The typical three-op-amp topology gains up the input differential signal in the front stage and rejects the common-mode signals in the back end at the difference amplifier stage. The difficulty in particular is to excel driving high gains, and thus tiny input signals, and still be able to reject high common-mode signals. A low-noise instrumentation amplifier such as the INA848 is designed for such requirementsh, with the ability to measure the smallest input signals surrounded by noisy or large common-mode voltages.

The methodology here is achieved by splitting up the gain stages. The front end preamplifies the input signal at a gain of 200, and the difference amplifier further amplifiers at a gain of 10. The resulting advantage is that the common-mode range versus the differential signal is improved compared to single gain stage approach, as shown in Figure 8-2.

The INA848 gives the super-beta input stage features very low input bias current as compared to standard bipolar technology. The low input bias current and current noise make the INA848 an excellent choice for high-performance applications. See Figure 7-10 through Figure 7-12 for reference.