Datasheet LTC6400-20 Datasheet (Linear) [ru]

LTC6400-20

1.8GHz Low Noise, Low

Distortion Differential ADC

Driver for 300MHz IF

FEATURES

■

1.8GHz –3dB Bandwidth

■

Fixed Gain of 10V/V (20dB)

■

–94dBc IMD3 at 70MHz (Equivalent OIP3 = 51dBm)

■

–65dBc IMD3 at 300MHz (Equivalent OIP3 = 36.5dBm)

■

1nV/√Hz Internal Op Amp Noise

■

2.1nV/√Hz Total Input Noise

■

6.2dB Noise Figure

■

Differential Inputs and Outputs

■

200Ω Input Impedance

■

2.85V to 3.5V Supply Voltage

■

90mA Supply Current (270mW)

■

1V to 1.6V Output Common Mode Voltage,

Adjustable

■

DC- or AC-Coupled Operation

■

Max Differential Output Swing 4.4V

■

Small 16-Lead 3mm × 3mm × 0.75mm QFN Package

P-P

APPLICATIONS

■

Differential ADC Driver

■

Differential Driver/Receiver

■

Single Ended to Differential Conversion

■

IF Sampling Receivers

■

SAW Filter Interfacing

DESCRIPTION

The LTC®6400-20 is a high-speed differential amplifi er
targeted at processing signals from DC to 300MHz. The
part has been specifi cally 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 LTC6400-20 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 fi xed
at 20dB (10V/V).

The LTC6400-20 saves space and power compared to
alternative solutions using IF gain blocks and transform­ers. The LTC6400-20 is packaged in a compact 16-lead
3mm × 3mm QFN package and operates over the –40°C
to 85°C temperature range.

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

TYPICAL APPLICATION

Single-Ended to Differential ADC Driver

0.1μF

INPUT

66.5Ω

1000pF

29Ω

0.1μF

0.1μF

+

V

V

OCM

+IN

LTC6400-20

–IN

ENABLE

–

V

+OUT

+OUTF

–OUTF

–OUT

20dB GAIN

1.25V

10Ω

10Ω

3.3V

VCMV

+

AIN

LTC2208

–

AIN

LTC2208 130Msps

16-Bit ADC

DD

640020 TA01a

0.1μF

Equivalent Output IP3 vs

60

50

40

30

20

OUTPUT IP3 (dBm)

10

0

050

Frequency

100 150 200
FREQUENCY (MHz)

(NOTE 7)

250 300

640020 TA01b

640020f

1

LTC6400-20

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

Specifi ed Temperature Range

(Note 4) ...............................................–40°C to 85°C

Storage Temperature Range ................... –65°C to 150°C

Maximum Junction Temperature .......................... 150°C

Lead Temperature (Soldering, 10 sec) ..................300°C

V

OCM

V

V

16-LEAD (3mm × 3mm) PLASTIC QFN

T

JMAX

EXPOSED PAD (PIN 17) IS V

TOP VIEW

–IN

–IN

+IN

+IN

16 15 14 13

+

1V

2

3

4

5 6 7 8

–OUT

UD PACKAGE

17

–OUTF

+OUTF

–

, MUST BE SOLDERED TO PCB

+

–

= 125°C, θJA = 68°C/W, θJC = 4.2°C/W

12

11

10

+OUT

9

–

V

ENABLE

+

V

–

V

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC6400CUD-20#PBF LTC6400CUD-20#TRPBF LCCS 16-Lead (3mm × 3mm) Plastic QFN 0°C to 70°C
LTC6400IUD-20#PBF LTC6400IUD-20#TRPBF LCCS 16-Lead (3mm × 3mm) Plastic QFN –40°C to 85°C
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container.

Consult LTC Marketing for information on non-standard lead based fi nish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/

LTC6400 AND LTC6401 SELECTOR GUIDE

PART NUMBER GAIN

(dB)

GAIN
(V/V)

Please check each datasheet for complete details.

ZIN (DIFFERENTIAL)

(Ω)

I

S

(mA)

LTC6400-20 20 10 200 90
LTC6401-20 20 10 200 50

In addition to the LTC6400 family of amplifi ers, a lower power LTC6401 family is available. The LTC6401 is pin compatible to the LTC6400, and has the
same low noise performance. The lower power consumption of the LTC6401 comes at the expense of slightly higher non-linearity, especially at input
frequencies above 140MHz. Please refer to the separate LTC6401 data sheets for complete details. Other gain versions from 8dB to 26dB will follow.

