6420-20 is a dual high-speed differential amplifier
targeted at processing signals from DC to 300MHz. 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 LTC6420-20 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 LTC6420-20 saves space and power compared to
alternative solutions using IF gain blocks and transformers.
The LTC6420-20 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.
Matched Gain ±0.1dB
Matched Phase ±0.1° at 100MHz
Channel Separation 80dB at 100MHz
1.8GHz –3dB Bandwidth; Fixed Gain of 10V/V (20dB)
IMD3 = –84dBc at 100MHz, 2V
P-P
Equivalent OIP3 = 46dBm at 100MHz
1nV/√Hz Internal Op Amp Noise
6.2dB Noise Figure
Differential Inputs and Outputs
Rail-to-Rail Output Swing
80mA Supply Current (240mW) per Amplifier
1.1V to 1.6V Output Common Mode Voltage,
Adjustable
DC- or AC-Coupled Operation
20-Lead 3mm
×
4mm
×
0.75mm QFN Package
APPLICATIONS
n
n
n
n
Differential ADC Driver
Differential Driver/Receiver
Single Ended to Differential Conversion
IF Sampling (Diversity) Receivers
TYPICAL APPLICATION
Matched Dual Amplifier with Output Common Mode Biasing
0.1μF
3V
1000pF
V
OCM
A
V+ A
V
OCM
A
1000Ω
100Ω
12.5Ω
ENABLEA
UNITS (%)
V
OCM
A
V
OCM
A
±0.1dB GAIN MATCHING
±0.1° PHASE MATCHING AT 100MHz
12.5Ω
40
35
30
25
20
15
10
5
0
– 0.25 – 0.15 – 0.05
0.05
0.15
0.25
CHANNEL-TO-CHANNEL GAIN MATCH (dB)
642020 TA01b
Distribution of Gain Match
Z
IN
= 200Ω
0.1μF
–IN A
V
IN
A
0.1μF
+IN A
V–
LTC6420-20
0.1μF
+IN B
V
IN
B
0.1μF
–IN B
100Ω
100Ω
–
1000Ω
Z
IN
= 200Ω
V+ B
0.1μF
1000pF
3V
+
1000Ω
1000Ω
100Ω
–
+
V
OCM
B
V
OCM
B
+OUT A
12.5Ω
–OUT A
V–
–OUT B
V
OCM
B
12.5Ω
+OUT B
V
OCM
B
ENABLEB
642020 TA01a
642020fa
1
LTC6420-20
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
ENABLEA
+OUTA
16 –OUTA
15 V + A
21
14 V –
13 V –
12 V + B
11 –OUTB
7
V+ B
8
V
OCMB
9 10
ENABLEB
+OUTB
V
OCMA
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
+INA 1
–INA 2
V– 3
V– 4
–INB 5
+INB 6
UDC PACKAGE
20-LEAD (3mm 4mm) PLASTIC QFN
T
JMAX
= 150°C,
θ
JA
= 43°C/W,
θ
JC
= 5°C/W
EXPOSED PAD (PIN 21) IS V
–
, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC6420CUDC-20#PBF
LTC6420IUDC-20#PBF
TAPE AND REEL
LTC6420IUDC-20#TRPBF
PART MARKING*
LDDM
PACKAGE DESCRIPTION
20-Lead (3mm
×
4mm) Plastic QFN
20-Lead (3mm
×
4mm) Plastic QFN
SPECIFIED TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
LTC6420CUDC-20#TRPBF LDDM
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
SINGLE
LTC6400-8
LTC6400-14
LTC6400-20
LTC6400-26
LTC6401-8
LTC6401-14
LTC6401-20
LTC6401-26
LTC6421-20
LTC6420-20
DUAL
GAIN
(dB)
8
14
20
26
8
14
20
26
GAIN
(V/V)
2.5
5
10
20
2.5
5
10
20
Z
IN
(DIFFERENTIAL)
(Ω)
400
200
200
50
400
200
200
50
COMMENT
Lowest Distortion
Lowest Distortion
Lowest Distortion
Lowest Distortion
Lowest Power
Lowest Power
Lowest Power
Lowest Power
V+ A
20 19 18 17
642020fa
2
LTC6420-20
DC ELECTRICAL CHARACTERISTICS
+
The
l
denotes the specifications which apply over the full operating
–
temperature range, otherwise specifications are at T
A
= 25°C. V = 3V, V = 0V, +IN = –IN = V
OCM
= 1.25V,
ENABLE
= 0V, No R
L
unless
otherwise noted.
