LTC6401-20_技术文档

LTC6401-20

1.3GHz Low Noise, Low

Distortion Differential ADC

Driver for 140MHz IF

FEATURES

DESCRIPTION

The LTC^®6401-20 is a high-speed differential ampliﬁer

targeted at processing signals from DC to 140MHz. The

part has been speciﬁcally designed to drive 12-, 14- and

16-bitADCswithlownoiseandlowdistortion,butcanalso

be used as a general-purpose broadband gain block.

■

1.3GHz –3dB Bandwidth

■

Fixed Gain of 10V/V (20dB)

■

–93dBc IMD at 70MHz (Equivalent OIP = 50.5dBm)

3

■

–74dBc IMD at 140MHz (Equivalent OIP = 41dBm)

3

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

50mA Supply Current (150mW)

1V to 1.6V Output Common Mode Voltage,

Adjustable

DC- or AC-Coupled Operation

The LTC6401-20 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 ca-

pacitors in many applications. The gain is internally ﬁxed

at 20dB (10V/V).

The LTC6401-20 saves space and power compared to

alternative solutions using IF gain blocks and transform-

ers. The LTC6401-20 is packaged in a compact 16-lead

3mm × 3mm QFN package and operates over the –40°C

to 85°C temperature range.

■

Max Differential Output Swing 4.4V

P-P

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

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

All other trademarks are the property of their respective owners.

APPLICATIONS

■

Differential ADC Driver

■

Differential Driver/Receiver

■

Single Ended to Differential Conversion

IF Sampling Receivers

■

SAW Filter Interfacing

TYPICAL APPLICATION

Single-Ended to Differential ADC Driver

Equivalent Output IP3 vs Frequency

70

(NOTE 7)

3.3V

1.25V

60

0.1μF + 1000pF

0.1μF

3.3V

50

+

V

0.1μF

V

OCM

40

10Ω

V

DD

CM

+

–

INPUT

66.5Ω

+IN

+OUT

+OUTF

AIN

30

20

10

0

LTC6401-20

LTC2208

–OUTF

–OUT

–IN

ENABLE

–

V

29Ω

LTC2208 130Msps

16-Bit ADC

20dB GAIN

640120 TA01a

0

50

100

150

200

FREQUENCY (MHz)

640120 TA01b

640120f

1

LTC6401-20

ABSOLUTE MAXIMUM RATINGS

PIN CONFIGURATION

(Note 1)

TOP VIEW

+

–

Supply Voltage (V – V )..........................................3.6V

Input Current (Note 2).......................................... 10mA

Operating Temperature Range

16 15 14 13

+

–

V

1

2

3

4

12 V

(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

V

11 ENABLE

+

OCM

+

17

V

10

9

–

V

5

6

7

8

UD PACKAGE

16-LEAD (3mm × 3mm) PLASTIC QFN

= 150°C, θ = 68°C/W, θ = 4.2°C/W

T

JMAX

JA

JC

–

EXPOSED PAD (PIN 17) IS V , MUST BE SOLDERED TO PCB

ORDER INFORMATION

LEAD FREE FINISH

LTC6401CUD-20#PBF

LTC6401IUD-20#PBF

TAPE AND REEL

LTC6401CUD-20#TRPBF LCDB

LTC6401IUD-20#TRPBF LCDB

PART MARKING*

PACKAGE DESCRIPTION

16-Lead (3mm × 3mm) Plastic QFN

TEMPERATURE RANGE

0°C to 70°C

–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/

LTC6400 AND LTC6401 SELECTOR GUIDE ^{Please check each datasheet for complete details.}

PART NUMBER

GAIN

(dB)

GAIN

(V/V)

Z

IN

(DIFFERENTIAL)

I

CC

(mA)

(Ω)

LTC6400-20

LTC6401-20

20

10

200

90

50

In addition to the LTC6401 family of ampliﬁers, a lower distortion LTC6400 family is available. The LTC6400 is pin compatible to the LTC6401, and has the

same low noise performance. The low distortion of the LTC6400 comes at the expense of higher power consumption. Please refer to the separate LTC6400

data sheets for complete details. Other gain versions from 8dB to 26dB will follow.

