LT6600CS8-15-PBF_技术文档

LT6600-15

Very Low Noise, Differential

Ampliﬁer and 15MHz Lowpass Filter

FEATURES

DESCRIPTION

TheLT^®6600-15combinesafullydifferentialampliﬁerwitha

4thorder15MHzlowpassﬁlterapproximatingaChebyshev

frequency response. Most differential ampliﬁers require

many precision external components to tailor gain and

n

Programmable Differential Gain via Two External

Resistors

n

Adjustable Output Common Mode Voltage

Operates and Speciﬁed with 3V, 5V, 5V Supplies

0.5dB Ripple 4th Order Lowpass Filter with 15MHz

Cutoff

76dB S/N with 3V Supply and 2V Output

n

bandwidth. In contrast, with the LT6600-15, two external

resistors program differential gain, and the ﬁlter’s 15MHz

cutoff frequency and passband ripple are internally set.

The LT6600-15 also provides the necessary level shifting

to set its output common mode voltage to accommodate

the reference voltage requirements of A/Ds.

n

P-P

Low Distortion, 2V , 800Ω Load, V = 3V

P-P

S

1MHz: 86dBc 2nd, 90dBc 3rd

10MHz: 63dBc 2nd, 69dBc 3rd

Fully Differential Inputs and Outputs

Compatible with Popular Differential Ampliﬁer

n

Using a proprietary internal architecture, the LT6600-15

integrates an antialiasing ﬁlter and a differential ampliﬁer/

driverwithoutcompromisingdistortionorlownoiseperfor-

mance. Atunitygainthemeasuredinbandsignal-to-noise

ratio is an impressive 76dB. At higher gains the input

referred noise decreases so the part can process smaller

input differential signals without signiﬁcantly degrading

the output signal-to-noise ratio.

Pinouts

SO-8 Package

n

APPLICATIONS

n

High Speed ADC Antialiasing and DAC Smoothing in

Networking or Cellular Base Station Applications

The LT6600-15 also features low voltage operation. The

differential design provides outstanding performance for

n

High Speed Test and Measurement Equipment

Medical Imaging

Drop-in Replacement for Differential Ampliﬁers

n

a 2V signal level while the part operates with a single

P-P

n

3V supply.

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

All other trademarks are the property of their respective owners.

The LT6600-15 is packaged in an SO-8 and is pin compat-

ible with stand alone differential ampliﬁers.

TYPICAL APPLICATION

An 8192 Point FFT Spectrum

0

LTC2249

3V

LT6600-15

INPUT 10.7MHz

–10

2V

SAMPLE

3V

P-P

–20

f

= 80MHz

0.1μF

–30

–40

–50

R

536ꢀ

5.6pF

IN

3

+

1

7

2

8

V

25ꢀ

–

4

+

A

+

–

–60

–70

V

MID

D

5.6pF

OUT

–

IN

V

0.01μF

OCM

–80

–

5

V

IN

+

V

CM

V

–90

R

6

IN

536ꢀ

–100

–110

–120

2.2μF

GAIN = 536ꢀ/R

IN

660015 TA01a

20

FREQUENCY (MHz)

0

10

30

40

660015 TA01b

660015fa

1

LT6600-15

ABSOLUTE MAXIMUM RATINGS

PIN CONFIGURATION

(Note 1)

TOP VIEW

Total Supply Voltage .................................................11V

–

+

Input Voltage (Note 8)............................................... V

IN

1

2

3

4

8

7

6

5

IN

S

Input Current (Note 8).......................................... 10mA

Operating Temperature Range (Note 6)....–40°C to 85°C

Speciﬁed Temperature Range (Note 7) .... –40°C to 85°C

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

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

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

V

OCM

MID

–

+

V

+

–

OUT

S8 PACKAGE

8-LEAD PLASTIC SO

= 150°C, θ = 100°C/W

T

JMAX

JA

ORDER INFORMATION

LEAD FREE FINISH

LT6600CS8-15#PBF

LT6600IS8-15#PBF

LEAD BASED FINISH

LT6600CS8-15

TAPE AND REEL

PART MARKING

660015

PACKAGE DESCRIPTION

8-Lead Plastic SO

TEMPERATURE RANGE

LT6600CS8-15#TRPBF

LT6600IS8-15#TRPBF

TAPE AND REEL

–40°C to 85°C

600I15

8-Lead Plastic SO

–40°C to 85°C

PART MARKING

660015

PACKAGE DESCRIPTION

8-Lead Plastic SO

TEMPERATURE RANGE

–40°C to 85°C

LT6600CS8-15#TR

LT6600IS8-15#TR

LT6600IS8-15

600I15

8-Lead Plastic SO

–40°C to 85°C

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

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

ELECTRICAL CHARACTERISTICS

The l denotes the speciﬁcations which apply over the full operating temperature

range, otherwise speciﬁcations are at T_A= 25°C. Unless otherwise speciﬁed V_S= 5V (V⁺= 5V, V^–= 0V), R_IN= 536Ω, and R_LOAD= 1k.

