LINER LTC6604IUFF-15

LT6604-15
Dual Very Low Noise,
Differential Amplifier and
15MHz Lowpass Filter
DESCRIPTION
FEATURES
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Dual Differential Amplifier with 15MHz Lowpass
Filters
4th Order Filters
Approximates Chebyshev Response
Guaranteed Phase and Gain Matching
Resistor-Programmable Differential Gain
76dB Signal-to-Noise (3V Supply, 2VP-P Output)
Low Distortion, 2VP-P, 800Ω Load, VS = 3V
1MHz: 86dBc 2nd, 90dBc 3rd
10MHz: 63dBc 2nd, 69dBc 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
The LT®6604-15 consists of two matched, fully differential
amplifiers, each with a 4th order, 15MHz 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 76dB. 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 highly matched between the two channels. Gain for each channel is independently programmed
using two external resistors. The LT6604-15 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 LT6604-15 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 datasheet 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
3V
LT6604-15
0.01μF
+
536Ω
+INA
VMIDA
+
V+A
–
VOCMA
–
0.01μF
+
536Ω
536Ω
–INA
–
+
VMIDB
536Ω
50Ω
+OUTA
50Ω
+
–INB
–
DUAL ADC
+
18pF
AIN
DOUT
16
50 TYPICAL UNITS
14 TA = 25°C
GAIN = 1
f = 15MHz
12 IN
10
–
8
–
VOCMB
–
–OUTA
V+B
+INB
LTC22xx
3V
+
3V
–OUTB
50Ω
+OUTB
50Ω
6
+
18pF
AIN
4
DOUT
2
–
0
V–
660415 TA01
–0.25 –0.2–0.15 –0.1–0.05 0 0.05 0.1 0.15 0.2 0.25
GAIN MATCH (dB)
660415 TA01b
660415fa
1
LT6604-15
PIN CONFIGURATION
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
Lead Temperature (Soldering, 10 sec) .................. 300°C
31 V–
32 V–
34 VMIDA
TOP VIEW
33 NC
ABSOLUTE MAXIMUM RATINGS
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
V+B 17
NC 16
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-15#PBF
LTC6604CUFF-15#TRPBF
60415
34-Lead (4mm × 7mm) Plastic QFN
0°C to 70°C
LT6604IUFF-15#PBF
LTC6604IUFF-15#TRPBF
60415
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 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 = 536Ω, 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 =1.5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 7.5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 12MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 15MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 45MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 75MHz (Gain Relative to 260kHz)
–0.5
–0.1
–0.3
–0.3
–0.7
0.1
0
0
0.2
0
–29
–46
0.5
0.1
0.4
1.0
1.0
–25
dB
dB
dB
dB
dB
dB
dB
l
l
l
l
l
l
660415fa
2
LT6604-15
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 = 536Ω, and RLOAD = 1k.
PARAMETER
CONDITIONS
TYP
MAX
Matching of Filter Gain, VS = 3V
VIN = 2VP-P, fIN = DC to 260kHz
VIN = 2VP-P, fIN = 1.5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 7.5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 12MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 15MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 45MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 75MHz (Gain Relative to 260kHz)
l
l
l
l
l
l
0.05
0.01
0.02
0.03
0.06
0.13
0.15
0.5
0.1
0.3
0.4
0.6
1.5
2.8
dB
dB
dB
dB
dB
dB
dB
Matching of Filter Phase, VS = 3V
VIN = 2VP-P, fIN = 1.5MHz
VIN = 2VP-P, fIN = 7.5MHz
VIN = 2VP-P, fIN = 12MHz
