Harmonic distortion in switched-current audio memory cells

Harmonic distortion in switched-current memory cells is investigated, and closed-form equations are presented concerning the effects of threshold voltage mismatch, signal dependent output conductance, and clock injection. We show that output conductance can be the main source of distortion in basic cells, but clock injection is dominant in regulated cascode (RgC), grounded-gate regulated cascode, and Shah-Toumazou cells. Concerning the V-I converter, we show that if this is simply a resistor at the input of either a GGRgC or an RgC Shah-Toumazou cell, the resulting distortion is very low. Our results have been confirmed by SPICE simulations and by measurements made on two 1.2 /spl mu/m CMOS prototype chips.