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ADA4638-1

Data Sheet

Rev. 0 | Page 16 of 24

APPLICATIONS INFORMATION

The ADA4638-1, with its wide supply voltage range of 4.5 V to

30 V, is a precision, rail-to-rail output, zero-drift operational

amplifier that features a patented combination of auto-zeroing

and chopping technique. This unique topology allows the

ADA4638-1 to maintain its low offset voltage over a wide tempera-

ture range and over its operating lifetime. This amplifier offers

ultralow input offset voltage of 4.5 μV maximum and an input

offset voltage drift of 80 nV/°C maximum. Offset voltage errors

due to common-mode voltage swings and power supply varia-

tions are also corrected by the auto-zeroing and chopping tech-

nique, resulting in a superb typical CMRR figure of 142 dB and

a PSRR figure of 143 dB at a ±15 V supply voltage. With ultrahigh

dc accuracy and no 1/f noise component, the ADA4638-1 is

ideal for high gain amplification of low level signals in dc or low

frequency applications without the risk of excessive output

voltage errors.

DIFFERENTIATION

Traditionally, zero-drift amplifiers are designed using either the

auto-zeroing or chopping technique. Each technique has its

benefits and drawbacks. Auto-zeroing usually results in low

noise energy at the auto-zeroing frequency, at the expense of

higher low frequency noise due to aliasing of wideband noise

into the auto-zeroed frequency band. Chopping results in lower

low frequency noise at the expense of larger noise energy at the

chopping frequency. The ADA4638-1 uses both auto-zeroing

and chopping in a patented ping-pong arrangement to obtain

lower low frequency noise together with lower energy at the

chopping and auto-zeroing frequencies, maximizing the signal-

to-noise ratio for the majority of applications. The relatively

high chopping frequency of 16 kHz and auto-zeroing frequency

of 8 kHz simplifies filter requirements for a wide, useful

bandwidth.

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