High impedance current source

Claim 1

A high impedance current source comprising: a voltage-to-current transducer having a current output terminal, a positive input terminal with a first input resistor extending therefrom, and a negative input terminal with a second input resistor extending therefrom, the first and second input resistors being substantially equal and receptive of a control voltage therebetween; a monitor resistor connected between the output terminal and an output point; a first feedback resistor connected between the output terminal and the negative input terminal; and a second feedback resistor connected between the output point and the positive input terminal, the first and second feedback resistors being substantially equal, the feedback resistors and the input resistors each being substantially greater than the monitor resistor, whereby the current output point constitutes a high impedance source of current, the current having a magnitude proportional to the control voltage, wherein the current output point communicates the current through a load to a base terminal, and the apparatus further comprises a pair of substantially equal grounding resistors each being connected between a different one of the input terminals and the base terminal and being substantially greater than the monitor resistor.