640120f

2

LTC6401-20

DC ELECTRICAL CHARACTERISTICS ^The● 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_Lunless

otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

20.6

170

UNITS

Input/Output Characteristic

●

G

Gain

V

=

100mV Differential

19.4

20

1

dB

mdB/°C

mV

DIFF

IN

Gain Temperature Drift

Output Swing Low

TEMP

IN

V

Each Output, V

=

400mV Differential

90

SWINGMIN

SWINGMAX

OUTDIFFMAX

OUT

IN

Output Swing High

2.3

2.44

4.4

V

Maximum Differential Output Swing

Output Current Drive

1dB Compressed

Single-Ended

Differential

V

P-P

●

I

10

–2

mA

mV

μV/°C

V

Input Offset Voltage

2

1

OS

TCV

Input Offset Voltage Drift

Input Common Mode Voltage Range, MIN

Input Common Mode Voltage Range, MAX

Input Resistance

Differential

1.4

OS

VRMIN

VRMAX

I

1.6

V

●

Ω

R

Differential

170

200

1

230

INDIFF

C

Input Capacitance

Differential, Includes Parasitic

Differential

pF

●

Ω

R

Output Resistance

18

85

25

32

OUTDIFF

OUTFDIFF

Ω

Filtered Output Resistance

Filtered Output Capacitance

Common Mode Rejection Ratio

Differential

100

2.7

66

115

C

Differential, Includes Parasitic

Input Common Mode Voltage 1.1V to 1.4V

pF

●

CMRR

45

dB

Output Common Mode Voltage Control

G

Common Mode Gain

V

= 1V to 1.6V

1

V/V

CM

OCM

V

Output Common Mode Range, MIN

1

V

OCMMIN

●

1.1

Output Common Mode Range, MAX

1.6

1.5

V

OCMMAX

●

Common Mode Offset Voltage

V

= 1.1V to 1.5V

–15

15

mV

μV/°C

μA

OSCM

TCV

Common Mode Offset Voltage Drift

6

5

OSCM

IV

V

Input Current

OCM

ENABLE Pin

●

V

ENABLE Input Low Voltage

ENABLE Input High Voltage

ENABLE Input Low Current

ENABLE Input High Current

0.8

V

IL

2.4

IH

I

IL

I

IH

ENABLE = 0.8V

ENABLE = 2.4V

0.5

3

μA

1.2

Power Supply

●

V

Operating Supply Range

Supply Current

2.85

38

3

50

1

3.5

62

3

V

mA

dB

S

I

ENABLE = 0.8V

ENABLE = 2.4V

2.85V to 3.5V

S

Shutdown Supply Current

SHDN

PSRR

Power Supply Rejection Ratio

(Differential Outputs)

55

84

640120f

3

LTC6401-20

AC ELECTRICAL CHARACTERISTICS Speciﬁcations are at T_A= 25°C. V⁺= 3V, V^–= 0V, +IN and –IN

ﬂoating, V_OCM= 1.25V, ENABLE = 0V, No R_Lunless otherwise noted.

SYMBOL

–3dBBW

0.1dBBW

0.5dBBW

1/f

PARAMETER

CONDITIONS

MIN

TYP

1.25

130

250

12.5

4500

2

MAX

UNITS

GHz

MHz

kHz

V/μs

ns

–3dB Bandwidth

200mV

(Note 6)

P-P,OUT

Bandwidth for 0.1dB Flatness

Bandwidth for 0.5dB Flatness

1/f Noise Corner

SR

Slew Rate

Differential (Note 6)

2V (Note 6)

t

1% Settling Time

S1%

OVDR

ON

P-P,OUT

Output Overdrive Recovery Time

Turn-On Time

1.9V

(Note 6)

7

ns

P-P,OUT

+OUT, –OUT Within 10% of Final Values

Falls to 10% of Nominal

78

ns

Turn-Off Time

I

146

15

ns

OFF

CC

–3dBBW

Common Mode Small Signal –3dB

BW

0.1V at V , Measured Single-Ended at

OCM

MHz

CM

P-P

Output (Note 6)

10MHz Input Signal

HD /HD

Second/Third Order Harmonic

Distortion

2V

, R = 400Ω

–122/–92

–110/–103

–113/–102

–96

dBc

dBm

2,10M

3,10M

P-P,OUT

L

, No R

P-P,OUT

L

, No R

P-P,OUTFILT

L

IMD

Third-Order Intermodulation

(f1 = 9.5MHz f2 = 10.5MHz)

Composite, R = 400Ω

P-P,OUT L

3,10M

Composite, No R

–108

P-P,OUT

L

Composite, No R

–105

P-P,OUTFILT

L

OIP

Third-Order Output Intercept Point

(f1 = 9.5MHz f2 = 10.5MHz)

Composite, No R (Note 7)

58

3,10M

P-P,OUT

L

P

1dB Compression Point

Noise Figure

R = 375Ω (Notes 5, 7)

17.3

6.2

2.1

21

dBm

dB

1dB,10M

L

NF

R = 375Ω (Note 5)

L

10M

e

Input Referred Voltage Noise Density Includes Resistors (Short Inputs)

Output Referred Voltage Noise Density Includes Resistors (Short Inputs)

nV/√Hz

IN,10M

ON,10M

70MHz Input Signal

HD /HD

Second/Third Order Harmonic

Distortion

2V

, R = 400Ω

–91/–80

–95/–88

–88

dBc

dBm

2,70M

3,70M

P-P,OUT

L

, No R

P-P,OUT

L

, No R

P-P,OUTFILT

L

IMD

Third-Order Intermodulation

(f1 = 69.5MHz f2 = 70.5MHz)

