5V
S
GAIN = 1
= 25°C
T
A
0.5
5.3
10.1
14.9
100k
1M
10M
100M
FREQUENCY (MHz)
FREQUENCY (Hz)
6600 G01
6600 G02
Output Impedance vs Frequency
(OUT+ or OUT–)
Passband Gain and Group Delay
Common Mode Rejection Ratio
12
11
10
9
60
55
50
45
40
35
30
25
20
15
10
100
10
1
80
75
70
65
60
55
50
45
40
35
V
= 5V
S
GAIN = 1
= 1V
V
A
IN
P-P
T
= 25°C
8
7
6
5
4
V
= 5V
S
GAIN = 4
3
T
= 25°C
A
2
0.1
0.5
5.3
10.1
14.9
100k
1M
10M
100M
10k
100k
1M
10M
FREQUENCY (MHz)
FREQUENCY (Hz)
FREQUENCY (Hz)
6600 G04
6600 G05
6600 G03
Distortion vs Frequency
VIN = 2VP-P, VS = 3V, RL = 800Ω
at Each Output, TA = 25°C
Distortion vs Frequency
VIN = 2VP-P, VS = ±5V, RL = 800Ω
at Each Output, TA = 25°C
Power Supply Rejection Ratio
–40
–50
–60
–70
90
80
70
60
50
40
30
20
10
0
–40
–50
–60
–70
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
–80
–90
–100
–80
–90
–100
V
V
A
V
= 3V
S
= 200mV
IN
= 25°C
P-P
T
+
TO DIFFOUT
0.1
1
10
1k
10k
100k
1M
10M
100M
0.1
1
10
FREQUENCY (MHz)
FREQUENCY (MHz)
FREQUENCY (Hz)
6600 G08
6600 G06
6600 G07
6600f
4
LT6600-10
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Distortion vs Signal Level
VS = 3V, RL = 800Ω at Each Output,
TA = 25°C
Distortion vs Signal Level
VS = ±5V, RL = 800Ω at Each Output,
TA = 25°C
Distortion vs Input Common Mode
Level, 2VP-P, 1MHz Input, 1x Gain,
RL = 800Ω at Each Output, TA = 25°C
–40
–50
–40
–50
–40
–50
–60
–70
–80
–90
–100
2ND HARMONIC,
5MHz INPUT
3RD HARMONIC,
5MHz INPUT
2ND HARMONIC,
1MHz INPUT
3RD HARMONIC,
1MHZ INPUT
2ND HARMONIC,
5MHz INPUT
2ND HARMONIC,
V
= 3V
S
3RD HARMONIC,
5MHz INPUT
3RD HARMONIC,
= 3V
V
S
2ND HARMONIC,
1MHz INPUT
3RD HARMONIC,
1MHZ INPUT
2ND HARMONIC,
= 5V
–60
–70
V
–60
–70
S
3RD HARMONIC,
= 5V
V
S
–80
–80
–90
–90
–100
–110
–100
1
2
3
5
0
1
2
3
4
5
0
4
–3
–1
0
1
2
3
–2
INPUT LEVEL (V
)
P-P
INPUT COMMON MODE VOLTAGE
RELATIVE TO PIN 7 (V)
INPUT LEVEL (V
)
P-P
6600 G09
6600 G10
6600 G11
Distortion vs Input Common Mode
Level, 0.5VP-P, 1MHz Input, 4x
Gain, RL = 800Ω at Each Output,
TA = 25°C
Transient Response,
Differential Gain = 1
Power Supply Current
vs Power Supply Voltage
–40
–50
–60
–70
–80
–90
–100
40
38
36
34
32
30
28
26
24
2ND HARMONIC,
V
= 3V
S
3RD HARMONIC,
= 3V
T
T
= 85°C
= 25°C
A
A
V
S
+
VOUT
2ND HARMONIC,
= 5V
50mV/DIV
V
S
3RD HARMONIC,
= 5V
V
S
DIFFERENTIAL
INPUT
200mV/DIV
T
A
= –40°C
100ns/DIV
6600 G13
–3
–1
0
1
2
3
–2
6
7
2
3
4
5
8
9
10
INPUT COMMON MODE VOLTAGE
RELATIVE TO PIN 7 (V)
TOTAL SUPPLY VOLTAGE (V)
6600 G12
6600 G14
Distortion vs Output Common Mode,
2VP-P 1MHz Input, 1x Gain, TA = 25°C
–40
–50
–60
–70
2ND HARMONIC, V = 3V
S
3RD HARMONIC, V = 3V
S
2ND HARMONIC, V = 5V
S
3RD HARMONIC, V = 5V
S
2ND HARMONIC, V = ±5V
S
3RD HARMONIC, V = ±5V
S
–80
–90
–100
–1
0
0.5
1
1.5
2
–0.5
OUTPUT COMMON MODE VOLTAGE (V)
6600 G15
6600f
5
LT6600-10
U
U
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PI FU CTIO S
IN– and IN+ (Pins 1, 8):Input Pins. Signals can be applied
to either or both input pins through identical external
resistors, RIN. The DC gain from differential inputs to the
differential outputs is 402Ω/RIN.