640020f

2

LTC6400-20

DC ELECTRICAL CHARACTERISTICS

The ● denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T

= 25°C. V+ = 3V, V– = 0V, +IN = –IN = V

A

otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Input/Output Characteristic

G

DIFF

TC

GAIN

V

SWINGMIN

V

SWINGMAX

V

OUTDIFFMAX

I

OUT

V

OSDIFF

TCV

OSDIFF

I

VRMIN

I

VRMAX

R

INDIFF

C

INDIFF

R

OUTDIFF

R

OUTFDIFF

C

OUTFDIFF

CMRR Common Mode Rejection Ratio Input Common Mode Voltage 1.1V~1.4V

Output Common Mode Voltage Control

G

CM

V

OCMMIN

V

OCMMAX

V

OSCM

TCV

OSCM

IV

OCM

⎯E⎯N⎯A⎯B⎯L⎯

E Pin

V

IL

V

IH

I

IL

I

IH

Power Supply

V

S

I

S

I

SHDN

PSRR Power Supply Rejection Ratio (Differential

Gain VIN = ±100mV Differential
Gain Temperature Drift VIN = ±100mV Differential
Output Swing Low Each Output, VIN = ±600mV Differential
Output Swing High Each Output, VIN = ±600mV Differential
Maximum Differential Output Swing 1dB Compressed
Output Current Drive Each Output
Input Differential Offset Voltage
Input Differential Offset Voltage Drift T

MIN

to T

MAX

Input Common Mode Voltage Range, MIN 1 V
Input Common Mode Voltage Range, MAX 1.6 V
Input Resistance (+IN, –IN) Differential
Input Capacitance (+IN, –IN) Differential, Includes Parasitic 1 pF
Output Resistance (+OUT, –OUT) Differential
Filtered Output Resistance (+OUTF, –OUTF) Differential
Filtered Output Capacitance (+OUTF, –OUTF) Differential, Includes Parasitic 2.7 pF

Common Mode Gain V

= 1V to 1.6V 1 V/V

OCM

Output Common Mode Range, MIN

Output Common Mode Range, MAX

Common Mode Offset Voltage V
Common Mode Offset Voltage Drift T
V

Input Current

OCM

⎯E⎯N⎯A⎯B⎯L⎯

E Input Low Voltage

⎯E⎯N⎯A⎯B⎯L⎯

E Input High Voltage

⎯E⎯N⎯A⎯B⎯L⎯

E Input Low Current

⎯E⎯N⎯A⎯B⎯L⎯

E Input High Current

= 1.1V to 1.5V

OCM

to T

MIN

⎯E⎯N⎯A⎯B⎯L⎯

E = 0.8V

⎯E⎯N⎯A⎯B⎯L⎯

E = 2.4V

MAX

Operating Supply Range
Supply Current
Shutdown Supply Current

⎯E⎯N⎯A⎯B⎯L⎯

E = 0.8V

⎯E⎯N⎯A⎯B⎯L⎯

E = 2.4V

+

= 2.85V to 3.5V

V

Outputs)

= 1.25V, ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless

OCM

●

19.4 20 20.6 dB

●

●

●

2.35 2.46 V

●

●

20 mA

●

–2 2 mV

●

●

170 200 230

●

18 25 32

●

85 100 115

●

45 65 dB

–1.5 mdB/°C

80 150 mV

4.4 V

1.2 μV/°C

1

●

1.1

1.6

●

1.5

●

–15 15 mV

●

●

●

●

2.4 V

●

●

●

2.85 3 3.5 V

●

75 90 105 mA

●

●

55 86 dB

16 μV/°C

515 μA

0.8 V

0.5 μA

1.2 3 μA

13 mA

P-P

Ω

Ω

Ω

V
V

V
V

640020f

3

LTC6400-20

AC ELECTRICAL CHARACTERISTICS

Specifi cations are at TA = 25°C. V+ = 3V, V– = 0V, V

⎯E⎯N⎯A⎯B⎯L⎯

E = 0V, No RL unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

–3dBBW –3dB Bandwidth 200mV

0.1dBBW Bandwidth for 0.1dB Flatness 200mV

0.5dBBW Bandwidth for 0.5dB Flatness 200mV
1/f 1/f Noise Corner 10.5 kHz
SR Slew Rate Differential (Note 6) 4.5 V/ns
t

S1%

t

OVDR

t

ON

t

OFF

–3dBBW

VOCM

1% Settling Time 2V
Overdrive Recovery Time 1.9V

P-P,OUT

P-P,OUT

Turn-On Time +OUT, –OUT Within 10% of Final Values 82 ns
Turn-Off Time ICC Falls to 10% of Nominal 190 ns
V

Pin Small Signal –3dB BW 0.1V

OCM

P-P

Output (Note 6)

10MHz Input Signal

HD

IMD

OIP

2,10M

3,10M

3,10M

/HD

3,10M

Second/Third Order Harmonic
Distortion

Third-Order Intermodulation
(f1 = 9.5MHz f2 = 10.5MHz)

Third-Order Output Intercept Point

2V

P-P,OUT

2V

P-P,OUT

2V

P-P,OUTFILT

2V

P-P,OUT

2V

P-P,OUT

2V

P-P,OUTFILT

2V

P-P,OUT

(f1 = 9.5MHz f2 = 10.5MHz)

P

1dB,10M

NF

10M

e

IN,10M

e

ON,10M

1dB Compression Point RL = 375Ω (Notes 5, 7) 18 dBm
Noise Figure RL = 375Ω (Note 5) 6.2 dB
Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 2.2 nV/√Hz
Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 21.7 nV/√Hz

70MHz Input Signal

HD

IMD

OIP

2,70M

3,70M

3,70M

/HD

3,70M

Second/Third Order Harmonic
Distortion

Third-Order Intermodulation
(f1 = 69.5MHz f2 = 70.5MHz)

Third-Order Output Intercept Point

2V

P-P,OUT

2V

P-P,OUT

2V

P-P,OUTFILT

2V

P-P,OUT

2V

P-P,OUT

2V

P-P,OUTFILT

2V

P-P,OUT

(f1 = 69.5MHz f2 = 70.5MHz)

