Parametric Amplifier

parametric amplifier [¦par·ə¦me·trik ′am·plə‚fī·ər]

(electronics)

A highly sensitive ultra-high-frequency or microwave amplifier having as its basic element an electron tube or solid-state device whose reactance can be varied periodically by an alternating-current voltage at a pumping frequency. Also known as mavar; paramp; reactance amplifier.

(optics)

A device consisting of an optically nonlinear crystal in which an optical or infrared beam draws power from a laser beam at a higher frequency and is amplified.

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Parametric Amplifier 

a radio-electronic device in which the power level of a signal is increased by means of energy from an external source—a pump—that periodically varies the capacitance or inductance of a nonlinear reactive element in the electric circuit of the amplifier. Parametric amplifiers are used mainly in radio astronomy, in long-range space and satellite communication, and in radar low-noise amplifiers of weak signals at the input of radio-receiving equipment, principally in the

Figure 1. Equivalent circuits of parametric amplifiers: (a) negative resistance amplifier, (b) amplifying-up converter. Symbols: (u_in) input signal at carrier frequency f_x; (u_in) pump voltage; (u_out) output signal at carrier frequency f_x; (u_out) output signal at carrier frequency (f_s+ f_p);(Tr₁) input transformer; (Tr₂) output transformer; (Tr_p) transformer in the pump circuit; (D) varactor diode; (L) inductance coil in the oscillatory circuit tuned to the frequency (f_s + f_p); (Φ_s), (Φ_sp), and (Φ_p) electric filters that have low impedance at, respectively, the frequencies f_s, (f_s + f_p), and f_o and sufficiently high impedance at all other frequencies.

superhigh-frequency range. The reactive element commonly used in these amplifiers is a varactor diode. In addition, electron-beam parametric amplifiers are used in the superhigh-frequency range, and ferrite, or ferromagnetic, in the low-frequency (audiofrequency) region.

Two-frequency, or two-circuit, parametric amplifiers are the most common. In the centimeter range these are negative resistance amplifiers that maintain the signal frequency (Figure 1,a), and for the decimeter range these are amplifying-up converters (Figure 1,b). The receiving oscillatory circuit and the oscillatory circuit tuned to the auxiliary, or idler, frequency (which is usually equal to the difference or the sum of the signal and pump frequencies) are generally in the form of cavity resonators containing varactor diodes. The pumps use avalanche transit time diodes, Gunn diodes, varactor frequency multipliers, and, more rarely, reflex klystrons. In most cases, the pump and the idler frequencies are chosen close to the critical frequency f_cr of the varactor diode—that is, close to the frequency at which the parametric amplifier no longer amplifies; in addition, the signal frequency must be substantially less than f_cr. In order to achieve minimal noise temperatures (10°-20°K or less), parametric amplifiers are cooled to the temperature of liquid nitrogen (77°K), the temperature of liquid helium (4.2°K), or intermediate temperatures (usually 15°-20°K). For amplifiers that are not cooled, the noise temperature is 50°-100°K or more. The maximum obtainable gain and bandwidth of a parametric amplifier depend basically on the parameters of the reactive element. Power gains of 10 to 30 decibels and bandwidths of 10 to 20 percent of the signal carrier frequency have been achieved.

REFERENCES

Etkin, V. S., and E. M. Gershenzon. Parametricheskie sistemy SVCh na poluprovodnikovykh diodakh. Moscow, 1964.
Lopukhin, V. M., and A. S. Roshal’. Elektronnoluchevye parametricheskie usiliteli. Moscow, 1968.
SVCh—poluprovodnikovye pribory i ikh primenenie. Moscow, 1972. (Translated from English.)
Kopylova K. F., and N. V. Terpugov. Parametricheskie emkostnye usiliteli nizkikh chastot. Moscow, 1973.
Penfield, P., and R. Rafuse. Varactor Applications Cambridge, Mass., 1962.

V. S. ETKIN