l
l
l
0.6
0.8
0.9
1
3
4
deg
deg
deg
Filter Gain Either Channel, VS = 5V
VIN = 2VP-P, fIN = DC to 260kHz
VIN = 2VP-P, fIN =1.5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 7.5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 12MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 15MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 45MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 75MHz (Gain Relative to 260kHz)
l
l
l
l
l
l
0
0
0
0.1
0
–29
–46
0.5
0.1
0.3
0.9
0.9
–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 =1.5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 7.5MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 12MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 15MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 45MHz (Gain Relative to 260kHz)
VIN = 2VP-P, fIN = 75MHz (Gain Relative to 260kHz)
l
l
l
l
l
l
0.05
0.01
0.02
0.03
0.06
0.13
0.15
0.5
0.1
0.3
0.4
0.6
1.5
2.8
dB
dB
dB
dB
dB
dB
dB
Matching of Filter Phase, VS = 5V
VIN = 2VP-P, fIN = 1.5MHz
VIN = 2VP-P, fIN = 7.5MHz
VIN = 2VP-P, fIN = 12MHz
l
l
l
0.6
0.8
0.9
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 = 133Ω
VIN = 2VP-P, fIN = DC to 260kHz
11.5
11.5
11.4
12.0
12.0
11.9
12.5
12.5
12.4
dB
dB
dB
Filter Gain Temperature Coefficient (Note 2)
fIN = 250kHz, VIN = 2VP-P
780
ppm/°C
Noise
Noise BW = 10kHz to 15MHz, RIN = 536Ω
109
μVRMS
Distortion (Note 4)
1MHz, 2VP-P, RL = 800Ω, VS = 3V
2nd Harmonic
3rd Harmonic
86
90
dBc
dBc
10MHz, 2VP-P, RL = 800Ω, VS = 3V 2nd Harmonic
3rd Harmonic
63
69
dBc
dBc
1MHz, 2VP-P, RL = 800Ω
–117
dB
10MHz, 2VP-P, RL = 800Ω
–102
dB
Channel Separation (Note 9)
MIN
VS = 3V
VS = 5V
VS = ±5V
–0.5
–0.1
–0.4
–0.4
–0.8
UNITS
Measured Between +OUT and –OUT, VOCM shorted to VMID
VS = 5V
VS = 3V
l
l
3.80
3.75
4.75
4.50
VP-P_DIFF
VP-P_DIFF
Input Bias Current
Average of IN+ and IN–
l
–90
–35
μA
Input Referred Differential Offset
RIN = 536Ω
VS = 3V
VS = 5V
VS = ±5V
l
l
l
5
10
10
25
30
35
mV
mV
mV
RIN = 133Ω
VS = 3V
VS = 5V
VS = ±5V
l
l
l
5
5
5
15
17
20
mV
mV
mV
Differential Output Swing
660415fa
3
LT6604-15
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 = 536Ω, and RLOAD = 1k.
PARAMETER
CONDITIONS
MIN
Differential Offset Drift
TYP
MAX
10
UNITS
μV/°C
l
l
l
0
0
–2.5
1.5
3
1
V
V
V
Differential Output = 2VP-P, VMID at Midsupply, Common
Mode Voltage at VOCM
VS = 3V
VS = 5V
VS = ±5V
l
l
l
1
1.5
–1
1.5
3
2
V
V
V
VS = 3V
VS = 5V
VS = ±5V
l
l
l
–35
–40
–55
40
40
35
mV
mV
mV
VS = 3V
VS = 5V
l
2.45
2.50
1.5
2.56
V
V
VMID Input Resistance
l
4.3
5.7
7.7
kΩ
VOCM Bias Current
VOCM = VMID = VS/2
l
l
–10
–10
–2
–2
Power Supply Current (per Channel)
VS = 3V, VS = 5V
VS = 3V
VS = 5V
VS = ±5V
Input Common Mode Voltage (Note 3)
Differential Input = 500mVP-P, RIN = 133Ω
Output Common Mode Voltage (Note 5)
Output Common Mode Offset
(with Respect to VOCM)
VS = 3V
VS = 5V
VS = ±5V
Common Mode Rejection Ratio
Voltage at VMID
5
5
–10
64
Power Supply Voltage
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-15 is guaranteed functional over the operating
temperature range –40°C to 85°C.
VS = 3V
VS = 5V
35
l
l
l
l
34
38
3
dB
μA
μA
39
44
45
48
mA
mA
mA
mA
11
V
Note 7: The LT6604C-15 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-15 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.
