LINER LTC6421-20

LTC6421-20
Dual Matched
1.3GHz Differential
Amplifiers/ADC Drivers
DESCRIPTION
FEATURES
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Matched Gain ±0.1dB
Matched Phase ±0.2° at 100MHz
Channel Separation 80dB at 100MHz
1.3GHz –3dB Bandwidth; Fixed Gain of 10V/V (20dB)
IMD3 = –76dBc at 100MHz, 2VP-P
Equivalent OIP3 = 42dBm at 100MHz
1nV/√Hz Internal Op Amp Noise
6.2dB Noise Figure
Differential Inputs and Outputs
Rail-to-Rail Output Swing
40mA Supply Current (120mW) per Amplifier
1V to 1.6V Output Common Mode Voltage,
Adjustable
DC- or AC-Coupled Operation
20-Lead 3mm × 4mm × 0.75mm QFN Package
APPLICATIONS
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The LTC®6421-20 is a dual high speed differential amplifier
targeted at processing signals from DC to 140MHz. The
part has been specifically designed to drive 12-, 14- and
16-bit ADCs with low noise and low distortion, but can also
be used as a general-purpose broadband gain block.
The LTC6421-20 is easy to use, with minimal support
circuitry required. The output common mode voltage
is set using an external pin, independent of the inputs,
which eliminates the need for transformers or AC-coupling
capacitors in many applications. The gain is internally
fixed at 20dB (10V/ V).
The LTC6421-20 saves space and power compared to
alternative solutions using IF gain blocks and transformers.
The LTC6421-20 is packaged in a compact 20-lead
3mm × 4mm QFN package and operates over the – 40°C
to 85°C temperature range.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Differential ADC Driver
Differential Driver/Receiver
Single Ended to Differential Conversion
IF Sampling (Diversity) Receivers
TYPICAL APPLICATION
Matched Dual Amplifiers with Output Common Mode Biasing
3V
1000pF
0.1μF
VOCMA
V+ A
0.1μF
VINA
0.1μF
VINB
Distribution of Gain Match
ENABLEA
40
1000Ω
–INA 100Ω
12.5Ω +OUTA
+INA 100Ω
12.5Ω – OUTA
V
0.1μF
VOCMA
LTC6421-20
–
VOCMA
V–
1000Ω
±0.1dB GAIN MATCHING
±0.1° PHASE MATCHING
AT 100MHz
1000Ω
+INB 100Ω
12.5Ω – OUTB
– INB 100Ω
12.5Ω +OUTB
35
VOCMA
PERCENTAGE OF UNITS
ZIN = 200Ω
30
25
20
15
10
VOCMB
5
0.1μF
ZIN = 200Ω
VOCMB
1000Ω
V+ B
1000pF 0.1μF
3V
VOCMB
0
– 0.25 – 0.15 – 0.05
0.05
0.25
0.15
CHANNEL-TO-CHANNEL GAIN MATCH (dB)
642120 TA01b
ENABLEB
642120 TA01a
VOCMB
642120fa
1
LTC6421-20
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
Supply Voltage (V + – V –) .........................................3.6V
Input Current (Note 2)..........................................±10mA
Operating Temperature Range (Note 3)....–40°C to 85°C
Specified Temperature Range (Note 4) ....–40°C to 85°C
Storage Temperature Range...................–65°C to 150°C
Maximum Junction Temperature........................... 150°C
Output Short-Circuit Duration .......................... Indefinite
+OUTA
ENABLEA
VOCMA
V+ A
TOP VIEW
20 19 18 17
+INA 1
16 –OUTA
15 V + A
–INA 2
V– 3
V– 4
14 V –
13 V –
21
+INB 6
11 –OUTB
9 10
+OUTB
8
ENABLEB
7
V+ B
12 V + B
VOCMB
–INB 5
UDC PACKAGE
20-LEAD (3mm × 4mm) PLASTIC QFN
TJMAX = 150°C, θJA = 43°C/W, θJC = 5°C/W