bypass should be as close as possible to the IC. For dual
supply applications, bypass Pin 3 to ground and Pin 6 to
ground with a quality 0.1µF ceramic capacitor.
OUT+ and OUT– (Pins 4, 5): Output Pins. Pins 4 and 5 are
the filter differential outputs. Each pin can drive a 100Ω
and/or 50pF load to AC ground.
V
OCM (Pin2):IstheDCCommonModeReferenceVoltage
for the 2nd Filter Stage. Its value programs the common
mode voltage of the differential output of the filter. Pin 2
is a high impedance input, which can be driven from an
external voltage reference, or Pin 2 can be tied to Pin 7 on
the PC board. Pin 2 should be bypassed with a 0.01µF
ceramic capacitor unless it is connected to a ground
plane.
V
MID (Pin 7): The VMID pin is internally biased at mid-
supply, seeblockdiagram. Forsinglesupplyoperationthe
MIDpinshouldbebypassedwithaquality0.01µFceramic
V
capacitor to Pin 6. For dual supply operation, Pin 7 can be
bypassed or connected to a high quality DC ground. A
ground plane should be used. A poor ground will increase
noise and distortion. Pin 7 sets the output common mode
voltage of the 1st stage of the filter. It has a 5.5KΩ
impedance, and it can be overridden with an external low
impedance voltage source.
V+ and V– (Pins 3, 6): Power Supply Pins. For a single
3.3V or 5V supply (Pin 6 grounded) a quality 0.1µF
ceramic bypass capacitor is required from the positive
supply pin (Pin 3) to the negative supply pin (Pin 6). The
W
BLOCK DIAGRA
R
IN
+
+
–
–
V
IN
IN
V
OUT
5
V
MID
8
7
6
+
V
11k
11k
PROPRIETARY
LOWPASS
402Ω
FILTER STAGE
200Ω
–
V
OP AMP
200Ω
200Ω
+
+
OCM
–
–
V
V
OCM
+
+
–
–
200Ω
402Ω
1
2
3
4
6600 BD
+
–
–
+
V
V
IN
IN
OCM
V
OUT
R
IN
6600f
6
LT6600-10
W U U
APPLICATIO S I FOR ATIO
U
Interfacing to the LT6600-10
is2VP-P forfrequenciesbelow10MHz.Thecommonmode
output voltage is determined by the voltage at pin 2. Since
pin 2 is shorted to pin 7, the output common mode is the
mid-supply voltage. In addition, the common mode input
voltage can be equal to the mid-supply voltage of Pin 7
(refer to the Distortion vs Input Common Mode Level
graphs in the Typical Performance Characteristics).
The LT6600-10 requires 2 equal external resistors, RIN, to
set the differential gain to 402Ω/RIN. The inputs to the
+
filter are the voltages VIN and VIN– presented to these
external components, Figure 1. The difference between
VIN+ and VIN– is the differential input voltage. The average
+
–
of VIN and VIN is the common mode input voltage.
Similarly, the voltages VOUT+ and VOUT– appearing at pins
4 and 5 of the LT6600-10 are the filter outputs. The
Figure 2 shows how to AC couple signals into the
LT6600-10. In this instance, the input is a single-ended
signal. AC coupling allows the processing of single-ended
or differential signals with arbitrary common mode levels.
The 0.1µF coupling capacitor and the 402Ω gain setting
resistor form a high pass filter, attenuating signals below
4kHz. Larger values of coupling capacitors will propor-
tionally reduce this highpass 3dB frequency.
+
–
+
difference between VOUT and VOUT is the differential
–
output voltage. The average of VOUT and VOUT is the
common mode output voltage.
