LINER LT6604IUFF-5-PBF Dual very low noise, differential amplifi er and 5mhz lowpass filter Datasheet

LT6604-5
Dual Very Low Noise,
Differential Amplifier and
5MHz Lowpass Filter
DESCRIPTION
FEATURES
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Dual Differential Amplifier with 5MHz 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 (1MHz, 2VP-P Output, 800Ω Load)
HD2: 93dBc
HD3: 96dBc
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
The LT®6604-5 consists of two matched, fully differential
amplifiers, each with a 4th order, 5MHz 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.
Gain and phase are well matched between the two channels. Gain for each channel is independently programmed
using two external resistors. The LT6604-5 enables level
shifting by providing an adjustable output common mode
voltage, making it ideal for directly interfacing to ADCs.
The LT6604-5 is fully specified for 3V operation. The differential design enables outstanding performance at a
2VP-P signal level for a single 3V supply.
APPLICATIONS
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Dual Differential ADC Driver and Filter
Single-Ended to Differential Converter
Matched, Dual, Differential Gain or 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
See the back page of this datasheet for a complete list of
related single and dual differential amplifiers with integrated
2.5MHz to 20MHz lowpass filters.
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
3V
25
–
806Ω
+INA
VMIDA
0.01μF
+
V+A
+
–
VOCMA
–INA
–
+
806Ω
–
806Ω
0.01μF
806Ω
+OUTA
V+B
+INB
VMIDB
+
–OUTA
+
–
VOCMB
–INB
–
+
–OUTB
+OUTB
LTC22xx
3V
50Ω
50Ω
+
18pF
AIN
DOUT
–
3V
50Ω
50Ω
+
18pF
AIN
50 TYPICAL UNITS
TA = 25°C
GAIN = 1
20 f = 5MHz
IN
DUAL ADC
NUMBER OF UNITS
LT6604-5
15
10
5
DOUT
–
0
V–
–0.20
66045 TA01
–0.10
0
0.10
GAIN MATCH (dB)
0.20
66045 TA01b
66045f
1
LT6604-5
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
31 V–
32 V–
33 NC
TOP VIEW
34 VMIDA
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 Voltage
+IN, –IN, VOCM, VMID (Note 8) ..............................±VS
Input Current
+IN, –IN, VOCM, VMID (Note 8) ........................±10mA
30 NC
NC 1
29 –OUTA
+INA 2
28 NC
NC 3
27 +OUTA
–INA 4
26 NC
NC 5
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 13
V+B 17
NC 16
NC 15
VOCMB 14
18 NC
UFF PACKAGE
34-LEAD (4mm s 7mm) PLASTIC QFN
TJMAX = 150°C, θJA = 43°C/W, θJC = 4°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-5#PBF
LT6604CUFF-5#TRPBF
66045
34-Lead (4mm × 7mm) Plastic QFN
0°C to 70°C
LT6604IUFF-5#PBF
LT6604IUFF-5#TRPBF
66045
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/
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 = 806Ω, 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 = 500kHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 2.5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 4MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 15MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 25MHz (Gain Relative to 260kHz)
–0.5
–0.15
–0.4
–0.7
–1.1
0
0
–0.1
–0.1
–0.2
–28
–44
0.5
0.1
0.3
0.6
0.8
–25
dB
dB
dB
dB
dB
dB
dB
l
l
l
l
l
l
66045f
2
LT6604-5
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 = 806Ω, and
RLOAD = 1k.