660415fa
4
LT6604-15
TYPICAL PERFORMANCE CHARACTERISTICS
Amplitude Response
Passband Gain and Phase
10
1
GAIN
0
–20
–3
45
–30
VS = 5V
GAIN = 1
TA = 25°C
–60
0.1
1
10
FREQUENCY (MHz)
100
PHASE
–4
20
–90
–6
15
–7
–135
–7
10
–8
–180
–8
5
–9
–225
–9
–6
5
0
15
10
FREQUENCY (MHz)
100
50
45
40
25
2
20
0
15
–2
10
–4
5
5
0
15
10
FREQUENCY (MHz)
20
25
DELAY (ns)
30
DELAY
4
VS = 5V
GAIN = 1
TA = 25°C
70
55
50
35
30
0.1
0.1
10
1
FREQUENCY (MHz)
0.1
100
–60
DISTORTION (dBc)
60
VS = 3V
VIN = 200mVP-P
TA = 25°C
V+ TO DIFFOUT
Distortion vs Signal Level
–70
–40
VIN = 2VP-P
VS = 3V
RL = 800Ω AT
EACH OUTPUT
GAIN = 1
TA = 25°C
–80
–90
–100
660415 G07
3RD HARMONIC
VS = 3V
10MHz INPUT
RL = 800Ω AT
–50 EACH OUTPUT
GAIN = 1
–60 TA = 25°C
–70
2ND
HARMONIC
10MHz INPUT
–80
–90
2ND
HARMONIC
1MHz INPUT
–100
–110
100
100
660415 G06
Distortion vs Frequency
30
1
10
FREQUENCY (MHz)
660415 G05
70
1
10
FREQUENCY (MHz)
60
45
–50
40
0
40
0
50
25
65
1
Power Supply Rejection Ratio
0
0.1
20
VIN = 1VP-P
VS = 5V
GAIN = 1
TA = 25°C
75
10
80
10
15
10
FREQUENCY (MHz)
Common Mode Rejection Ratio
80
660415 G04
20
5
0
660415 G03
DISTORTION (dBc)
–6
25
660415 G02
35
6
20
CMRR (dB)
8
30
DELAY
25
OUTPUT IMPEDANCE (Ω)
GAIN
10
40
35
–3
Output Impedance
VS = 5V
GAIN = 4
TA = 25°C
45
–5
–45
Passband Gain and Delay
12
GAIN
–4
0
–5
660415 G01
14
GAIN (dB)
–2
50
VS = 5V
GAIN = 1
TA = 25°C
DELAY (ns)
–1
90
PHASE (DEG)
135
–50
GAIN (dB)
180
–2
–40
PSRR (dB)
1
–10
GAIN (dB)
–1
GAIN (dB)
VS = 5V
GAIN = 1
TA = 25°C
0
0
Passband Gain and Delay
225
0.1
1
10
FREQUENCY (MHz)
100
660415 G08
DIFFERENTIAL INPUT, 2ND HARMONIC
DIFFERENTIAL INPUT, 3RD HARMONIC
SINGLE-ENDED INPUT, 2ND HARMONIC
SINGLE-ENDED INPUT, 3RD HARMONIC
3RD
HARMONIC
1MHz INPUT
–110
0
1
2
3
4
5
INPUT LEVEL (VP-P)
660415 G09
660415fa
5
LT6604-15
TYPICAL PERFORMANCE CHARACTERISTICS
Distortion vs Input Common Mode
Level
–40
VS = ±5V
RL = 800Ω AT EACH OUTPUT
–50 GAIN = 1
TA = 25°C
–60
2ND HARMONIC,
10MHz INPUT
–70
DISTORTION COMPONENT (dBc)
DISTORTION (dBc)
–40
3RD
HARMONIC,
10MHz INPUT
–80
–90
2ND HARMONIC,
1MHz INPUT
–100
1
0
2
3
–50
–60
–70
–40
GAIN = 1
RL = 800Ω AT EACH
OUTPUT
TA = 25°C
2VP-P 1MHz INPUT
–80
–90
–100
3RD HARMONIC,
1MHz INPUT
–110
2ND HARMONIC,
VS = 3V
3RD HARMONIC,
VS = 3V
2ND HARMONIC,
VS = 5V
3RD HARMONIC,
VS = 5V
Distortion vs Input Common Mode
Level
DISTORTION COMPONENT (dBc)
Distortion vs Signal Level
–110
–2
–1
0
1
2
–3
3
INPUT COMMON MODE VOTLAGE RELATIVE TO VMID (V)
5
4
INPUT LEVEL (VP-P)
2ND HARMONIC,
VS = 3V
3RD HARMONIC,
VS = 3V
2ND HARMONIC,
VS = 5V
3RD HARMONIC,
VS = 5V
