Dual-Current Sink for Digital-To-Analog Converter
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
A high accuracy dual-current sink from a single output current sink digital-to-analog converter (DAC) is shown in the figure. The DAC module in the figure requires a current reference IREF . This current is generated by using an operational amplifier (op-amp) A3 buffer to a 1% zener diode 11. IREF = V2/R3 The output current Io = IREF x [Binary Digital Input] where all ones input = 2n-1 x IREF . 2n The head driver module for a printer has 2 chips, each which needs a digitally controlled current reference which is referenced to the rail voltage. Since the DAC has only 1 output Io, the circuit comprising components A1, A2, Q1, Q2, R1, R2 is used to generate IR1 and IR2 . R1 and R2 are in an R pac and their ratio is important but their absolute value is not.