PARAMETER
CONDITIONS
Matching of Filter Gain, VS = 3V
VIN = 2VP-P, fIN = DC to 260kHz
VIN = 2VP-P, fIN = 500kHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 2.5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 4MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 15MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 25MHz (Gain Relative to 260kHz)
Matching of Filter Phase, VS = 3V
TYP
MAX
l
l
l
l
l
l
0.05
0.005
0.01
0.03
0.05
0.15
0.1
0.7
0.1
0.2
0.5
0.6
1.8
2.8
dB
dB
dB
dB
dB
dB
dB
VIN = 2VP-P, fIN = 2.5MHz
VIN = 2VP-P, fIN = 4MHz
l
l
0.2
0.5
2
3
deg
deg
Filter Gain Either Channel, VS = 5V
VIN = 2VP-P, fIN = DC to 260kHz
VIN = 2VP-P, fIN = 500kHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 2.5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 4MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 15MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 25MHz (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
0.6
0.8
–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 = 500kHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 2.5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 4MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 15MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 25MHz (Gain Relative to 260kHz)
l
l
l
l
l
l
0.05
0.005
0.01
0.03
0.05
0.15
0.1
0.7
0.1
0.2
0.5
0.6
1.8
2.8
dB
dB
dB
dB
dB
dB
dB
Matching of Filter Phase, VS = 5V
VIN = 2VP-P, fIN = 2.5MHz
VIN = 2VP-P, fIN = 4MHz
l
l
0.2
0.5
2
3
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 = 229Ω
VOUT = 2VP-P, fIN = DC to 260kHz
VS = 3V
VS = 5V
VS = ±5V
10.4
10.3
10.1
10.9
10.8
10.7
11.5
11.4
11.3
Filter Gain Temperature Coefficient (Note 2)
fIN = 260kHz, VIN = 2VP-P
780
ppm/°C
Noise
Distortion (Note 4)
Noise BW = 10kHz to 5MHz, RIN = 806Ω
VIN = 2VP-P, fIN = 1MHz, RL = 800Ω
2nd Harmonic
3rd Harmonic
VIN = 2VP-P, fIN = 5MHz, RL = 800Ω
2nd Harmonic
3rd Harmonic
VIN = 2VP-P, fIN = 1MHz
Measured Between OUT+ and OUT–, VOCM Shorted to VMID
VS = 5V
VS = 3V
Average of IN+ and IN–
45
μVRMS
93
96
dBc
dBc
66
73
–117
dBc
dBc
dB
4.8
4.8
–30
VP-P_DIFF
VP-P_DIFF
μA
Channel Separation (Note 9)
Differential Output Swing
Input Bias Current
MIN
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l
l
–0.5
–0.15
–0.4
–0.7
–1.1
3.85
3.85
–70
UNITS
dB
dB
dB
66045f
3
LT6604-5
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 = 806Ω, and
RLOAD = 1k.
PARAMETER
CONDITIONS
Input Referred Differential Offset
RIN = 806Ω
VS = 3V
VS = 5V
VS = ±5V
RIN = 229Ω
VS = 3V
VS = 5V
VS = ±5V
Differential Offset Drift
Input Common Mode Voltage (Note 3)
Output Common Mode Voltage (Note 5)
Output Common Mode Offset
(with Respect to VOCM)
Common Mode Rejection Ratio
Voltage at VMID
VMID Input Resistance
VOCM Bias Current
Power Supply Current
(Per Channel)
MIN
Differential Input = 500mVP-P, RIN = 229Ω
VS = 3V
VS = 5V
VS = ±5V
Differential Output = 2VP-P, VMID at Mid Supply
VS = 3V
VS = 5V
VS = ±5V
VS = 3V
VS = 5V
VS = ±5V
VS = 5V
VS = 3V
VOCM = VMID = VS/2
VS = 5V
VS = 3V
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 ≥
229Ω.
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-5 is guaranteed functional over the operating
temperature range –40°C to 85°C.
TYP
MAX
UNITS
l
l
l
5
10
8
25
30
35
mV
mV
mV
l
l
l
5
5
5
10
13
16
20
mV
mV
mV
μV/°C
l
l
l
0
0
–2.5
1.5
3
1
V
V
V
l
l
l
l
l
l
1
1.5
–1
–25
–30
–55
1.5
3
2
50
45
35
l
2.45
l
4.3
7.7
V
V
V
mV
mV
mV
dB
V
V
kΩ
l
–15
–10
31
34
38
μA
μA
mA
mA
mA
l
l
5
5
–5
61
2.51
1.5
5.5
–3
–3
28
30
2.56
Note 7: The LT6604C-5 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 to 85°C. The LT6604I-5 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.
