LT6600-10
Very Low Noise, Differential
Amplifier and 10MHz Lowpass Filter
FEATURES
DESCRIPTION
n
The LT®6600-10 combines a fully differential amplifier with a
4th order 10MHz lowpass filter approximating a Chebyshev
frequency response. Most differential amplifiers require
many precision external components to tailor gain and
bandwidth. In contrast, with the LT6600-10, two external
resistors program differential gain, and the filter’s 10MHz
cutoff frequency and passband ripple are internally set.
The LT6600-10 also provides the necessary level shifting
to set its output common mode voltage to accommodate
the reference voltage requirements of A/Ds.
n
n
n
n
n
n
n
n
Programmable Differential Gain via Two External
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
Compatible with Popular Differential Amplifier Pinouts
SO-8 and DFN-12 Packages
APPLICATIONS
n
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High Speed ADC Antialiasing and DAC Smoothing in
Networking or Cellular Base Station Applications
High Speed Test and Measurement Equipment
Medical Imaging
Drop-In Replacement for Differential Amplifiers
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 signalto-noise ratio is an impressive 82dB. At higher gains the
input referred noise decreases so the part can process
smaller input differential signals without significantly
degrading the output signal-to-noise ratio.
The LT6600-10 also features low voltage operation. The
differential design provides outstanding performance for
a 2VP-P signal level while the part operates with a single
3V supply.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
For similar devices with other cutoff frequencies, refer to
the LT6600-20, LT6600-15, LT6600-5 and LT6600-2.5.
TYPICAL APPLICATION
(S8 pin numbers shown)
An 8192 Point FFT Spectrum
0
5V
–20
0.1μF
7
0.01μF
VIN
RIN
402Ω
2
8
3
–
VMID
VOCM
+
+
–
4
5V
49.9Ω
49.9Ω
5
6
–30
V+
+
18pF
AIN
–
LTC1748
DOUT
–40
–50
–60
–70
–80
V–
VCM
FREQUENCY (dB)
RIN
402Ω 1
INPUT IS A 4.7MHz SINEWAVE
2VP-P
fSAMPLE = 66MHz
–10
LT6600-10
–90
–100
1μF
–110
GAIN = 402Ω/RIN
6600 TA01a
0
4
8
12 16 20 24
FREQUENCY (MHz)
28
32
6600 TA01b
66001fe
1
LT6600-10
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Total Supply Voltage .................................................11V
Input Current (Note 8)..........................................±10mA
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
PIN CONFIGURATION
TOP VIEW
IN–
1
12 IN+
NC
2
11 NC
VOCM
3
10 VMID
V+
4
NC
5
8 V–
OUT+
6
7 OUT–
13
TOP VIEW
9 V–
IN– 1
8
IN+
VOCM 2
7
VMID
V+ 3
6
V–
OUT+ 4
5
OUT–
S8 PACKAGE
8-LEAD PLASTIC SO
DF PACKAGE
12-LEAD (4mm s 4mm) PLASTIC DFN
TJMAX = 150°C, θJA = 100°C/W
TJMAX = 150°C, θJA = 43°C/W, θJC = 4°C/W
EXPOSED PAD (PIN 13) IS V–, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT6600CS8-10#PBF
LT6600CS8-10#TRPBF
660010
8-Lead Plastic SO
0°C to 70°C
LT6600IS8-10#PBF
LT6600IS8-10#TRPBF
600I10
8-Lead Plastic SO
–40°C to 85°C
LT6600CDF-10#PBF
LT6600CDF-10#TRPBF
60010
12-Lead (4mm × 4mm) Plastic DFN
0°C to 70°C
LT6600IDF-10#PBF
LT6600IDF-10#TRPBF
60010
12-Lead (4mm × 4mm) Plastic DFN
–40°C to 85°C
LEAD BASED FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT6600CS8-10
LT6600CS8#TR
660010
8-Lead Plastic SO
0°C to 70°C
LT6600IS8-10
LT6600IS8-10#TR
600I10
8-Lead Plastic SO
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts.