Composite, R = 400Ω

P-P,OUT L

3,70M

Composite, No R

–93

P-P,OUT

L

Composite, No R

–92

P-P,OUTFILT

L

OIP

Third-Order Output Intercept Point

(f1 = 69.5MHz f2 = 70.5MHz)

Composite, No R (Note 7)

50.5

3,70M

P-P,OUT

L

P

1dB Compression Point

Noise Figure

R = 375Ω (Notes 5, 7)

17.3

6.1

2.1

21

dBm

dB

1dB,70M

L

NF

R = 375Ω (Note 5)

L

70M

e

Input Referred Voltage Noise Density Includes Resistors (Short Inputs)

Output Referred Voltage Noise Density Includes Resistors (Short Inputs)

nV/√Hz

IN,70M

ON,70M

140MHz Input Signal

HD /HD

Second/Third Order Harmonic

Distortion

2V

, R = 400Ω

–80/–57

–81/–60

–80/–65

dBc

2,140M

3,140M

P-P,OUT

L

, No R

P-P,OUT

L

, No R

P-P,OUTFILT

L

640120f

4

LTC6401-20

AC ELECTRICAL CHARACTERISTICS Speciﬁcations are at T_A= 25°C. V⁺= 3V, V^–= 0V, +IN and –IN

ﬂoating, V_OCM= 1.25V, ENABLE = 0V, No R_Lunless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

–71

–74

–72

41

MAX

UNITS

dBc

IMD

Third-Order Intermodulation

(f1 = 139.5MHz f2 = 140.5MHz)

2V

Composite, R = 400Ω

3,140M

P-P,OUT L

Composite, No R

dBc

P-P,OUT

L

Composite, No R

dBc

P-P,OUTFILT

L

OIP

Third-Order Output Intercept Point

(f1 = 139.5MHz f2 = 140.5MHz)

Composite, No R (Note 7)

dBm

3,140M

P-P,OUT

L

P

1dB Compression Point

Noise Figure

R = 375Ω (Notes 5, 7)

18

6.4

2.1

22

dBm

dB

1dB,140M

L

NF

R = 375Ω (Note 5)

L

140M

e

Input Referred Voltage Noise Density Includes Resistors (Short Inputs)

Output Referred Voltage Noise Density Includes Resistors (Short Inputs)

nV/√Hz

dBc

IN,140M

ON,140M

IMD

Third-Order Intermodulation

(f1 = 130MHz f2 = 150MHz) Measure

at 170MHz

2V

P-P,OUT

Composite, R = 375Ω (Note 5)

–61

–69

3,130M/150M

L

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.

temperatures. The LTC6401I 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.

Note 7: Since the LTC6401-20 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

LTC6401-20 with ampliﬁers that require 50Ω output load, the LTC6401-20

Note 3: The LTC6401C and LTC6401I are guaranteed functional over the

operating temperature range of –40°C to 85°C.

output voltage swing driving a given R is converted to OIP and P as

L

3

1dB

Note 4: The LTC6401C 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

if it were driving a 50Ω load. Using this modiﬁed convention, 2V is by

P-P

deﬁnition equal to 10dBm, regardless of the actual R .

L

TYPICAL PERFORMANCE CHARACTERISTICS

S21 Phase and Group Delay vs

Frequency

Frequency Response

Gain 0.1dB Flatness

25

20

15

10

5

1.0

0.8

100

0

1.5

1.2

0.9

0.6

0.3

0

TEST CIRCUIT B

0.6

0.4

0.2

–100

–200

–300

–400

0

–0.2

–0.4

–0.6

–0.8

–1.0

PHASE

GROUP DELAY

0

10

100

1000

3000

10

100

1000

0

200

400

600

800

1000

FREQUENCY (MHz)

640120 G03

640120 G01

640120 G02

640120f

5

LTC6401-20

TYPICAL PERFORMANCE CHARACTERISTICS

Input and Output Reﬂection and

Reverse Isolation vs Frequency

Input and Output Impedance vs

Frequency

PSRR and CMRR vs Frequency

0

–10

–20

–30

–40

–50

–60

–70

–80

250

225

200

175

150

125

100

75

100

80

100

90

80

70

60

50

40

30

20

10

0

TEST CIRCUIT B

Z

IN

60

PSRR

CMRR

S11

S22

40

Z

OUT

20

0

Z

IN

–20

–40

–60

–80

–100

PHASE

IMPEDANCE MAGNITUDE

S12

50

25

Z

OUT

0

10

100

1000

3000

1

10

100

1000

1

10

100

1000

FREQUENCY (MHz)