66045f
4
LT6604-5
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency Response
Passband Gain and Group Delay
VS = 5V
GAIN = 1
TA = 25°C
0
110
12
–1
100
11
100
–2
90
10
90
–3
80
GAIN
–30
–40
DELAY
–4
70
120
GAIN
9
110
80
DELAY
8
70
–5
60
7
60
–6
50
6
50
–60
–7
40
5
40
–70
–8 GAIN = 1
TA = 25°C
–9
0 1 2
30
4 GAIN = 4
TA = 25°C
3
0 1 2 3 4 5 6 7
FREQUENCY (MHz)
30
–50
–80
0.1
1
10
FREQUENCY (MHz)
100
3 4 5 6 7
FREQUENCY (MHz)
8
66045 G01
VS = 5V
GAIN = 1
TA = 25°C
80
1
VS = 5V
GAIN = 1
VIN = 1VP-P
TA = 25°C
70
60
PSRR (dB)
50
60
40
30
20
40
30
0.01
100
0.1
1
10
FREQUENCY (MHz)
Distortion vs Frequency
–80
–90
–110
VS = 3V, VIN = 2VP-P
RL = 800Ω, TA = 25°C, GAIN = 1
0.1
1
FREQUENCY (MHz)
–70
–80
–90
–110
10
66045 G07
100
1
FREQUENCY (MHz)
–60 3RD HARMONIC,
5MHz INPUT
–70
2ND HARMONIC,
5MHz INPUT
–80
3RD HARMONIC,
1MHz INPUT
–90
–100
VS = p5V, VIN = 2VP-P
RL = 800Ω, TA = 25°C, GAIN = 1
0.1
VS = 3V, RL = 800Ω
TA = 25°C, GAIN = 1
–50
–100
–100
1
10
FREQUENCY (MHz)
Distortion vs Signal Level
–40
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
–60
DISTORTION (dBc)
DISTORTION (dBc)
–70
0.1
66045 G06
Distortion vs Frequency
–50
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
–60
0
0.01
100
66045 G05
66045 G04
–50
VS = 3V
VIN = 200mVP-P
TA = 25°C
V+ TO DIFFOUT
10
DISTORTION (dBc)
1
10
FREQUENCY (MHz)
10
Power Supply Rejection Ratio
50
0.1
9
80
70
10
0.1
20
8
66045 G03
Common Mode Rejection Ratio
90
CMRR (dB)
OUTPUT IMPEDANCE (Ω)
20
10
66045 G02
Output Impedance vs Frequency
100
9
DELAY (ns)
GAIN (dB)
–20
DELAY (ns)
13
0
–10
GAIN (dB)
Passband Gain and Group Delay
120
1
GAIN (dB)
10
2ND HARMONIC,
1MHz INPUT
–110
10
66045 G08
0
1
2
3
INPUT LEVEL (VP-P)
4
5
66045 G09
66045f
5
LT6604-5
TYPICAL PERFORMANCE CHARACTERISTICS
Distortion vs Input Common Mode
Voltage
–40
–40
DISTORTION (dBc)
–50
–60
2ND HARMONIC
5MHz INPUT
–70
3RD HARMONIC
1MHz INPUT
–80
2ND HARMONIC
1MHz INPUT
–90
–100
VS = p5V
RL = 800Ω, TA = 25°C, GAIN = 1
–110
0
1
2
3
5
4
INPUT LEVEL (VP-P)
66045 G10
–60
–70
–80
–90
–100 GAIN = 1, VMID = VS/2
2VP-P 1MHz INPUT
RL = 800Ω, TA = 25°C
–110
–1
0
1
2
3
–3
–2
INPUT COMMON MODE VOLTAGE
RELATIVE TO VMID (V)
66045 G11
2ND HARMONIC,
VS = 3V
3RD HARMONIC,
VS = 3V
2ND HARMONIC,
VS = 5V
3RD HARMONIC,
VS = 5V
–50
–60
–70
–80
–90
–100 GAIN = 4, VMID = VS/2
2VP-P 1MHz INPUT
RL = 800Ω, TA = 25°C
–110
–1
0
1
2
3
–3
–2
INPUT COMMON MODE VOLTAGE
RELATIVE TO VMID (V)
66045 G12
Transient Response, Differential
Gain = 1, Single-Ended Input,
Differential Output
Single Channel Supply Current vs
Total Supply Voltage
36
OUT–
200mV/DIV
34
SUPPLY CURRENT (mA)
–40
2ND HARMONIC,
VS = 3V
3RD HARMONIC,
VS = 3V
2ND HARMONIC,
VS = 5V
3RD HARMONIC,
VS = 5V
–50
DISTORTION COMPONENT (dBc)
3RD HARMONIC
5MHz INPUT
Distortion vs Input Common Mode
Voltage
DISTORTION COMPONENT (dBc)
Distortion vs Signal Level
TA = 85°C
32
30
OUT+
200mV/DIV
TA = 25°C
28
26
TA = –40°C
24
IN–
500mV/DIV
IN+
22
20
6
10
4
8
TOTAL SUPPLY VOLTAGE (V)
2
100ns/DIV
12
66045 G14
