LT1124 datasheet(9/16 Pages) LINER

9 / 16 page

LT1124/LT1125

High Speed Operation

When the feedback around the op amp is resistive (RF),

a pole will be created with RF, the source resistance and

capacitance (RS, CS), and the amplifier input capacitance

(CIN ≈ 2pF). In low closed loop gain configurations and

with RS and RF in the kilohm range, this pole can create

excess phase shift and even oscillation. A small capacitor

(CF) in parallel with RF eliminates this problem (see

Figure 2). With RS (CS + CIN) = RFCF, the effect of the

feedback pole is completely removed.

During the fast feedthrough-like portion of the output, the

input protection diodes effectively short the output to the

input and a current, limited only by the output short circuit

protection, will be drawn by the signal generator. With RF

≥500Ω, the output is capable of handling the current

requirements (IL ≤ 20mA at 10V) and the amplifier stays

in its active mode and a smooth transition will occur.

Noise Testing

Each individual amplifier is tested to 4.2nV/

√Hz voltage

noise; i.e., for the LT1124 two tests, for the LT1125 four

tests are performed. Noise testing for competing multiple

op amps, if done at all, may be sample tested or tested

using the circuit shown in Figure 4.

en OUT = √(enA)2 + (enB)2 + (enC)2 + (enD)2

If the LT1125 were tested this way, the noise limit would

√ 4 • (4.2nV/√Hz)2 = 8.4nV/√Hz. But is this an effective

screen? What if three of the four amplifiers are at a typical

2.7nV/

√Hz, and the fourth one was contaminated and has

6.9nV/

√Hz noise?

RMS Sum =

√(2.7)2 + (2.7)2 + (2.7)2 + (6.9)2 = 8.33nV/√Hz

This passes an 8.4nV/

√Hz spec, yet one of the amplifiers

is 64% over the LT1125 spec limit. Clearly, for proper

noise measurement, the op amps have to be tested

individually.

APPLICATI

I FOR ATIO

–

1124/25 F03

OUTPUT

4.5V/

µs

Figure 3. Unity-Gain Buffer Applications

1124/25 F04

–

OUT

Figure 4. Competing Quad Op Amp Noise Test Method

–

OUTPUT

1124/25 F02

CIN

Figure 2. High Speed Operation

Unity Gain Buffer Applications

When RF ≤ 100Ω and the input is driven with a fast, large

signal pulse (>1V), the output waveform will look as

shown in Figure 3.

LT1124 Scheda tecnica(PDF) 9 Page - Linear Technology

LT1124 Scheda tecnica(HTML) 9 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Scheda tecnica Scarica

Link URL