PARAMETER

Filter Gain, V = 3V

CONDITIONS

= 2V , f = DC to 260kHz

MIN

– 0.5

–0.1

–0.3

–0.7

TYP

0.1

0

MAX

0.5

UNITS

dB

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

S

P-P IN

l

= 2V , f = 1.5MHz (Gain Relative to 260kHz)

0.1

P-P IN

= 2V , f = 7.5MHz (Gain Relative to 260kHz)

0

0.4

P-P IN

= 2V , f = 12MHz (Gain Relative to 260kHz)

0.2

0

1.0

P-P IN

= 2V , f = 15MHz (Gain Relative to 260kHz)

1.0

P-P IN

= 2V , f = 45MHz (Gain Relative to 260kHz)

– 29

–46

0

–25

P-P IN

= 2V , f = 75MHz (Gain Relative to 260kHz)

P-P IN

Filter Gain, V = 5V

= 2V , f = DC to 260kHz

–0.5

– 0.1

–0.4

–0.8

0.5

0.1

0.3

0.9

–25

S

P-P IN

l

= 2V , f = 1.5MHz (Gain Relative to 260kHz)

0

P-P IN

= 2V , f = 7.5MHz (Gain Relative to 260kHz)

0

P-P IN

= 2V , f = 12MHz (Gain Relative to 260kHz)

0.1

0

P-P IN

= 2V , f = 15MHz (Gain Relative to 260kHz)

P-P IN

= 2V , f = 45MHz (Gain Relative to 260kHz)

–29

–46

–0.1

P-P IN

= 2V , f = 75MHz (Gain Relative to 260kHz)

P-P IN

Filter Gain, V = 5V

= 2V , f = DC to 260kHz

–0.6

0.4

S

P-P IN

Filter Gain, R = 133Ω

V

= 2V , f = DC to 260kHz, V = 3V

11.5

11.4

12.0

11.9

12.5

12.4

dB

IN

OUT

P-P IN

S

= 2V , f = DC to 260kHz, V = 5V

P-P IN

S

= 2V , f = DC to 260kHz, V = 5V

P-P IN

S

660015fa

2

LT6600-15

ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating temperature

range, otherwise speciﬁcations are at T_A= 25°C. Unless otherwise speciﬁed V_S= 5V (V⁺= 5V, V^–= 0V), R_IN= 536Ω, and R_LOAD= 1k.

PARAMETER

CONDITIONS

= 250kHz, V = 2V

P-P

MIN

TYP

780

109

MAX

UNITS

Filter Gain Temperature Coefﬁcient (Note 2)

f

IN

ppm/C

IN

Noise

Noise BW = 10kHz to 15MHz

1MHz, 2V , R = 800Ω, V = 3V

μV

RMS

Distortion (Note 4)

2nd Harmonic

3rd Harmonic

86

90

dBc

P-P

L

S

10MHz, 2V , R = 800Ω, V = 3V

2nd Harmonic

3rd Harmonic

63

69

dBc

P-P

L

S

Differential Output Swing

Measured Between Pins 4 and 5

V = 5V

S

●

3.80

3.75

4.75

4.50

V

S

P-P DIFF

V = 3V

Input Bias Current

Average of Pin 1 and Pin 8

●

– 90

–35

μA

Input Referred Differential Offset

R

= 536Ω

= 133Ω

V = 3V

●

5

25

30

35

mV

IN

S

V = 5V

10

S

V = 5V

S

V = 3V

●

5

15

17

20

mV

IN

S

V = 5V

S

V = 5V

S

Differential Offset Drift

10

μV/°C

Input Common Mode Voltage (Note 3)

Differential Input = 500mV

IN

,

V = 3V

●

0.0

–2.5

1.5

3.0

1.0

V

P-P

S

R

= 133Ω

V = 5V

S

V = 5V

S

Output Common Mode Voltage (Note 5)

Differential Input = 2V

Pin 7 at Mid-Supply

,

V = 3V

●

1.0

1.5

–1.0

1.5

3.0

2.0

V

P-P

S

V = 5V

S

Common Mode Voltage at Pin 2

V = 5V

S

Output Common Mode Offset

(with Respect to Pin 2)

V = 3V

●

–35

–40

–55

5

0

–10

40

35

mV

S

V = 5V

S

V = 5V

S

Common Mode Rejection Ratio

64

dB

l

Voltage at V

(Pin 7)

V = 5V

S

2.45

4.3

2.50

1.50

2.55

7.7

V

MID

S

V = 3V

V

Input Resistance

Bias Current

5.7

kΩ

MID

V

OCM

= V = V /2

V = 5V

●

–10

–2

μA

OCM

MID

S

V = 3V

S

Power Supply Current

V = 3V, V = 5V

35

39

44

45

48

mA

S

V = 3V

●

S

V = 5V

S

V = 5V

38

S

l

Power Supply Voltage

3

11

V

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 5: Output common mode voltage is the average of the voltages at

Pins 4 and 5. The output common mode voltage is equal to the voltage

applied to Pin 2.