The temperature grade is identified by a label on the shipping container for the DFN Package.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
66001fe
2
LT6600-10
ELECTRICAL CHARACTERISTICS The l denotes the specifications
which 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
Filter Gain, VS = 3V
VIN = 2VP-P , fIN = DC to 260kHz
Filter Gain, VS = 5V
MIN
TYP
MAX
UNITS
–0.4
0
0.5
dB
VIN = 2VP-P , fIN = 1MHz (Gain Relative to 260kHz)
l
–0.1
0
0.1
dB
VIN = 2VP-P , fIN = 5MHz (Gain Relative to 260kHz)
l
–0.4
–0.1
0.3
dB
VIN = 2VP-P , fIN = 8MHz (Gain Relative to 260kHz)
l
–0.3
0.1
1
dB
VIN = 2VP-P , fIN = 10MHz (Gain Relative to 260kHz)
l
–0.2
0.3
1.7
dB
VIN = 2VP-P , fIN = 30MHz (Gain Relative to 260kHz)
l
–28
–25
VIN = 2VP-P , fIN = 50MHz (Gain Relative to 260kHz)
l
–44
VIN = 2VP-P , fIN = DC to 260kHz
–0.5
0
dB
dB
0.5
dB
VIN = 2VP-P , fIN = 1MHz (Gain Relative to 260kHz)
l
–0.1
0
0.1
dB
VIN = 2VP-P , fIN = 5MHz (Gain Relative to 260kHz)
l
–0.4
–0.1
0.3
dB
VIN = 2VP-P , fIN = 8MHz (Gain Relative to 260kHz)
l
–0.4
0.1
0.9
dB
VIN = 2VP-P , fIN = 10MHz (Gain Relative to 260kHz)
l
–0.3
0.2
1.4
dB
VIN = 2VP-P , fIN = 30MHz (Gain Relative to 260kHz)
l
–28
–25
dB
VIN = 2VP-P , fIN = 50MHz (Gain Relative to 260kHz)
l
–44
dB
Filter Gain, VS = ±5V
VIN = 2VP-P , fIN = DC to 260kHz
–0.6
Filter Gain, RIN = 100Ω, VS = 3V, 5V, ±5V
VIN = 0.5VP-P , fIN = DC to 260kHz
11.4
Filter Gain Temperature Coefficient (Note 2)
fIN = 260kHz, VIN = 2VP-P
780
ppm/C
Noise
Noise BW = 10kHz to 10MHz, RIN = 402Ω
56
μVRMS
Distortion (Note 4)
1MHz, 2VP-P , RL = 800Ω
2nd Harmonic
3rd Harmonic
88
97
dBc
dBc
5MHz, 2VP-P , RL = 800Ω
2nd Harmonic
3rd Harmonic
74
77
dBc
dBc
Differential Output Swing
Measured Between Pins 4 and 5
Pin 7 Shorted to Pin 2
VS = 5V
VS = 3V
Input Bias Current
Average of Pin 1 and Pin 8
Input Referred Differential Offset
RIN = 402Ω
VS = 3V
VS = 5V
VS = ±5V
l
l
l
5
10
8
20
30
35
mV
mV
mV
RIN = 100Ω
VS = 3V
VS = 5V
VS = ±5V
l
l
l
5
5
5
13
22
30
mV
mV
mV
Differential Offset Drift
–0.1
0.4
12
12.6
dB
dB
l
l
3.85
3.85
5.0
4.9
VP-P DIFF
VP-P DIFF
l
–85
–40
μA
10
μV/°C
66001fe
3
LT6600-10
ELECTRICAL CHARACTERISTICS The l denotes the specifications
which 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
Input Common Mode Voltage (Note 3)
Differential Input = 500mVP-P ,
RIN = 100Ω
VS = 3V
VS = 5V
VS = ±5V
l
l
l
0.0
0.0
–2.5
1.5
3.0
1.0
V
V
V
Output Common Mode Voltage (Note 5)
Differential Input = 2VP-P ,
Pin 7 = OPEN
VS = 3V
VS = 5V
VS = ±5V
l
l
l
1.0
1.5
–1.0
1.5
3.0
2.0
V
V
V
VS = 3V
VS = 5V
VS = ±5V
l
l
l
–35
–40
–55
40
40
35
mV
mV
mV
Output Common Mode Offset
(With Respect to Pin 2)
MIN
Common Mode Rejection Ratio
5
0
–5
MAX
61
Voltage at VMID (Pin 7)
VOCM = VMID = VS /2
Power Supply Current
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: This is the temperature coefficient of the internal feedback
resistors assuming a temperature independent external resistor (RIN).
