Current-feedback operational amplifier

The classic four-resistor differential amplifier configuration also works with a CFA, but the common-mode rejection ratio is poorer than that from a VFA.

Referring to the schematic shown, the section marked in red forms the input stage and error amplifier.

In practice, due to device mismatches, the collector currents are unequal, resulting in the difference flowing into the buffer's input and an offset at its output.

Due to the wide open-loop bandwidth of a CFA, there is a high risk of the circuit breaking into oscillations.

Cs ensures that frequencies, where oscillations might start are attenuated, especially when running with a low closed-loop gain.

When fabricated using high-speed complementary bipolar processes, CFAs can be orders of magnitude faster than VFAs.

CFA circuits must never include a direct capacitance between the output and inverting input pins as this often leads to oscillation.

The current-feedback operational amplifier is a type of current controlled voltage source (CCVS).