EXPOSED PAD (PIN 21) IS V–, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PACKAGE DESCRIPTION
SPECIFIED TEMPERATURE RANGE
LTC6421CUDC-20#PBF
LTC6421CUDC-20#TRPBF LDDN
PART MARKING*
20-Lead (3mm × 4mm) Plastic QFN
0°C to 70°C
LTC6421IUDC-20#PBF
LTC6421IUDC-20#TRPBF
20-Lead (3mm × 4mm) Plastic QFN
–40°C to 85°C
LDDN
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/
SELECTOR GUIDE
PART NUMBER
GAIN
(dB)
GAIN
(V/V)
Z IN (DIFFERENTIAL)
(Ω)
COMMENT
8
2.5
400
Lowest Distortion
14
5
200
Lowest Distortion
20
10
200
Lowest Distortion
26
20
50
Lowest Distortion
LTC6401-8
8
2.5
400
Lowest Power
LTC6401-14
14
5
200
Lowest Power
20
10
200
Lowest Power
26
20
50
Lowest Power
SINGLE
DUAL
LTC6400-8
LTC6400-14
LTC6400-20
LTC6420-20
LTC6400-26
LTC6401-20
LTC6401-26
LTC6421-20
642120fa
2
LTC6421-20
DC ELECTRICAL CHARACTERISTICS + The l –denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. V = 3V, V = 0V, +IN = –IN = VOCM = 1.25V, ENABLE = 0V, No RL unless
otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input/Output Characteristic
GDIFF
Gain
VIN = ±100mV Differential
l
20
20.4
dB
ΔG
Gain Matching
Channel-to-Channel
l
±0.1
±0.25
dB
TCGAIN
Gain Temperature Drift
VIN = ±100mV Differential
l
0.0015
VSWINGMIN
Output Swing Low (VOCM = 1.5V)
Each Output, VIN = ±400mV Differential
l
0.1
Each Output, VIN = ±400mV Differential
l
2.75
2.9
V
l
5
5.6
VP-P
19.6
VSWINGMAX
Output Swing High (VOCM = 1.5V)
VOUTDIFFMAX
Maximum Differential Output Swing
IOUT
Output Current Drive
2VP-P, OUT (Note 10)
l
10
VOS
Input Offset Voltage
Differential
l
–2
Differential
l
TCVOS
Input Offset Voltage Drift
IVRMIN
Input Common Mode Voltage Range, MIN
l
IVRMAX
Input Common Mode Voltage Range, MAX
l
1.6
RINDIFF
Input Resistance (+IN, –IN)
Differential
l
170
l
dB/°C
0.25
V
mA
±0.4
2
1.4
mV
μV/°C
1
V
V
200
230
±1
±2.5
Ω
ΔRIN
Input Impedance Matching
Channel-to-Channel
CINDIFF
Input Capacitance (+IN, –IN)
Differential, Includes Parasitic
ROUTDIFF
Output Resistance (+OUT, –OUT)
Differential
l
20
25
CMRR
Common Mode Rejection Ratio
Input Common Mode Voltage 1V to 1.6V
l
45
68
dB
1
V/V
1
%
pF
36
Ω
Output Common Mode Voltage Control
GCM
Common Mode Gain
VOCM = 1V to 1.6V
VOCMMIN
Output Common Mode Range, MIN
l
VOCMMAX
Output Common Mode Range, MAX
l
1.6
VOSCM
Common Mode Offset Voltage
l
–10
TCVOSCM
Common Mode Offset Voltage Drift
l
IVOCM
VOCM Input Current
l
VOCM = 1.25V to 1.5V
1
V
±2
10
6
–15
V
–3
mV
μV/°C
0
μA
0.8
V
ENABLEx Pins (x = A, B)
VIL
ENABLEx Input Low Voltage
l
VIH
ENABLEx Input High Voltage
l
ENABLEx Input Current
ENABLEx ≤ 0.8V
ENABLEx ≥ 2.4V
2.4
l
l
V
1.5
±0.5
3
μA
μA
3
3.5
V
Power Supply
l
VS
Operating Supply Range
2.85
IS
Supply Current
ENABLEx ≤ 0.8V; per Amplifier
l
40
50
mA
ISHDN
Shutdown Supply Current
ENABLEx ≥ 2.4V; per Amplifier,
Inputs Floating
l
1
3
mA
PSRR
Power Supply Rejection Ratio (Differential
Outputs)
V + = 2.85V to 3.5V
l
55
86
dB
642120fa
3
LTC6421-20
AC ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V, ENABLE = 0V, No RL unless otherwise
noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
