Amplifier compensation circuits and methods

A frequency-compensated amplifier circuit 100 comprises a multi-stage amplifier 102 having an input node 104, an output node 106 and an intermediate node 118. A first feedback path 110 from the output node to the input node comprises a feedback resistance RFA and RFB. A second feedback path 112 between the output node and the intermediate node comprises a first capacitor Cc and a portion of the feedback resistance. A switching circuit 114, which may be a multiplexor, connects the capacitor to the feedback resistance. The switch 114 may connect the capacitor to various tap points on the feedback resistance, thereby controlling the value of the resistance in the second feedback path 112 and hence the frequency compensation applied to the amplifier (fig.8). The amplifier may be controlled to give wide bandwidth at switch-on, allowing fast settling, and then set for reduced bandwidth, which may reduce noise. The fast settling may allow the amplifier to be powered up for shorter periods, when required to sample a sensor signal. An instrumentation amplifier based the amplifier circuit is disclosed (fig.5).