P

1dB,70M

NF

70M

e

IN,70M

e

ON,70M

1dB Compression Point RL = 375Ω (Notes 5, 7) 18 dBm
Noise Figure RL = 375Ω (Note 5) 6.2 dB
Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 2.1 nV/√Hz
Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 21 nV/√Hz

(Note 6) 1.84 GHz

P-P,OUT

(Note 6) 0.3 GHz

P-P,OUT

(Note 6) 0.7 GHz

P-P,OUT

(Note 6) 0.8 ns

(Note 6) 4 ns

at V

, Measured Single-Ended at

OCM

15 MHz

, RL = 400Ω –97/–93 dBc
, No R

, No R

L

L

–98/–97 dBc

–100/–98 dBc
Composite, RL = 400Ω –95 dBc
Composite, No R

Composite, No R

L

L

–99 dBc

–100 dBc

Composite, No RL (Note 7) 53.8 dBm

, RL = 400Ω –86/–85 dBc
, No R

, No R

L

L

–88/–87 dBc

–86/–88 dBc
Composite, RL = 400Ω –93 dBc
Composite, No R

Composite, No R

L

L

–94 dBc
–93 dBc

Composite, No RL (Note 7) 51 dBm

OCM

= 1.25V,

4

640020f

LTC6400-20

AC ELECTRICAL CHARACTERISTICS

Specifi cations are at TA = 25°C. V+ = 3V, V– = 0V, V

⎯E⎯N⎯A⎯B⎯L⎯

E = 0V, No RL unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

140MHz Input Signal

2,140M

3,140M

3,140M

1dB,140M

140M

IN,140M

ON,140M

/HD

HD

IMD

OIP

P
NF
e
e

240MHz Input Signal

2,240M

3,240M

3,240M

1dB,240M

240M

N, 240M

ON,240M

/HD

HD

IMD

OIP

P
NF
e
e

Second/Third Order Harmonic

3,140M

Distortion

Third-Order Intermodulation
(f1 = 139.5MHz f2 = 140.5MHz)

Third-Order Output Intercept Point

2V

P-P,OUT

2V

P-P,OUT

2V

P-P,OUTFILT

2V

P-P,OUT

2V

P-P,OUT

2V

P-P,OUTFILT

2V

P-P,OUT

, RL = 400Ω –74/–74 dBc
, No R

, No R

L

L

–73/–83 dBc

–77/–76 dBc
Composite, RL = 400Ω –93 dBc
Composite, No R

Composite, No R

L

L

–87 dBc
–89 dBc

Composite, No RL (Notes 7) 47.7 dBm

(f1 = 139.5MHz f2 = 140.5MHz)
1dB Compression Point RL = 375Ω (Notes 5, 7) 18.4 dBm
Noise Figure RL = 375Ω (Note 5) 6.5 dB
Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 2.1 nV/√Hz
Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 21.5 nV/√Hz

Second-Order Harmonic Distortion 2V

3,240M

Third-Order Intermodulation
(f1 = 239.5MHz f2 = 240.5MHz)

Third-Order Output Intercept Point

2V
2V
2V
2V
2V
2V

, RL = 400Ω –66/–58 dBc

P-P,OUT

, No R

P-P,OUT

P-P,OUTFILT

P-P,OUT

P-P,OUT

P-P,OUTFILT

P-P,OUT

L

, No R

L

Composite, RL = 400Ω –71 dBc
Composite, No R

Composite, No R

L

L

Composite, No RL (Note 7) 41 dBm

–65/–63 dBc

–65/–58 dBc

–74 dBc
–67 dBc

(f1 = 239.5MHz f2 = 240.5MHz)
1dB Compression Point RL = 375Ω (Notes 5, 7) 17.9 dBm
Noise Figure RL = 375Ω (Note 5) 7.1 dB
Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 1.9 nV/√Hz
Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 21.7 nV/√Hz

OCM

= 1.25V,

640020f

5

LTC6400-20

AC ELECTRICAL CHARACTERISTICS

Specifi cations are at TA = 25°C. V+ = 3V, V– = 0V, V

⎯E⎯N⎯A⎯B⎯L⎯

E = 0V, No RL unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

300MHz Input Signal

HD

2,300M

IMD

3,300M

OIP

3,300M

P

1dB,300M

NF

300M

e

N,300M

e

ON,300M

IMD

3,280M/320M

/HD

Second-Order Harmonic Distortion 2V

3,300M

Third-Order Intermodulation
(f1 = 299.5MHz f2 = 300.5MHz)

Third-Order Output Intercept Point

2V
2V
2V
2V
2V
2V

, RL = 400Ω –61/–53 dBc

P-P,OUT

, No R

P-P,OUT

P-P,OUTFILT

P-P,OUT

P-P,OUT

P-P,OUTFILT

P-P,OUT

L

, No R

L

Composite, RL = 400Ω –64 dBc
Composite, No R

Composite, No R

L

L

Composite, No RL (Note 7) 36.6 dBm

–60/–55 dBc

–63/–46 dBc

–65 dBc
–58 dBc

(f1 = 299.5MHz f2 = 300.5MHz)
1dB Compression Point RL = 375Ω (Notes 5, 7) 17.5 dBm
Noise Figure RL = 375Ω (Note 5) 7.5 dB
Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 1.8 nV/√Hz
Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 22 nV/√Hz
Third-Order Intermodulation

2V

Composite, RL = 375Ω –64 –70 dBc

P-P,OUT

(f1 = 280MHz f2 = 320MHz) Measure
at 360MHz

OCM

= 1.25V,

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 LTC6400C and LTC6400I are guaranteed functional over the
operating temperature range of –40°C to 85°C.