Note 6: The LT6600C-15 is guaranteed functional over the operating

Note 2: This is the temperature coefﬁcient of the internal feedback

temperature range –40°C to 85°C.

resistors assuming a temperature independent external resistor (R ).

Note 3: The input common mode voltage is the average of the voltages

IN

Note 7: The LT6600C-15 is guaranteed to meet 0°C to 70°C speciﬁcations

and is designed, characterized and expected to meet the extended

temperature limits, but is not tested at –40°C and 85°C. The LT6600I-15 is

guaranteed to meet speciﬁed performance from –40°C to 85°C.

applied to the external resistors (R ). Speciﬁcation guaranteed for

IN

R

≥ 100Ω.

IN

Note 8: The inputs are protected by back-to-back diodes. If the differential

input voltage exceeds 1.4V, the input current should be limited to less than

10mA.

Note 4: Distortion is measured differentially using a differential stimulus,

The input common mode voltage, the voltage at Pin 2, and the voltage at

Pin 7 are equal to one half of the total power supply voltage.

660015fa

3

LT6600-15

TYPICAL PERFORMANCE CHARACTERISTICS

Amplitude Response

Passband Gain and Phase

Passband Gain and Delay

10

0

1

0

50

45

40

35

30

25

20

15

10

5

1

0

225

180

135

90

V

= 5V

V

= 5V

S

GAIN = 1

= 25°C

GAIN = 1

= 25°C

GAIN

T

A

–1

–2

–3

–4

–5

–6

–7

–8

–9

–1

–2

–3

–4

–5

–6

–7

–8

–9

–10

–20

–30

–40

–50

–60

DELAY

45

PHASE

0

–45

–90

–135

–180

–225

V

= 5V

S

GAIN = 1

= 25°C

T

A

0

0.1

1

10

100

0

5

20

10

15

FREQUENCY (MHz)

25

0

5

10

15

20

25

FREQUENCY (MHz)

66005 G01

660015 G03

660015 G02

Passband Gain and Delay

Output Impedance

Common Mode Rejection Ratio

100

10

1

80

75

70

65

60

55

50

45

40

35

30

14

12

10

8

50

45

40

35

30

25

20

15

10

5

V

= 1V

= 5V

V

= 5V

V

= 5V

IN

S

P-P

S

GAIN = 1

= 25°C

GAIN = 4

= 25°C

GAIN = 1

T

A

GAIN

T

= 25°C

A

6

DELAY

4

2

0

–2

–4

–6

0.1

0

0.1

1

10

100

0

5

10

15

20

25

0.1

1

10

100

FREQUENCY (MHz)

660015 G05

660015 G06

660015 G04

Power Supply Rejection Ratio

Distortion vs Frequency

Distortion vs Signal Level

–50

–60

–70

–80

–90

80

70

60

50

40

30

20

10

0

–40

–50

3RD HARMONIC

10MHz INPUT

V

= 2V

= 3V

V = 3V

S

L

IN

S

L

P-P

R

= 800ꢀ AT

R

= 800ꢀ AT

EACH OUTPUT

GAIN = 1

EACH OUTPUT

GAIN = 1

–60

T = 25°C

A

T

= 25°C

A

–70

2ND

HARMONIC

10MHz INPUT

–80

3RD

–90

HARMONIC

1MHz INPUT

2ND

HARMONIC

1MHz INPUT

V

A

V

= 3V

S

= 200mV

–100

–110

IN

= 25°C

P-P

–100

–110

T

+

TO DIFFOUT

0.1

1

10

100

0.1

1

10

100

660015 G08

1

2

3

5

0

4

FREQUENCY (MHz)

INPUT LEVEL (V

)