640120 G04

640120 G05

640120 G06

Noise Figure and Input Referred

Noise Voltage vs Frequency

Small Signal Transient Response

Large Signal Transient Response

1.35

1.30

1.25

1.20

1.15

2.5

15

14

13

12

11

10

9

8

7

6

5

6

4

2

R

= 87.5Ω PER OUTPUT

R

= 87.5Ω PER OUTPUT

L

2.0

1.5

1.0

0.5

0

+OUT

NOISE FIGURE

e

IN

4

3

2

1

–OUT

0

1000

0

5

10

TIME (ns)

15

20

0

5

10

TIME (ns)

15

20

10

100

FREQUENCY (MHz)

640120 G08

640120 G09

640120 G07

1% Settling Time for 2V

Output Step

Overdrive Transient Response

2.5

2.0

1.5

1.0

0.5

0

5

4

R

= 87.5Ω PER OUTPUT

R = 87.5Ω PER OUTPUT

L

–OUT

3

2

1

0

–1

–2

–3

–4

–5

+OUT

50

0

100

TIME (ns)

150

200

0

1

2

3

4

5

6

TIME (ns)

640120 G10

640120 G11

640120f

6

LTC6401-20

TYPICAL PERFORMANCE CHARACTERISTICS

Harmonic Distortion (Unﬁltered)

vs Frequency

Harmonic Distortion (Filtered) vs

Frequency

Third Order Intermodulation

Distortion vs Frequency

–40

–50

–40

–50

–40

–50

DIFFERENTIAL INPUT

UNFILTERED NO R

L

V

= 2V

V

= 2V

L

UNFILTERED 200Ω R

L

OUT

P-P

OUT

P-P

NO R

FILTERED NO R

L

–60

–70

–80

–90

–100

–110

–120

–100

–110

–120

–100

–110

–120

HD2 NO R

L

HD2 200Ω R

L

HD3 NO R

L

HD3 200Ω R

DIFFERENTIAL INPUT

HD2

HD3

V

= 2V COMPOSITE

L

OUT

P-P

0

50

100

FREQUENCY (MHz)

150

200

0

50

100

150

200

0

50

100

150

200

FREQUENCY (MHz)

640120 G12

640120 G13

640120 G14

Harmonic Distortion (Unﬁltered)

vs Frequency

Harmonic Distortion (Filtered) vs

Frequency

Third Order Intermodulation

Distortion vs Frequency

–40

–50

–40

–50

–40

–50

UNFILTERED NO R

L

SINGLE-ENDED INPUT

UNFILTERED 200Ω R

FILTERED NO R

L

V

= 2V

V

= 2V

L

OUT

P-P

OUT P-P

NO R

–60

–70

–80

–90

–100

–110

–120

–100

–110

–120

–100

–110

–120

HD2 NO R

L

HD2 200Ω R

L

SINGLE-ENDED INPUT

HD3 NO R

L

HD3 200Ω R

HD2

HD3

V

= 2V COMPOSITE

OUT

P-P

L

0

50

100

150

200

0

50

100

FREQUENCY (MHz)

150

200

0

50

100

150

200

FREQUENCY (MHz)

640120 G17

640120 G15

640120 G16

Harmonic Distortion vs Output

Common Mode Voltage

(Unﬁltered Outputs)

Equivalent Output 1dB

Compression Point vs Frequency

–40

–50

–60

–70

–80

–90

–100

20

19

18

17

16

15

DIFFERENTIAL INPUT

V

R

= 2V at 100MHz

R

= 400Ω

OUT

L

P-P

L

= 400Ω

(NOTE 7)

HD3

HD2

1.0

1.1

1.2

1.3

1.4

1.5

50

80

110

140

170

200

OUTPUT COMMON MODE VOLTAGE (V)

FREQUENCY (MHz)

640020 G19

640120 G18

640120f

7

LTC6401-20

TYPICAL PERFORMANCE CHARACTERISTICS

Equivalent Output Third Order

Intercept vs Frequency

Turn-On Time

Turn-Off Time

70

60

50

40

30

20

10

0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

70

60

50

40

30

20

10

0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

70

60

50

40

30

20

10

0

UNFILTERED NO R

R

= 87.5Ω PER OUTPUT

R = 87.5Ω PER OUTPUT

L

UNFILTERED 200Ω R

L

FILTERED NO R

L

I

CC

ENABLE

–OUT

+OUT

ENABLE

I

CC

DIFFERENTIAL INPUT

V

= 2V COMPOSITE

OUT

P-P

(NOTE 7)

–0.5

–10

–0.5

–10

0

50

100

150

200

–100

0

100

200

TIME (ns)

300

400

500

–100

0

100

200

TIME (ns)

300

400

500

FREQUENCY (MHz)

640120 G20

640120 G21

640120 G22

640120f

8

LTC6401-20

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 capaci-

tors as close to the pins as possible.