Note 3: The input common mode voltage is the average of the voltages
applied to the external resistors (RIN). Specification guaranteed for
RIN ≥ 100Ω.
Note 4: Distortion is measured differentially using a differential stimulus,
The input common mode voltage, the voltage at VOCM, and the voltage at
VMID are equal to one half of the total power supply voltage.
UNITS
dB
l
l
2.46
2.45
2.51
2.51
1.5
2.55
2.56
V
V
V
l
4.3
5.5
7.7
kΩ
VS = 5V
VS = 3V
l
l
–15
–10
–3
–3
VS = 3V, VS = 5V
VS = 3V, VS = 3V
VS = ±5V
l
l
VS = 5V (S8)
VS = 5V (DFN)
VS = 3V
VMID Input Resistance
VOCM Bias Current
TYP
35
36
μA
μA
39
43
46
mA
mA
mA
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 VOCM.
Note 6: The LT6600C is guaranteed functional over the operating
temperature range –40°C to 85°C.
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.
Note 8: The inputs are protected by back-to-back diodes. If the differential
input voltage exceeds 1.4V, the input current should be limited to less than
10mA.
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4
LT6600-10
TYPICAL PERFORMANCE CHARACTERISTICS
Amplitude Response
Passband Gain and Group Delay
10
60
0
55
–10
–1
50
–20
–2
45
–3
40
–4
35
–5
30
–6
25
–7 V = 5V
S
–8 GAIN = 1
TA = 25°C
–9
0.5
20
VS = 5V
GAIN = 1
GAIN (dB)
–30
–40
(
GAIN 20LOG
DIFFOUT
DIFFIN
)
0
–50
–60
–70
–80
100k
1M
10M
FREQUENCY (Hz)
100M
15
10
14.9
5.3
10.1
FREQUENCY (MHz)
6600 G01
6600 G02
Output Impedance
vs Frequency (OUT + or OUT–)
60
11
55
10
50
9
45
8
40
7
35
6
30
5
25
4 V = 5V
S
3 GAIN = 4
TA = 25°C
2
0.5
20
100
OUTPUT IMPEDANCE (Ω)
12
GROUP DELAY (ns)
GAIN (dB)
Passband Gain and Group Delay
10
1
15
0.1
100k
10
14.9
5.3
10.1
FREQUENCY (MHz)
1M
10M
FREQUENCY (Hz)
Common Mode Rejection Ratio
Power Supply Rejection Ratio
VS = 5V
75 GAIN = 1
VIN = 1VP-P
70 TA = 25°C
70
65
60
–40
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
80
60
55
50
40
50
30
45
20
40
10
0
1M
10M
FREQUENCY (Hz)
100M
6600 G05
–50
DISTORTION (dB)
PSRR (dB)
CMRR (dB)
Distortion vs Frequency
VIN = 2VP-P, VS = 3V, RL = 800Ω
at Each Output, TA = 25°C
90
80
VS = 3V
VIN = 200mVP-P
TA = 25oC
V+ TO DIFFOUT
1k
100M
6600 G04
6600 G03
35
100k
GROUP DELAY (ns)
1
10k
100k
1M
FREQUENCY (Hz)
–60
–70
–80
–90
10M
100M
6600 G06
–100
0.1
1