P-P

600015 G07

DIFFERENTIAL INPUT, 2ND HARMONIC

DIFFERENTIAL INPUT, 3RD HARMONIC

SINGLE-ENDED INPUT, 2ND HARMONIC

SINGLE-ENDED INPUT, 3RD HARMONIC

660015 G09

660015fa

4

LT6600-15

TYPICAL PERFORMANCE CHARACTERISTICS

Distortion

Distortion vs Signal Level

vs Input Common Mode Level

–40

–50

–40

–50

–40

–50

2ND HARMONIC,

V

=

5V

2ND HARMONIC,

= 3V

GAIN = 1

= 800ꢀ AT EACH

S

L

V

S

= 3V

R

= 800ꢀ AT EACH OUTPUT

V

S

R

L

3RD HARMONIC,

= 3V

GAIN = 1

= 25°C

3RD HARMONIC,

= 3V

OUTPUT

= 25°C

V

T

V

T

S

A

S

A

2ND HARMONIC,

= 5V

–60

2ND HARMONIC,

= 5V

–60

2V 1MHz INPUT

P-P

2ND HARMONIC,

10MHz INPUT

–60

–70

V

S

3RD HARMONIC,

= 5V

3RD HARMONIC,

= 5V

–70

V

S

3RD

–80

HARMONIC,

10MHz INPUT

–80

–90

2ND HARMONIC,

1MHz INPUT

–100

–110

–100

–110

GAIN = 4, R = 800ꢀ AT EACH OUTPUT

3RD HARMONIC,

1MHz INPUT

L

T

= 25°C, 500mV 1MHz INPUT

P-P

A

–100

–3

–2

–1

0

1

2

3

–3

–2

–1

0

1

2

3

1

2

3

5

0

4

INPUT COMMON MODE VOTLAGE RELATIVE TO PIN 7 (V)

INPUT LEVEL (V

)

P-P

66002 G11

660015 G12

660015 G10

Distortion

vs Output Common Mode

–40

2ND HARMONIC,

V

= 3V

S

–50

–60

3RD HARMONIC,

= 3V

V

S

2ND HARMONIC,

= 5V

V

S

3RD HARMONIC,

= 5V

–70

V

S

2ND HARMONIC,

5V

3RD HARMONIC,

5V

–80

V

=

S

V

=

S

–90

2V 1MHz INPUT

P-P

–100

GAIN = 1,

R

= 800ꢀ AT EACH OUTPUT

= 25°C

L

T

A

–110

–1.5 –1 –0.5

0

2

2.5

0.5

1

1.5

VOLTAGE PIN 2 TO PIN 7 (V)

660015 G13

Total Supply Current

vs Total Supply Voltage

Transient Response

50

45

–

OUT

200mV/DIV

T

= 85°C

= 25°C

A

+

OUT

40

35

200mV/DIV

T

A

–

T

= –40°C

A

IN

+

30

25

20

500mV/DIV

660015 G15

100ns/DIV

DIFFERENTIAL GAIN = 1

SINGLE-ENDED INPUT

DIFFERENTAL OUTPUT

2

4

6

8

10

12

TOTAL SUPPLY VOLTAGE (V)

660015 G14

660015fa

5

LT6600-15

PIN FUNCTIONS

–

+

IN and IN (Pins 1, 8): Input Pins. Signals can be ap-

applications, bypass Pin 3 to ground and Pin 6 to ground

with a quality 0.1μF ceramic capacitor.

plied to either or both input pins through identical external

resistors, R . The DC gain from differential inputs to the

+

–

IN

OUT and OUT (Pins 4, 5): Output Pins. Pins 4 and 5 are

the ﬁlter differential outputs. Each pin can drive a 100Ω

and/or 50pF load.

differential outputs is 536Ω/R .

IN

V

OCM

(Pin 2): Is the DC Common Mode Reference Voltage

for the 2nd Filter Stage. Its value programs the common

modevoltageofthedifferentialoutputoftheﬁlter.Pin2isa

highimpedanceinput,whichcanbedrivenfromanexternal

voltage reference, or Pin 2 can be tied to Pin 7 on the PC

board. Pin 2 should be bypassed with a 0.01μF ceramic

capacitor unless it is connected to a ground plane.

V

(Pin 7): The V

pin is internally biased at mid-

MID

supply, see block diagram. For single supply operation,

the V pin should be bypassed with a quality 0.01μF

MID

ceramic capacitor to Pin 6. For dual supply operation,

Pin 7 can be bypassed or connected to a high quality DC

ground. A ground plane should be used. A poor ground

will increase noise and distortion. Pin 7 sets the output

common mode voltage of the 1st stage of the ﬁlter. It has

a 5.5kΩ impedance, and it can be overridden with an

external low impedance voltage source.