ΔG
Gain Matching
f = 100MHz (Note 9)
ΔP
Phase Matching
f = 100MHz
l
TYP
MAX
UNITS
±0.1
±0.25
dB
±0.2
deg
Channel Separation (Note 8)
f = 100MHz
80
dB
–3dBBW
–3dB Bandwidth
200mVP-P, OUT (Note 6)
1.3
GHz
0.5dBBW
Bandwidth for 0.5dB Flatness
200mVP-P, OUT (Note 6)
250
MHz
0.1dBBW
Bandwidth for 0.1dB Flatness
200mVP-P, OUT (Note 6)
130
MHz
NF
Noise Figure
RL = 375Ω (Note 5), f = 100MHz
6.2
dB
eIN
Input Referred Voltage Noise Density
Includes Resistors (Short Inputs), f = 100MHz
2.2
nV/√Hz
eON
Output Referred Voltage Noise Density Includes Resistors (Short Inputs), f = 100MHz
22
nV/√Hz
1/f
1/f Noise Corner
12.5
kHz
SR
Slew Rate
Differential (Note 6)
4500
V/μs
tS1%
1% Settling Time
2VP-P, OUT (Note 6)
2
ns
tOVDR
Overdrive Recovery Time
1.9VP-P, OUT (Note 6) Single Ended
7
ns
P1dB
1dB Compression Point
RL = 375Ω (Notes 5, 7), f = 100MHz
18
dBm
tON
Turn-On Time
+OUT, –OUT Within 10% of Final Values
80
ns
tOFF
Turn-Off Time
ICC Falls to 10% of Nominal
150
ns
–3dBBWVOCM
VOCM Pin Small Signal –3dB BW
0.1VP-P at VOCM , Measured Single-Ended at
Output (Note 6)
15
MHz
IMD3
3rd Order Intermodulation Distortion
f = 100MHz (1MHz Spacing),
VOUT = 2VP-P Composite
–76
dBc
OIP3
3rd Order Output Intercept
f = 100MHz (Note 7)
42
dBc
IIP3
3rd Order Input Intercept
f = 100MHz (ZIN = 50Ω)
f = 100MHz (ZIN = 200Ω)
22
16
dBc
dBc
HD2
2nd Order Harmonic Distortion
f = 100MHz, VOUT = 2VP-P
–74
dBc
HD3
3rd Order Harmonic Distortion
f = 100MHz, VOUT = 2VP-P
–78
dBc
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: Input pins (+IN, –IN) are protected by steering diodes to either
supply. If the inputs go beyond either supply rail, the input current should
be limited to less than 10mA.
Note 3: The LTC6421C and LTC6421I are guaranteed functional over the
operating temperature range of –40°C to 85°C.
Note 4: The LTC6421C is guaranteed to meet specified performance from
0°C to 70°C. It is designed, characterized and expected to meet specified
performance from –40°C to 85°C but is not tested or QA sampled at these
temperatures. The LTC6421I is guaranteed to meet specified performance
from –40°C to 85°C.
Note 5: Input and output baluns used. See Test Circuit A.
Note 6: Measured using Test Circuit B. RL = 87.5Ω on each output.
Note 7: Since the LTC6421-20 is a feedback amplifier with low output
impedance, a resistive load is not required when driving an AD converter.
Therefore, typical output power is very small. In order to compare the
LTC6421-20 with amplifiers that require 50Ω output load, the output
voltage swing driving a given RL is converted to OIP3 and P1dB as if it were
driving a 50Ω load. Using this modified convention, 2VP-P is by definition
equal to 10dBm, regardless of actual RL.
Note 8: 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 channel that is not driven.
Note 9: Not production tested. Guaranteed by design and by correlation to
production tested parameters.
Note 10: The output swing range is at least 2VP-P differential even when
sourcing or sinking 20mA. Tested at VOCM = 1.5V.