FREQUENCY (MHz)
10
6600 G07
66001fe
5
LT6600-10
TYPICAL PERFORMANCE CHARACTERISTICS
–60
–70
–80
–40
2ND HARMONIC,
5MHz INPUT
3RD HARMONIC,
5MHz INPUT
2ND HARMONIC,
1MHz INPUT
3RD HARMONIC,
1MHZ INPUT
–50
DISTORTION (dB)
–50
DISTORTION (dB)
–40
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
–60
–70
–80
0.1
1
FREQUENCY (MHz)
1
2
3
INPUT LEVEL (VP-P)
4
6600 G08
–70
–80
–90
–100
3
–60
Power Supply Current
vs Power Supply Voltage
40
2ND HARMONIC,
VS = 3V
3RD HARMONIC,
VS = 3V
2ND HARMONIC,
VS = 5V
3RD HARMONIC,
VS = 5V
–50
5
4
6600 G10
POWER SUPPLY CURRENT (mA)
–60
DISTORTION COMPONENT (dB)
DISTORTION COMPONENT (dB)
–50
2
INPUT LEVEL (VP-P)
6600 G09
–40
2ND HARMONIC,
VS = 3V
3RD HARMONIC,
VS = 3V
2ND HARMONIC,
VS = 5V
3RD HARMONIC,
VS = 5V
1
0
5
Distortion vs Input Common Mode
Level, 0.5VP-P, 1MHz Input, 4x Gain,
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
–80
–110
0
10
–70
–100
–100
–100
–60
–90
–90
–90
2ND HARMONIC,
5MHz INPUT
3RD HARMONIC,
5MHz INPUT
2ND HARMONIC,
1MHz INPUT
3RD HARMONIC,
1MHZ INPUT
–50
DISTORTION (dB)
–40
Distortion vs Signal Level
VS = ±5V, RL = 800Ω at Each
Output, TA = 25°C
Distortion vs Signal Level
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
–70
–80
–90
38
TA = 85°C
36
34
TA = 25°C
32
30
TA = –40°C
28
26
–100
–3
2
–1
0
1
–2
INPUT COMMON MODE VOLTAGE
RELATIVE TO VMID (V)
3
–3
6600 G11
–1
0
1
2
–2
INPUT COMMON MODE VOLTAGE
RELATIVE TO VMID (V)
3
24
2
3
6
7
4
5
8
9
TOTAL SUPPLY VOLTAGE (V)
6600 G12
10
6600 G13
Distortion vs Output Common Mode,
2VP-P 1MHz Input, 1x Gain, TA = 25°C
Transient Response,
Differential Gain = 1
VOUT+
50mV/DIV
DIFFERENTIAL
INPUT
200mV/DIV
100ns/DIV
6600 G14
DISTORTION COMPONENT (dB)
–40
–50
–60
2ND HARMONIC, VS = 3V
3RD HARMONIC, VS = 3V
2ND HARMONIC, VS = 5V
3RD HARMONIC, VS = 5V
2ND HARMONIC, VS = ±5V
3RD HARMONIC, VS = ±5V
–70
–80
–90
–100
–1
0
0.5
1
1.5
–0.5
OUTPUT COMMON MODE VOLTAGE (V)
2
6600 G15
66001fe
6
LT6600-10
PIN FUNCTIONS
(DFN/S8)
IN – and IN+ (Pins 1, 12/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 1580Ω/RIN.
NC (Pin 2, 5, 11/NA): No Connection.
VOCM (Pin 3/Pin 2): Is the DC Common Mode Reference
Voltage for the 2nd Filter Stage. Its value programs the
common mode voltage of the differential output of the filter.
