The circuit described delivers small current pulses from a high impedance source. The 20 nsec pulse enables the circuit to be used as a charge source, variable from 10−15to >10−12C/pulse, for testing charge sensitive amplifiers. Rates up to 107pps are available. An external gate input enables pulse bursts to be obtained, and single shot operation is possible, either manually or remotely triggered. A simple calibration check can be used.