LINER LT6604-10 Dual very low noise, differential amplifier and 10mhz lowpass filter Datasheet

LT6604-10
Dual Very Low Noise,
Differential Amplifier and
10MHz Lowpass Filter
DESCRIPTION
FEATURES
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The LT®6604-10 consists of two matched, fully differential
amplifiers, each with a 4th order, 10MHz lowpass filter. The
fixed frequency lowpass filter approximates a Chebyshev
response. By integrating a filter and a differential amplifier, distortion and noise are made exceptionally low. At
unity gain, the measured in band signal-to-noise ratio is
an impressive 82dB. At higher gains, the input referred
noise decreases, allowing the part to process smaller
input differential signals without significantly degrading
the signal-to-noise ratio.
Dual Differential Amplifier with 10MHz Lowpass Filters
4th Order Filters
Approximates Chebyshev Response
Guaranteed Phase and Gain Matching
Resistor-Programmable Differential Gain
82dB Signal-to-Noise (3V Supply, 2VP-P Output)
Low Distortion, 2VP-P, 800Ω Load
1MHz: 88dBc 2nd, 97dBc 3rd
5MHz: 74dBc 2nd, 77dBc 3rd
Specified for Operation with 3V, 5V and ±5V Supplies
Fully Differential Inputs and Outputs
Adjustable Output Common Mode Voltage
Small 4mm × 7mm × 0.75mm QFN Package
Gain and phase are highly matched between the two channels. Gain for each channel is independently programmed
using two external resistors. The LT6604-10 enables level
shifting by providing an adjustable output common mode
voltage, making it ideal for directly interfacing to ADCs.
APPLICATIONS
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The LT6604-10 is fully specified for 3V operation. The
differential design enables outstanding performance at
a 2VP-P signal level for a single 3V supply. See the back
page of this data sheet for a complete list of related single
and dual differential amplifiers with integrated 2.5MHz to
20MHz lowpass filters.
Dual Differential ADC Driver Plus Filter
Single-Ended to Differential Converter
Matched, Dual, Differential Filter Stage
Common Mode Translation of Differential Signals
High Speed ADC Antialiasing and DAC Smoothing in
Wireless Infrastructure or Networking Applications
High Speed Test and Measurement Equipment
Medical Imaging
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
Channel to Channel Gain Matching, VS = 5V
3V
20
LT6604-10
0.01μF
+
402Ω
+INA
VMIDA
+
V+A
–
VOCMA
–
0.01μF
+
402Ω
402Ω
–INA
–
+
VMIDB
+
–
VOCMB
–
402Ω
–OUTA
50Ω
+OUTA
50Ω
V+B
+INB
–INB
–
+
LTC22xx
3V
DUAL ADC
16
+
18pF
AIN
14
DOUT
–OUTB
+OUTB
50Ω
50 TYPICAL UNITS
TA = 25°C
GAIN = 1
fIN = 10MHz
12
–
10
8
3V
50Ω
18
6
+
18pF
AIN
4
DOUT
2
–
0
V–
660410 TA01
–0.15 –0.1 –0.05 0 0.05 0.1 0.15 0.2 0.25
GAIN MATCH (dB)
660410 TA01b
660410fb
1
LT6604-10
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
31 V–
32 V–
34 VMIDA
33 NC
TOP VIEW
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
Input Current
+IN, –IN, VOCM, VMID (Note 8) .........................±10mA
Lead Temperature (Soldering, 10 sec) .................. 300°C
NC 1