642120fa
4
LTC6421-20
TYPICAL PERFORMANCE CHARACTERISTICS
Channel-to-Channel Group Delay
Match vs Frequency
0.5
0.4
0.3
0.3
0.2
0.1
0
–0.1
– 0.2
– 0.3
– 0.4
Channel-to-Channel Phase Match
vs Frequency
1.0
PHASE MATCH (DEG)
0.5
0.4
GROUP DELAY MATCH (ns)
GAIN MATCH (dB)
Channel-to-Channel Gain Match
vs Frequency
0.2
0.1
0
–0.1
–0.2
–0.3
0.5
0
–0.5
–0.4
– 0.5
–0.5
10
100
FREQUENCY (MHz)
10
1000 2000
100
FREQUENCY (MHz)
642120 G01
100
FREQUENCY (MHz)
10
500
642120 G02
642120 G03
S21 Phase and Group Delay
vs Frequency
Frequency Response
25
–1.0
1000 2000
100
TEST CIRCUIT B
Input and Output Reflection and
Reverse Isolation vs Frequency
0
1.5
TEST CIRCUIT B
TEST CIRCUIT B
–10
PHASE (DEGREE)
15
10
PHASE
0.9
–100
GROUP DELAY
–200
0.6
–300
0.3
S PARAMETERS (dB)
1.2
0
GROUP DELAY (ns)
GAIN (dB)
20
–20
S11
–30
S22
–40
–50
S12
–60
5
–70
0
100
1000
FREQUENCY (MHz)
–400
3000
0
200
400
600
FREQUENCY (MHz)
800
225
80
60
40
175
ZOUT
125
20
0
ZIN
–20
100
PHASE
IMPEDANCE MAGNITUDE
75
50
25
ZOUT
0
1
10
100
FREQUENCY (MHz)
–40
–60
–80
–100
1000
642120 G07
NOISE FIGURE (dB)
100
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
4
NOISE FIGURE
2
eIN
10
100
FREQUENCY (MHz)
3000
Small-Signal Transient Response
6
0
1000
642120 G08
INPUT REFERRED NOISE VOLTAGE (nV/√Hz)
250
ZIN
100
1000
FREQUENCY (MHz)
642120 G06
Noise Figure and Input Referred
Noise Voltage vs Frequency
IMPEDANCE PHASE (DEGREE)
IMPEDANCE MAGNITUDE (Ω)
Input and Output Impedance
vs Frequency
150
10
642120 G05
642120 G04
200
–80
0
1000
1.35
OUTPUT VOLTAGE (V)
10
RL = 87.5Ω PER OUTPUT
1.30
+OUT
1.25
1.20
1.15
–OUT
0
5
10
TIME (ns)
15
20
642120 G09
642120fa
5
LTC6421-20
TYPICAL PERFORMANCE CHARACTERISTICS
HARMONIC DISTROTION (dBc)
2.0
OUTPUT VOLTAGE (V)
–40
RL = 87.5Ω PER OUTPUT
– OUT
1.5
1.0
0.5
–40
DIFFERENTIAL INPUT
VOUT = 2VP-P
–50 DRIVING LTC2285
–60
–70
HD2
HD3
–80
–90
–100
0
50
100
TIME (ns)
150
–60
–70
–80
–90
–100
–110
+OUT
0
DIFFERENTIAL INPUT
VOUT = 2VP-P COMPOSITE
DRIVING LTC2235
–50
THIRD ORDER IMD (dBc)
2.5
Third Order Intermodulation
Distortion vs Frequency
Harmonic Distortion vs Frequency
Overdrive Transient Response
0
200
50
100
150
FREQUENCY (MHz)
200
–120
0
50
100
150
FREQUENCY (MHz)
200
642120 G12
642120 G10
642120 G11
Equivalent Output Third Order
Intercept vs Frequency
70
120
DIFFERENTIAL INPUT
VOUT = 2VP-P COMPOSITE
(NOTE 7)
DRIVING LTC2285
(NOTE 8)
CHANNEL SEPARATION (dB)
60
OUTPUT IP3 (dBm)
Channel Separation
vs Frequency
50
40
30
20
80
60
40
20
10
0
100
40
0
50
100
150
FREQUENCY (MHz)
200
642120 G13
1
10
100
FREQUENCY (MHz)
1000
642120 G14
642120fa
6
LTC6421-20
PIN FUNCTIONS
+INA, –INA, –INB, +INB (Pins 1, 2, 5, 6): Differential
Inputs of A and B channel respectively.
