LT1228

1

1228fd

TYPICAL APPLICATION

FEATURES

DESCRIPTION

100MHz Current Feedback

Amplifier with DC Gain Control

gain of signals from DC to video frequencies. The LT1228

implements gain control with a transconductance ampli-

fier (voltage to current) whose gain is proportional to an

externally controlled current. A resistor is typically used

to convert the output current to a voltage, which is then

amplified with a current feedback amplifier. The LT1228

combines both amplifiers into an 8-pin package, and oper-

ates on any supply voltage from 4V (±2V) to 30V (±15V).

A complete differential input, gain controlled amplifier can

be implemented with the LT1228 and just a few resistors.

TheLT1228transconductanceamplifierhasahighimped-

ancedifferentialinputandacurrentsourceoutputwithwide

holds over several decades of set current. The voltage at

Pin 5 is two diode drops above the negative supply, Pin 4.

The LT1228 current feedback amplifier has very high input

impedanceandthereforeitisanexcellentbufferfortheout-

putofthetransconductanceamplifier.Thecurrentfeedback

amplifiermaintainsitswidebandwidthoverawiderangeof

voltage gains making it easy to interface the transconduc-

tance amplifier output to other circuitry. The current feed-

back amplifier is designed to drive low impedance loads,

suchascables,withexcellentlinearityathighfrequencies.

APPLICATIONS

n

Very Fast Transconductance Amplifier

Bandwidth: 75MHz

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Very Fast Current Feedback Amplifier

Bandwidth: 100MHz

Slew Rate: 1000V/µs

Output Drive Current: 30mA

Differential Gain: 0.04%

Differential Phase: 0.1°

High Input Impedance: 25MΩ, 6pF

n

Wide Supply Range: ±2V to ±15V

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Inputs Common Mode to Within 1.5V of Supplies

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Outputs Swing Within 0.8V of Supplies

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Supply Current: 7mA

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Available in 8-Lead PDIP and SO Packages

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Video DC Restore (Clamp) Circuits

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Video Differential Input Amplifiers

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Video Keyer/Fader Amplifiers

n

AGC Amplifiers

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Tunable Filters

n

Oscillators

L

, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

LT1228 • TA01

–

+

–

+

+

R3A

10k

R2A

10k

R3

100Ω

R2

100Ω

4.7µF

R4

1.24k

R6

6.19k

R5

10k

R1

270Ω

10Ω

470Ω

4.7µF

15V

CFA

1

8

6

3

2

7

5

4

–15V

+

–

HIGH INPUT RESISTANCE

EVEN WHEN POWER IS OFF

–18dB < GAIN < 2dB

FREQUENCY (Hz)

100k

–24

–15

–3

3

6

1M

10M

100M

LT1228 • TA02

0

–6

–9

–12

–18

–21

Differential Input Variable Gain Amp

Frequency Response