30 NC
+INA 2
29 –OUTA
NC 3
28 NC
–INA 4
27 +OUTA
NC 5
26 NC
25 V+A
VOCMA 6
V– 7
24 V–
35
VMIDB 8
23 NC
NC 9
22 NC
+INB 10
21 –OUTB
NC 11
20 NC
–INB 12
19 +OUTB
NC 16
V+B 17
NC 15
18 NC
VOCMB 14
NC 13
UFF PACKAGE
34-LEAD (4mm × 7mm) PLASTIC QFN
TJMAX = 150°C, θJA = 34°C/W, θJC = 2.7°C/W
EXPOSED PAD (PIN 35) IS V–, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
SPECIFIED TEMPERATURE RANGE
LT6604CUFF-10#PBF
LT6604CUFF-10#TRPBF
60410
34-Lead (4mm × 7mm) Plastic QFN
0°C to 70°C
LT6604IUFF-10#PBF
LT6604IUFF-10#TRPBF
60410
34-Lead (4mm × 7mm) Plastic QFN
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
660410fb
2
LT6604-10
ELECTRICAL CHARACTERISTICS
The l 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
Filter Gain Either Channel, VS = 3V
VIN = 2VP-P, fIN = DC to 260kHz
VIN = 2VP-P, fIN =1MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 8MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 10MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 30MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 50MHz (Gain Relative to 260kHz)
l
l
l
l
l
l
–0.4
–0.1
–0.4
–0.3
–0.2
0
0
–0.1
0.1
0.3
–28
–44
0.5
0.1
0.3
1
1.7
–25
dB
dB
dB
dB
dB
dB
dB
Matching of Filter Gain, VS = 3V
VIN = 2VP-P, fIN = DC to 260kHz
VIN = 2VP-P, fIN =1MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 8MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 10MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 30MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 50MHz (Gain Relative to 260kHz)
l
l
l
l
l
l
0.1
0.01
0.03
0.08
0.15
0.3
0.4
0.6
0.1
0.3
0.4
0.7
1.8
2.8
dB
dB
dB
dB
dB
dB
dB
Matching of Filter Phase, VS = 3V
VIN = 2VP-P, fIN =1MHz
VIN = 2VP-P, fIN = 5MHz
VIN = 2VP-P, fIN = 8MHz
l
l
l
0.2
0.5
1
1
3
4
deg
deg
deg
Filter Gain Either Channel, VS = 5V
VIN = 2VP-P, fIN = DC to 260kHz
VIN = 2VP-P, fIN =1MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 8MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 10MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 30MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 50MHz (Gain Relative to 260kHz)
l
l
l
l
l
l
0
0
–0.1
0.1
0.2
–28
–44
0.5
0.1
0.3
0.9
1.4
–25
dB
dB
dB
dB
dB
dB
dB
Matching of Filter Gain, VS = 5V
VIN = 2VP-P, fIN = DC to 260kHz
VIN = 2VP-P, fIN =1MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 8MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 10MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 30MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 50MHz (Gain Relative to 260kHz)
l
l
l
l
l
l
0.1
0.01
0.03
0.08
0.15
0.3
0.4
0.6
0.1
0.3
0.4
0.7
1.8
2.8
dB
dB
dB
dB
dB
dB
dB
Matching of Filter Phase, VS = 5V
VIN = 2VP-P, fIN =1MHz
VIN = 2VP-P, fIN = 5MHz
VIN = 2VP-P, fIN = 8MHz
l
l
l
0.2
0.5
1
1
3
4
deg
deg
deg
Filter Gain Either Channel, VS = ±5V
VIN = 2VP-P, fIN = DC to 260kHz
–0.6
–0.1
0.4
dB
Filter Gain, RIN = 100Ω
VIN = 0.5VP-P, fIN = DC to 260kHz
11.4
11.4
11.4
12
12
12
12.6
12.6
12.6
dB
dB
dB
Filter Gain Temperature Coefficient (Note 2)
fIN = 260kHz, VIN = 2VP-P
Noise
Noise BW = 10kHz to 10MHz, RIN = 402Ω
