1

LT1251/LT1256

40MHz Video Fader and

DC Gain Controlled Amplifier

Two-Input Video Fader

–

+

–

+

IN1

IN2

2.5VDC

INPUT

1.5k

1.5k

NULL

1251/56 TA01

0V TO 2.5V

CONTROL

2

–

+

–

+

1

2

3

4

5

6

7

14

13

12

11

10

9

8

CONTROL

LT1251/LT1256

1

CFS

5k

5k

LT1256

Gain Accuracy vs Control Voltage

FEATURES

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Accurate Linear Gain Control:

s

Constant Gain with Temperature

s

Wide Bandwidth: 40MHz

s

High Slew Rate: 300V/

µs

s

Fast Control Path: 10MHz

s

Low Control Feedthrough: 2.5mV

s

High Output Current: 40mA

s

Low Output Noise

45nV/

270nV/

s

Low Distortion: 0.01%

s

Wide Supply Range:

±2.5V to ±15V

s

Low Supply Current: 13mA

s

Low Differential Gain and Phase: 0.02%, 0.02

°

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

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Composite Video Gain Control

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RGB, YUV Video Gain Control

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Video Faders, Keyers

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Gamma Correction Amplifiers

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Audio Gain Control, Faders

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Multipliers, Modulators

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Electronically Tunable Filters

The LT

rent feedback amplifiers with a linear control circuit that

sets the amount each input contributes to the output.

These parts make excellent electronically controlled vari-

able gain amplifiers, filters, mixers and faders. The only

external components required are the power supply by-

pass capacitors and the feedback resistors. Both parts

operate on supplies from

±2.5V (or single 5V) to ±15V

(or single 30V).

Absolute gain accuracy is trimmed at wafer sort to mini-

mize part-to-part variations. The circuit is completely

temperature compensated.

The LT1251 includes circuitry that eliminates the need for

accurate control signals around zero and full scale. For

control signals of less than 2% or greater than 98%, the

LT1251 sets one input completely off and the other

completely on. This is ideal for fader applications because

it eliminates off-channel feedthrough due to offset or gain

errors in the control signals.

The LT1256 does not have this on/off feature and operates

linearly over the complete control range. The LT1256 is

recommended for applications requiring more than 20dB

of linear control range.

CONTROL VOLTAGE (V)

0

5

4

3

2

1

0

–1

–2

–3

–4

–5

2.0

1251/56 TA02

0.5

1.0

1.5

2.5

100