Voltage to current conversion circuit

Claim 1

An improved multiplier circuit for providing an analog output signal which is proportional to the product of two binary numbers including: a first digital-to-analog converter means for receiving a binary input and for producing a reference output voltage proportional to the binary input; a second digital-to-analog converter, said second digital-to-analog circuit including an input reference resistor; a current ladder means including a plurality of transistors for controlling the magnitude of current flow at successive binary digit flow points in said ladder in accordance with the reference output voltage applied to said reference resistor from said first digital-to-analog converter, wherein the improvement involves an improved circuit for biasing said ladder current control transistors comprising: first and second transistors connected to receive current in parallel from said reference resistor; third and fourth mirror connected transistors connected respectively in series with said first and second transistors to insure substantially proportional flow of current in the two parallel paths including said first and third, and said second and fourth transistors; means including a fifth transistor having its emitter-to-base circuit connected from a fixed voltage level to the emitter-to-base circuit of said first transistor and its collector to the collector of said first transistor, to hold the output from said reference resistor virtually at said fixed voltage level; and means for supplying bias current from the bases of said mirror-connected third and fourth transistors to said ladder current control transistors.