Figure 1 illustrates the LT6600-10 operating with a single
3.3V supply and unity passband gain; the input signal is
DC coupled. The common mode input voltage is 0.5V and
the differential input voltage is 2VP-P. The common mode
output voltage is 1.65V and the differential output voltage
In Figure 3 the LT6600-10 is providing 12dB of gain. The
gain resistor has an optional 62pF in parallel to improve
3.3V
0.1µF
V
V
3
–
402Ω
3
2
1
0
3
2
1
0
1
7
2
8
–
+
V
V
4
IN
IN
+
–
+
–
V
V
+
OUT
V
OUT
LT6600-10
+
V
0.01µF
IN
V
OUT
–
OUT
5
+
402Ω
6
t
t
–
6600 F01
V
IN
Figure 1
3.3V
3
0.1µF
V
V
0.1µF
0.1µF
402Ω
402Ω
1
3
2
1
0
2
1
–
4
+
+
V
V
+
7
2
8
OUT
OUT
V
V
OUT
LT6600-10
+
–
V
0.01µF
IN
–
OUT
–
0
t
+
5
V
+
IN
6
–1
6600 F02
Figure 2
62pF
5V
0.1µF
V
V
3
100Ω
1
–
+
3
3
V
V
–
4
IN
+
+
–
V
V
OUT
+
7
2
8
OUT
LT6600-10
2
1
0
2
1
V
0.01µF
OUT
–
V
OUT
500mV (DIFF)
P-P
–
5
+
IN
+
V
V
100Ω
IN
6
t
t
0
+
–
2V
6600 F03
IN
–
0.01µF
62pF
Figure 3
6600f
7
LT6600-10
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W U U
APPLICATIO S I FOR ATIO
the passband flatness near 10MHz. The common mode
output voltage is set to 2V.
Figure 5 is a laboratory setup that can be used to charac-
terizetheLT6600-10usingsingle-endedinstrumentswith
50Ω source impedance and 50Ω input impedance. For a
unity gain configuration the LT6600-10 requires a 402Ω
source resistance yet the network analyzer output is
calibrated for a 50Ω load resistance. The 1:1 transformer,
53.6Ω and 388Ω resistors satisfy the two constraints
above. The transformer converts the single-ended source
into a differential stimulus. Similarly, the output the
LT6600-10 will have lower distortion with larger load
resistance yet the analyzer input is typically 50Ω. The 4:1
turns (16:1 impedance) transformer and the two 402Ω
resistors of Figure 5, present the output of the LT6600-10
with a 1600Ω differential load, or the equivalent of 800Ω
to ground at each output. The impedance seen by the
network analyzer input is still 50Ω, reducing reflections in
the cabling between the transformer and analyzer input.
Use Figure 4 to determine the interface between the
LT6600-10 and a current output DAC. The gain, or “trans-
impedance”, is defined as A = VOUT/IIN Ω. To compute the
transimpedance, use the following equation:
402 •R1
R1+R2
A =
Ω
By setting R1 + R2 = 402Ω, the gain equation reduces to
A = R1Ω.
The voltage at the pins of the DAC is determined by R1,
+
R2, the voltage on Pin 7 and the DAC output current (IIN
or IIN–). Consider Figure 4 with R1 = 49.9Ω and R2 =
348Ω. The voltage at Pin 7 is 1.65V. The voltage at the
DAC pins is given by:
2.5V
R1
R1+R2 + 402 IN R1+R2
= 103mV +I 43.6Ω
R1•R2
0.1µF
V
DAC = VPIN7
•
+I
COILCRAFT
TTWB-16A
4:1
COILCRAFT
TTWB-1010
NETWORK
ANALYZER
SOURCE
NETWORK
ANALYZER
INPUT
3
388Ω
1:1
1
7
2
8
IN
402Ω
–
4
+
50Ω
LT6600-10
–
+
IIN is IIN or IIN .The transimpedance in this example is
53.6Ω
50Ω
–
50.4Ω.