This is a high impedance input, which can be driven from
an external voltage reference, or can be tied to VMID on the
PC board. VOCM should be bypassed with a 0.01μF ceramic
capacitor unless it is connected to a ground plane.
V+ and V – (Pins 4, 8, 9/Pins 3, 6): Power Supply Pins. For
a single 3.3V or 5V supply (V– grounded) a quality 0.1μF
ceramic bypass capacitor is required from the positive
supply pin (V+) to the negative supply pin (V–). The bypass
should be as close as possible to the IC. For dual supply
applications, bypass V+ to ground and V– to ground with
a quality 0.1μF ceramic capacitor.
OUT+ and OUT– (Pins 6, 7/Pins 4, 5): Output Pins. These
are the filter differential outputs. Each pin can drive a 100Ω
and/or 50pF load to AC ground.
VMID (Pin 10/Pin 7): The VMID pin is internally biased
at mid-supply, see block diagram. For single-supply
operation the VMID pin should be bypassed with a quality
0.01μF ceramic capacitor to V–. For dual supply operation,
VMID 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. VMID 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.
BLOCK DIAGRAM
VIN+
RIN
IN+
OUT–
V–
VMID
V+
11k
PROPRIETARY
LOWPASS
FILTER STAGE
402Ω
11k
200Ω
V–
OP AMP
+
200Ω
+ –
–
VOCM
–
VOCM
+
– +
200Ω
200Ω
402Ω
6600 BD
VIN–
IN–
VOCM
V+
OUT+
RIN
66001fe
7
LT6600-10
APPLICATIONS INFORMATION
Interfacing to the LT6600-10
Note: The referenced pin numbers correspond to the S8
package. See the Pin Functions section for the equivalent
DFN-12 package pin numbers.
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 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
is 2VP-P for frequencies below 10MHz. The common mode
output voltage is determined by the voltage at VOCM. Since
VOCM is shorted to VMID 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 VMID (refer
to the Distortion vs Input Common Mode Level graphs in
the Typical Performance Characteristics section).
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 proportionally reduce this highpass 3dB frequency.
In Figure 3 the LT6600-10 is providing 12dB of gain. The
gain resistor has an optional 62pF in parallel to improve
the passband flatness near 10MHz. The common mode
output voltage is set to 2V.
Use Figure 4 to determine the interface between the
LT6600-10 and a current output DAC. The gain, or
“transimpedance”, is defined as A = VOUT/IIN Ω. To compute
the transimpedance, use the following equation:
A=
402 • R1
Ω
R1+ R2
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 VMID and the DAC output current (IIN+
or IIN–). Consider Figure 4 with R1 = 49.9Ω and R2 =
348Ω. The voltage at VMID is 1.65V. The voltage at the
DAC pins is given by:
R1
R1• R2
+IIN
R1+ R2 + 402
R1+ R2
= 103mV +IIN 43.6Ω
VDAC = VPIN7 •
IIN is IIN– or IIN+.The transimpedance in this example is
50.4Ω.