2ND HARMONIC,
VS = ±5V
3RD HARMONIC,
VS = ±5V
–80
–90
–100
GAIN = 4, RL = 800Ω AT EACH OUTPUT
TA = 25°C, 500mVP-P 1MHz INPUT
–3
3
–2
–1
0
1
2
INPUT COMMON MODE VOTLAGE RELATIVE TO VMID (V)
–50
–60
–70
–80
–90
50
SUPPLY CURRENT (mA)
DISTORTION COMPONENT (dBc)
–70
Single Channel Supply Current
vs Total Supply Voltage
–40
2VP-P 1MHz INPUT
GAIN = 1,
RL = 800Ω AT EACH OUTPUT
TA = 25°C
–100
0.5 1 1.5
(VOCM – VMID) VOLTAGE (V)
–60
660415 G12
Distortion vs Output Common
Mode Level
0
–50
660415 G11
660415 G10
–110
–1.5 –1 –0.5
2ND HARMONIC,
VS = 3V
3RD HARMONIC,
VS = 3V
2ND HARMONIC,
VS = 5V
3RD HARMONIC,
VS = 5V
2
45
TA = 85°C
40
TA = 25°C
35
TA = –40°C
30
25
20
2
2.5
10
4
6
8
TOTAL SUPPLY VOLTAGE (V)
12
660415 G14
660415 G13
Channel Separation vs Frequency
(Note 9)
Transient Response,
–40
OUT+
200mV/DIV
IN–
IN+
500mV/DIV
100ns/DIV
DIFFERENTIAL GAIN = 1
SINGLE-ENDED INPUT
DIFFERENTAL OUTPUT
660415 G15
CHANNEL SEPARATION (dB)
OUT–
200mV/DIV
VIN = 2VP-P
–50 VS = 5V
RL = 800Ω AT
–60 EACH OUTPUT
GAIN = 1
–70
–80
–90
–100
–110
–120
–130
0.1
1
10
FREQUENCY (MHz)
100
660415 G16
660415fa
6
LT6604-15
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 536Ω/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 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 536Ω/RIN.
VOCMB (Pin 14): Is the 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 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 stage 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.
660415fa
7
LT6604-15
BLOCK DIAGRAM
NC
VIN+A
RIN
+INA
VMIDA
NC
V–
V–
34
33
32
31
1
VIN A
RIN
–INA
NC
30 NC
11k
2
536Ω
11k
NC 3
–
V+A
4
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
536Ω
V–
7
VMIDB
8
V+B
24 V–
11k
536Ω
11k
RIN
+INB
10
+
OP AMP
VOCM
–
VIN B
RIN
–INB
+ –
VOCM
+
200Ω
NC 11
–
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
536Ω
14
15
16
17
VOCMB
NC
NC
V+B
18 NC
660415 BD
660415fa
8
LT6604-15
APPLICATIONS INFORMATION
Interfacing to the LT6604-15
mode output voltage. Figure 1 illustrates the LT6604-15
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
15MHz. 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 LT6604-15 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
The LT6604-15 channel requires two equal external resistors, RIN, to set the differential gain to 536Ω/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 LT6604-15 are the filter outputs. The difference between VOUT+ and VOUT– is the differential output
voltage. The average of VOUT+ and VOUT– is the common
Figure 2 shows how to AC couple signals into the LT6604-15.
