Correction circuit for beta mismatch between thermometer encoded and R-2R ladder segments of a current steering DAC

摘要

A current correction circuit 500 eliminates beta mismatches between a thermometer encoded segment 102 and a R-2R ladder segment 106 of a current steering digital-to-analog converter 100. The circuit 500 consists of three replica MSB unit current sources, I₁, I₂ and I₃. The replica current I₁ acts as a replica to a cascode device 206 of the MSB unit 200 of the current steering DAC 100. The replica current I₂ replicates an effective base current equal to the total base current in the R-2R ladder circuit portion 300 of the current steering DAC 100. The replica current I₃ replicates the total base current of the L output switches 310 in the LSB segment 106 of the current steering DAC 100. A high impedance summing node 506 produces a correction current I_COR=I₁−(I₂+I₃). This current is equal to the current difference between an MSB unit 200 and the LSB segment 106. This correction current is then subtracted from the MSB unit current source 200 that supplies current into the R-2R ladder 300 such that the current supplied to the R-2R ladder 300 will be equal to the MSB replica current source minus the correction current.