+

–OUTF,+OUTF(Pins6,7):FilteredOutputs.Thesepinshave

50Ω series resistors and a 1.7pF shunt capacitance.

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

–

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

V

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

and draws approximately 1mA supply current.

OCM

voltage. A 0.1μF external bypass capacitor is recom-

+IN (Pins 13, 14): Positive Input. Pins 13 and 14 are

internally shorted together.

mended.

–

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

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

internally shorted together.

pins must be connected to the same voltage/ground.

–OUT, +OUT (Pins 5, 8): Unﬁltered Outputs. These pins

have 12.5Ω series resistors.

–

Exposed Pad (Pin 17): V . The Exposed Pad must be con-

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

BLOCK DIAGRAM

–

+

–

V

ENABLE

V

12

11

10

9

BIAS CONTROL

R

F

R

OUT

G

+IN

13

+OUT

1000Ω

100Ω

12.5Ω

8

7

R

FILT

+OUTF

50Ω

+IN

–IN

IN+

IN–

OUT–

14

15

C

FILT

R

FILT

1.7pF

–OUTF

–OUT

50Ω

6

5

OUT+

R

G

100Ω

R

OUT

12.5Ω

F

–IN

16

1000Ω

2k

COMMON

MODE CONTROL

5.3pF

640120 BD

1

2

3

4

+

–

V

OCM

640120f

9

LTC6401-20

APPLICATIONS INFORMATION

Circuit Operation

thedifferentialinputsmayneedtobeterminatedtoalower

value impedance, e.g. 50Ω, in order to provide an imped-

ance match to the source. Several choices are available.

One approach is to use a differential shunt resistor (Figure

1).Anotherapproachistoemployawidebandtransformer

(Figure 2). Both methods provide a wideband 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

narrowbandimpedancematchattheinputsoftheLTC6401-

20 for frequency selection and/or noise reduction.

The LTC6401-20 is a low noise and low distortion fully

differential op amp/ADC driver with:

• Operation from DC to 1.3GHz –3dB bandwidth

impedance

• Fixed gain of 10V/V (20dB)

• Differential input impedance 200Ω

• Differential output impedance 25Ω

• Differential impedance of output ﬁlter 100Ω

ReferringtoFigure3,LTC6401-20canbeeasilyconﬁgured

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

thesamematchingnetworkandasourceresistor.Because

the return ratios of the two feedback paths are equal, the

TheLTC6401-20iscomposedofafullydifferentialampliﬁer

with on chip feedback and output common mode voltage

controlcircuitry. Differentialgainandinputimpedanceare

set by 100Ω/1000Ω resistors in the feedback network.

Smalloutputresistorsof12.5Ωimprovethecircuitstability

over various load conditions. They also provide a possible

external ﬁltering option, which is often desirable when the

load is an ADC.

LTC6401-20

1000Ω

25Ω

100Ω

12.5Ω

50Ω

13 +IN

+OUT

8

7

Filter resistors of 50Ω are available for additional ﬁltering.

Lowpass/bandpassﬁltersareeasilyimplementedwithjust

a couple of external components. Moreover, they offer

single-ended 50Ω matching in wideband applications and

no external resistor is needed.

IN+

IN–

OUT–

+OUTF

V

IN

14 +IN

+

66.5Ω

–

50Ω

1.7pF

15 –IN

–OUTF

6

5

OUT+

1000Ω

25Ω

100Ω

12.5Ω

The LTC6401-20 is very ﬂexible 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

16 –IN

–OUT

640120 F01

Figure 1. Input Termination for Differential 50Ω Input Impedance

Using Shunt Resistor

LTC6401-20

1000Ω

25Ω

100Ω

12.5Ω

50Ω

is automatically biased close to V

and thus no external

OCM

13 +IN

+OUT

8

7

circuitry is needed for bias. The LTC6401-20 provides an

output common mode voltage set by V , which allows

1:4

• •

OCM

IN+

IN–

OUT–

+OUTF

V

IN

drivinganADCdirectlywithoutexternalcomponentssuch

as a transformer or AC coupling capacitors. The input

signal can be either single-ended or differential with only

minor differences in distortion performance.

14 +IN

15 –IN

+

–

50Ω

1.7pF

–OUTF

6

5

OUT+

1000Ω

25Ω

100Ω

12.5Ω

16 –IN

–OUT

640120 F02

Input Impedance and Matching

Figure 2. Input Termination for Differential 50Ω Input Impedance

Using a 1:4 Balun

The differential input impedance of the LTC6401-20 is

200Ω. If a 200Ω source impedance is unavailable, then

640120f

10

LTC6401-20

APPLICATIONS INFORMATION

R

LTC6401-20

S

input Smith Chart, based on which users can choose the

optimal source impedance for a given gain and noise

requirement.