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 impedance
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. Figure 5
is a laboratory setup that can be used to characterize the
LT6600-10 using single-ended instruments with 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
66001fe
8
LT6600-10
APPLICATIONS INFORMATION
3.3V
0.1μF
V
3
VIN–
402Ω
1
VIN+
1
0
VIN–
2
0.01μF
VIN+
t
8
3
–
7
2
V
3
+
4
VOUT+
LT6600-10
+
402Ω
VOUT–
–5
6
2
VOUT+
1
VOUT–
t
0
6600 F01
Figure 1. (S8 Pin Numbers)
3.3V
0.1μF
V
0.1μF
402Ω
2
1
–
7
1
VIN+
0
0.1μF
t
0.01μF
VIN+
3
4
+
VOUT+
LT6600-10
2
8
–
+
402Ω
–1
V
3
2
VOUT–
5
1
6
VOUT+
VOUT–
0
6600 F02
Figure 2. (S8 Pin Numbers)
62pF
5V
0.1μF
V
3
VIN–
100Ω
1
7
2
1
0
VIN+
VIN–
2
0.01μF
500mVP-P (DIFF)
VIN+
100Ω
8
+
–
t
V
3
–
+
3
4
VOUT+
LT6600-10
–
+
VOUT+
2
VOUT–
5
6
1
0
2V
VOUT–
6600 F03
t
0.01μF
62pF
Figure 3. (S8 Pin Numbers)
CURRENT
OUTPUT
DAC
3.3V
0.1μF
IIN–
R2
R1
IIN+
7
0.01μF
R2
R1
1
3
–
+
4
VOUT+
2 LT6600-10
8
–
+
5
VOUT–
6
6600 F04
Figure 4. (S8 Pin Numbers)
66001fe
9
LT6600-10
APPLICATIONS INFORMATION
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.
voltage of VMID. 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 VMID.
20
2.5V
0
NETWORK
ANALYZER
SOURCE
50Ω
COILCRAFT
TTWB-1010
1:1 388Ω 1
7
53.6Ω
2
8
388Ω
3
–
+
4
COILCRAFT
TTWB-16A
4:1
402Ω
NETWORK
ANALYZER
INPUT
LT6600-10
–
+
6
5
50Ω
402Ω
0.1μF
6600 F05
–2.5V
OUTPUT LEVEL (dBV)
0.1μF
1dB PASSBAND GAIN
COMPRESSION POINTS
1MHz 25°C
1MHz 85°C
–20
3RD HARMONIC
85°C
–40
3RD HARMONIC
25°C
2ND HARMONIC
85°C
–60
–80
2ND HARMONIC
25°C
–100
–120
0
1
4
3
5
2
1MHz INPUT LEVEL (VP-P)
6
6600 F06
Figure 5. (S8 Pin Numbers)
Figure 6
Differential and Common Mode Voltage Ranges
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 supply
voltage.
The two amplifiers inside the LT6600-10 have independent
control of their output common mode voltage (see the
Block Diagram section). The following guidelines will
optimize the performance of the filter for single-supply
operation.
VMID must be bypassed to an AC ground with a 0.01μF or
higher capacitor. VMID can be driven from a low impedance
source, provided it remains at least 1.5V above V – and at
least 1.5V below V+. An internal resistor divider sets the
VOCM can be shorted to VMID for simplicity. If a different
common mode output voltage is required, connect VOCM
to a voltage source or resistor network. For 3V and 3.3V
supplies the voltage at VOCM must be less than or equal to
the mid-supply level. For example, voltage (VOCM) ≤1.65V
on a single 3.3V supply. For power supply voltages higher
than 3.3V the voltage at VOCM can be set above mid-supply.
The voltage on VOCM should not be more than 1V below
the voltage on VMID. The voltage on VOCM should not be
more than 2V above the voltage on VMID. VOCM is a high
impedance input.
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
average of VIN+ and VIN– in Figure 1) is determined by
the power supply level and gain setting (see the Electrical
Characteristics section).
Common Mode DC Currents
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
66001fe
10
LT6600-10
APPLICATIONS INFORMATION
currents will be generated through the DC path between
input and output terminals. Minimize these currents to
decrease power dissipation and distortion.
Consider the application in Figure 3. VMID sets the output
common mode voltage of the 1st differential amplifier
inside the LT6600-10 (see the Block Diagram 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 absorbed by
the sources VIN+ and VIN–. VOCM sets the 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, VOCM
differs from VMID by 0.5V, an additional 2.5mA (1.25mA
per side) of DC current will flow 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.
A simple modification to Figure 3 will reduce the DC
common mode currents by 36%. If VMID is shorted to
VOCM 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.
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.
