9

LT1357

Large-Signal Transient

Large-Signal Transient

1357 TA34

1357 TA35

1357 TA36

Large-Signal Transient

The LT1357 may be inserted directly into many high

speed amplifier applications improving both DC and AC

performance, provided that the nulling circuitry is

removed. The suggested nulling circuit for the LT1357 is

shown below.

Offset Nulling

1357 AI01

6

7

4

8

1

2

10k

3

–

+

LT1357

Layout and Passive Components

The LT1357 amplifier is easy to apply and tolerant of less

than ideal layouts. For maximum performance (for

example, fast settling time) use a ground plane, short lead

lengths and RF-quality bypass capacitors (0.01

µFto0.1µF).

For high drive current applications use low ESR bypass

capacitors (1

µF to 10µF tantalum). Sockets should be

avoided when maximum frequency performance is

required, although low profile sockets can provide

reasonable performance up to 50MHz. For more details

see Design Note 50.

The parallel combination of the feedback resistor and gain

setting resistor on the inverting input can combine with

the input capacitance to form a pole which can cause

peaking or oscillations. For feedback resistors greater

than 5k

Ω, a parallel capacitor of value

should be used to cancel the input pole and optimize

dynamic performance. For unity-gain applications where

Capacitive Loading

The LT1357 is stable with any capacitive load. This is

accomplished by sensing the load induced output pole and

adding compensation at the amplifier gain node. As the

capacitive load increases, both the bandwidth and phase

margin decrease so there will be peaking in the frequency

domain and in the transient response as shown in the

typical performance curves.The photo of the small-signal

response with 1000pF load shows 50% peaking. The

large-signal response with a 10,000pF load shows the

output slew rate being limited to 5V/

µs by the short-circuit

current. Coaxial cable can be driven directly, but for best

pulse fidelity a resistor of value equal to the characteristic

impedance of the cable (i.e., 75

Ω) should be placed in