–OUTA, +OUTA, –OUTB, +OUTB (Pins 16, 17, 11, 10):
Differential Outputs of channels A and B respectively.
V – (Pins 3, 4, 13, 14, 21): Negative Power Supply. All
four pins, as well as the exposed back, must be connected
to same voltage/ground.
VOCMA , VOCMB (Pins 19, 8): These pins set the output
common mode voltage for the respective channel. They
are internally separate. A 0.1μF external bypass capacitor
is recommended.
ENABLEA, ENABLEB (Pins 9, 18): Logic inputs. If low,
the amplifier is enabled. If high, the amplifier is disabled
and placed in a low-power shutdown mode, making
the amplifier outputs high impedance. These pins are
internally separate. These pins should not be left
floating.
Exposed Pad (Pin 21): V –. The Exposed Pad must be
connected to same voltage/ground as pins 3, 4, 13, 14.
V + A , V + B (Pins 15, 20, 7, 12 ): Positive Power Supply
(Normally tied to 3V or 3.3V). Supply pins of A and B channels
are internally separate. Bypass each pin with 1000pF and
0.1μF capacitors as close to the pins as possible.
642120fa
7
LTC6421-20
BLOCK DIAGRAM
V+ A
VOCMA
ENABLEA
+OUTA
20
19
18
17
RG
100Ω
+INA 1
RG
100Ω
–INA 2
RG
100Ω
–INB 5
+INB 6
ROUT
12.5Ω
– +
16 –OUTA
ROUT
12.5Ω
+ –
15 V + A
RF
1000Ω
V– 3
V– 4
RF
1000Ω
RG
100Ω
14 V –
13 V –
RF
1000Ω
ROUT
12.5Ω
+ –
+
12 V B
ROUT
12.5Ω
– +
11 –OUTB
RF
1000Ω
7
8
9
10
V+ B
VOCMB
ENABLEB
+OUTB
642120 BD
642120fa
8
LTC6421-20
APPLICATIONS INFORMATION
Circuit Operation
Input Impedance and Matching
Each of the two channels of the LTC6421-20 is composed
of a fully differential amplifier with on chip feedback and
output common mode voltage control circuitry. Differential
gain and input impedance are set by 100Ω/1000Ω
resistors in the feedback network. Small output resistors
of 12.5Ω improve the circuit stability over various load
conditions.
The differential input impedance of the LTC6421-20 is
200Ω. If a 200Ω source impedance is unavailable, then
the differential inputs may need to be terminated to a
lower value impedance, e.g. 50Ω, in order to provide
an impedance match for the source. Several choices
are available. One approach is to use a differential shunt
resistor (Figure 1). Another approach is to employ a wide
band transformer (Figure 2). Both methods provide a
wide band impedance match. The termination resistor or
the transformer must be placed close to the input pins in
order to minimize the reflection due to input mismatch.
Alternatively, one could apply a narrowband impedance
match at the inputs of the LTC6421-20 for frequency
selection and/or noise reduction.
The LTC6421-20 is very flexible in terms of I/O coupling.
It can be AC- or DC-coupled at the inputs, the outputs or
both. If the inputs are AC-coupled, the input common mode
voltage is automatically biased close to VOCM and thus
no external circuitry is needed for bias. The LTC6421-20
provides an output common mode voltage set by VOCM ,
which allows driving an ADC directly without external
components such as a transformer or AC coupling capacitors.
The input signal can be either single-ended or differential
with only minor differences in distortion performance.