5
+
402Ω
388Ω
6
0.1µF
6600 F05
CURRENT
3.3V
0.1µF
OUTPUT
–2.5V
DAC
Figure 5
–
+
3
R2
I
I
IN
IN
1
7
2
8
–
4
+
–
+
V
V
OUT
R1
R1
Differential and Common Mode Voltage Ranges
0.01µF
LT6600-10
R2
–
OUT
The differential amplifiers inside the LT6600-10 contain
circuitry to limit the maximum peak-to-peak differential
voltage through the filter. This limiting function prevents
excessive power dissipation in the internal circuitry
and provides output short-circuit protection. The limiting
function begins to take effect at output signal levels above
2VP-P and it becomes noticeable above 3.5VP-P. This is
illustrated in Figure 6; the LTC6600-10 was configured
with unity passband gain and the input of the filter was
driven with a 1MHz signal. Because this voltage limiting
takes place well before the output stage of the filter
reaches the supply rails, the input/output behavior of the
IC shown in Figure 6 is relatively independent of the power
5
+
6
6600 F04
Figure 4
Evaluating the LT6600-10
The low impedance levels and high frequency operation of
the LT6600-10 require some attention to the matching
networks between the LT6600-10 and other devices. The
previous examples assume an ideal (0Ω) source imped-
ance and a large (1kΩ) load resistance. Among practical
examples where impedance must be considered is the
evaluation of the LT6600-10 with a network analyzer.
supply voltage.
6600f
8
LT6600-10
U
W U U
APPLICATIO S I FOR ATIO
+
–
20
average of VIN and VIN in Figure 1) is determined by
the power supply level and gain setting (see “Electrical
Characteristics”).
1dB PASSBAND GAIN
1MHz 25°C
COMPRESSION POINTS
0
1MHz 85°C
–20
3RD HARMONIC
85°C
–40
Common Mode DC Currents
3RD HARMONIC
25°C
–60
In applications like Figure 1 and Figure 3 where the
LT6600-10 not only provides lowpass filtering but also
level shifts the common mode voltage of the input signal,
DC currents will be generated through the DC path be-
tweeninputandoutputterminals.Minimizethesecurrents
to decrease power dissipation and distortion.
2ND HARMONIC
85°C
–80
2ND HARMONIC
25°C
–100
–120
4
6
0
1
2
3
5
1MHz INPUT LEVEL (V
)
P-P
6600 F06
Consider the application in Figure 3. Pin 7 sets the output
common mode voltage of the 1st differential amplifier
insidetheLT6600-10(seethe“BlockDiagram”section)at
2.5V. Since the input common mode voltage is near 0V,
there will be approximately a total of 2.5V drop across the
series combination of the internal 402Ω feedback resistor
and the external 100Ω input resistor. The resulting 5mA
common mode DC current in each input path, must be
Figure 6
The two amplifiers inside the LT6600-10 have indepen-
dent control of their output common mode voltage (see
the“blockdiagram”section). Thefollowingguidelineswill
optimize the performance of the filter for single supply
operation.
+
absorbed by the sources VIN and VIN–. Pin 2 sets the
Pin 7 must be bypassed to an AC ground with a 0.01µF or
higher capacitor. Pin 7 can be driven from a low imped-
ance source, provided it remains at least 1.5V above V–
andatleast1.5VbelowV+. Aninternalresistordividersets
the voltage of Pin 7. While the internal 11k resistors are
well matched, their absolute value can vary by ±20%. This
should be taken into consideration when connecting an
external resistor network to alter the voltage of Pin 7.
common mode output voltage of the 2nd differential
amplifier inside the LT6600-10, and therefore sets the
common mode output voltage of the filter. Since in the
example, Figure 3, Pin 2 differs from Pin 7 by 0.5V, an
additional2.5mA(1.25mAperside) ofDCcurrentwillflow
in the resistors coupling the 1st differential amplifier
output stage to filter output. Thus, a total of 12.5mA is
used to translate the common mode voltages.
Pin 2 can be shorted to Pin 7 for simplicity. If a different
common mode output voltage is required, connect Pin 2
to a voltage source or resistor network. For 3V and 3.3V
supplies the voltage at Pin 2 must be less than or equal to
the mid supply level. For example, voltage (Pin 2) ≤1.65V
on a single 3.3V supply. For power supply voltages higher
than 3.3V the voltage at Pin 2 can be set above mid supply.
ThevoltageonPin2shouldnotbemorethan1Vbelowthe
voltage on Pin 7. The voltage on Pin 2 should not be more
than 2V above the voltage on PIn 7. Pin 2 is a high
impedance input.
A simple modification to Figure 3 will reduce the DC
common mode currents by 36%. If Pin 7 is shorted to
Pin 2 the common mode output voltage of both op amp
stages will be 2V and the resulting DC current will be 8mA.
