Design of differential-voltage-controlled current source

General purpose, precise, d.c.-coupled, large-signal and wide-band differential-voltage-controlled current source (d.v.c.c.s.) suitable for monolithic fabrication has been designed. The transconductance is controlled by an external precision resistor and hence is linear and relatively temperature insensitive. The influence of transistor parameters and bias conditions on the behaviour of d.v.c.c.s. has been discussed. Tests on bread-boarded circuits using monolithic transistor arrays indicate a precision in transconductance of about 0.25% over a temperature range of 75 deg C, excellent linearity, and bandwidth in excess of 20 MHz.