On the optimal choice of the output stage in CMOS transconductors

The optimal choice of output stages in CMOS transconductors in the presence of nonideal effects is analyzed. It is shown that current folding employing source-coupled differential pairs is advantageous versus the conventional approach based on current mirrors. Two versions of a CMOS transconductor, each one using one of the mentioned approaches, have been fabricated in a 0.5μm CMOS technology and tested. Measurement results confirm the linearity improvements of current folding at the output stage.