Characterization of MOS differential pair current offsets due to parameter variations

The MOSFET differential pair is an important building block for a wide variety of analog integrated circuit applications. Designing with differential pairs necessitates knowledge of offset currents resulting from differences between the individual FETs that compose the pair. In this paper, we have developed an offset model for a MOSFET differential pair. By fitting the model to measured offsets at selected biases, estimates of MOS parameter variations can be extracted. An equivalent circuit for implementation of the offset in SPICE is also presented.