Of course, by AC coupling the inputs of Figure 3, the
common mode DC current can be reduced to 2.5mA.
Noise
ThenoiseperformanceoftheLT6600-10canbeevaluated
with the circuit of Figure 7.
The LT6600-10 was designed to process a variety of input
signals including signals centered around the mid-supply
voltage and signals that swing between ground and a
positive voltage in a single supply system (Figure 1). The
range of allowable input common mode voltage (the
Given the low noise output of the LT6600-10 and the 6dB
attenuation of the transformer coupling network, it will be
necessary to measure the noise floor of the spectrum
analyzer and subtract the instrument noise from the filter
noise measurement.
6600f
9
LT6600-10
U
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APPLICATIO S I FOR ATIO
35
30
25
20
15
10
5
140
120
100
80
2.5V
0.1µF
SPECTRUM
ANALYZER
INPUT
COILCRAFT
TTWB-1010
1:1
R
R
3
IN
IN
V
IN
1
7
2
8
25Ω
–
4
+
LT6600-10
50Ω
SPECTRAL DENSITY
–
60
5
+
25Ω
0.1µF
6
40
6600 F07
INTEGRATED
NOISE
20
–2.5V
0
0
100
0.1
1.0
10
Figure 7
FREQUENCY (MHz)
6600 F08
Example: With the IC removed and the 25Ω resistors
grounded, measure the total integrated noise (eS) of the
spectrum analyzer from 10kHz to 10MHz. With the IC
inserted, the signal source (VIN) disconnected, and the
input resistors grounded, measure the total integrated
noise out of the filter (eO). With the signal source con-
nected, set the frequency to 1MHz and adjust the ampli-
tude until VIN measures 100mVP-P. Measure the output
amplitude, VOUT, and compute the passband gain
A = VOUT/VIN. Now compute the input referred integrated
noise (eIN) as:
Figure 8
noiseandgivesatruemeasureofthe S/Nachievableinthe
system. Conversely, if each output is measured individu-
ally and the noise power added together, the resulting
calculated noise level will be higher than the true differen-
tial noise.
Power Dissipation
The LT6600-10 amplifiers combine high speed with large-
signal currents in a small package. There is a need to
ensure that the dies’s junction temperature does not
exceed 150°C. The LT6600-10 package has Pin 6 fused to
the lead frame to enhance thermal conduction when
connecting to a ground plane or a large metal trace. Metal
trace and plated through-holes can be used to spread the
heat generated by the device to the backside of the PC
board. For example, on a 3/32" FR-4 board with 2oz
copper, a total of 660 square millimeters connected to Pin
6 of the LT6600-10 (330 square millimeters on each side
of the PC board) will result in a thermal resistance, θJA, of
about 85°C/W. Without extra metal trace connected to the
(eO)2 –(eS)2
eIN =
A
Table 1 lists the typical input referred integrated noise for
various values of RIN.
Figure 8 is plot of the noise spectral density as a function
of frequency for an LT6600-10 with RIN = 402Ω using the
fixture of Figure 7 (the instrument noise has been sub-
tracted from the results).
Table 1. Noise Performance
INPUT REFERRED
PASSBAND
GAIN (V/V)
INTEGRATED NOISE
10kHz TO 10MHz
INPUT REFERRED
NOISE dBm/Hz
Table 2. LT6600-10 SO-8 Package Thermal Resistance
COPPER AREA
R
IN
4
2
1
100Ω
200Ω
402Ω
24µV
34µV
56µV
–149
–146
–142
RMS
RMS
RMS
TOPSIDE BACKSIDE BOARD AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
2
2
2
(mm )
(mm )
(mm )
1100
330
35
1100
330
35
2500
2500
2500
2500
2500
65°C/W
85°C/W
95°C/W
100°C/W
105°C/W
The noise at each output is comprised of a differential
component and a common mode component. Using a
transformer or combiner to convert the differential out-
puts to single-ended signal rejects the common mode
35
0
0
0
6600f
10
LT6600-10
U
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APPLICATIO S I FOR ATIO
V– pin to provide a heat sink, the thermal resistance will be
around 105°C/W. Table 2 can be used as a guide when
considering thermal resistance.
