When balancing bandwidth, offset, and
noise in a high-gain, multi-stage amplifier:
- Use the lowest input offset op
amps that are practical and cost permits.
- If different op amps are used in
a cascade, use the lowest offset/noise op amp in the first stage.
- If low offset/noise is the
highest priority, apply the highest closed-loop gain in the first stage.
- If bandwidth is the highest
priority, a more even distribution of gain across stages is appropriate.
- Expect a greater variance in Voso
across multiple boards due to Gaussian distributions of Vosi for each stage.
Higher closed-loop gain in the first stage will result in less variance.
- Use small resistor values to keep
the thermal noise well below the intrinsic noise of the op amp
- A low source impedance and a low
parallel combination of the feedback resistor network (Req) will
reduce the effects of current noise.
As discussed, high-gain applications
typically require multiple stages to provide the desired bandwidth and performance.
Precision op amps, especially in the early stages of a cascaded amplifier will
provide the best performance. The dual-channel op amps recommended below can
simplify layout and save board space when multiple stages are necessary.