Distortion (Note 4)
1MHz, 2VP-P, RL = 800Ω
2nd Harmonic
3rd Harmonic
5MHz, 2VP-P, RL = 800Ω
2nd Harmonic
3rd Harmonic
74
77
dBc
dBc
1MHz, 2VP-P, RL = 800Ω
–119
dB
5MHz, 2VP-P, RL = 800Ω
–111
dB
Channel Separation (Note 9)
Differential Output Swing
VS = 3V
VS = 5V
VS = ±5V
Measured Between +OUT and –OUT, VOCM Shorted to VMID
VS = 5V
VS = 3V
l
l
–0.5
–0.1
–0.4
–0.4
–0.3
3.85
3.85
780
ppm/°C
56
μVRMS
88
97
dBc
dBc
5.0
4.9
VP-P_DIFF
VP-P_DIFF
660410fb
3
LT6604-10
ELECTRICAL CHARACTERISTICS
The l 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
Input Bias Current
Average of +IN and –IN
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
l
MIN
TYP
–85
–40
Differential Offset Drift
MAX
UNITS
μA
10
μV/°C
Input Common Mode Voltage (Note 3)
Differential Input = 500mVP-P, RIN = 100Ω
VS = 3V
VS = 5V
VS = ±5V
l
l
l
0
0
–2.5
1.5
3
1
V
V
V
Output Common Mode Voltage (Note 5)
Differential Output = 2VP-P, VMID = OPEN
VS = 3V
VS = 5V
VS = ±5V
l
l
l
1
1.5
–1
1.5
3
2
V
V
V
Output Common Mode Offset
(with Respect to VOCM)
VS = 3V
VS = 5V
VS = ±5V
l
l
l
–35
–40
–55
40
40
35
mV
mV
mV
Common Mode Rejection Ratio
Voltage at VMID
5
5
–5
61
VS = 5V
VS = 3V
VMID Input Resistance
VOCM Bias Current
VOCM = VMID = VS/2
Power Supply Current (per Channel)
VS = 3V, VS = 5V
VS = 3V, VS = 5V
VS = ±5V
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.
Note 5: Output common mode voltage is the average of the +OUT and
–OUT voltages. The output common mode voltage is equal to VOCM.
Note 6: The LT6604C-10 is guaranteed functional over the operating
temperature range –40°C to 85°C.
VS = 5V
VS = 3V
dB
l
2.45
2.51
1.5
2.56
V
V
l
4.3
5.5
7.7
kΩ
l
l
–15
–10
–3
–3
l
l
35
36
μA
μA
39
43
46
mA
mA
mA
Note 7: The LT6604C-10 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 LT6604I-10 is
guaranteed to meet specified performance from –40°C to 85°C.
Note 8: Input pins (+IN, –IN, VOCM and VMID) are protected by steering
diodes to either supply. If the inputs should exceed either supply voltage,
the input current should be limited to less than 10mA. In addition, the
inputs +IN, –IN are protected by a pair of back-to-back diodes. If the
differential input voltage exceeds 1.4V, the input current should be limited
to less than 10mA.
Note 9: Channel separation (the inverse of crosstalk) is measured by
driving a signal into one input, while terminating the other input. Channel
separation is the ratio of the resulting output signal at the driven channel
to the output at the channel that is not driven.
660410fb
4
LT6604-10
TYPICAL PERFORMANCE CHARACTERISTICS
Amplitude Response
Passband Gain and Group Delay
10
1
VS = 5V
GAIN = 1
0
60
0
55
GAIN
–1
50
GAIN (dB)
–30
–40
(
GAIN 20LOG
–20
–50
–60
–70
–80
100k
1M
10M
FREQUENCY (Hz)
100M
–2
45
–3
40
–4
–5
35
GROUP DELAY
30
–6
25
–7 V = 5V
S
–8 GAIN = 1
TA = 25°C
–9
0.5
20
15
60
80
10
65
VS = 5V
75 GAIN = 1
VIN = 1VP-P
70 TA = 25°C
45
8
40
35
GROUP DELAY
6
30
5
25
4 V = 5V
S
3 GAIN = 4
TA = 25°C
2
0.5
20
CMRR (dB)
50
9
OUTPUT IMPEDANCE (Ω)
10
50
45
40
15
10
14.9
5.3
10.1
FREQUENCY (MHz)
0.1
100k