1/2 LTC6421-20
100Ω
25Ω
1000Ω
1/2 LTC6421-20
100Ω
25Ω
+IN
OUT –
VIN
1:4
+
–
66.5Ω
IN –
25Ω
100Ω
VIN
• •
OUT +
1000Ω
25Ω
–IN
IN +
OUT –
IN –
OUT +
TCM4-19
IN +
+
–
1000Ω
+IN
100Ω
1000Ω
–IN
642120 F01
Figure 1. Input Termination for Differential 50Ω Input Impedance
Using Shunt Resistor
642120 F02
Figure 2. Input Termination for Differential 50Ω Input Impedance
Using a 1:4 Balun
642120fa
9
LTC6421-20
APPLICATIONS INFORMATION
Referring to Figure 3, LTC6421-20 can be easily configured
for single-ended input and differential output without a
balun. The signal is fed to one of the inputs through a
matching network while the other input is connected to the
same matching network and a source resistor. Because the
return ratios of the two feedback paths are equal, the two
outputs have the same gain and thus symmetrical swing. In
general, the single-ended input impedance and termination
resistor RT are determined by the combination of RS, RG
and RF. For example, when RS is 50Ω, it is found that the
single-ended input impedance is 202Ω and RT is 66.5Ω
in order to match to a 50Ω source impedance.
The LTC6421-20 is unconditionally stable. However,
the overall differential gain is affected by both source
impedance and load impedance as follows:
AV =
VOUT
RL
2000
=
•
VIN
RS + 200 25 + RL
RS
50Ω
+
–
0.1μF
VIN
The LTC6421-20 can drive an ADC directly without external
output impedance matching. Alternatively, the differential
output impedance of 25Ω can be matched to a higher
value impedance, e.g. 50Ω, by series resistors or an LC
network.
Output Common Mode Adjustment
The output common mode voltage is set by the VOCM pin,
which is a high impedance input. The output common
mode voltage is capable of tracking VOCM in a range from
1V to 1.6V. The bandwidth of VOCM control is typically
15MHz, which is dominated by a low pass filter connected
to the VOCM pin and is aimed to reduce common mode
noise generation at the outputs. The internal common
mode feedback loop has a –3dB bandwidth of 300MHz,
allowing fast rejection of any common mode output voltage
disturbance. The VOCM pin should be tied to a DC bias
LTC6421-20
100Ω
1000Ω
+IN
RT
66.5Ω
RS //RT 0.1μF
28.7Ω
Output Impedance Match
100Ω
IN +
OUT –
IN –
OUT +
1000Ω
–IN
642120 F03
Figure 3. Input Termination for Single-Ended 50Ω Input Impedance
642120fa
10
LTC6421-20
APPLICATIONS INFORMATION
voltage with a 0.1μF bypass capacitor. When interfacing
with A/D converters such as the LTC22xx families, the
VOCM pin can be connected to the VCM pin of the ADC.
Driving A/D Converters
The LTC6421-20 has been specifically designed to interface
directly with high speed A/D converters. The back page of
this data sheet shows the LTC6421-20 driving an LTC2285,
which is a dual 14-bit, 125Msps ADC.
The VOCM pins of the LTC6421-20 are connected to the
VCM pins of the LTC2285, which provide a DC voltage
level of 1.5V. Both ICs are powered from the same 3V
supply voltage.
The inputs to the LTC6421-20 can be configured in various
ways, as described in the Input Impedance and Matching
section of this datasheet. The outputs of the LTC6421-20
may be connected directly to the analog inputs of an ADC,
or a simple lowpass or bandpass filter network may be
inserted to reduce out-of-band noise.
Test Circuits
Due to the fully-differential design of the LTC6421 and
its usefulness in applications with differing characteristic
specifications, two test circuits are used to generate the
information in this datasheet. Test Circuit A is DC1299, a
two-port demonstration circuit for the LTC6420/LTC6421
family. The schematic and silkscreen are shown in Figure 4.
This circuit includes input and output transformers (baluns)
for single-ended-to-differential conversion and impedance
transformation, allowing direct hook-up to a 2-port network
analyzer. There are also series resistors at the output to
avoid loading the amplifier directly with a 50Ω load. Due
to the input and output transformers, the –3dB bandwidth
is reduced from 1.3GHz to approximately 1.1GHz.
Test Circuit B uses a 4-port network analyzer to measure
S-parameters and gain/phase response. This removes the
effects of the wideband baluns and associated circuitry,
for a true picture of the >1GHz S-parameters and AC
characteristics.