66045 G13
Distortion vs Output
Common Mode Voltage
Distortion vs Temperature
1dB PASSBAND GAIN
COMPRESSION POINTS
OUTPUT LEVEL (dBV)
0
–40
1MHz TA = 25°C
1MHz TA = 85°C
DISTORTION COMPONENT (dBc)
20
3RD HARMONIC
TA = 85°C
–20
3RD HARMONIC
TA = 25°C
–40
–60
–80
2ND HARMONIC
TA = 85°C
–100
0
1
4
3
5
2
1MHz INPUT LEVEL (VP-P)
6
2ND HARMONIC, VS = 3V
3RD HARMONIC, VS = 3V
2ND HARMONIC, VS = 5V
3RD HARMONIC, VS = 5V
2ND HARMONIC, VS = p5V
3RD HARMONIC, VS = p5V
–70
–80
–90
–100
2ND HARMONIC
TA = 25°C
–120
GAIN = 4
VMID = VS/2
–50 T = 25°C
A
0.5VP-P 1MHz INPUT
R
–60 L = 800Ω
7
66045 G15
–110
–1.5 –1.0 –0.5
0 0.5 1.0 1.5 2.0
VOLTAGE VOCM TO VMID (V)
2.5
66045 G16
66045f
6
LT6604-5
TYPICAL PERFORMANCE CHARACTERISTICS
Channel Separation vs Frequency
(Note 9)
Input Referred Noise
35
80
70
30
60
25
50
20
40
15
30
10
20
5
10
INTEGRATED NOISE (μV)
NOISE DENSITY (nV/√Hz)
40
–10
90
INTEGRATED NOISE, GAIN = 1X
INTEGRATED NOISE, GAIN = 4X
NOISE DENSITY, GAIN = 1X
NOISE DENSITY, GAIN = 4X
CHANNEL SEPARATION (dB)
45
VIN = 2VP-P
VS = 5V
–30 RL = 800Ω AT
EACH OUTPUT
GAIN = 1
–50
–70
–90
–110
0
0.01
0.1
1
10
FREQUENCY (MHz)
0
100
–130
100k
1M
10M
FREQUENCY (Hz)
100M
66045 G18
66045 G17
PIN FUNCTIONS
+INA, –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 the differential
inputs to the differential outputs is 806Ω/RIN.
+INB, –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 806Ω/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.
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 or greater capacitor unless it is
connected to a ground plane.
V– (Pins 7, 24, 31, 32, 35): Negative Power Supply Pin
(can be ground).
V+A, V+B (Pins 25, 17): Positive Power Supply Pins
for Channels A and B. For a single 3.3V or 5V supply
(V– grounded) a quality 0.1μF ceramic bypass capacitor
is required from each positive supply pin (V+A, V+B) to
the negative supply pin (V–). The bypass should be as
close as possible to the IC. For dual supply applications,
bypass the negative supply pins to ground and each of the
positive supply pins (V+A, V+B) to ground with a quality
0.1μF ceramic capacitor.
VMIDB (Pin 8): The VMIDB pin is internally biased at mid
supply, see Block Diagram. For single supply operation
the VMIDB pin should be bypassed with a quality 0.01μF
ceramic capacitor to V–. 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 stage of the filter in channel B. It has a
5.5kΩ impedance, and it can be overridden with an external
low impedance voltage source.
+OUTB, –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.
66045f
7
LT6604-5
PIN FUNCTIONS
+OUTA, – 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 mid
supply, see Block Diagram. For single supply operation
the VMIDA pin should be bypassed with a quality 0.01μF
ceramic capacitor to Pins V–. 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 stage of the filter 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 PCB. If V– is separate from ground, tie the
Exposed Pad to V–.