Note 4: The LTC6400C is guaranteed to meet specifi ed performance from
0°C to 70°C. It is designed, characterized and expected to meet specifi ed

performance from –40°C to 85°C but is not tested or QA sampled at these
temperatures. The LTC6400I is guaranteed to meet specifi ed 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.
Note 7: Since the LTC6400-20 is a feedback amplifi er 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
LTC6400-20 with amplifi ers that require 50Ω output load, the LTC6400-20
output voltage swing driving a given R
if it were driving a 50Ω load. Using this modifi ed convention, 2V
defi nition equal to 10dBm, regardless of actual R

is converted to OIP3 and P

L

.

L

P-P

1dB

is by

as

6

640020f

TYPICAL PERFORMANCE CHARACTERISTICS

Frequency Response Gain 0.1dB Flatness

25

20

15

GAIN (dB)

10

5

0

10 100 1000 3000

FREQUENCY (MHz)

TEST CIRCUIT B

640020 G01

1.0

0.8

0.6

0.4

0.2

0

–0.2

–0.4

GAIN FLATNESS (dB)

–0.6

–0.8

–1.0

10 100 1000 3000

FREQUENCY (MHz)

TEST CIRCUIT B

640020 G02

LTC6400-20

S21 Phase and Group Delay vs
Frequency

0

–100

–200

PHASE (DEGREE)

–300

PHASE

–400

GROUP DELAY

0

200 400 600 800

FREQUENCY (MHz)

TEST CIRCUIT B

640020 G03

1000

1.2

0.9

0.6

0.3

0

GROUP DELAY (ns)

Input and Output Refl ection and
Reverse Isolation vs Frequency

0

TEST CIRCUIT B

–10

–20

–30

–40

–50

S PARAMETERS (dB)

–60

–70

–80

10

S11

S22

S12

100 1000 3000

FREQUENCY (MHz)

640020 G04

Input and Output Impedance vs
Frequency PSRR and CMRR vs Frequency

250

Z

200

150

100

PHASE

IMPEDANCE MAGNITUDE (Ω)

50

IMPEDANCE MAGNITUDE

0

1

IN

Z

OUT

Z

IN

Z

OUT

10 100 1000

FREQUENCY (MHz)

640020 G05

50

30

PHASE (DEGREES)

10

–10

–30

–50

100

90

80

70

60

50

40

PSRR, CMRR (dB)

30

20

10

0

1

PSRR

CMRR

10 100 1000

FREQUENCY (MHz)

Noise Figure and Input Referred
Noise Voltage vs Frequency Small Signal Transient Response Large Signal Transient Response

15
14
13
12
11
10

9
8

NOISE FIGURE

7
6
5

NOISE FIGURE (dB)

4
3
2
1
0

10

EN

100 1000

FREQUENCY (MHz)

640020 G07

INPUT REFERRED NOISE VOLTAGE (nV/√Hz)

6

4

2

0

1.35
RL = 87.5Ω PER OUTPUT

1.30

1.25

OUTPUT VOLTAGE (V)

1.20

1.15

0

2468

+OUT

–OUT

TIME (ns)

640020 G08

2.5

2.0

1.5

1.0

OUTPUT VOLTAGE (V)

0.5

10

0

RL = 87.5Ω PER OUTPUT

+OUT

–OUT

2468

0

TIME (ns)

640020 G06

10

640020 G09

640020f

7

LTC6400-20

TYPICAL PERFORMANCE CHARACTERISTICS

Overdrive Recovery Time

2.5
RL = 87.5Ω PER OUTPUT

2.0

1.5

1.0

OUTPUT VOLTAGE (V)

0.5

0

0

+OUT

–OUT

50 100 150

TIME (ns)

Harmonic Distortion (Filtered) vs
Frequency

–40

DIFFERENTIAL INPUT

= 2V

V

OUT

P-P

NO R

–50

–60

–70

–80

HARMONIC DISTORTION (dBc)

–90

–100

L

0 50 100 150 200 250 300

FREQUENCY (MHz)

640020 G10

HD2
HD3

640020 G13

200

THIRD ORDER IMD (dBc)

–100

–110

1% Settling Time for 2V
Output Step

5

4

3

2

1

0

–1

SETTLING (%)

–2

–3

–4

–5

0

0.5 1.0 1.5 2.52.0

RL = 87.5Ω PER OUTPUT

TIME (ns)

Third Order Intermodulation
Distortion vs Frequency

–40

–50

–60

–70

–80

–90

UNFILTERED NO R
UNFILTERED 200Ω R
FILTERED NO R

0 50 100 150 200 250 300

FREQUENCY (MHz)

L

L

L

DIFFERENTIAL INPUT

= 2V

V

OUT

COMPOSITE

P-P

640020 G11

640020 G14

Harmonic Distortion (Unfi ltered)
vs Frequency

–40

–50

–60

–70

–80

HARMONIC DISTORTION (dBc)

