Negative Resistance Amplifier Research Articles

Shot Noise in p-n Junction Frequency Converters*

General equations are derived for the noise figure of a frequency converter using a p-n junction diode with arbitrary minority-carrier storage. A p-n junction with a purely capacitive nonlinear admittance permits, theoretically, noiseless amplification. Structures are suggested for approximating this ideal. A diffused silicon junction diode gave 9 db of gain with a 2-db noise figure in converting 460 to 9375 mc and gave a 3-db noise figure as a 6000-mc negative-resistance amplifier. Nonlinear-resistance diodes cannot amplify but can give low-noise frequency conversion if the local-oscillator drive produces a sharply pulsed current waveform in the diode.

Microwave amplification by means of intrinsic negative resistances

Intrinsic-negative-resistance amplifiers with matched input, known for some time at low frequencies, are easily transposed at microwave frequencies. With amplifiers based on the parallel coupling of load and negative conductance, a unidirectional line can ensure or improve separation between input and load. In another circuit a circulator is used. The two-way amplifier, consisting of a T-network, can be so realized that matching persists if the two negative conductances vary in common. The gain of any negative-resistance amplifier is practically limited by the diminution in amplitude stability, the increase in harmonic distortion and the reduction in bandwidth. In the best cases, the expressions defining the limiting quantities contain the gain to the power of one-half. The noise figure increases as a linear function of gain in the case of the previously matched circuit, but does not depend on the gain in the other circuits. Although the main importance of negative-resistance amplifiers is in connection with molecular and parametric devices, electronic valves, designed at the outset as oscillators, may be used. Their most promising application seems to be high-power amplification.

Network Realization of Optimum Amplifier Noise Performance

Network realizations of the optimum noise performance (lowest noise figure at high gain) of a two-terminal-pair amplifier are presented. Two amplifier classes are distinguished: 1) networks that can both generate and absorb power and 2) networks that only generate power, or negative resistance networks. Amplifiers of class 1) can be optimized by first making them unilateral, subsequently employing input mismatch. Negative resistance amplifiers can be first brought into "canonic" form. Subsequent imbedding of part of the canonic network in an ideal circulator optimizes the noise performance. Both optimizations result in source impedances having a positive real part. High gain is achieved by subsequent cascading. The optimization using the ideal circulator yields maser noise performance optimization.