Currently I'm using a Microchip PGA for applying gain factors of 1, 2, 4, 8, 16 and 32. It's used in a design of strain gauge amplifier. The part number is MCP6S21 and I am happy with its performance in these areas listed below: -
- Noise - it doesn't seem to introduce any but there is a large gain stage preceding it. It is specified as having 10nV / \$\sqrt{Hz}\$ but like I say, the circuit isn't challenging in this area.
- Input offset voltage is quite good at +/-275uV and I expect, at the output this could be up to 32 times higher on maximum gain. Again, this is easily acceptable for the product.
- Gain error is +/-1% - providing this is a stable gain error with temperature then no problem. The MCP6S21 is specified as having a gain drift of ±0.0004% per deg C
- Bandwidth and slew rate are flat easily beyond 100kHz at all gains.
The input to the PGA is from an op-amp and the PGA feeds an ADC via a low-pass RC filter i.e. the output isn't feeding a low-load and the input impedance could be a few hundred ohms without too much bother.
There may be better PGAs that are rail-to-rail input/output devices but does a digital pot combined with an op-amp come close to challenging this "moderate" level of performance?