–90

3.0

–100

050

Harmonic Distortion (Unfi ltered)
vs Frequency

–40

–50

–60

–70

–80

HARMONIC DISTORTION (dBc)

–90

–100

0 50 100 150 200 250 300

DIFFERENTIAL INPUT

= 2V

V

OUT

P-P

100 150 200 250 300
FREQUENCY (MHz)

SINGLE-ENDED INPUT

= 2V

V

OUT

P-P

FREQUENCY (MHz)

HD2 NO R
HD2 200Ω R
HD3 NO R
HD3 200Ω R

640020 G12

HD2 NO R
HD2 200Ω R
HD3 NO R
HD3 200Ω R

640020 G15

L

L

L

L

L

L

L

L

Harmonic Distortion (Filtered) vs
Frequency

–40

SINGLE-ENDED INPUT

= 2V

V

OUT

P-P

NO R

–50

–60

–70

–80

HARMONIC DISTORTION (dBc)

–90

–100

L

0 50 100 150 200 250 300

FREQUENCY (MHz)

8

HD2
HD3

640020 G16

Third Order Intermodulation
Distortion vs Frequency

–40

–50

–60

–70

–80

THIRD ORDER IMD (dBc)

–90

–100

UNFILTERED NO R
UNFILTERED 200Ω R
FILTERED NO R

0 50 100 150 200 250 300

FREQUENCY (MHz)

L

L

L

SINGLE-ENDED INPUT

= 2V

V

OUT

P-P

COMPOSITE

640020 G17

Harmonic Distortion vs Output
Common Mode Voltage
(Unfi ltered Outputs)

–40

V

= 2V

OUT

R

L

–50

–60

–70

–80

HARMONIC DISTORTION (dBc)

–90

–100

1.0 1.1 1.2 1.3 1.4

at 100MHz

P-P

= 400Ω

HD3

HD2

OUTPUT COMMON MODE VOLTAGE (V)

1.5

640020 G18

640020f

TYPICAL PERFORMANCE CHARACTERISTICS

LTC6400-20

Output 1dB Compression Point vs
Frequency

20

DIFFERENTIAL INPUT

= 400Ω

R

L

(NOTE 7)

19

18

17

16

OUTPUT 1dB COMPRESSION (dBm)

15

100 150 200 250 300

50

FREQUENCY (MHz)

640020 G19

Output Third Order Intercept vs
Frequency

60

50

40

DIFFERENTIAL INPUT
V

OUT

30

(NOTE 7)

20

OUTPUT IP3 (dBm)

10

0

0 50 100 150 200 250 300

Turn-On Time Turn-Off Time

3.5

3.0

2.5

2.0

1.5

VOLTAGE (V)

1.0

0.5

0

RL = 87.5Ω PER OUTPUT

–0.5

0–100

I

CC

–OUT

+OUT

ENABLE

100 200 300 400

TIME (ns)

640020 G21

140

120

SUPPLY CURRENT (mA)

100

80

60

40

20

0

–20

500

3.5
RL = 87.5Ω PER OUTPUT

3.0

2.5

2.0

1.5

VOLTAGE (V)

1.0

0.5

0

ENABLE

–0.5

= 2V

COMPOSITE

P-P

UNFILTERED NO R
UNFILTERED 200Ω R
FILTERED NO R

FREQUENCY (MHz)

+OUT

0–100 100 200 300 400 500

L

–OUT

TIME (ns)

L

L

640020 G20

I

CC

640020 G22

140

120

SUPPLY CURRENT (mA)

100

80

60

40

20

0

–20

640020f

9

LTC6400-20

–

–

PIN FUNCTIONS

V+ (Pins 1, 3, 10): Positive Power Supply (Normally tied
to 3V or 3.3V). All three pins must be tied to the same
voltage. Bypass each pin with 1000pF and 0.1μF capaci­tors as close to the pins as possible.

(Pin 2): This pin sets the output common mode

V

OCM

voltage. A 0.1μF external bypass capacitor is recom­mended.

–

(Pins 4, 9, 12, 17): Negative Power Supply (GND). All

V

four pins must be connected to same voltage/ground.
–OUT, +OUT (Pins 5, 8): Unfi ltered Outputs. These pins

have series resistors, R

OUT

12.5Ω.

BLOCK DIAGRAM

–

V

12

ENABLE

11

BIAS CONTROL

–OUTF, +OUTF (Pins 6, 7): Filtered Outputs. These pins
have 50Ω series resistors and a 2.7pF shunt capacitor.

⎯E⎯N⎯A⎯B⎯L⎯

V

E (Pin 11): This pin is a logic input referenced to

. If low, the part is enabled. If high, the part is disabled

EE

and draws approximately 1mA supply current.
+IN (Pins 13, 14): Positive Input. Pins 13 and 14 are

internally shorted together.
–IN (Pins 15, 16): Negative Input. Pins 15 and 16 are

internally shorted together.

–

Exposed Pad (Pin 17): V

. The Exposed Pad must be

connected to same voltage/ground as pins 4, 9, 12.