BLOCK DIAGRAM
VMIDA
V–
NC
V+A
NC
RIN
NC
11k
+INA
VIN+A
V–
LOWPASS
FILTER STAGE
806Ω
–OUTA
11k
400Ω
V–
NC
OP AMP
+
–INA
VIN–A
+ –
–
VOCM
VOCM
+
–
RIN
NC
400Ω
– +
400Ω
NC
+OUTA
NC
400Ω
806Ω
VOCMA
V–
VMIDB
V+A
V+B
V–
11k
LOWPASS
FILTER STAGE
806Ω
NC
11k
400Ω
V–
NC
OP AMP
+INB
+
VIN+B
RIN
NC
400Ω
+ –
–
VOCM
NC
–
–OUTB
VOCM
+
– +
400Ω
NC
–INB
VIN–B
+OUTB
RIN
400Ω
806Ω
NC
NC
66045 BD
VOCMB
NC
NC
V+B
66045f
8
LT6604-5
APPLICATIONS INFORMATION
Interfacing to the LT6604-5
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
5MHz. 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 LT6604-5 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 A channel
filter.
Each LT6604-5 channel requires two equal external resistors, RIN, to set the differential gain to 806Ω/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 LT6604-5 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 LT6604-5
operating with a single 3.3V supply and unity passband
Figure 2 shows how to AC couple signals into the LT6604-5.
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 806Ω gain setting resistor form
a high pass filter, attenuating signals below 2kHz. Larger
values of coupling capacitors will proportionally reduce
this highpass 3dB frequency.
In Figure 3 the LT6604-5 is providing 12dB of gain. The
gain resistor has an optional 62pF in parallel to improve
the passband flatness near 5MHz. The common mode
output voltage is set to 2V.
3.3V
0.1μF
V
3
VIN
–
806Ω
4
VIN+
1
0.01μF
+
VIN
0
t
VIN–
3
–
34
2
V
25
6
2
27
1/2 +
LT6604-5
VOUT+
– 29
VOUT–
+
806Ω
7
2
VOUT+
1
VOUT–
t
0
66045 F01
Figure 1
3.3V
0.1μF
V
0.1μF
2
4
–
27
34 1/2 +
LT6604-5
6
1
VIN
0
+
0.1μF
t
VIN
0.01μF
2
+
–1
V
25
806Ω
–
+
806Ω
29
3
VOUT+
2
VOUT–
1
7
VOUT+
VOUT–
0
66045 F02
t
Figure 2
62pF
5V
0.1μF
V
3
VIN
–
4
–
27
34 1/2 +
LT6604-5
6
2
1
0
0.01μF
500mVP-P (DIFF)
VIN+
VIN–
VIN
2
+
+
–
–
+
200Ω
t
V
25
200Ω
7
2V
29
3
VOUT+
VOUT+
2
VOUT–
1
0
VOUT–
66045 F03
t
62pF
Figure 3
66045f
9
LT6604-5
APPLICATIONS INFORMATION
Use Figure 4 to determine the interface between the
LT6604-5 and a current output DAC. The gain, or “transimpedance,” is defined as A = VOUT/IIN. To compute the
transimpedance, use the following equation:
A=
806 • R1
Ω
R1 + R2
By setting R1 + R2 = 806Ω, the gain equation reduces to A
= R1(Ω). The voltage at the pins of the DAC is determined
by R1, R2, the voltage on VMID and the DAC output current.
Consider Figure 4 with R1 = 49.9Ω and R2 = 750Ω. The
voltage at VMID, for VS = 3.3V, is 1.65V. The voltage at the
DAC pins is given by:
R1
R1• R2
+ IIN
R1+ R2 + 806
R1+ R2
= 51mV + IIN 46.8Ω
VDAC = VMID •
and 787Ω resistors satisfy the two constraints above.
The transformer converts the single-ended source into a
differential stimulus. Similarly, the output of the LT6604-5
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 LT6604-5 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 be2.5V
0.1μF
NETWORK
ANALYZER
SOURCE
50Ω
COILCRAFT
TTWB-1010
1:1 787Ω 4
51.1Ω
–
27
34 1/2 +
LT6604-5
6
2
787Ω
CURRENT
OUTPUT
DAC
–
+
7
29
COILCRAFT
TTWB-16A
4:1
402Ω
NETWORK
ANALYZER
INPUT
50Ω
402Ω
0.1μF
66045 F05
3.3V
0.1μF
–2.5V
–
R2
IIN
R1
0.01μF
25
4
27
–
34 1/2 +
LT6604-5
6
IIN+
66045 F04
25
R1
2
R2
–
+
7
29
Figure 5
VOUT+
tween the transformer and analyzer input.