Applications Information regarding common mode DC
currents), the load impedance is small and the ambient
temperature is maximum. To compute the junction tem-
perature, measure the supply current under these worst-
case conditions, estimate the thermal resistance from
Table2, thenapplytheequationforTJ. Forexample, using
the circuit in Figure 3 with DC differential input voltage of
250mV, a differential output voltage of 1V, no load resis-
tance and an ambient temperature of 85°C, the supply
current (current into Pin 3) measures 48.9mA. Assuming
a PC board layout with a 35mm2 copper trace, the θJA is
100°C/W. The resulting junction temperature is:
Junction temperature, TJ, is calculated from the ambient
temperature, TA, and power dissipation, PD. The power
dissipation is the product of supply voltage, VS, and
supply current, IS. Therefore, the junction temperature is
given by:
TJ = TA + (PD • θJA) = TA + (VS • IS • θJA)
where the supply current, IS, is a function of signal level,
load impedance, temperature and common mode volt-
ages.
TJ = TA + (PD • θJA) = 85 + (5 • 0.0489 • 100) = 109°C
For a given supply voltage, the worst-case power dissi-
pation occurs when the differential input signal is maxi-
mum, the common mode currents are maximum (see
When using higher supply voltages or when driving small
impedances, more copper may be necessary to keep TJ
below 150°C.
U
PACKAGE DESCRIPTIO
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.189 – .197
(4.801 – 5.004)
.045 ±.005
.160 ±.005
NOTE 3
.050 BSC
7
5
8
6
.245
MIN
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
1
3
4
2
RECOMMENDED SOLDER PAD LAYOUT
.010 – .020
(0.254 – 0.508)
× 45°
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
.008 – .010
(0.203 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
.050
(1.270)
BSC
.014 – .019
(0.355 – 0.483)
TYP
NOTE:
INCHES
1. DIMENSIONS IN
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
SO8 0303
6600f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
11
LT6600-10
U
TYPICAL APPLICATIO S
5th Order, 10MHz Lowpass Filter
Amplitude Response
Transient Response
5th Order, 10MHz Lowpass Filter
Differential Gain = 1
10
0
+
V
0.1µF
3
–10
–20
–30
–40
–50
–60
–70
–80
R
R
R
1
7
2
8
–
+
V
V
–
IN
4
+
–
V
V
+
OUT
OUT
LT6600-10
+
VOUT
C
50mV/DIV
R
–
5
+
IN
0.1µF
6
DIFFERENTIAL
INPUT
200mV/DIV
1
C =
2π • R • 10MHz
6600 TA02a
402Ω
–
DIFFERENTIAL GAIN = 1
GAIN =
, MAXIMUM GAIN = 4
V
2R
R = 200Ω
100ns/DIV
6600 TA02c
C = 82pF
100k
1M
10M
100M
FREQUENCY (Hz)
6600 TA02b
A WCDMA Transmit Filter
(10MHz Lowpass Filter with a 28MHz Notch)
Amplitude Response
22
12
+
33pF
V
0.1µF
2
3
1µH
100Ω
100Ω
–8
1
7
2
8
–
+
V
–
IN
4
+
–
V
V
+
–18
–28
–38
–48
–58
–68
–78
OUT
OUT
33pF
1µH
R
301Ω
Q
LT6600-10
27pF
–
5
V
+
IN
0.1µF
6
GAIN = 12dB
INDUCTORS ARE COILCRAFT 1008PS-102M
6600 TA03a
–
V
200k
1M
10M
100M
FREQUENCY (Hz)
6600 TA03b
RELATED PARTS
PART NUMBER
LTC®1565-31
LTC1566-1
LT1567
DESCRIPTION
COMMENTS
650kHz Linear Phase Lowpass Filter
Low Noise, 2.3MHz Lowpass Filter
Continuous Time, SO8 Package, Fully Differential
Continuous Time, SO8 Package, Fully Differential
1.4nV/√Hz Op Amp, MSOP Package, Differential Output
Very Low Noise, High Frequency Filter Building Block
Very Low Noise, 4th Order Building Block
LT1568
Lowpass and Bandpass Filter Designs Up to 10MHz,
Differential Outputs
LTC6600-2.5
LTC6600-20
Very Low Noise, Differential Amplifier
and 2.5MHz Lowpass Filter
Adjustable Output Common Mode Voltage
Very Low Noise, Differential Amplifier
and 20MHz Lowpass Filter
Adjustable Output Common Mode Voltage
6600f
LT/TP 0403 2K • PRINTED IN USA
12 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
LINEAR TECHNOLOGY CORPORATION 2002
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