LT1010CDD datasheet(10/20 Pages) LINER

10 / 20 page

LT1010

1010fc

APPLICATIO S I FOR ATIO

This is a good example of how fast op amps can be made

quite easy to use by employing an output buffer.

Integrator

A lowpass amplifier can be formed just by using large CF

in the inverter described earlier, as long as the increasing

closed-loop output impedance above the cutoff frequency

is not a problem and the op amp is capable of supplying

the required current at the summing junction.

LT1010

20k

500pF

IIN

1010 AI07

VOUT

–

LT1012

BIAS

LT1010

µF

TYPICAL SPECIFICATIONS

1VP-P INTO 75Ω

AT A = 2

0.5dB TO 10MHz

3dB DOWN AT 16MHz

AT A = 10

0.5dB TO 4MHz

–3dB = 8MHz

µF

1010 AI08

PEAKING

5pF to 25pF

Ω

900

Ω

OUTPUT

(75

Ω)

0.01

µF

GAIN SET

5.1k

Q1, Q2: 2N3866

–15V

8.2k

15V

–15V

INPUT

stage. Feedback is arranged in the conventional manner,

although the 68

µF-0.01µF combination limits DC gain to

unity for all gain settings. For applications sensitive to

NTSC requirements, dropping the 25

Ω output stage bias

value will aid performance.

If the integrating capacitor must be driven from the buffer

output, the circuit above can be used to provide capacitive

load isolation. As before, the stability with large capacitive

loads is determined by RFCF.

Wideband Amplifiers

This simple circuit provides an adjustable gain video

amplifier that will drive 1VP-P into 75Ω. The differential

pair provides gain with the LT1010 serving as an output

LT1010

100

Ω

800

Ω

15pF

VIN

1010 AI09

VOUT

–

HA2625

LT1010

400

Ω

1.6k

INPUT

1010 AI10

OUTPUT

–

HA2625

This shows the buffer being used with a wideband ampli-

fier that is not unity-gain stable. In this case, C1 cannot be

used to isolate large capacitive loads. Instead, it has an

optimum value for a limited range of load capacitances.

The buffer can cause stability problems in circuits like

this. With the TO-220 packages, behavior can be im-

proved by raising the quiescent current with a 20

Ω

resistor from the bias terminal to V+. Alternately, devices

in the miniDIP can be operated in parallel.

It is possible to improve capacitive load stability by

operating the buffer class A at high frequencies. This is

done by using quiescent current boost and bypassing the

bias terminal to V– with more than 0.02

µF.

Putting the buffer outside the feedback loop as shown

here will give capacitive load isolation, with large output

capacitors only reducing bandwidth. Buffer offset, re-

ferred to the op amp input, is divided by the gain. If the

load resistance is known, gain error is determined by the

output resistance tolerance. Distortion is low.

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