5 Cascaded Amplifier Offset

Cascading gain stages is effective to increase the gain and bandwidth of the system, but at the cost of more noise and offset voltage at the output.

To mitigate this, a good rule of thumb is to design for most of the gain to be applied in the first stage of the amplifier circuit. This technique ensures that most of the output noise and Voso is due to the first op amp stage, with minimal contributions from later stages. In this case, a precision op amp with low Vosi and low noise in the first stage will produce the best results.

The Voso of the two-stage amplifier circuit in Figure 4-1 can be described by the following formula:

Where:

It is apparent from equation 3 that the Vosi of the first op amp is amplified by the gain of the entire system. The Vosi of the second op amp is amplified only by the gain of the second stage, lessening its impact on Voso.