Power Supply Rejection Ratio
90
1M
10M
FREQUENCY (Hz)
DISTORTION (dBc)
PSRR (dB)
50
40
30
0
VS = 3V
VIN = 200mVP-P
TA = 25°C
V+ TO DIFFOUT
1k
10k
100k
1M
FREQUENCY (Hz)
660410 G05
–40
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
–60
–70
100M
660410 G06
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
–50
–80
–60
–70
–80
–90
–90
10M
100M
Distortion vs Frequency
VIN = 2VP-P, VS = ±5V, RL = 800Ω
at Each Output, TA = 25°C, Gain = 1
–50
60
1M
10M
FREQUENCY (Hz)
660410 G04
–40
70
35
100k
100M
Distortion vs Frequency
VIN = 2VP-P, VS = 3V, RL = 800Ω
at Each Output, TA = 25°C, Gain = 1
80
10
55
1
660410 G03
20
60
DISTORTION (dBc)
7
Common Mode Rejection Ratio
100
55
GAIN
GROUP DELAY (ns)
GAIN (dB)
11
660410 G02
Output Impedance
vs Frequency (OUT + or OUT–)
12
10
14.9
5.3
10.1
FREQUENCY (MHz)
660410 G01
Passband Gain and Group Delay
GROUP DELAY (ns)
DIFFOUT
DIFFIN
)
–10
–100
–100
0.1
1
FREQUENCY (MHz)
10
660410 G07
0.1
1
FREQUENCY (MHz)
10
660410 G08
660410fb
5
LT6604-10
TYPICAL PERFORMANCE CHARACTERISTICS
Distortion vs Signal Level
VS = 3V, RL = 800Ω at Each Output,
TA = 25°C, Gain = 1
–60
–70
–80
–90
–60
–70
–80
–90
–100
–110
–100
0
1
2
3
INPUT LEVEL (VP-P)
4
1
0
5
2
38
–3
2
3
–1
0
1
–2
INPUT COMMON MODE VOLTAGE
RELATIVE TO VMID (V)
660410 G11
Transient Response,
Differential Gain = 1
–70
–80
TA = 85°C
VOUT+
50mV/DIV
36
34
TA = 25°C
DIFFERENTIAL
INPUT
200mV/DIV
32
30
TA = –40°C
28
–90
100ns/DIV
660410 G14
26
–3
24
2
3
–1
0
1
–2
INPUT COMMON MODE VOLTAGE
RELATIVE TO VMID (V)
660410 G12
6
7
4
5
8
9
TOTAL SUPPLY VOLTAGE (V)
10
–40
DISTORTION COMPONENT (dBc)
VIN = 2VP-P
VS = 5V
–40 RL = 800Ω AT
EACH OUTPUT
GAIN = 1
–60
–80
–100
–120
–50
–60
100
660410 G15
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
10
FREQUENCY (MHz)
3
660410 G13
–20
–140
0.1
2
Distortion vs Output Common
Mode Level, 2VP-P 1MHz Input,
1x Gain, TA = 25°C
Channel Separation
vs Frequency (Note 9)
CHANNEL SEPARATION (dB)
–90
Single Channel Supply Current
vs Total Supply Voltage
SUPPLY CURRENT (mA)
DISTORTION COMPONENT (dBc)
–60
–80
40
2ND HARMONIC,
VS = 3V
3RD HARMONIC,
VS = 3V
2ND HARMONIC,
VS = 5V
3RD HARMONIC,
VS = 5V
–50
–70
–100
5
4
–60
660410 G10
660410 G09
–40
3
2ND HARMONIC,
VS = 3V
3RD HARMONIC,
VS = 3V
2ND HARMONIC,
VS = 5V
3RD HARMONIC,
VS = 5V
–50
INPUT LEVEL (VP-P)
Distortion vs Input Common Mode
Level, 0.5VP-P, 1MHz Input, 4x Gain,
RL = 800Ω at Each Output, TA = 25°C
–100
–40
2ND HARMONIC,
5MHz INPUT
3RD HARMONIC,
5MHz INPUT
2ND HARMONIC,
1MHz INPUT
3RD HARMONIC,
1MHZ INPUT
–50
DISTORTION (dBc)
–50
DISTORTION (dBc)
–40
2ND HARMONIC,
5MHz INPUT
3RD HARMONIC,
5MHz INPUT
2ND HARMONIC,
1MHz INPUT
3RD HARMONIC,
1MHZ INPUT
Distortion vs Input Common Mode
Level, 2VP-P, 1MHz Input, 1x Gain,
RL = 800Ω at Each Output, TA = 25°C
DISTORTION COMPONENT (dBc)
–40
Distortion vs Signal Level
VS = ±5V, RL = 800Ω at Each Output,
TA = 25°C, Gain = 1
–1
1.5
0
0.5
1
–0.5
(VOCM – VMID) VOLTAGE (V)
2
660410 G16
660410fb
6
LT6604-10
PIN FUNCTIONS
+INA and –INA (Pins 2, 4): Channel A 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.