PARAMETER
Gain
Gain Matching
Gain Temperature Drift
Output Swing Low (V
OCM
= 1.5V)
Output Swing High (V
OCM
= 1.5V)
Maximum Differential Output Swing
Output Current Drive
Input Offset Voltage
Input Offset Voltage Drift
Input Common Mode Voltage Range, MIN
Input Common Mode Voltage Range, MAX
Input Resistance (+IN, –IN)
Input Impedance Matching
Input Capacitance (+IN, –IN)
Output Resistance (+OUT, – OUT)
Common Mode Rejection Ratio
Common Mode Gain
Output Common Mode Range, MIN
Output Common Mode Range, MAX
Common Mode Offset Voltage
Common Mode Offset Voltage Drift
V
OCM
Input Current
ENABLEx
Input Low Voltage
ENABLEx
Input High Voltage
ENABLEx
Input Current
Power Supply
V
S
I
S
I
SHDN
PSRR
Operating Supply Range
Supply Current
Shutdown Supply Current
Power Supply Rejection Ratio (Differential
Outputs)
ENABLEx
≤ 0.8V; per Amplifier
ENABLEx
≥ 2.4V; per Amplifier. Inputs Floating
V
+
= 2.85V to 3.5V
l
l
l
l
SYMBOL
G
DIFF
ΔG
TC
GAIN
V
SWINGMIN
V
SWINGMAX
V
OUTDIFFMAX
I
OUT
V
OS
TCV
OS
I
VRMIN
I
VRMAX
R
INDIFF
ΔR
IN
C
INDIFF
R
OUTDIFF
CMRR
G
CM
V
OCMMIN
V
OCMMAX
V
OSCM
TCV
OSCM
IV
OCM
V
IL
V
IH
CONDITIONS
V
IN
= ±100mV Differential
Channel-to-Channel
V
IN
= ±100mV Differential
Each Output, V
IN
= ±400mV Differential
Each Output, V
IN
= ±400mV Differential
2V
P-P, OUT
(Note 10)
Differential
Differential
l
l
l
l
l
l
l
l
l
l
l
MIN
19.6
TYP
20
±0.1
0.0015
0.2
MAX
20.4
±0.25
0.35
UNITS
dB
dB
dB/°C
V
V
V
P-P
mA
Input/Output Characteristic
2.65
4.6
20
–2
2.8
5.2
±0.4
1.2
1
2
mV
μV/°C
V
V
Ω
%
pF
Ω
dB
V/V
1.6
170
200
±0.5
1
20
45
25
68
1
230
±2.5
36
Differential
Channel-to-Channel
Differential, Includes Parasitic
Differential
Input Common Mode Voltage 1V to 1.6V
V
OCM
= 1.1V to 1.6V
l
l
l
l
Output Common Mode Voltage Control
l
l
1.1
1.6
–10
–15
±2
16
–3
0
0.8
2.4
1.5
2.85
3
80
1
55
86
±0.5
4
3.5
95
3
10
V
V
mV
μV/°C
μA
V
V
μA
μA
V
mA
mA
dB
V
OCM
= 1.25V to 1.5V
l
l
l
l
l
ENABLEx
Pins (x = A, B)
ENABLEx
≤ 0.8V
ENABLEx
≥ 2.4V
l
l
642020fa
3
LTC6420-20
AC ELECTRICAL CHARACTERISTICS
+
SYMBOL
ΔG
ΔP
–3dBBW
0.5dBBW
0.1dBBW
NF
e
IN
e
ON
1/f
SR
t
S1%
t
OVDR
P
1dB
t
ON
t
OFF
PARAMETER
Gain Matching
Phase Matching
Channel Separation (Note 8)
–3dB Bandwidth
Bandwidth for 0.5dB Flatness
Bandwidth for 0.1dB Flatness
Noise Figure
Input Referred Voltage Noise Density
1/f Noise Corner
Slew Rate
1% Settling Time
Overdrive Recovery Time
1dB Compression Point
Turn-On Time
Turn-Off Time
Differential (Note 6)
2V
P-P, OUT
(Note 6)
1.9V
P-P, OUT
(Note 6): Single Ended
R
L
= 375Ω (Notes 5, 7), f = 100MHz
+OUT, –OUT Within 10% of Final Values
I
CC
Falls to 10% of Nominal
0.1V
P-P
at V
OCM
, Measured Single-Ended at
Output (Note 6)
f = 100MHz (1MHz Spacing)
V
OUT
= 2V
P-P
Composite
f = 100MHz (Note 7)
f = 100MHz (Z
IN
= 50Ω)
f = 100MHz (Z
IN
= 200Ω)
f = 100MHz; V
OUT
= 2V
P-P
f = 100MHz; V
OUT
= 2V
P-P
CONDITIONS
f = 100MHz (Note 9)
f = 100MHz
f = 100MHz
200mV
P-P, OUT
(Note 6)
200mV
P-P, OUT
(Note 6)
200mV
P-P, OUT
(Note 6)
R
L
= 375Ω (Note 5), f = 100MHz
Includes Resistors (Short Inputs), f = 100MHz
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V = 3V, V
–
= 0V, V
OCM
= 1.25V,
ENABLE
= 0V, No R
L
unless otherwise noted.
MIN
TYP
±0.1
±0.1
80
1.8
0.7
0.3
6.2
2.2
22
10
4500
0.8
4
18
82
190
15
–84
46
26
20
–80
–88
MAX
±0.25
UNITS
dB
deg
dB
GHz
GHz
GHz
dB
nV/√Hz
nV/√Hz
kHz
V/μs
ns
ns
dBm
ns
ns
MHz
dBc
dBm
dBm
dBm
dBc
dBc
Output Referred Voltage Noise Density Includes Resistors (Short Inputs), f = 100MHz
–3dBBW
VOCM
V
OCM
Pin Small Signal –3dB BW
IMD3
OIP3
IIP3
HD
2
HD
3
3rd Order Intermodulation Distortion
3rd Order Output Intercept
3rd Order Input Intercept
2nd Order Harmonic Distortion
3rd Order Harmonic Distortion
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 LTC6420C and LTC6420I are guaranteed functional over the
operating temperature range of –40°C to 85°C.
Note 4:
The LTC6420C 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 LTC6420I 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. R
L
= 87.5Ω on each output.
Note 7:
Since the LTC6420-20 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
LTC6420-20 with amplifiers that require 50Ω output load, the output
voltage swing driving a given R
L
is converted to OIP
3
and P
1dB
as if it were
driving a 50Ω load. Using this modified convention, 2V
P-P
is by definition
equal to 10dBm, regardless of actual R
L
.
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