0.1μF

1000Ω

50Ω

100Ω

12.5Ω

13 +IN

+OUT

8

7

V

IN

+

50Ω

–

R

T

IN+

IN–

OUT–

66.5Ω

+OUTF

14 +IN

15 –IN

0.1μF

50Ω

1.7pF

Output Match and Filter

–OUTF

6

5

OUT+

1000Ω

R

S

50Ω

The LTC6401-20 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.

0.1μF

100Ω

12.5Ω

16 –IN

–OUT

640120 F03

R

T

66.5Ω

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

Impedance

The internal low pass ﬁlter outputs at +OUTF/–OUTF

have a –3dB bandwidth of 590MHz. External capacitor

can reduce the low pass ﬁlter bandwidth as shown in

Figure 5. A bandpass ﬁlter is easily implemented with

only a few components as shown in Figure 6. Three

39pF capacitors and a 16nH inductor create a bandpass

ﬁlter with 165MHz center frequency, –3dB frequencies at

138MHz and 200MHz.

two outputs have the same gain and thus symmetrical

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

terminationresistorR aredeterminedbythecombination

T

of R , R and R . For example, when R is 50Ω, it is found

S

G

F

S

that the single-ended input impedance is 200Ω and R is

T

66.5Ω in order to match to a 50Ω source impedance.

The LTC6401-20 is unconditionally stable. However, the

overall differential gain is affected by both source imped-

ance and load impedance as shown in Figure 4:

LTC6401-20

1000Ω

100Ω

12.5Ω

50Ω

13 +IN

+OUT

8

7

8.2pF

FILTERED OUTPUT

IN+

IN–

OUT–

V_OUT

R_L

R_S+ 200 25+R_L

2000

+OUTF

14 +IN

15 –IN

A_V=

=

•

12pF

(87.5MHz)

50Ω

V

1.7pF

IN

–OUTF

6

5

OUT+

1000Ω

8.2pF

100Ω

12.5Ω

The noise performance of the LTC6401-20 also depends

uponthesourceimpedanceandtermination. Forexample,

an input 1:4 balun transformer in Figure 2 improves SNR

by adding 6dB of gain at the inputs. A trade-off between

gain and noise is obvious when constant noise ﬁgure

circle and constant gain circle are plotted within the same

16 –IN

–OUT

640120 F05

Figure 5. LTC6401-20 Internal Filter Topology Modiﬁed for Low

Filter Bandwidth (Three External Capacitors)

39pF

LTC6401-20

12.5Ω

LTC6401-20

1000Ω

100Ω

10Ω

4.99Ω

1000Ω

1/2 R

S

100Ω

12.5Ω

50Ω

1/2 R

L

13 +IN

+OUT

8

7

13 +IN

+OUT

8

7

50Ω

IN+

IN–

OUT–

+OUTF

IN+

IN–

OUT–

+OUTF

14 +IN

15 –IN

V

IN

16nH

LTC2208

14 +IN

15 –IN

V

+

OUT

1.7pF

39pF

50Ω

–

50Ω

1.7pF

OUT+

1000Ω

–OUTF

6

5

–OUTF

6

5

OUT+

1000Ω

100Ω

12.5Ω

10Ω

4.99Ω

1/2 R

S

100Ω

12.5Ω

1/2 R

L

16 –IN

–OUT

39pF

16 –IN

–OUT

640120 F06

640120 F04

Figure 4. Calculate Differential Gain

Figure 6. LTC6401-20 Application Circuit for Bandpass

Filtering (Three External Capacitors, One External Inductor)

640120f

11

LTC6401-20

APPLICATIONS INFORMATION

Output Common Mode Adjustment

1.25V

0.1μF

The LTC6401-20’s output common mode voltage is set

0.1μF

by the V

pin, which is a high impedance input. The

V

OCM

+OUT

+OUTF

OCM

10Ω

V

+

–

CM

IF IN

66.5Ω

+IN

AIN

output common mode voltage is capable of tracking V

OCM

control is

LTC6401-20

LTC2208

in a range from 1V to 1.6V. Bandwidth of V

–OUTF

–OUT

OCM

–IN

ENABLE

AIN

typically 15MHz, which is dominated by a low pass ﬁlter

connected to the V pin and is aimed to reduce com-

10Ω

29Ω

LTC2208 130Msps

16-Bit ADC

OCM

20dB GAIN

640120 F07

mon mode noise generation at the outputs. The internal

common mode feedback loop has a –3dB bandwidth

around 300MHz, allowing fast common mode rejection at

Figure 7. Single-Ended Input to LTC6401-20 and LTC2208

Test Circuits

the outputs of the LTC6401-20. The V

pin should be

OCM

tied to a DC bias voltage where a 0.1μF bypass capacitor

is recommended. When interfacing with A/D converters

Due to the fully-differential design of the LTC6401 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 DC987B,

a two-port demonstration circuit for the LTC6401 family.