+

–

V and V (Pins 3, 6): Power Supply Pins. For a single

3.3Vor5Vsupply(Pin6grounded)aquality0.1μFceramic

bypass capacitor is required from the positive supply pin

(Pin 3) to the negative supply pin (Pin 6). The bypass

should be as close as possible to the IC. For dual supply

BLOCK DIAGRAM

R

IN

+

–

V

IN

V

OUT

5

V

IN

MID

8

7

6

+

V

11k

PROPRIETARY

LOWPASS

536Ω

FILTER STAGE

200Ω

–

V

OP AMP

200Ω

+

OCM

–

V

OCM

+

–

200Ω

536Ω

1

2

3

4

–

+

V

IN

OCM

V

OUT

R

IN

660015 BD

660015fa

6

LT6600-15

APPLICATIONS INFORMATION

Interfacing to the LT6600-15

output voltage is 1.65V, and the differential output voltage

is2V forfrequenciesbelow15MHz.Thecommonmode

P-P

The LT6600-15 requires two equal external resistors, R ,

IN

output voltage is determined by the voltage at Pin 2. Since

Pin 2 is shorted to Pin 7, the output common mode is the

mid-supply voltage. In addition, the common mode input

voltage can be equal to the mid-supply voltage of Pin 7

(see the Distortion vs Input Common Mode Level graphs

in the Typical Performance Characteristics section).

to set the differential gain to 536Ω/R . The inputs to the

IN

+

–

ﬁlter are the voltages V and V presented to these

IN

external components, Figure 1. The difference between

+

–

V

and V is the differential input voltage. The aver-

IN

+

–

age of V and V

Similarly,thevoltagesV

is the common mode input voltage.

IN

+

–

andV

appearingatPins4

OUT

and 5 of the LT6600-15 are the ﬁlter outputs. The differ-

Figure 2 shows how to AC couple signals into the

LT6600-15. In this instance, the input is a single-ended

signal. AC coupling allows the processing of single-ended

or differential signals with arbitrary common mode levels.

The 0.1μF coupling capacitor and the 536Ω gain setting

resistor form a high pass ﬁlter, attenuating signals below

3kHz.Largervaluesofcouplingcapacitorswillproportion-

ally reduce this highpass 3dB frequency.

+

–

ence between V

and V

is the differential output

OUT

+

–

voltage. The average of V

mode output voltage.

and V

is the common

OUT

Figure 1 illustrates the LT6600-15 operating with a single

3.3V supply and unity passband gain; the input signal is

DC coupled. The common mode input voltage is 0.5V, and

the differential input voltage is 2V . The common mode

P-P

3.3V

0.1μF

V

3

–

536ꢀ

3

2

1

0

3

2

1

0

1

7

2

8

–

+

V

4

IN

+

–

+

–

V

+

V

OUT

LT6600-15

+

V

0.01μF

IN

V

OUT

–

5

+

536ꢀ

6

t

–

660015 F01

V

IN

Figure 1

3.3V

3

0.1μF

4

V

0.1μF

536ꢀ

1

3

2

1

–

+

–

+

–

V

+

7

OUT

V

OUT

LT6600-15

2

1

0

2

8

+

V

IN

0.01μF

V

OUT

–

0

t

+

IN

5

V

+

6

–1

660015 F02

Figure 2

62pF

5V

0.1μF

V

3

133ꢀ

1

–

3

V

–

4

IN

+

–

V

OUT

+

7

2

8

OUT

LT6600-15

2

1

0

2

1

V

OUT

0.01μF

–

V

OUT

500mV (DIFF)

P-P

–

+

5

V

IN

+

V

133ꢀ

62pF

IN

6

t

0

–

+

660015 F03

2V

IN

–

Figure 3

660015fa

7

LT6600-15

APPLICATIONS INFORMATION

In Figure 3 the LT6600-15 is providing 12dB of gain. The

gain resistor has an optional 62pF in parallel to improve

the passband ﬂatness near 15MHz. The common mode

output voltage is set to 2V.

ampleswhereimpedancemustbeconsideredistheevalu-

ation of the LT6600-15 with a network analyzer. Figure 5

is a laboratory setup that can be used to characterize the

LT6600-15 using single-ended instruments with 50Ω

source impedance and 50Ω input impedance. For a unity

gain conﬁguration the LT6600-15 requires a 536Ω source

resistance yet the network analyzer output is calibrated

for a 50Ω load resistance. The 1:1 transformer, 52.3Ω

and 523Ω resistors satisfy the two constraints above.

The transformer converts the single-ended source into a

differentialstimulus.Similarly,theoutputoftheLT6600-15

will have lower distortion with larger load resistance yet

the analyzer input is typically 50Ω. The 4:1 turns (16:1

impedance) transformer and the two 402Ω resistors of

Figure5,presenttheoutputoftheLT6600-15witha1600Ω

differential load, or the equivalent of 800Ω to ground at

each output. The impedance seen by the network analyzer

input is still 50Ω, reducing reﬂections in the cabling be-

tween the transformer and analyzer input.

Use Figure 4 to determine the interface between the

LT6600-15 and a current output DAC. The gain, or “tran-

simpedance,” is deﬁned as A = V /I . To compute the

OUT IN

transimpedance, use the following equation:

536 •R1

A =

Ω

( )

R1+R2

(

)

By setting R1 + R2 = 536Ω, the gain equation reduces

to A = R1(Ω).