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
connected, set the frequency to 1MHz and adjust the
amplitude 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:
eIN =
(eO )2 – (eS )2
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
subtracted from the results).
Table 1. Noise Performance
Noise
The noise performance of the LT6600-10 can be evaluated
with the circuit of Figure 7.
2.5V
0.1μF
VIN
RIN
1
7
2
8
RIN
3
– +
4
COILCRAFT
TTWB-1010
25Ω
1:1
LT6600-10
SPECTRUM
ANALYZER
INPUT
50Ω
–
+
6
5
0.1μF
25Ω
6600 F07
–2.5V
Figure 7. (S8 Pin Numbers)
PASSBAND
GAIN (V/V)
RIN
INPUT REFERRED
INTEGRATED NOISE
10kHz TO 10MHz
INPUT REFERRED
NOISE dBm/Hz
4
100Ω
24μVRMS
–149
2
200Ω
34μVRMS
–146
1
402Ω
56μVRMS
–142
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 outputs
to single-ended signal rejects the common mode noise and
gives a true measure of the S/N achievable in the system.
Conversely, if each output is measured individually and
the noise power added together, the resulting calculated
noise level will be higher than the true differential noise.
66001fe
11
LT6600-10
35
140
30
120
25
100
80
20
15
SPECTRAL DENSITY
10
60
40
INTEGRATED
NOISE
5
0
1.0
10
FREQUENCY (MHz)
0.1
INTEGRATED NOISE (mVRMS)
SPECTRAL DENSITY (nVRMS/√Hz)
APPLICATIONS INFORMATION
20
0
100
6600 F08
Figure 8
Power Dissipation
The LT6600-10 amplifiers combine high speed with largesignal 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 S8 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 S8 (330 square millimeters on each side of the
PC board) will result in a thermal resistance, θJA,of about
85°C/W. Without the extra metal trace connected to the
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.
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 voltages.
For a given supply voltage, the worst-case power dissipation occurs when the differential input signal is
maximum, the common mode currents are maximum
(see the Applications Information section regarding common mode DC currents), the load impedance is small and
the ambient temperature is maximum. To compute the
junction temperature, measure the supply current under
these worst-case conditions, estimate the thermal resistance from Table 2, then apply the equation for TJ. For
example, using the circuit in Figure 3 with DC differential
input voltage of 250mV, a differential output voltage of 1V,
no load resistance and an ambient temperature of 85°C,
the supply current (current into V+) measures 48.9mA.
Assuming a PC board layout with a 35mm2 copper trace,
the θJA is 100°C/W. The resulting junction temperature is:
TJ = TA + (PD • θJA) = 85 + (5 • 0.0489 • 100) = 109°C
When using higher supply voltages or when driving small
impedances, more copper may be necessary to keep TJ
below 150°C.