+

V

10

–

V

9

R

+IN

13

+IN

14

IN

15

IN

100Ω

R

100Ω

G

G

1

V

R

F

1000Ω

IN+ OUT–

IN– OUT+

R

F

1000Ω

2k

5.3pF

2

+

V

OCM

R

OUT

12.5Ω

R

FILT

50Ω

R

FILT

50Ω

R

OUT

12.5Ω

COMMON

MODE CONTROL

3

+

V

+OUT

8

+OUTF

7

C

FILT

1.7pF

–OUTF

6

–OUT

516

4

–

V

640020 BD

640020f

10

APPLICATIONS INFORMATION

LTC6400-20

Circuit Operation

The LTC6400 is a low noise and low distortion fully dif­ferential op amp/ADC driver with:

• Operation from DC to 1.8GHz (–3dB bandwidth)

• Fixed gain of 10V/V (20dB)

• Differential input impedance 200Ω

• Differential output impedance 25Ω

• On-Chip 590MHz output fi lter
The LTC6400 is composed of a fully differential amplifi er

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. They also provide a possible
external fi ltering option, which is often desirable when the
load is an ADC.

Filter resistors of 50Ω are available for additional fi ltering.
Lowpass/bandpass fi lters are easily implemented with just
a couple of external components. Moreover, they offer
single-ended 50Ω matching in wideband applications and
no external resistor is needed.

The LTC6400-20 is very fl exible in terms of I/O coupling.
It can be AC- or DC-coupled at the inputs, the outputs or
both. Due to the internal connection between input and
output, users are advised to keep input common mode
voltage between 1V and 1.6V for proper operation. If the
inputs are AC-coupled, the input common mode voltage
is automatically biased close to V

and thus no external

OCM

circuitry is needed for bias. The LTC6400-20 provides an
output common mode voltage set by V

, which allows

OCM

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.

Input Impedance and Matching

The differential input impedance of the LTC6400-20 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 refl ection due to input mismatch. Alternatively, one
could apply a narrowband impedance match at the inputs
of the LTC6400-20 for frequency selection and/or noise
reduction.

Referring to Figure 3, LTC6400-20 can be easily confi gured
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

25Ω

13

V

IN

+
–

25Ω

66.5Ω

14

15

16

100Ω

+IN

+IN

–IN

100Ω

–IN

1000Ω

IN+ OUT–

IN– OUT+

1000Ω

Figure 1. Input Termination for Differential 50Ω Input Impedance
Using Shunt Resistor

25Ω

13

1:4

••

V

IN

+
–

25Ω

14

15

16

100Ω 12.5Ω

+IN

+IN

–IN

100Ω

–IN

1000Ω

IN+ OUT–

IN– OUT+

1000Ω

Figure 2. Input Termination for Differential 50Ω Input Impedance
Using a 1:4 Balun

12.5Ω

50Ω

50Ω

12.5Ω

50Ω

50Ω

12.5Ω

LTC6400-20

+OUT

+OUTF

1.7pF

–OUTF

–OUT

640020 F01

LTC6400-20

+OUT

+OUTF

1.7pF

–OUTF

–OUT

640020 F02

8

7

6

5

8

7

6

5

640020f

11

LTC6400-20

APPLICATIONS INFORMATION

R

S

0.1μF

50Ω

V

IN

+

R

–

T

66.5Ω

0.1μF

R

S

0.1μF

50Ω

R

T

66.5Ω

100Ω

+IN

13

+IN

14

–IN

15

100Ω

–IN

16

1000Ω

IN+ OUT–

IN– OUT+

1000Ω

12.5Ω

50Ω

50Ω

12.5Ω

LTC6400-20

+OUT

+OUTF

1.7pF

–OUTF

–OUT

640020 F03

8

7

6

5

Figure 3. Input Termination for Single-Ended 50Ω Input
Impedance

swing. In general, the single-ended input impedance and
termination resistor R

, RG and RF. For example, when RS is 50Ω, it is found

of R

S

that the single-ended input impedance is 202Ω and R

are determined by the combination

T

is

T

66.5Ω in order to match to a 50Ω source impedance.
The LTC6400-20 is unconditionally stable. However, the

overall differential gain is affected by both source imped­ance and load impedance as shown in Figure 4:

Output Match and Filter

The LTC6400-20 can drive an ADC directly without
external output impedance matching. Alternatively, the
differential output impedance of 25Ω can be matched to
higher value impedance, e.g. 50Ω, by series resistors or
an LC network.

The internal low pass fi lter outputs at +OUTF/–OUTF
have a –3dB bandwidth of 590MHz. External capacitors
can reduce the low pass fi lter bandwidth as shown in
Figure 5. A bandpass fi lter is easily implemented with
only a few components as shown in Figure 6. Three
39pF capacitors and a 16nH inductor create a bandpass
fi lter with 165MHz center frequency, –3dB frequencies at
138MHz and 200MHz.

Output Common Mode Adjustment

The output common mode voltage is set by the V

OCM

pin,
which is a high impedance input. The output common mode
voltage is capable of tracking V

in a range from 1V to

OCM

V

A

OUT

==

V

VR

IN S

2000

++

200 25

R

L

•
R

L

The noise performance of the LTC6400-20 also depends
upon the source impedance and termination. For example,
an input 1:4 balun transformer in Figure 2 improves SNR
by adding 6dB of voltage gain at the inputs. A trade-off
between gain and noise is obvious when constant noise
fi gure circle and constant gain circle are plotted within
the same input Smith Chart, based on which users can
choose the optimal source impedance for a given gain
and noise requirement.