The voltage at the pins of the DAC is determined by R1,

R2, the voltage on Pin 7 and the DAC output current.

Consider Figure 4 with R1 = 49.9Ω and R2 = 487Ω. The

voltage at Pin 7 is 1.65V. The voltage at the DAC pins is

given by:

R1

R1•R2

R1+R2

Differential and Common Mode Voltage Ranges

V

_DAC= V_PIN7

•

+I •

IN

R1+R2+ 536

= 77mV +I • 45.3Ω

The differential ampliﬁers inside the LT6600-15 contain

circuitry to limit the maximum peak-to-peak differential

voltage through the ﬁlter. This limiting function prevents

excessive power dissipation in the internal circuitry and

provides output short-circuit protection. The limiting

function begins to take effect at output signal levels above

IN

+

–

I is I or I . The transimpedance in this example is

IN

49.8Ω.

Evaluating the LT6600-15

2V and it becomes noticeable above 3.5V . This is

P-P

The low impedance levels and high frequency operation

of the LT6600-15 require some attention to the matching

networks between the LT6600-15 and other devices. The

previousexamplesassumeanideal(0Ω)sourceimpedance

and a large (1kΩ) load resistance. Among practical ex-

illustrated in Figure 6; the LT6600-15 was conﬁgured with

unity passband gain and the input of the ﬁlter was driven

with a 1MHz signal. Because this voltage limiting takes

place well before the output stage of the ﬁlter reaches the

2.5V

0.1μF

CURRENT

OUTPUT

DAC

3.3V

COILCRAFT

TTWB-16A

4:1

COILCRAFT

TTWB-1010

NETWORK

ANALYZER

SOURCE

NETWORK

ANALYZER

INPUT

0.1μF

4

3

523ꢀ

1:1

1

7

2

8

402ꢀ

–

4

–

3

+

R2

I

IN

1

7

2

8

50ꢀ

LT6600-15

–

+

–

52.3ꢀ

50ꢀ

V

+

OUT

R1

+

–

0.011μF

LT6600-15

5

+

402ꢀ

523ꢀ

–

IN

6

OUT

0.1μF

5

+

660015 F05

6

R1

660015 F04

–2.5V

Figure 4

Figure 5

660015fa

8

LT6600-15

APPLICATIONS INFORMATION

20

The LT6600-15 was designed to process a variety of input

signals including signals centered around the mid-sup-

ply voltage and signals that swing between ground and

a positive voltage in a single supply system (Figure 1).

The range of allowable input common mode voltage (the

1dB COMPRESSION

25°C

POINTS

0

–20

85°C

3RD HARMONIC

85°C

–40

3RD HARMONIC

25°C

+

–

average of V and V

in Figure 1) is determined by

IN

the power supply level and gain setting (see Distortion vs

Input Common Mode Level in the Typical Performance

Characteristics section).

–60

2ND

HARMONIC

85°C

–80

2ND HARMONIC, 25°C

–100

4

6

7

0

1

2

3

5

Common Mode DC Currents

1MHz INPUT LEVEL (V

)

P-P

660015 F06

In applications like Figure 1 and Figure 3 where the

LT6600-15notonlyprovideslowpassﬁlteringbutalsolevel

shifts the common mode voltage of the input signal, DC

currents will be generated through the DC path between

input and output terminals. Minimize these currents to

decrease power dissipation and distortion.

Figure 6. Output Level vs Input Level,

Differential 1MHz Input, Gain = 1

supply rails, the input/output behavior of the IC shown

in Figure 6 is relatively independent of the power supply

voltage.

Consider the application in Figure 3. Pin 7 sets the output

common mode voltage of the 1st differential ampliﬁer

inside the LT6600-15 (see the Block Diagram section) at

2.5V.Sincetheinputcommonmodevoltageisnear0V,there

will be approximately a total of 2.5V drop across the series

combinationoftheinternal536Ωfeedbackresistorandthe

external133Ωinputresistor.Theresulting3.7mAcommon

mode DC current in each input path, must be absorbed by

The two ampliﬁers inside the LT6600-15 have indepen-

dent control of their output common mode voltage (see

the Block Diagram section). The following guidelines will

optimize the performance of the ﬁlter.

Pin 7 must be bypassed to an AC ground with a 0.01μF or

larger capacitor. Pin 7 can be driven from a low impedance

source, provided it remains at least 1.5V above V and at

least 1.5V below V . An internal resistor divider sets the

voltage of Pin 7. While the internal 11k resistors are well

matched, their absolute value can vary by 20ꢁ. This

should be taken into consideration when connecting an

external resistor network to alter the voltage of Pin 7.