VOCMA (Pin 6): DC Common Mode Reference Voltage
for the 2nd Filter Stage in Channel A. Its value programs
the common mode voltage of the differential output of
the filter. Pin 6 is a high impedance input, which can be
driven from an external voltage reference, or Pin 6 can be
tied to Pin 34 on the PC board. Pin 6 should be bypassed
with a 0.01μF ceramic capacitor unless it is connected to
a ground plane.
V– (Pins 7, 24, 31, 32, 35): Negative Power Supply Pin
(can be ground).
VMIDB (Pin 8): The VMIDB pin is internally biased at midsupply, see the Block Diagram. For single supply operation
the VMIDB pin should be bypassed with a quality 0.01μF
ceramic capacitor to ground. For dual supply operation,
Pin 8 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 8 sets the output
common mode voltage of the 1st filter stage in channel B.
It has a 5.5kΩ impedance, and it can be overridden with
an external low impedance voltage source.
+INB and –INB (Pins 10, 12): Channel B 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.
VOCMB (Pin 14): DC Common Mode Reference Voltage
for the 2nd Filter Stage in Channel B. Its value programs
the common mode voltage of the differential output of
the filter. Pin 14 is a high impedance input, which can
be driven from an external voltage reference, or Pin 14
can be tied to Pin 8 on the PC board. Pin 14 should be
bypassed with a 0.01μF ceramic capacitor unless it is
connected to a ground plane.
V+A and V+B (Pins 25, 17): Positive Power Supply Pins for
Channels A and B. For a single 3.3V or 5V supply (Pins 7,
24, 31, 32 and 35 grounded) a quality 0.1μF ceramic
bypass capacitor is required from the positive supply pin
(Pins 25, 17) to the negative supply pin (Pins 7, 24, 31,
32 and 35). The bypass should be as close as possible to
the IC. For dual supply applications, bypass the negative
supply pins to ground and Pins 25 and 17 to ground with
a quality 0.1μF ceramic capacitor.
+OUTB and –OUTB (Pins 19, 21): Output Pins. Pins 19 and
21 are the filter differential outputs for channel B. With a
typical short-circuit current limit greater than ±40mA, each
pin can drive a 100Ω and/or 50pF load to AC ground.
+OUTA and –OUTA (Pins 27, 29): Output Pins. Pins 27 and
29 are the filter differential outputs for channel A. With a
typical short-circuit current limit greater than ±40mA, each
pin can drive a 100Ω and/or 50pF load to AC ground.
VMIDA (Pin 34): The VMIDA pin is internally biased at midsupply, see the Block Diagram. For single supply operation
the VMIDA pin should be bypassed with a quality 0.01μF
ceramic capacitor to ground. For dual supply operation,
Pin 34 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 34 sets the output
common mode voltage of the 1st filter stage in channel A.
It has a 5.5kΩ impedance, and it can be overridden with
an external low impedance voltage source.
Exposed Pad (Pin 35): V–. The exposed pad must be
soldered to the PCB.