The schematic and silkscreen are shown below. This

circuit includes input and output transformers (baluns)

for single-ended-to-differential conversion and imped-

ance transformation, allowing direct hook-up to a 2-port

network analyzer. There are also series resistors at the

output to present the LTC6401 with a 375Ω differential

load, optimizing distortion performance. Due to the input

and output transformers, the –3dB bandwidth is reduced

from 1.3GHz to approximately 1.1GHz.

such as the LT22xx families, the V

can be normally

OCM

connected to the V pin of the ADC.

CM

Driving A/D Converters

The LTC6401-20 has been speciﬁcally designed to inter-

face directly with high speed A/D converters. In Figure 7,

an example schematic shows the LTC6401-20 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 wire inductance of either the ADC

input or the driver output. V

of the LTC6401-20 is

OCM

connected to V of the LTC2208 at 1.25V. Alternatively,

CM

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.

asingle-endedinputsignalcanbeconvertedtodifferential

signal via a balun and fed to the input of the LTC6401-20.

The balun also converts input impedance to match 50Ω

source impedance.

640120f

12

LTC6401-20

APPLICATIONS INFORMATION

Top Silkscreen

640120f

13

LTC6401-20

TYPICAL APPLICATION

Demo Circuit 987B Schematic (Test Circuit A)

V

CC

ENABLE

DIS

1

3

V

CC

2

JP1

C17

1000pF

C18

0.1μF

R16

0Ω

12

–

11

10

+

9

–

V

ENABLE

V

R10

R2

(1)

R14

(1)

86.6Ω

13

14

15

16

8

7

6

5

+IN

–IN

+OUT

+OUTF

–OUTF

–OUT

R6

0Ω

R12

0Ω

T2

TCM 4-19

1:4

R8

(1)

C2

0.1μF

C4

R4

(2)

T1

(2)

5

4

1

2

3

2

1

4

J1

+IN

J4

+OUT

0.1μF

C21

0.1μF

R24

(1)

SL1

(2)

SL2

(2)

R7

(1)

LTC6401-20

R5

(1)

R11

(1)

SL3

(2)

J5

–OUT

0dB

5

J2

–IN

R3

(2)

C1

0.1μF

C3

0.1μF

R9

86.6Ω

–IN

V

R13

0Ω

C22

R1

0Ω

+

–

V

OCM

V

0.1μF

1

2

3

4

V

CC

V

CC

C10

0.1μF

C9

1000pF

C12

1000pF

C13

0.1μF

V

CC

R19

1.5k

TP5

V

OCM

R20

1k

C7

0.1μF

T3

TCM 4-19

1:4

T4

TCM 4-19

1:4

R17

R18

0Ω

5

4

1

2

3

2

1

4

J6

TEST IN

J7

C23

C5

C19

0.1μF

C20

0.1μF

TEST OUT

0.1μF

R21

(1)

R22

(1)

R25

0Ω

R26

0Ω

C24

0.1μF

C6

0.1μF

5

V

CC

TP2

V

CC

NOTE: UNLESS OTHERWISE SPECIFIED.

(1) DO NOT STUFF.

C14

4.7μF

C15

1μF

2.85V TO 3.5V

(2) VERSION

-G

SL = SIGNAL LEVEL

IC

R3

R4

T1

SL1

SL2

SL3

TP3

GND

LTC6401CUD-20 OPEN OPEN MINI-CIRCUITS TCM4-19 (1:4) 6dB

20dB 14dB

640120 TA03

640120f

14

LTC6401-20

TYPICAL APPLICATION

Test Circuit B, 4-Port Analysis

+

V

1000pF

0.1μF

–

+

V

–

V

ENABLE

12

G

11

10

9

BIAS CONTROL

R

F

1000Ω

R

OUT

12.5Ω

+IN

13

+OUT

100Ω

37.4Ω

PORT 1

(50Ω)

0.1μF

PORT 3

(50Ω)

8

7

R

FILT

50Ω

0.1μF

+OUTF

+IN

–IN

IN+

IN–

OUT–

14

15

1/2

AGILENT

E5O71A

1/2

AGILENT

E5O71A

C

FILT

1.7pF

R

FILT

200Ω

–OUTF

–OUT

50Ω

6

5

OUT+

R

G

100Ω

R

OUT

12.5Ω

F

–IN

16

1000Ω

37.4Ω

PORT 2

(50Ω)

PORT 4

(50Ω)

0.1μF

COMMON

MODE CONTROL

640120 TA02

1

2

3

4

+

V

–

V

OCM

1000pF

0.1μF

+

V

OCM

PACKAGE DESCRIPTION

UD Package

16-Lead Plastic QFN (3mm × 3mm)

