Presently using two cascading amplifiers, and feeding in a very low voltage. The first stage gain is set to 84 and the second stage gain can be varied using a digital potentiometer to ensure that the circuit is tuned to give us the best range depending upon the source that we are using. Once tuned the digital potentiometer is set and does not vary. the second stage gain can be set between 7 and 67. This circuit is working for most input sources that we manufacture, but if the input source is at the higher end, and the gain on the second stage is at the lower end we are finding that the second amplifier appears to saturate well before we expect it to. typically it saturates at about 2.8v, but with the lower second stage gain we are finding that it saturates at about 2.1v (supply voltage of 3v).
We are using a TLV2254 chip, and have a voltage on the -'ive input of the amplifier to provide a small offset.
Any ideas where we are going wrong?