660410fb
7
LT6604-10
BLOCK DIAGRAM
VMIDA
NC
34
33
NC 1
VIN+A
RIN
+INA
VIN A
RIN
–INA
V–
32
31
30 NC
11k
2
402Ω
11k
NC 3
–
V+A
V–
4
NC 5
V–
+
OP AMP
VOCM
–
200Ω
–
PROPRIETARY
LOWPASS
FILTER STAGE
200Ω
+ –
VOCM
+
200Ω
– +
200Ω
VOCMA 6
29 –OUTA
28 NC
27 +OUTA
26 NC
25 V+A
402Ω
V+B
V– 7
24 V–
11k
VMIDB 8
402Ω
11k
RIN
+INB
10
+
OP AMP
VOCM
–
RIN
–INB
+ –
VOCM
+
200Ω
NC 11
VIN–B
22 NC
200Ω
–
23 NC
200Ω
V–
NC 9
VIN+B
PROPRIETARY
LOWPASS
FILTER STAGE
21 –OUTB
– +
20 NC
200Ω
12
NC 13
19 +OUTB
402Ω
14
15
16
17
VOCMB
NC
NC
V+B
18 NC
660410 BD
660410fb
8
LT6604-10
APPLICATIONS INFORMATION
Interfacing to the LT6604-10
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.
Note: The LT6604-10 contains two identical filters. The
following applications information only refers to one filter.
The two filters are independent except that they share
the same negative supply voltage V –. The two filters
can be used simultaneously by replicating the example
circuits. The referenced pin numbers correspond to the
channel A filter.
The LT6604-10 channel requires two 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 27
and 29 of the LT6604-10 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 LT6604-10
Figure 2 shows how to AC couple signals into the LT6604-10.
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.
3.3V
0.1μF
V
3
–
402Ω
VIN
2
1
0
VIN+
0.01μF
+
VIN
VIN–
t
V
25
3
4
–
27
34 1/2 +
LT6604-10
6
VOUT+
– 29
VOUT–
2
+
402Ω
7
2
VOUT+
1
VOUT–
t
0
660410 F01
Figure 1
3.3V
0.1μF
V
0.1μF
2
402Ω
1
0
–1
VIN+
0.1μF
t
0.01μF
+
VIN
402Ω
V
25
4
–
27
34 1/2 +
LT6604-10
6
VOUT+
– 29
VOUT–
2
+
7
3
2
1
0
VOUT+
VOUT–
660410 F02
Figure 2
660410fb
9
LT6604-10
APPLICATIONS INFORMATION
In Figure 3 the LT6604-10 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.
The voltage at VMID, for VS = 3.3V, is 1.65V. The voltage at
the DAC pins is given by:
VDAC = VMID •
Use Figure 4 to determine the interface between the
LT6604-10 and a current output DAC. The gain, or “transimpedance,” is defined as A = VOUT/IIN. To compute the
transimpedance, use the following equation:
A=
R1
R1• R2
+IIN •
R1+R2+ 402
R1+R2
=103mV +IIN • 43.6Ω
IIN is IIN+ or IIN–. The transimpedance in this example is
50.4Ω.
402 • R1
(Ω)
(R1+R2)
Evaluating the LT6604-10
By setting R1 + R2 = 402Ω, the gain equation reduces to
A = R1 (Ω).
The low impedance levels and high frequency operation
of the LT6604-10 require some attention to the matching
networks between the LT6604-10 and other devices. The
previous examples assume an ideal (0Ω) source impedance
and a large (1k) load resistance. Among practical examples
where impedance must be considered is the evaluation of
the LT6604-10 with a network analyzer.
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.
62pF
5V
0.1μF
V
100Ω
–
3
VIN
2
1
0
0.01μF
500mVP-P (DIFF)
VIN–
VIN
100Ω
+
–
t
4
–
27
34 1/2 +
LT6604-10
6
VOUT+
– 29
VOUT–
2
+
VIN+
V
25
+
3
VOUT+
2
7
1
0
2V
VOUT–
660410 F03
t
62pF
Figure 3
CURRENT
OUTPUT
DAC
3.3V
0.1μF
IIN–
R2
R1
0.01μF
IIN+
R2
4
25
–
27
34 1/2 +
6 LT6604-10
2
–
+
29
VOUT+
VOUT–
7
R1
402 • R1
VOUT+ – VOUT–
=
R1 + R2
IIN+ – IIN–
660410 F04
Figure 4
660410fb
10
LT6604-10
APPLICATIONS INFORMATION
2.5V
0.1μF
NETWORK
ANALYZER
SOURCE
50Ω
COILCRAFT
TTWB-1010
1:1 388Ω 4
53.6Ω
25
–
27
34 1/2 +
LT6604-10
6
2
388Ω
–
+
7
29
COILCRAFT
TTWB-16A
4:1
402Ω
NETWORK
ANALYZER
INPUT
50Ω
402Ω
0.1μF
660410 F05
–2.5V
Figure 5
Figure 5 is a laboratory setup that can be used to characterize the LT6604-10 using single-ended instruments
with 50Ω source impedance and 50Ω input impedance.