50Ω

50Ω

12.5Ω

LTC6400-20

+OUT

+OUTF

1.7pF

–OUTF

–OUT

640020 F04

1/2 R

L

8

7

V

OUT

6

1/2 R

L

5

1/2 R

S

V

IN

+
–

1/2 R

S

100Ω 12.5Ω

+IN

13

+IN

14

–IN

15

100Ω

–IN

16

1000Ω

IN+ OUT–

IN– OUT+

1000Ω

Figure 4. Calculate Differential Gain

50Ω

50Ω

12.5Ω

LTC6400-20

+OUT

+OUTF

1.7pF

–OUTF

–OUT

640020 F05

8

8.2pF

7

6

5

FILTERED OUTPUT

12pF

(87.5MHz)

8.2pF

100Ω 12.5Ω

13

+IN

14

+IN

15

–IN

16

–IN

IN+ OUT–

IN– OUT+

100Ω

1000Ω

1000Ω

Figure 5. LTC6400-20 Internal Filter Topology Modifi ed for Low
Filter Bandwidth (Three External Capacitors)

+OUT

+OUTF

1.7pF

–OUTF

–OUT

640020 F06

39pF

10Ω

8

7

16nH

6

10Ω

5

39pF

4.99Ω

39pF

4.99Ω

LTC2208

100Ω 12.5Ω

13

+IN

14

+IN

15

–IN

16

–IN

IN+ OUT–

IN– OUT+

100Ω

1000Ω

1000Ω

LTC6400-20

50Ω

50Ω

12.5Ω

Figure 6. LTC6400-20 Internal Filter Topology Modifi ed
for Bandpass Filtering (Three External Capacitors, One
External Inductor)

640020f

12

APPLICATIONS INFORMATION

LTC6400-20

1.6V. The bandwidth of V

control is typically 15MHz,

OCM

which is dominated by a low pass fi lter connected to the

pin and is aimed to reduce common mode noise

V

OCM

generation at the outputs. The internal common mode
feedback loop has a –3dB bandwidth around 300MHz,
allowing fast common mode rejection at the outputs of
the LTC6400-20. The V

pin should be tied to a DC bias

OCM

voltage with a 0.1μF bypass capacitor. When interfacing
with A/D converters such as the LT22xx families, the V
pin can be connected to the V

pin of the ADC.

CM

OCM

Driving A/D Converters

The LTC6400-20 has been specifi cally designed to inter­face directly with high speed A/D converters. In Figure 7,
an example schematic shows the LTC6400-20 with a
single-ended input driving the LTC2208, which is a 16-bit,
130Msps ADC. Two external 10Ω resistors help eliminate
potential resonance associated with stray capacitance of
PCB traces and bond wires of either the ADC input or
the driver output. V
to V

of the LTC2208 VCM pin at 1.25V. Alternatively, a

CM

of the LTC6400-20 is connected

OCM

single-ended input signal can be converted to differential
signal via a balun and fed to the input of the LTC6400-20.
The balun also converts input impedance to match 50Ω
source impedance.

94

92

90

88

SFDR (dB)

86

84

82

70

120 170 220

FREQUENCY (MHz)

270 300

640020 F08

Figure 8. SFDR for the Combination of LTC6400-20 and LTC2208

specifi cations, two test circuits are used to generate the
information in this datasheet. Test Circuit A is DC987B,
a two-port demonstration circuit for the LTC6400 family.
The schematic and silkscreen are shown below. 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

Top Silkscreen

Figure 8 summarizes the spurious free dynamic range
(SFDR) for IMD3 of the whole system in Figure 7.

Test Circuits

Due to the fully-differential design of the LTC6400 and
its usefulness in applications with differing characteristic

1.25V

0.1μF

0.1μF

IF IN

66.5Ω

0.1μF

29Ω

Figure 7. Single-Ended Input to LTC6400-20 and LTC2208

V

OCM

+IN

LTC6400-20

–IN

ENABLE

+OUT

–OUT

+OUTF

–OUTF

20dB GAIN

10Ω

10Ω

V

CM

–

AIN

LTC2208

+

AIN

LTC2208 130Msps

16-Bit ADC

640020 F07

640020f

13

LTC6400-20

APPLICATIONS INFORMATION

network analyzer. There are also series resistors at the
output to present the LTC6400 with a 375Ω differential
load, optimizing distortion performance. Due to the input
and output transformers, the –3dB bandwidth is reduced
from 1.8GHz to approximately 1.3GHz.

TYPICAL APPLICATIONS

Demo Circuit 987B Schematic (Test Circuit A)

ENABLE DIS

13

2

JP1

R2
(1)

R6

0dB

0Ω

R5
(1)

J1

+IN

J2

–IN

T1

5

(2)

•

•

4

R1
0Ω

R4

1

(2)

2

3

C2

0.1μF

C21

0.1μF

R24

C1

0.1μF

(1)

V

CC

R3
(2)

SL1

13

14

(2)

15

16

V

R16

0Ω

12 11 10 9

–

V

ENABLE

+IN

+IN

LTC6400-20

–IN

–IN –OUT

+

V

V

OCM

1234

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 true picture of the >1GHz S-parameters and
AC characteristics.