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 536Ω gain setting resistor
form a high pass filter, attenuating signals below 3kHz.
Larger values of coupling capacitors will proportionally
reduce this highpass 3dB frequency.
3.3V
0.1μF
V
3
–
536Ω
VIN
2
1
0
VIN+
0.01μF
+
VIN
VIN–
t
V
25
3
4
–
27
34 1/2 +
LT6604-15
6
VOUT+
– 29
VOUT–
2
+
536Ω
7
2
VOUT+
1
VOUT–
t
0
660415 F01
Figure 1
3.3V
0.1μF
V
0.1μF
2
536Ω
1
0
–1
VIN+
0.1μF
t
0.01μF
+
VIN
536Ω
V
25
4
–
27
34 1/2 +
LT6604-15
6
VOUT+
– 29
VOUT–
2
+
7
3
2
1
0
VOUT+
VOUT–
660415 F02
Figure 2
660415fa
9
LT6604-15
APPLICATIONS INFORMATION
In Figure 3 the LT6604-15 is providing 12dB of gain. The
gain resistor has an optional 62pF in parallel to improve
the passband flatness near 15MHz. The common mode
output voltage is set to 2V.
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
LT6604-15 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+ 536
R1+R2
= 77mV +IIN • 45.3Ω
IIN is IIN+ or IIN –. The transimpedance in this example is
49.8Ω.
536 • R1
(Ω)
(R1+R2)
Evaluating the LT6604-15
By setting R1 + R2 = 536Ω, the gain equation reduces
to A = R1 (Ω).
The low impedance levels and high frequency operation
of the LT6604-15 require some attention to the matching
networks between the LT6604-15 and other devices. The
previous examples assume an ideal (0Ω) source impedance
and a large (1k) load resistance. Among practical examples
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 = 487Ω. The
62pF
5V
0.1μF
V
–
3
133Ω
VIN
2
0.01μF
500mVP-P (DIFF)
1
VIN
0
133Ω
t
VIN–
4
–
27
34 1/2 +
LT6604-15
6
VOUT+
– 29
VOUT–
2
+
VIN+
V
25
+
–
+
3
VOUT+
2
7
VOUT–
1
0
2V
660415 F03
t
62pF
Figure 3
CURRENT
OUTPUT
DAC
2.5V
3.3V
0.1μF
0.1μF
IIN–
R2
R1
4
25
–
34 1/2
0.01μF
IIN+
R2
+
27
VOUT+
6 LT6604-15
2
–
+
29
50Ω
VOUT–
7
R1
536 • R1
VOUT+ – VOUT–
=
R1 + R2
IIN+ – IIN–
COILCRAFT
TTWB-1010
1:1 523Ω 4
52.3Ω
25
27
–
34 1/2 +
LT6604-15
6
2
523Ω
660415 F04
Figure 4
NETWORK
ANALYZER
SOURCE
–
+
7
29
0.1μF
COILCRAFT
TTWB-16A
4:1
402Ω
NETWORK
ANALYZER
INPUT
50Ω
402Ω
660415 F05
–2.5V
Figure 5
660415fa
10
LT6604-15
APPLICATIONS INFORMATION
where impedance must be considered is the evaluation of
the LT6604-15 with a network analyzer.
Figure 5 is a laboratory setup that can be used to characterize the LT6604-15 using single-ended instruments
with 50Ω source impedance and 50Ω input impedance.
For a unity gain configuration the LT6604-15 requires
an 536Ω source resistance yet the network analyzer
output is calibrated for a 50Ω load resistance. The 1:1
transformer, 52.3Ω and 523Ω resistors satisfy the two
constraints above. The transformer converts the singleended source into a differential stimulus. Similarly, the
output of the LT6604-15 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
LT6604-15 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.
Differential and Common Mode Voltage Ranges
The differential amplifiers inside the LT6604-15 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
20
1dB COMPRESSION
POINTS
OUTPUT LEVEL (dBV)
0
25°C
85°C
3RD HARMONIC
85°C
–20
–40
3RD HARMONIC
25°C
–60
2ND
HARMONIC
85°C
–80
2ND HARMONIC, 25°C
–100
0
1
4
3
5
2
1MHz INPUT LEVEL (VP-P)
6
7
above 2VP-P and it becomes noticeable above 3.5VP-P.
