Patent GB-772235-A (GB)
Title: Improvements relating to low frequency oscillators
Inventor: CATHERALL REGINALD
IPC: H03B5/22
Filed: 1954-02-24
Abstract: 772,235. Valve amplifiers; valve oscillators SOLARTRON ELECTRONIC GROUP, Ltd. Feb. 23, 1955 [Feb. 24, 1954], No. 5465/54. Class 40(6) A low frequency oscillator, Fig. 1, comprises an amplifier in a regenerative loop circuit containing a phase shifting network. the gain of the amplifier being sufficient to overcome the loss in the loop circuit at a frequency at which the phase shift of said loop is zero and an amplitude stabilizing loop circuit connected to regeneratively couple the output of the amplifier or section thereof to the input of the amplifier or section and containing means for squaring the wave-form of the oscillations passing therethrough. It is explained that if in operation the oscillatory input of the amplifier increases the resultant output is insufficient to sustain the increase since the feed back through the amplitude stabilizing loop does not also increase. Furthermore the amplifier with its main feed back loop forms a highly selective circuit so that harmonics introduced into the amplifier from the squaring circuit are removed. The oscillator described, Fig. 3, comprises three amplifiers 1, 3, 4 of zero phase shift and approximately unity gain, two 90 degree phase shifting networks 16 and 17 and a positive feedback connection 11. Amplifier- - 4 which is of adjustable gain is provided with a regenerative circuit including tne squaring circuit 18. The phase shifting networks each comprise a condenser and resistance in a series circuit with one end fed directly from one of the amplifiers and the other through a phase reversing amplifier (2, 5). Amplifiers 1 and 3 (Fig. 4, not shown) comprise two pentode valve stages feeding a cathode follower output stage which also provides negative feedback to the cathode circuit of the first stage. Amplifiers 2 and 5 (Fig. 5, not shown) comprise a pentode valve feeding two triode valves operating as a cathode coupled pair which in turn feeds a cathode follower the output of which is coupled back to the grid of the first valve to provide negative feed back. Resistances are provided in series with the input and with the feed back path such that the gain of the amplifier is zero. Amplifier 4, Fig. 6, comprises a cathode input stage feeding a cathode follower com- - prising two valves in parallel. Negative feed back is provided from the output to the grid of the input circuit. The two inputs to the amplifier are applied through resistors 52 and a variable resistor 57 which adjusts the D.C. level of the output. The potentiometer 55 provides an adjustment of the gain of the amplifier. The squaring circuit (Fig. 7, not shown) comprises two valves coupled by a common cathode resistor, one valve squaring one half cycle and the other squaring the other half cycle and feeding a cathode follower output circuit. The values of the resistance and capacitance in the phase shifting network may be varied (Fig. 8, not shown) to provide frequency range of the oscillator of .01 c/s to 100 kc/s. Four outputs differing in phase by 90 degrees may be obtained from amplifiers 1, 2, 4 and 5 and two of these may feed an amplitude measuring device as described in Specification 772,236 [Group XXXVI]