GB706516A - Improvements in or relating to oscillators, particularly for radio receiving circuits, employing semi-conductor devices - Google Patents

Abstract

706,516. Semi-conductor oscillators. STANDARD TELEPHONES & CABLES, Ltd. Oct. 3, 1952 [Oct. 12, 1951], No. 23862/51. Class 40 (6). [Also in Group XXXV] An oscillator circuit, particularly for use in super-regenerative or super-heterodyne radio receivers, comprises an N-type crystal rectifier of the kind described and claimed in Specification 706,514 and having a negative-resistance portion to its forward characteristic, a circuit having a reactive-component connected between the elec trodes of the rectifier, and means for biasing the rectifier, to operate over the negative-resistance portion of its characteristic. The crystal used may be of N-type germanium and may be employed either in an L-c oscillatory circuit or in an R-c circuit providing relaxation oscillations. In the super regenerative-receiver shown in Fig. 1 the rectifier 1 is associated with a circuit tuned to resonate, for example, at 100 Mc/s, and comprising an inductive loop 2, 3, coupled to the aerial 5, and a tuning condenser 4. A quenching oscillator, operating for example at 200 Kc/s, comprises a rectifier 13 condenser 14 and resistor 15 and generates relaxation oscillations which are applied to the rectifier 1 to bias it periodically to the negative resistance portion of its characteristic whereupon oscillations of ampliture corresponding to the received signals build up until quenched by the changing bias produced by the relaxation oscillator. In a modification, Fig. 3, the rectifier 37 is used to generate both the radio-frequency and quenching oscillations. The rectifier is associated with condenser 47 and resistor 48 and thus operates as a relaxation oscillator passing periodically through the negative resistance portion of its characteristic whereupon radio-frequency oscillations build up in the tuned circuit 38, 39 in accordance with the signal induced therein from the aerial 40. A superheterodyne receiver, Fig. 2 (not shown) comprises an L-c oscillator similar to that shown in Fig. 1, the output from which is heterodyned with the received signals by means of a conventional crystal rectifier (e.g. a silicon rectifier), the resulting signals being passed to the I.F. amplifying stages which may employ transistor triode amplifiers. Automatic frequency control may be achieved by deriving a direct-current error signal from a frequency discriminator operating at intermediate frequency and applying the same as a bias voltage to the oscillator rectifier. The oscillator circuit may also include a piezo-electric crystal, which may either be tuned to the fundamental of a sub-harmonic of the desired localoscillator frequency. In this case, automatic frequency control cannot be employed.