For a unity gain configuration the LT6604-10 requires an
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 of the
LT6604-10 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 LT6604-10
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.
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 LT6604-10 channel have
independent control of their output common mode voltage
(see the Block Diagram section). The following guidelines
will optimize the performance of the filter.
VMID can be allowed to float, but it must be bypassed to an
AC ground with a 0.01μF capacitor or some instability may
be observed. 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
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.
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.
20
Differential and Common Mode Voltage Ranges
OUTPUT LEVEL (dBV)
The differential amplifiers inside the LT6604-10 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 LT6604-10 channel 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
0
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
660410 F06
Figure 6
660410fb
11
LT6604-10
APPLICATIONS INFORMATION
The LT6604-10 was designed to process a variety of
input signals including signals centered on 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).
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 per
channel. Of course, by AC coupling the inputs of Figure 3,
the common mode DC current can be reduced to 2.5mA
per channel.
Noise
Common Mode DC Currents
In applications like Figures 1 and 3 where the LT6604-10
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 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 LT6604-10 channel
(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 LT6604-10 channel, and therefore sets the common
mode output voltage of the filter. Since, in the example of
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 the filter output. Thus, a total of 12.5mA per channel is
used to translate the common mode voltages.
The noise performance of the LT6604-10 channel can be
evaluated with the circuit of Figure 6. Given the low noise
output of the LT6604-10 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, Figure 6, 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.
Table 1. Noise Performance
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
PASSBAND
GAIN
660410fb
12
LT6604-10
APPLICATIONS INFORMATION
Power Dissipation
The LT6604-10 amplifiers combine high speed with large
signal currents in a small package. There is a need to ensure that the die’s junction temperature does not exceed
150°C. The LT6604-10 has an exposed pad (pin 35) which
is connected to the lower supply (V–). Connecting the pad
to a ground plane helps to dissipate the heat generated
by the chip. Metal trace and plated through-holes can be
used to spread the heat generated by the device to the
backside of the PC board.
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
0.1μF
VIN
RIN
4
–
27
34 1/2 +
LT6604-10
6
2
RIN
25
COILCRAFT
TTWB-1010
25Ω
1:1
SPECTRUM
ANALYZER
INPUT
50Ω
–
+
7
29
0.1μF
25Ω
660410 F07
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, use 34°C/W as the package
thermal resistance, 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 per
channel. The resulting junction temperature is:
TJ = TA + (PD • θJA) = 85 + (5 • 2 • 0.0489 • 34) = 102°C.
The thermal resistance can be affected by the amount of
copper on the PCB that is connected to V–. The thermal
resistance of the circuit can increase if the exposed pad
is not connected to a large ground plane with a number
of vias.
35
140
30
120
25
100
80
20
15
SPECTRAL DENSITY
10
40
INTEGRATED
NOISE
5
0
0.1
–2.5V
60
1.0
10
FREQUENCY (MHz)
INTEGRATED NOISE (μVRMS)
2.5V
supply current, IS. Therefore, the junction temperature
is given by:
SPECTRAL DENSITY (nVRMS/√Hz)
Figure 8 is plot of the noise spectral density as a function
of frequency for an LT6604-10 channel with RIN = 402Ω
using the fixture of Figure 7 (the instrument noise has been
subtracted from the results). 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.