V

CC

CC

+

V

+OUTF

–OUTF

V+V

V

+OUT

C17
1000pF

–

–

C18

0.1μF

R10

86.6Ω

8

R8
(1)

7

R7
(1)

6

R9

86.6Ω

5

V

CC

C4

0.1μF

C3

0.1μF

SL2

3

2

(2)

1

C22

0.1μF

R14

(1)

R12
0Ω

4

T2

•

•

R13

5

0Ω

R11

J4
+OUT

SL3

(1)

(2)
J5
–OUT

TP5

V

OCM

TEST IN

TP2
V

2.85V TO 3.5V

TP3

GND

C5

0.1μF

C6

0.1μF

C12
1000pF

R22
(1)

C13

0.1μF

C20

0.1μF

T4

TCM 4:19

3

1:4

2

•

1

NOTE: UNLESS OTHERWISE SPECIFIED.
(1) DO NOT STUFF.

R18

0Ω

4

R26

•

0Ω

5

640020 TA03

J7
TEST OUT

640020f

C9
1000pF

R21
(1)

C7

0.1μF

C23

0.1μF

C24

0.1μF

C10

0.1μF

V

CC

R19

TCM 4:19

5

4

V

T3

1:4

•

•

CC

C15
1μF

R17

J6

CC

0Ω

R25

0Ω

C14

4.7μF

1.5k

R20
1k

1

C19

0.1μF

2

3

VERSION IC R3 R4 T1 SL1 SL2 SL3

(2)

-C LTC6400CUD-20 OPEN OPEN MINI-CIRCUITS TCM4-19 (1:4) 6dB 20dB 14dB

SL = SIGNAL LEVEL

14

TYPICAL APPLICATIONS

Test Circuit B, 4-Port Analysis

+

V

1000pF

0.1μF

LTC6400-20

0.1μF

0.1μF

+IN

+IN

–IN

–IN

1000pF

1/2

AGILENT

E5O71A

PORT 1

(50Ω)

PORT 2

(50Ω)

200Ω

PACKAGE DESCRIPTION

–

V

12

R

G

100Ω

13

14

15

R

G

100Ω

1

+

V

ENABLE

11

BIAS CONTROL

R

F

1000Ω

IN+ OUT–

IN– OUT+

R

F

1000Ω

COMMON

MODE CONTROL

2

V

OCM

0.1μF

0.1μF

V

OCM

+

V

10

12.5Ω

12.5Ω

3

+

V

+

V

R

R

50Ω

R

50Ω

R

OUT

FILT

FILT

OUT

–

V

9

+OUT

37.4Ω

8

+OUTF

7

C

FILT

1.7pF

–OUTF

6

–OUT

37.4Ω

516

4

V

640020 TA02

–

0.1μF

0.1μF

PORT 3
(50Ω)

AGILENT

PORT 4
(50Ω)

1/2

E5O71A

3.50 ± 0.05

2.10 ± 0.05

0.70 ±0.05

1.45 ± 0.05

(4 SIDES)

0.25 ±0.05

0.50 BSC

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

UD Package

16-Lead Plastic QFN (3mm × 3mm)

(Reference LTC DWG # 05-08-1691)

3.00 ± 0.10

(4 SIDES)

PIN 1
TOP MARK
(NOTE 6)

PACKAGE
OUTLINE

NOTE:

1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2)

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

0.75 ± 0.05

1.45 ± 0.10

(4-SIDES)

0.200 REF

0.00 – 0.05

BOTTOM VIEW—EXPOSED PAD

R = 0.115

TYP

15 16

0.50 BSC

PIN 1 NOTCH R = 0.20 TYP
OR 0.25 × 45° CHAMFER

0.40 ± 0.10

1

2

(UD16) QFN 0904

0.25 ± 0.05

640020f

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

LTC6400-20

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LT6230/LT6231/

LT6232
LT6233/LT6234/

LT6235

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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

Controlled Gain

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Amplifi er

High Slew Rate Low Cost Single/Dual/Quad Op Amps 8nV/√Hz Noise, 750V/μs, 3mA Supply Current

Very High Slew Rate Low Cost Single/Dual/Quad Op Amps 6nV/√Hz Noise, 1500V/μs, 6.5mA Supply Current

Rail-to-Rail Input and Output Low Noise Single/Dual/Quad
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Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps 1.1nV/√Hz Noise, 3.5mA Supply Current, 215MHz GBW

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V

= 2V/V, OIP3 = 40dBm at 70MHz

V

OIP3 = 47dBm at 100MHz, Gain Control Range 10.5dB to 33dB

OIP3 = 40dBm at 100MHz, Gain Control Range 4.5dB to 37dB

= 20dB, 50mA Supply Current, IMD3 = –74dBc at 140MHz

V

= 6dB, Distortion < –80dBc at 25MHz

V

= 12dB, Distortion < –80dBc at 25MHz

V

= 20dB, Distortion < –80dBc at 25MHz

V

16mA Supply Current, IMD3 = –83dBc at 70MHz, A

1.9nV/√Hz Noise, 3mA Supply Current, 100MHz GBW

= 1, –1 or 2

V

16

Linear Technology Corporation

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