Shot noise in microwave parametric amplifiers using gallium-arsenide varactors

Measurements of forward-current shot noise in a 4GHz parametric amplifier using a gallium-arsenide varactor are compared with simple theory. Good agreement is obtained for low diode currents (a few microamperes) and low pump levels (or low input/output impedances), but at higher currents or higher pump levels an additional noise source must be included, thought to be due to significant current from stored minority carriers.