20
0
100
660410 F08
Figure 7
Figure 8
660410fb
13
LT6604-10
TYPICAL APPLICATION
Dual, Matched, 5th Order, 10MHz Lowpass Filter
V+
0.1μF
VINA–
R
R
C
VINA+
C=
R
R
4
25
–
27
34 1/2 +
LT6604-10
6
VOUTA+
– 29
VOUTA–
2
+
7 0.1μF
1
2π • R • 10MHz
GAIN = 402Ω , MAXIMUM GAIN = 4 V–
2R
V+
0.1μF
VINB–
VINB+
C=
R
R
R
12
17
VOUTB+
C
–
19
8 1/2 +
LT6604-10
14
R
10
– 21
VOUTB–
1
2π • R • 10MHz
+
24
GAIN = 402Ω , MAXIMUM GAIN = 4 V–
2R
0.1μF
660410 TA02a
Transient Response
5th Order, 10MHz Lowpass Filter
Differential Gain = 1
Amplitude Response
10
0
–10
VOUT*
50mV/DIV
GAIN (dB)
–20
–30
DIFFERENTIAL
INPUT
200mV/DIV
–40
–50
–60
DIFFERENTIAL GAIN = 1
–70 R = 200Ω
C = 82pF
–80
100k
1M
10M
FREQUENCY (Hz)
100ns/DIV
660410 TA02c
100M
660410 TA02b
660410fb
14
LT6604-10
PACKAGE DESCRIPTION
UFF Package
34-Lead Plastic QFN (4mm × 7mm)
(Reference LTC DWG # 05-08-1758 Rev Ø)
0.70 ± 0.05
1.90 ± 0.05
4.50 ± 0.05
PACKAGE OUTLINE
1.83 ± 0.05
3.10 ± 0.05
1.50 REF
1.90 ± 0.05
1.47 ± 0.05
2.64 ± 0.05
1.29 ± 0.05
0.25 ± 0.05
0.50 BSC
6.00 REF
6.10 ± 0.05
7.50 ± 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 ± 0.10
PIN 1 NOTCH
R = 0.30 OR
0.25 × 45°
CHAMFER
R = 0.10
TYP
0.75 ± 0.05
1.50 REF
33
34
0.40 ± 0.10
1
PIN 1
TOP MARK
(NOTE 6)
1.90 ± 0.10
2
1.47 ± 0.10
7.00 ± 0.10
6.00 REF
1.83 ± 0.10
1.90 ± 0.10
2.64 ± 0.10
(UFF34) QFN 0807 REV Ø
0.200 REF
0.00 – 0.05
R = 0.125
TYP
0.25 ± 0.05
0.50 BSC
0.99 ± 0.10
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
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 0.20mm 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
660410fb
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
LT6604-10
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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Very Low Noise, 8th Order Filter Building Block
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LTC1565-31
650kHz Linear Phase Lowpass Filter
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LTC1566-1
Low Noise, 2.3MHz Lowpass Filter
Continuous Time, 7th Order, Differential
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LTC1569-7
Linear Phase, Tunable 10th Order Lowpass Filter
Single-Resistor Programmable Cutoff to 300kHz
LT6600-2.5
Very Low Noise Differential 2.5MHz Lowpass Filter
SNR = 86dB at 3V Supply, 4th Order Filter
LT6600-5
Very Low Noise Differential 5MHz Lowpass Filter
SNR = 82dB at 3V Supply, 4th Order Filter
LT6600-10
Very Low Noise Differential 10MHz Lowpass Filter
SNR = 82dB at 3V Supply, 4th Order Filter
LT6600-15
Very Low Noise Differential 15MHz Lowpass Filter
SNR = 76dB at 3V Supply, 4th Order Filter
LT6600-20
Very Low Noise Differential 20MHz Lowpass Filter
SNR = 76dB at 3V Supply, 4th Order Filter
LT6604-2.5
Dual Very Low Noise, Differential Amplifier and 2.5MHz
Lowpass Filter
SNR = 86dB at 3V Supply, 4th Order Filter
LT6604-5
Dual Very Low Noise, Differential Amplifier and 5MHz
Lowpass Filter
SNR = 82dB at 3V Supply, 4th Order Filter
LT6604-15
Dual Very Low Noise, Differential Amplifier and 15MHz
Lowpass Filter
SNR = 76dB at 3V Supply, 4th Order Filter
Integrated Filters
660410fb
16 Linear Technology Corporation
LT 0409 REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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