Voltage to current converter

Claim 1

A voltage to current converter circuit having a high input impedance and zero temperature coefficient for providing an accurate output current from an input voltage, said circuit comprising: an input circuit for accepting applied voltages, including first and second transistors arranged to provide a high input impedance, third and fourth mirror connected transistors arranged as an output current mirror and having commonly connected base electrodes, an impedance connected between the emitter electrode of said second transistor and said fourth transistor, fifth and sixth mirror connected transistors connected respectively to the emitter of said second transistor and to the collector of said third transistor to ensure that the current flow through said input circuit equals the current flow through said output current mirror, means, including a seventh transistor for compensating for the base to emitter voltage drop of said first transistor, said compensating transistor having its base connected to said impedance and its emitter connected to said base of said fourth transistor, said fourth transistor functioning to compensate for the base to emitter voltage drop of said second transistor, an output circuit including an eighth transistor having its base electrode connected to said commonly connected base electrodes of said output current mirror, and clamping means responsive to said input voltage for providing an output current whenever said input voltage decreases below a predetermined threshold.