VOUT–
VOUT+ – VOUT–
IIN+ – IIN–
=
806 • R1
R1 + R2
Figure 4
Evaluating the LT6604-5
The low impedance levels and high frequency operation
of the LT6604-5 require some attention to the matching
networks between the LT6604-5 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 LT6604-5 with a network analyzer.
Figure 5 is a laboratory setup that can be used to characterize the LT6604-5 using single-ended instruments with 50Ω
source impedance and 50Ω input impedance. For a unity
gain configuration the LT6604-5 requires an 806Ω source
resistance yet the network analyzer output is calibrated
for a 50Ω load resistance. The 1:1 transformer, 51.1Ω
Differential and Common Mode Voltage Ranges
The differential amplifiers inside the LT6604-5 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 LT6604-5 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
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 LT6604-5 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.
66045f
10
LT6604-5
APPLICATIONS INFORMATION
20
1dB PASSBAND GAIN
COMPRESSION POINTS
OUTPUT LEVEL (dBV)
0
Common Mode DC Currents
1MHz TA = 25°C
In applications like Figure 1 and Figure 3 where the LT6604-5
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.
1MHz TA = 85°C
3RD HARMONIC
TA = 85°C
–20
3RD HARMONIC
TA = 25°C
–40
–60
–80
2ND HARMONIC
TA = 85°C
–100
2ND HARMONIC
TA = 25°C, GAIN = 1
–120
0
1
4
3
5
2
1MHz INPUT LEVEL (VP-P)
6
7
6600 F06
Figure 6. Differential Voltage Range
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.
The LT6604-5 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
allowable range of the input common mode voltage (the
average of VIN+ and VIN– in Figure 1) is determined by
the power supply level and gain setting (see “Electrical
Characteristics”).
Consider the application in Figure 3. VMID sets the output
common mode voltage of the 1st differential amplifier inside
the LT6604-5 (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 806Ω feedback resistor and the
external 200Ω input resistor. The resulting 2.5mA 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
LT6604-5 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 1.25mA
(625μA 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 6.25mA 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 4mA. Of course,
by AC coupling the inputs of Figure 3 and shorting VMID to
VOCM, the common mode DC current is eliminated.
Noise
The noise performance of the LT6604-5 channel can be
evaluated with the circuit of Figure 7. Given the low noise
output of the LT6604-5 and the 6dB attenuation of the
transformer coupling network, it is 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 7, measure the total integrated noise
66045f
11
LT6604-5
APPLICATIONS INFORMATION
(eO )2 – (eS )2
eIN =
A
45
NOISE DENSITY (nV/√Hz)
35
4
34
6
2
RIN
25
50
20
40
15
30
10
20
5
10
0.1
0
100
1
10
FREQUENCY (MHz)
66045 F08
25
– +
1/2
Figure 8. Input Referred Noise
27
COILCRAFT
TTWB-1010
25Ω
1:1
LT6604-5
–
+
70
60
0
0.01
0.1μF
RIN
80
30
2.5V
VIN
90
INTEGRATED NOISE, GAIN = 1X
INTEGRATED NOISE, GAIN = 4X
NOISE DENSITY, GAIN = 1X
NOISE DENSITY, GAIN = 4X
40
INTEGRATED NOISE (μV)
(eS) of the spectrum analyzer from 10 kHz to 5MHz. 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:
29
7
SPECTRUM
ANALYZER
INPUT
50Ω
25Ω
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.
66045 F07
Power Dissipation
0.1μF
–2.5V
Figure 7
Table 1 lists the typical input referred integrated noise for
various values of RIN.
