Parametric Semiconductor Diode

a semiconductor diode belonging to the group of varactor diodes whose operating principle is based on the dependence of the capacitance of a p-n junction on the voltage applied to it.

Parametric semiconductor diodes are used as variable capacitance elements in the oscillatory circuits of parametric amplifiers —the use of a p-n junction for this purpose was first suggested by B. M. Vul in 1954. The diode is supplied with a DC reverse bias (usually between 0.3 and 2.0 volts) and two superhigh-frequency AC signals (up to several hundred gigahertz)—a signal from a pump oscillator and the signal that is being amplified. Parametric semiconductor diodes are characterized by a low intrinsic noise level, which depends basically on the resistance of the semiconductor material and on its temperature. In order to raise the upper limit of the frequency band for the amplified oscillations, the diode’s capacitance at the operating point Co and time constant τ_s = r_s• C₀ are kept small; here r_s is the sum of the resistances of the volume of the diode adjoining the p-n junction and of the contacts. The power of the pump oscillations is limited by the permissible value of the reverse voltage U_per on the diode.

Parametric semiconductor diodes are usually made from silicon, germanium, or gallium arsenide. The values of the basic parameters of the parametric semiconductor diodes manufactured in the USSR and abroad are C₀ = 0.01 to 2 picofarads, τ_S = 0.1 to 2 picoseconds, and U_per = 6 to 10 volts; the operating-temperature range is from 4° to 350°K.