LT1227C 查看數據表（PDF） - Linear Technology

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LT1227C

140MHz Video Current Feedback Amplifier

Linear Technology 

LT1227

TYPICAL APPLICATI S

MUX Amplifier

The shutdown function can be effectively used to con-

struct a MUX amplifier. A two-channel version is shown,

but more inputs could be added with suitable logic. By

configuring each amplifier as a unity-gain follower, there

is no loading by the feedback network when the amplifier

is off. The open drains of the 74C906 buffers are used to

interface the 5V logic to the shutdown pin. Feedthrough

from the unselected input to the output is –70dB at

10MHz. The differential voltage between MUX inputs VIN1

and VIN2 appears across the inputs of the shutdown

device, this voltage should be less than ±5V to avoid

turning on the clamp diodes discussed previously. If the

inputs are sinusoidal having a zero DC level, this implies

that the amplitude of each input should be less than

5VP-P. The output impedance of the off amplifier remains

high until the output level exceeds approximately 6VP-P at

10MHz, this sets the maximum usable output level. Switch-

ing time between inputs is about 4µs without an external

pullup. Adding a 10k pullup resistor from each shutdown

pin to V+ will reduce the switching time to 2µs but will

increase the positive supply current in shutdown by 1.5mA.

MUX Output

VOUT

INPUT

SELECT

VIN1 = 1VP-P, VIN2 = 0V

TA03

VIN1

VOUT

VIN

=1

VIN2

INPUT

SELECT

MUX Amplifier

15V

+

LT1227 S/D

–

VOUT

–15V

1.5k

5V

74C906

15V

+

LT1227 S/D

–

–15V

1.5k

5V

5V

74HC04

74C906

1227 TA04

MUX Input Crosstalk vs Frequency

–40

–50

–60

–70

–80

–90

1

10

FREQUENCY (MHz)

100

LT1227 TA05

10

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