Table 1. Noise Performance
PASSBAND
GAIN
RIN
INPUT REFERRED
INTEGRATED NOISE
10kHz TO 5MHz
INPUT REFERRED
NOISE dBm/Hz
4
200Ω
24μVRMS
–149
2
402Ω
38μVRMS
–145
1
806Ω
69μVRMS
–140
Figure 8 is plot of the noise spectral density as a function
of frequency for an LT6604-5 with RIN = 806Ω 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
The LT6604-5 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 LT6604-5 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 total
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 Applications
66045f
12
LT6604-5
APPLICATIONS INFORMATION
Information 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
43°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, 1k load resistance and an ambient
temperature of 85°C, the supply current (current into V+)
measures 32.2mA per channel. The resulting junction
temperature is: TJ = TA + (PD • θJA) = 85 + (5 • 2 • 0.0322
• 43) = 99°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.
TYPICAL APPLICATIONS
Dual, Matched, 5MHz Lowpass Filter
5MHz Phase Distribution
(50 Units)
3V 0.1μF
0.01μF
IIN
30
4
25
– + 27
34 1/2
LT6604-5
6
2
RIN
+ –
QOUT
29
7
GAIN =
VOCM
(1V-1.5V)
3V 0.1μF
RIN
0.01μF
QIN
12
19
–
8 1/2 +
LT6604-5
14
10
RIN
17
+ –
24
806Ω
RIN
PERCENTAGE OF UNITS (%)
RIN
25
20
15
10
5
IOUT
0
21
–135 –134.5 –134 –133.5 –133 –132.5 –132 –131.5
5MHz PHASE (DEG)
66045 TA02
66045f
13
LT6604-5
TYPICAL APPLICATIONS
Dual, Matched, 6th Order, 5MHz Lowpass Filter
Single-Ended Input (IIN and QIN) and Differential Output (IOUT and QOUT)
V+ 0.1μF
IIN
0.1μF
V+
806Ω
1
249Ω
V+
16
V+
LT1568
2
15
INVA
INVB
3
14
SA
SB
4
13
OUTA OUTB
5
12
OUTA OUTB
6
11
GNDA GNDB
7
10
NC
EN
8 –
9
V
V–
249Ω
QIN
249Ω
4
34
249Ω
249Ω
6
2
249Ω
806Ω
25
– +
27
1/2 LT6604-5
+ –
IOUT
29
7
0.1μF
V–
I
Q
GAIN = OUT OR OUT = 1
IIN
QIN
806Ω
0.1μF
V+ 0.1μF
12
8
V–
14
10
806Ω
17
– +
19
1/2 LT6604-5
+ –
24
QOUT
21
0.1μF
66045 TA03
V–
Frequency Response
Transient Response
12
GAIN (dB) 20 LOG (IOUT/IIN) OR
20 LOG (QOUT/QIN)
0
OUTPUT
(IOUT OR QOUT)
200mV/DIV
–12
–24
–36
–48
–60
INPUT
(IIN OR QIN)
500mV/DIV
–72
–84
–96
–108
0.1
1
10
FREQUENCY (MHz)
40
100ns/DIV
66045 TA04b
66045 TA04a
66045f
14
LT6604-5
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
R = 0.125
TYP
0.00 – 0.05
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
66045f
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
LT6604-5
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
Integrated Filters
LTC1562-2
Very Low Noise, 8th Order Filter Building Block
Lowpass and Bandpass Filters up to 300kHz
LTC1565-31
650kHz Linear Phase Lowpass Filter
Continuous Time, 7th Order, Differential
LTC1566-1
Low Noise, 2.3MHz Lowpass Filter
Continuous Time, 7th Order, Differential
LT1568
Very Low Noise, 4th Order Filter Building Block
Lowpass and Bandpass Filters up to 10MHz
LTC1569-7
Linear Phase, Tunable 10th Order Lowpass Filter
Single-Resistor Programmable Cut-Off 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
LTC6601
Low Noise, Fully Differential, Pin Configurable Amplifier/Driver/2nd Order
Filter Building Block
LTC6602
Dual Adjustable Lowpass Filter for RFID
LTC6603
Dual Adjustable Lowpass Filter for Communications
LT6604-2.5
Dual Very Low Noise, Differential Amplifier and 2.5MHz Lowpass Filter
SNR = 86dB at 3V Supply, 4th Order Filter
LT6604-10
Dual Very Low Noise, Differential Amplifier and 10MHz 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
66045f
16 Linear Technology Corporation
LT 0708 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008
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