For gains

≥10V/V, the decompensated devices

(MAX4249/MAX4255/MAX4256/MAX4257) deliver the

best distortion performance, since they have a higher

slew rate and provide a higher amount of loop gain for

a given closed-loop gain setting. Capacitive loads

below 400pF do not significantly affect distortion

results. Distortion performance remains relatively con-

stant over supply voltages.

Low Noise

The amplifier’s input-referred noise voltage density is

dominated by flicker noise at lower frequencies, and by

thermal noise at higher frequencies. Because the ther-

mal noise contribution is affected by the parallel combi-

Figure 1), these resistors should be reduced in cases

where the system bandwidth is large and thermal noise

is dominant. This noise-contribution factor decreases,

however, with increasing gain settings.

For example, the input noise voltage density of the cir-

expense of greater current consumption and potentially

Ω,

Using a Feed-Forward

The amplifier’s input capacitance is 11pF. If the resis-

tance seen by the inverting input is large (feedback

network), this can introduce a pole within the amplifier’s

bandwidth, resulting in reduced phase margin.

Compensate the reduced phase margin by introducing

input and the output (Figure 1). This effectively cancels

the pole from the inverting input of the amplifier.

In the unity-gain-stable MAX4250–MAX4254, the use

mula above achieves a higher bandwidth at the

expense of reduced phase and gain margin. As a gen-

greater than 5k

Ω (MAX4249/MAX4255/MAX4256/

MAX4257).

SOT23, Single-Supply, Low-Noise,

Low-Distortion, Rail-to-Rail Op Amps

_______________________________________________________________________________________

9

(100mV/

div)

0mV

100mV

(50mV/

div)

2

µs/div

Figure 1. Adding Feed-Forward Compensation

Figure 2a. Pulse Response with No Feed-Forward

Compensation

100mV/

div

0mV

100mV

50mV/

div

2

µs/div

Figure 2b. Pulse Response with 10pF Feed-Forward

Compensation