642120fa
11
LTC6421-20
APPLICATIONS INFORMATION
Figure 4a. Top Silkscreen of DC1299 (Test Circuit A)
642120fa
12
LTC6421-20
APPLICATIONS INFORMATION
V+
R1
1.21k
1%
TD4
VOCMA
TD5
GND
R2
1k
1%
J1
+INA
C22
0.1μF
1
2
C18
0.1μF
C21
[1]
T1
5
1
J2
–INA
1
• •
4
3
[2]
C22
0.1μF
2
C19
0.1μF
R5 C25
[2] 0.1μF
2
C22
[1]
20
19
18
17
U1
V + A VOCMA ENABLEA +OUTA [2]
R7
OPT
R9
[2]
1
J5
–INB
1
T2
5
4
5
1
R10 C34
[2] 0.1μF
2
J7
+INB
C30
0.1μF
1
2
• •
4
[2]
C22
[1]
TD2
V+
2.85V TO
3.5V
3
V+
R16
1.21k
1%
TD1
VOCMB
V+
C14
4.7μF
C15
1μF
–OUTA
–INA
C30
0.1μF
2
+INA
2
3
C31
[1]
C16
V + ENA
0.1μF
JP1
1
DIS
2
3
EN
R3
1.5k
1%
V+
R18
1k
1%
6
R11
OPT
R12
[2]
V+
C18
0.1μF
V–
LTC6421-20
V–
V+ A
15
V–
14
V–
13
–INB
V+ B
+INB
–OUTB
TCM4-19+
C35
1000pF
1
R15
88.7
J4
–OUTA
C35
[1] J6
1
2
C32
0.1μF
T4
–OUTB
4
2
1
5
TCM4-19+
C44
0.1μF
C40
0.1μF J8
1
2
C41
[1]
NOTES: UNLESS OTHERWISE SPECIFIED
[1] DO NOT STUFF
[2] VERSION
U1
R5, R9, R10, R13
–A
–B
2
2
3
R12 R14
88.7 [1]
1
C28
0.1μF
C39
0.1μF
11
C34
[1]
5
1
C43
0.1μF
C32
1000pF
+OUTA
4
2
V+
12
T2
3
R5 R5
88.7 [1]
V + B VOCMB ENABLEB +OUTB
21 7
8
9
10
R17 V + ENB
JP2
1.5k
1
1%
DIS
2
3
C19
EN
0.1μF
C42
0.1μF
R4
88.7
16
C30
0.1μF J3
1
2
C17
[1]
LTC6420CUDC-20
LTC6421CUDC-20
NONE
NONE
+OUTB
T1, T3
TCM4-19+
TCM4-19+
642020 F04b
TD3
GND
Figure 4b. Demo Circuit 1299 Schematic (Test Circuit A)
642120fa
13
LTC6421-20
TYPICAL APPLICATIONS
Test Circuit B, 4-Port Measurements
(Only the Signal-Path Connections Are Shown)
0.1μF
PORT 1
(507)
RF
10007
RG
1007
+INA
––
1/2
AGILENT
E5071C
2007
+OUTA
0.1μF
37.47
PORT 3
(507)
+
RG
1007
–INA
ROUT
12.57
ROUT
12.57
–OUTA
37.47
–
+
0.1μF
RF
10007
PORT 2
(507)
0.1μF
PORT 4
(507)
1/2
AGILENT
E5071C
642120 F04b
(B CHANNEL NOT SHOWN)
Parallel ADC Drivers to Reduce Wideband Noise
3.3V
3.3V
C1
0.1μF
C4
0.1μF
R5
49.9Ω
1/2
LTC6421-20
+
–
VIN
R6
49.9Ω
R7
49.9Ω
1/2
LTC6421-20
VOCM
R8
49.9Ω
C2
R3
12pF 10Ω
C5
R4
12pF 10Ω
C3
12pF
LTC2208
VCM
642120 TA02
–3dB FILTER BANDWIDTH = 120MHz
C6
2.2μF
642120fa
14
LTC6421-20
PACKAGE DESCRIPTION
UDC Package
20-Lead Plastic QFN (3mm × 4mm)
(Reference LTC DWG # 05-08-1742 Rev Ø)
0.70 ±0.05
3.50 ± 0.05
2.10 ± 0.05
1.50 REF
2.65 ± 0.05
1.65 ± 0.05
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
2.50 REF
3.10 ± 0.05
4.50 ± 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
0.75 ± 0.05
3.00 ± 0.10
1.50 REF
19
R = 0.05 TYP
PIN 1 NOTCH
R = 0.20 OR 0.25
s 45° CHAMFER
20
0.40 ± 0.10
1
PIN 1
TOP MARK
(NOTE 6)
2
2.65 ± 0.10
4.00 ± 0.10
2.50 REF
1.65 ± 0.10
(UDC20) QFN 1106 REV Ø
0.200 REF
0.00 – 0.05
R = 0.115
TYP
0.25 ± 0.05
0.50 BSC
