Patent GB-749827-A (GB)
Title: Improvements in or relating to electric frequency dividers
Inventor: GRAYSON HARRY
IPC: H04L25/24
Filed: 1952-12-23
Abstract: 749,827. Frequency-divider circuits. STANDARD TELEPHONES & CABLES, Ltd. April 17, 1953 [Dec. 23, 1952], No. 32604/52. Class 40 (6). A frequency-dividing circuit comprises an amplifier having an input circuit which includes a normally-conducting rectifier, which is, however, rendered periodically non-conducting by the application to the input circuit of a signal of predetermined frequency, and a feedback circuit connected between the output and the input of the amplifier and including a further rectifier, the amplifier itself being blocked when either rectifier is conducting and the feedback circuit comprising means, responding to the output signal delivered by the amplifier circuit, such that the feedback, rectifier is rendered periodically conducting at a submultiple of the input frequency to block the operation of the amplifier at this submultiple rate, and thus supply an output signal at the sub-multiple frequency. In the preferred embodiment, a crystal triode 1 is employed as the amplifier. In the absence of an input signal at terminals 7, 8 the rectifier 10 conducts owing to its connection in series with the batteries 6 and 11 and the emitter electrode 3 is biased slightly negatively thus cutting the emitter current off. A further rectifier 24 connected between the emitter electrode and a secondary winding of a transformer 13 in the output circuit of the crystal triode is rendered normally non-conducting by the battery 20. Upon the application of an input signal to the terminals 7, 8 the rectifier 10 is rendered non-conducting during the positive half-cycles of the signal. During the first positive half-cycle the emitter electrode goes slightly positive as it is now disconnected from the battery 11 and current flows in both the emitter and collector circuits of the crystal triode. The current in the collector circuit shock-excites the tuned circuit comprising condenser 18 and the primary winding of transformer 13 and which is tuned, in the example given to one half the input frequency. The feedback secondary winding is so connected that the potential therein initially rises so maintaining rectifier 24 cut-off. During the next positive half-cycle of the input signal, however, the.potential in the secondary winding will have gone negative, thus making rectifier 24 conduct and maintaining the emitter electrode negative despite the fact that the rectifier 10 has been rendered non-conducting. Consequently no current flows in the crystal triode during this half-cycle. Thus during alternate positive half-cycles of the signal applied to the rectifier 10 collector current flows to shock-excite the transformer 13, and an output signal of the half the input frequency is obtained across the terminals 35, 36. A square-wave output of half the input frequency may be taken from the terminal 37. The circuit may be modified by the reversal of the battery 20 in 'which case the rectifier 24 is normally conducting and a positive triggering potential has to be applied to terminal 39 to start the operation of the circuit. The operation, once started, can be stopped by the application of a negative pulse to the terminal 39. For division by integers greater than 4, the condenser 18 is removed from the circuit and a delay line of appropriate length is inserted between the terminals 21, 22. It is stated that the crystal triode may be of either junction or point-contact type; furthermore, by suitably modifying the circuit the crystal triode may be replaced by a thermionic valve.