Bidirectional CMOS DAC CURRENT Switch
Original Publication Date: 1988-Jun-01
Included in the Prior Art Database: 2005-Feb-15
A digital-to-analog converter (DAC) with accurate bidirectional current output can be built as shown in Fig. 1 using a bidirectional CMOS DAC current switch shown in Fig. 2. To build a DAC of this nature using a traditional one direction DAC requires an accurate current mirror to be dotted with the DAC to provide both source and sink capability. Due to (Image Omitted) inaccuracies in the mirror, the middle input code (zero output current) can be offset from zero by several least significant bits (LSBs). If the DAC is built using the switch shown in Fig. 2, the middle input code causes zero output current. Errors in the mirrors of this DAC cause a mismatch between sourcing and sinking currents of the same magnitude.