9

LT1354

Large-Signal Transient

Large-Signal Transient

1354 TA34

1354 TA35

1354 TA36

Large-Signal Transient

The LT1354 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 LT1354 is

shown below.

Offset Nulling

1354 AI01

6

7

4

8

1

2

10k

3

–

+

LT1354

Layout and Passive Components

The LT1354 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

µF to

0.1

µF). For high drive current applications use low ESR

bypass capacitors (1

µFto10µFtantalum).Socketsshould

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 LT1354 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 43% 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

series with the output. The other end of the cable should

be terminated with the same value resistor to ground.