–

+

–

the sources V and V . Pin 2 sets the common mode

+

IN

output voltage of the 2nd differential ampliﬁer inside the

LT6600-15, and therefore sets the common mode output

voltage of the ﬁlter. Since, in the example of Figure 3, Pin 2

differs from Pin 7 by 0.5V, an additional 2.5mA (1.25mA

per side) of DC current will ﬂow in the resistors coupling

the 1st differential ampliﬁer output stage to ﬁlter output.

Thus, a total of 9.9mA is used to translate the common

mode voltages.

Pin 2 can be shorted to Pin 7 for simplicity. If a different

common mode output voltage is required, connect Pin 2

to a voltage source or resistor network. For 3V and 3.3V

supplies the voltage at Pin 2 must be less than or equal to

the mid supply level. For example, voltage (Pin 2) ≤ 1.65V

on a single 3.3V supply. For power supply voltages higher

than 3.3V the voltage at Pin 2 should be within the voltage

of Pin 7 – 1V to the voltage of Pin 7 + 2V. Pin 2 is a high

impedance input.

A simple modiﬁcation to Figure 3 will reduce the DC com-

mon mode currents by 40ꢁ. If Pin 7 is shorted to Pin 2

the common mode output voltage of both op amp stages

will be 2V and the resulting DC current will be 6mA. Of

course, byACcouplingtheinputsofFigure3, thecommon

mode DC current can be reduced to 2.5mA.

660015fa

9

LT6600-15

APPLICATIONS INFORMATION

Noise

2.5V

0.1μF

4

SPECTRUM

ANALYZER

INPUT

The noise performance of the LT6600-15 can be evaluated

with the circuit of Figure 7.

COILCRAFT

TTWB-1010

1:1

R

3

IN

V

IN

1

7

2

8

25ꢀ

–

+

LT6600-15

Given the low noise output of the LT6600-15 and the

6dB attenuation of the transformer coupling network, it

is necessary to measure the noise ﬂoor of the spectrum

analyzer and subtract the instrument noise from the ﬁlter

noise measurement.

50ꢀ

–

5

+

0.1μF

6

IN

660015 F07

–2.5V

Figure 7

Example: With the IC removed and the 25Ω resistors

grounded,Figure7,measurethetotalintegratednoise(e )

45

180

S

NOISE DENSITY,

GAIN = 1x

NOISE DENSITY,

GAIN = 4x

INTEGRATED NOISE,

GAIN = 1x

INTEGRATED NOISE,

GAIN = 4x

of the spectrum analyzer from 10kHz to 15MHz. With the

40

35

30

25

20

15

10

5

160

140

120

100

80

IC inserted, the signal source (V ) disconnected, and the

IN

inputresistorsgrounded,measurethetotalintegratednoise

out of the ﬁlter (e ). With the signal source connected,

O

set the frequency to 1MHz and adjust the amplitude until

V measures 100mV . Measure the output amplitude,

IN

OUT

P-P

60

V

, and compute the passband gain A = V /V . Now

OUT IN

40

compute the input referred integrated noise (e ) as:

IN

20

0

0.01

0

100

(e_O)²–(e_S)²

0.1

1

10

FREQUENCY (MHz)

e_IN=

660015 F08

A

Figure 8. Input Referred Noise, Gain = 1

Table 1 lists the typical input referred integrated noise for

various values of R .

noise power added together, the resulting calculated noise

level will be higher than the true differential noise.

IN

Figure 8 is plot of the noise spectral density as a func-

tion of frequency for an LT6600-15 using the ﬁxture of

Figure 7 (the instrument noise has been subtracted from

the results).

Power Dissipation

The LT6600-15 ampliﬁers combine high speed with large-

signal currents in a small package. There is a need to

ensure that the die junction temperature does not exceed

150°C. The LT6600-15 package has Pin 6 fused to the

lead frame to enhance thermal conduction when connect-

ing to a ground plane or a large metal trace. Metal trace

and plated through-holes can be used to spread the heat

generated by the device to the backside of the PC board.

For example, on a 3/32" FR-4 board with 2oz copper, a

total of 660 square millimeters connected to Pin 6 of the

LT6600-15 (330 square millimeters on each side of the PC

Table 1. Noise Performance

INPUT REFERRED

INTEGRATED NOISE

10kHz TO 15MHz

INPUT REFERRED

INTEGRATED NOISE

10kHz TO 30MHz

PASSBAND

GAIN (V/V)

R

IN

4

2

1

133Ω

267Ω

536Ω

36ꢂV

62ꢂV

51ꢂV

92ꢂV

RMS

109ꢂV

169ꢂV

RMS

The noise at each output is comprised of a differential

component and a common mode component. Using a

transformerorcombinertoconvertthedifferentialoutputs

tosingle-endedsignalrejectsthecommonmodenoiseand

gives a true measure of the S/N achievable in the system.