Table 2. LT6600-10 SO-8 Package Thermal Resistance
COPPER AREA
TOPSIDE
(mm2)
BACKSIDE
(mm2)
BOARD AREA
(mm2)
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
1100
1100
2500
65°C/W
330
330
2500
85°C/W
35
35
2500
95°C/W
35
0
2500
100°C/W
0
0
2500
105°C/W
66001fe
12
LT6600-10
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
DF Package
12-Lead Plastic DFN (4mm × 4mm)
(Reference LTC DWG # 05-08-1733 Rev Ø)
2.50 REF
0.70 ±0.05
3.38 ±0.05
4.50 ± 0.05
3.10 ± 0.05
2.65 ± 0.05
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 ± 0.10
(4 SIDES)
2.50 REF
7
12
0.40 ± 0.10
3.38 ±0.10
2.65 ± 0.10
PIN 1 NOTCH
R = 0.20 TYP OR
0.35 × 45°
CHAMFER
PIN 1
TOP MARK
(NOTE 6)
(DF12) DFN 0806 REV Ø
0.200 REF
6
R = 0.115
TYP
0.75 ± 0.05
1
0.25 ± 0.05
0.50 BSC
BOTTOM VIEW—EXPOSED PAD
0.00 – 0.05
NOTE:
1. DRAWING IS PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220
VARIATION (WGGD-X)—TO BE APPROVED
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
66001fe
13
LT6600-10
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.189 – .197
(4.801 – 5.004)
NOTE 3
.045 ±.005
.050 BSC
8
.245
MIN
7
6
5
.160 ±.005
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
1
RECOMMENDED SOLDER PAD LAYOUT
.010 – .020
× 45°
(0.254 – 0.508)
.008 – .010
(0.203 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
NOTE:
1. DIMENSIONS IN
.053 – .069
(1.346 – 1.752)
.014 – .019
(0.355 – 0.483)
TYP
INCHES
(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)
2
3
4
.004 – .010
(0.101 – 0.254)
.050
(1.270)
BSC
SO8 0303
66001fe
14
LT6600-10
REVISION HISTORY
(Revision history begins at Rev D)
REV
DATE
DESCRIPTION
D
5/10
Updated Order Information section
PAGE NUMBER
2
E
10/11
Corrected Conditions for Voltage at VMID (Pin 7) and Power Supply Current
4
66001fe
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LT6600-10
TYPICAL APPLICATIONS
5th Order, 10MHz Lowpass Filter
(S8 Pin Numbers Shown)
V
Amplitude Response
10
+
0
0.1μF
VIN+
C=
R
R
1
7
R
C
2
R
8
–10
3
–
+
4
LT6600-10
–
+
6
1
2P • R • 10MHz
5
0.1μF
–20
VOUT+
GAIN (dB)
VIN–
Transient Response
5th Order, 10MHz Lowpass Filter
Differential Gain = 1
VOUT–
VOUT+
50mV/DIV
–30
–40
DIFFERENTIAL
INPUT
200mV/DIV
–50
–60
DIFFERENTIAL GAIN = 1
–70 R = 200Ω
C = 82pF
–80
1M
10M
100k
FREQUENCY (Hz)
6600 TA02a
GAIN = 402Ω , MAXIMUM GAIN = 4 V–
2R
100ns/DIV
6600 TA02c
100M
6600 TA02b
Amplitude Respo A WCDMA Transmit Filter
(10MHz Lowpass Filter with a 28MHz Notch, S8 Pin Numbers Shown)
33pF
V+
33pF
1μH
VIN+
100Ω
RQ
301Ω
27pF 100Ω
1
7
2
8
0.1μF
12
4
–8
2
3
–
+
VOUT+
LT6600-10
–
+
6
GAIN = 12dB
INDUCTORS ARE COILCRAFT 1008PS-102M
VOUT
5
0.1μF
GAIN (dB)
1μH
VIN–
Amplitude Response
22
–
–18
–28
–38
–48
V–
–58
6600 TA03a
–68
–78
200k
1M
10M
FREQUENCY (Hz)
100M
6600 TA03b
RELATED PARTS
PART NUMBER
®
DESCRIPTION
COMMENTS
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650kHz Linear Phase Lowpass Filter
Continuous Time, SO8 Package, Fully Differential
LTC1566-1
Low Noise, 2.3MHz Lowpass Filter
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LT1567
Very Low Noise, High Frequency Filter Building Block
1.4nV/√Hz Op Amp, MSOP Package, Differential Output
LT1568
Very Low Noise, 4th Order Building Block
Lowpass and Bandpass Filter Designs Up to 10MHz, Differential Outputs
LTC6600-2.5
Very Low Noise, Differential Amplifier and 2.5MHz
Lowpass Filter
Adjustable Output Common Mode Voltage
LTC6600-20
Very Low Noise, Differential Amplifier and 20MHz
Lowpass Filter
Adjustable Output Common Mode Voltage
66001fe
16 Linear Technology Corporation
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