(Reference LTC DWG # 05-08-1691)

BOTTOM VIEW—EXPOSED PAD

PIN 1 NOTCH R = 0.20 TYP

OR 0.25 × 45° CHAMFER

R = 0.115

TYP

0.75 ± 0.05

3.00 ± 0.10

(4 SIDES)

15 16

0.70 ±0.05

PIN 1

TOP MARK

(NOTE 6)

0.40 ± 0.10

1

2

1.45 ± 0.10

(4-SIDES)

3.50 ± 0.05

2.10 ± 0.05

1.45 ± 0.05

(4 SIDES)

PACKAGE

OUTLINE

(UD16) QFN 0904

0.200 REF

0.25 ± 0.05

0.25 ±0.05

0.50 BSC

0.00 – 0.05

0.50 BSC

NOTE:

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

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

640120f

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 representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

15

LTC6401-20

RELATED PARTS

PART NUMBER DESCRIPTION

COMMENTS

High-Speed Differential Ampliﬁers/Differential Op Amps

LT1993-2

LT1993-4

LT1993-10

LT1994

800MHz Differential Ampliﬁer/ADC Driver

900MHz Differential Ampliﬁer/ADC Driver

700MHz Differential Ampliﬁer/ADC Driver

Low Noise, Low Distortion Differential Op Amp

A = 2V/V, OIP3 = 38dBm at 70MHz

V

A = 4V/V, OIP3 = 40dBm at 70MHz

V

A = 10V/V, OIP3 = 40dBm at 70MHz

V

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

LTC6400-20

LT6402-6

LT6402-12

LT6402-20

LTC6406

1.8GHz Low Noise, Low Distortion, Differential ADC Driver

300MHz Differential Ampliﬁer/ADC Driver

3GHz Rail-to-Rail Input Differential Op Amp

A = 20dB, 90mA Supply Current, IMD = –65dBc at 300MHz

V 3

A = 6dB, Distortion < –80dBc at 25MHz

V

A = 12dB, Distortion < –80dBc at 25MHz

V

A = 20dB, Distortion < –80dBc at 25MHz

V

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, A = 1, –1 or 2

V

High-Speed Single-Ended Output Op Amps

LT1812/LT1813/ High Slew Rate Low Cost Single/Dual/Quad Op Amps

LT1814

8nV/√Hz Noise, 750V/μs, 3mA Supply Current

6nV/√Hz Noise, 1500V/μs, 6.5mA Supply Current

6nV/√Hz Noise, 2500V/μs, 9mA Supply Current

LT1815/LT1816/ Very High Slew Rate Low Cost Single/Dual/Quad Op Amps

LT1817

LT1818/LT1819 Ultra High Slew Rate Low Cost Single/Dual Op Amps

LT6200/LT6201 Rail-to-Rail Input and Output Low Noise Single/Dual Op Amps 0.95nV/√Hz Noise, 165MHz GBW, Distortion = –80dBc at 1MHz

LT6202/LT6203/ Rail-to-Rail Input and Output Low Noise Single/Dual/Quad

LT6204 Op Amps

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

1.1nV/√Hz Noise, 3.5mA Supply Current, 215MHz GBW

1.9nV/√Hz Noise, 1.2mA Supply Current, 60MHz GBW

LT6230/LT6231/ Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps

LT6232

LT6233/LT6234/ Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps

LT6235

Integrated Filters

LTC1562-2

LT1568

Very Low Noise, 8th Order Filter Building Block

Very Low Noise, 4th Order Filter Building Block

Linear Phase, Tunable 10th Order Lowpass Filter

Very Low Noise Differential 2.5MHz Lowpass Filter

Very Low Noise Differential 5MHz Lowpass Filter

Very Low Noise Differential 10MHz Lowpass Filter

Very Low Noise Differential 15MHz Lowpass Filter

Very Low Noise Differential 20MHz Lowpass Filter

Lowpass and Bandpass Filters up to 300kHz

Lowpass and Bandpass Filters up to 10MHz

Single-Resistor Programmable Cut-Off to 300kHz

SNR = 86dB at 3V Supply, 4th Order Filter

SNR = 82dB at 3V Supply, 4th Order Filter

SNR = 76dB at 3V Supply, 4th Order Filter

LTC1569-7

LT6600-2.5

LT6600-5

LT6600-10

LT6600-15

LT6600-20

640120f

LT 0907 • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

16

●

(408) 432-1900 FAX: (408) 434-0507 www.linear.com


型号：	LTC6401-20
厂家：	Linear
描述：	1.3GHz Low Noise, Low Distortion Differential ADC Driver for 140MHz IF 1.3GHz的低噪声，低失真差分ADC驱动器为140MHz的IF 驱动器
文件：	总16页 (文件大小：221K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LTC6401-20 [Linear]

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