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 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
642120fa
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
LTC6421-20
TYPICAL APPLICATION
Dual ADC Driver for Wideband Direct-Conversion Receivers
3V
3V
C1
0.1μF
C4
0.1μF
R3
10Ω
R1
40.2Ω
+
–
1/2
VIN LTC6421-20
R2
40.2Ω
C2
12pF
R4
10Ω
C3
12pF
1/2 LTC2285
VCM
–3dB FILTER BANDWIDTH = 140MHz
642120 TA03
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
High-Speed Differential Amplifiers/Differential Op Amps
LT®1993-2
800MHz Differential Amplifier/ADC Driver
AV = 2V/V, OIP3 = 38dBm at 70MHz
LT1993-4
900MHz Differential Amplifier/ADC Driver
AV = 4V/V, OIP3 = 40dBm at 70MHz
LT1993-10
700MHz Differential Amplifier/ADC Driver
AV = 10V/V, OIP3 = 40dBm at 70MHz
LT1994
Low Noise, Low Distortion Differential Op Amp
16-Bit SNR and SFDR at 1MHz, Rail-to-Rail Outputs
LT5514
Ultralow Distortion IF Amplifier/ADC Driver with Digitally
Controlled Gain
OIP3 = 47dBm at 100MHz, Gain Control Range 10.5dB to 33dB
LT5524
Low Distortion IF Amplifier/ADC Driver with Digitally
Controlled Gain
OIP3 = 40dBm at 100MHz, Gain Control Range 4.5dB to 37dB
LTC6400-14/
LTC6400-20/
LTC6400-26
Low Noise, Low Distortion, Differential ADC Drivers
AV = 14dB/20dB/26dB, Single Amplifier per IC, High Performance
LTC6401-8/
LTC6401-14/
LTC6401-20/
LTC6401-26
Low Noise, Low Distortion, Differential ADC Drivers
AV = 8dB/14dB/20dB/26dB, Single Amplifier per IC, Low Power
LT6402-6
300MHz Differential Amplifier/ADC Driver
AV = 6dB, Distortion < –80dBc at 25MHz
LT6402-12
300MHz Differential Amplifier/ADC Driver
AV = 12dB, Distortion < –80dBc at 25MHz
LT6402-20
300MHz Differential Amplifier/ADC Driver
AV = 20dB, Distortion < –80dBc at 25MHz
LTC6404-1
600MHz, Low Noise, AC Precision, Fully Differential
Input/Output Amplifier/Driver
AV = Unity Gain, en = 1.5nV/Hz, Distortion < –90dBc at 10MHz
LTC6404-2
900MHz, Low Noise, AC Precision, Fully Differential
Input/Output Amplifier/Driver
AV = 2V/V, en = 1.5nV/Hz, Distortion < –95dBc at 10MHz
LTC6404-4
1800MHz, Low Noise, AC Precision, Fully Differential
Input/Output Amplifier/Driver
AV = 4V/V, en = 1.5nV/Hz, Distortion < –98dBc at 10MHz
LTC6406
3GHz Rail-to-Rail Input Differential Op Amp
1.6nV/√Hz Noise, –72dBc Distortion at 50MHz, 18mA
LT6411
Low Power Differential ADC Driver/Dual Selectable Gain
Amplifier
16mA Supply Current, IMD3 = –83dBc at 70MHz, AV = 1, –1 or 2
642120fa
16 Linear Technology Corporation
LT 1008 REV A • PRINTED IN USA
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