Conversely,ifeachoutputismeasuredindividuallyandthe

board) will result in a thermal resistance, θ , of about

JA

85°C/W. Without the extra metal trace connected to the

–

V pin to provide a heat sink, the thermal resistance will

be around 105°C/W. Table 2 can be used as a guide when

considering thermal resistance.

660015fa

10

LT6600-15

APPLICATIONS INFORMATION

Table 2. LT6600-15 SO-8 Package Thermal Resistance

For a given supply voltage, the worst-case power dis-

sipation occurs when the differential input signal is

maximum, the common mode currents are maximum

(see Applications Information regarding common mode

DC currents), the load impedance is small and the ambi-

ent temperature is maximum. To compute the junction

temperature, measure the supply current under these

worst-case conditions, estimate the thermal resistance

from Table 2, then apply the equation for T_J. For example,

using the circuit in Figure 3 with a DC differential input

voltage of 250mV, a differential output voltage of 1V, no

load resistance and an ambient temperature of 85°C, the

supply current (current into Pin 3) measures 50mA. As-

suming a PC board layout with a 35mm²copper trace, the

θ_JAis 100°C/W. The resulting junction temperature is:

COPPER AREA

TOPSIDE BACKSIDE BOARD AREA

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

2

(mm )

1100

330

35

1100

330

35

0

2500

65°C/W

85°C/W

95°C/W

100°C/W

105°C/W

35

0

Junction temperature, T , is calculated from the ambient

J

temperature, T , and power dissipation, P . The power

A

D

dissipation is the product of supply voltage, V , and

S

supply current, I . Therefore, the junction temperature

S

is given by:

T = T + (P • θ ) = T + (V • I • θ )

J

A

D

JA

A

S

JA

T = T + (P • θ ) = 85 + (5 • 0.05 • 100) = 110°C

J

A

D

JA

where the supply current, I , is a function of signal

S

When using higher supply voltages or when driving small

level, load impedance, temperature and common mode

voltages.

impedances, more copper may be necessary to keep T

below 150°C.

J

PACKAGE DESCRIPTION

S8 Package

8-Lead Plastic Small Outline (Narrow .150 Inch)

(Reference LTC DWG # 05-08-1610)

.189 – .197

(4.801 – 5.004)

NOTE 3

.045 ±.005

.050 BSC

7

5

8

6

.245

MIN

.160 ±.005

.150 – .157

(3.810 – 3.988)

NOTE 3

.228 – .244

(5.791 – 6.197)

.030 ±.005

TYP

1

2

3

4

RECOMMENDED SOLDER PAD LAYOUT

.010 – .020

(0.254 – 0.508)

× 45°

.053 – .069

(1.346 – 1.752)

.004 – .010

(0.101 – 0.254)

.008 – .010

(0.203 – 0.254)

0°– 8° TYP

.016 – .050

(0.406 – 1.270)

.050

(1.270)

BSC

.014 – .019

(0.355 – 0.483)

TYP

NOTE:

INCHES

1. DIMENSIONS IN

(MILLIMETERS)

2. DRAWING NOT TO SCALE

3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)

SO8 0303

660015fa

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.

11

LT6600-15

TYPICAL APPLICATION

Dual Matched I and Q Lowpass Filter and ADC

(Typical Phase Matching 1 Degree)

3V

0.1μF

V

CMA

3V

2.2μF

0.1μF

R

536ꢀ

IN

5.6pF

3

1

7

2

8

25ꢀ

–

4

+

LT6600-15

I

5.6pF

INA

0.1μF

–

5

+

5.6pF

R

IN

6

536ꢀ

LTC2299

3V

0.1μF

R

536ꢀ

IN

5.6pF

3

1

7

2

8

25ꢀ

–

4

+

LT6600-15

Q

5.6pF

INB

0.1μF

–

5

+

R

IN

6

536ꢀ

GAIN = 536ꢀ/R

IN

V

CMB

2.2μF

660015 TA02

RELATED PARTS

PART NUMBER

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LTC1566-1

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DESCRIPTION

COMMENTS

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S

LT6600-2.5

Very Low Noise Differential Ampliﬁer and 2.5MHz

Lowpass Filter

86dB S/N with 3V Supply, SO-8

82dB S/N with 3V Supply, SO-8

76dB S/N with 3V Supply, SO-8

LT6600-5

LT6600-10

LT6600-20

Very Low Noise Differential Ampliﬁer and 5MHz

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Lowpass Filter

660015fa

LT 0408 REV A • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

12

●

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


型号：	LT6600CS8-15-PBF
厂家：	Linear
描述：	Very Low Noise, Differential Amplifi er and 15MHz Lowpass Filter 非常低噪声，差分功率放大器ER和15MHz的低通滤波器放大器功率放大器
文件：	总12页 (文件大小：156K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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