A current feed-back instrumentation amplifier (CFIA) comprises a differential pair with degeneration for amplifying small differential voltages in the presence of large common-mode voltages. The CFIA includes input and feedback transconductors and a trimming circuit that trims the back-bias voltages of the transistors in each transconductor. The trimming circuit includes a plurality of selectable resistors disposed in the signal path of the tail current in each transconductor. Each of the plurality of selectable resistors has a switch coupled to it. When a switch is closed, only the resistors up to the respective switch are in the signal path of the bulk-to-source voltage of the differentially paired transistors. The resistor trimming circuit reduces the mismatch between transconductances of the respective differential pair transistors, in turn reducing mismatch of the overall transconductances of the transconductors, and thereby reducing the CFIA's gain error.

To perform a rail-to-rail input operation, provided is a differential amplifier circuit including a first differential input pair and a second differential input pair which has a threshold value different from that of the first differential input pair. Both the differential input pairs do not operate at the same time. A transistor is connected between the first differential input pair and a current source to achieve a configuration in which the first differential input pair and the second differential input pair do not operate at the same time.

A transconductor circuitry (10) with adaptive biasing comprises a first input terminal (E10a) to apply a first input signal (inp), and a second input terminal (E10b) to apply a second input signal (inn). A control circuit (200) is configured to control a first controllable current source (110) in a first current path (101) and a second controllable current source (120) in a second current path (102) in response to at least one of a first potential of a first node (N1) of the first current path (101) and a second potential of a second node (N2) of the second current path (102). The first node (N1) is located between a first transistor (150) and the first controllable current source (110), and the second node (N2) is located between a second transistor (160) and the second controllable current source (120).