This is illustrated in Figure 6; the LT6604-15 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 LT6604-15 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.
The LT6604-15 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 Distortion vs Input Common
Mode Level in the Typical Performance Characteristics).
660415 F06
Figure 6. Output Level vs Input Level, Differential
1MHz Input, Gain = 1
660415fa
11
LT6604-15
APPLICATIONS INFORMATION
Common Mode DC Currents
Noise
In applications like Figure 1 and Figure 3 where the LT6604-15
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 LT6604-15 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 536Ω feedback resistor and the external
133Ω input resistor. The resulting 3.7mA 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
LT6604-15 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 9.9mA per channel is used
to translate the common mode voltages.
The noise performance of the LT6604-15 channel can
be evaluated with the circuit of Figure 6. Given the low
noise output of the LT6604-15 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.
A simple modification to Figure 3 will reduce the DC common mode currents by 40%. 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 6mA 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.
Table 1. Noise Performance
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 15MHz. 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 1 MHz 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.
PASSBAND
GAIN
RIN
INPUT REFERRED
INTEGRATED NOISE
10kHz TO 15MHz
INPUT REFERRED
INTEGRATED NOISE
10kHz TO 30MHz
4
133Ω
36μVRMS
51μVRMS
2
267Ω
62μVRMS
92μVRMS
1
536Ω
109μVRMS
169μVRMS
660415fa
12
LT6604-15
APPLICATIONS INFORMATION
Figure 8 is plot of the noise spectral density as a function
of frequency for an LT6604-15 with RIN = 536Ω 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.
Power Dissipation
The LT6604-15 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 LT6604-15 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
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
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 worstcase 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 50mA The resulting junction temperature is:
TJ = TA + (PD • θJA) = 85 + (5 • 2 • 0.05 • 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.
45
0.1μF
VIN
RIN
4
–
27
34 1/2 +
LT6604-15
6
2
RIN
COILCRAFT
TTWB-1010
25Ω
1:1
25
SPECTRUM
ANALYZER
INPUT
50Ω
–
+
7
29
0.1μF
25Ω
660415 F07
–2.5V
35
30
25
160
140
120
100
20
80
15
60
10
40
5
20
0
0.01
0.1
1
10
FREQUENCY (MHz)
INTEGRATED NOISE (μV)
2.5V
NOISE DENSITY (nVRMS/√Hz)
40
180
NOISE DENSITY,
GAIN = 1x
NOISE DENSITY,
GAIN = 4x
INTEGRATED NOISE,
GAIN = 1x
INTEGRATED NOISE,
GAIN = 4x
0
100
660415 F08
Figure 7
Figure 8. Input Referred Noise, Gain = 1
660415fa
13
LT6604-15
TYPICAL APPLICATION
Dual Matched I and Q Lowpass Filter and ADC
(Typical Phase Matching ±1 Degree)
3V
0.1μF
VCMA
2.2μF
3V
0.1μF
RIN
536Ω
4
I
0.1μF
5.6pF
25
–
27
+
– 29
34 1/2 +
LT6604-15
6
2
25Ω
7
RIN
536Ω
INA
5.6pF
25Ω
5.6pF
LTC2299
3V
0.1μF
RIN
536Ω
12
Q
0.1μF
RIN
536Ω
5.6pF
17
–
19
8 1/2 +
LT6604-15
14
10
+
– 21
25Ω
5.6pF
25Ω
24
INB
5.6pF
GAIN = 536Ω/RIN
VCMB
2.2μF
660415 TA02
660415fa
14
LT6604-15
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
660415fa
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
LT6604-15
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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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
LT6604-10
Dual Very Low Noise, Differential Amplifier and 10MHz
Lowpass Filter
SNR = 82dB at 3V Supply, 4th Order Filter
Integrated Filters
660415fa
16 Linear Technology Corporation
LT 0908 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008