Patent GB-1180518-A (GB)
Title: Decadic Frequency Generator
IPC: H03B23/00
Filed: 1968-10-24
Abstract: 1,180,518. Frequency generators. WANDEL U. GOLTERMANN. 24 Oct., 1968 [24 Oct., 1967], No. 50613/68. Heading H3A. A decadic frequency generator comprises an adjustable oscillator 12, Fig. 1, working into a frequency counter 14 under the control of a timer 15, the output of the frequency counter 14 being applied to a comparison circuit 17 which also receives a signal from a presettable digital frequency selector 16 and, in response to a disparity between the output and the signal, readjusts the operating frequency of the oscillator in a sense reducing such disparity. As shown, timer 15 also operates a switch 18 which is closed subsequent to each counting period to charge a capacitor 19 to the voltage developed in comparison circuit 17: the charge on the capacitor controls the frequency of oscillator 12 by means of control circuit 11. A sweep voltage generator 15 may be interposed between capacitor 19 and control circuit 11 to vary the oscillator frequency over a small range, its operating period being an aliquot fraction of a cycle of timer 15 and also of the counting period. In a second embodiment the digital frequency counter 24, Fig. 2, and manual frequency selector 26 feed into a coincidence gate 210 which, when coincidences occur, feeds pulses into test circuit 211, to the second input of which are applied delayed pulses from the timer 25. According to whether the oscillator 22 is running fast or slow the coincidence pulses will arrive before or after the pulses from timer 25 and are arranged to control a source of charging voltage 212 accordingly, whereby the capacitor 29 is charged so as to decrease or increase the frequency of the oscillator respectively. In a third embodiment comprising a modification of the second embodiment, the source of charging voltage and capacitor are omitted, the output of the oscillator being fed to an auxiliary counter (313, Fig. 3, not shown) the output of which controls the oscillator frequency control circuit (31) via a digital to analogue converter (314). In this arrangement the test circuit (311) controls the auxiliary counter. In a fourth embodiment in which the frequency of the oscillator 42, Fig. 4, is automatically swept over a range, a switch operated by the timer 45 alternately connects the second input of coincidence gate 410 to two manually settable digital frequency selectors 46, 46<SP>1</SP> which respectively determine the lower and upper limits of the frequency sweep. A second switch ganged to the first alternately connects the output of test circuit 411 to source of charging voltage 412 and to a second source of charging voltage 412<SP>1</SP> which feeds into a second capacitor 49<SP>1</SP>. The charge on capacitor 49<SP>1</SP> controls the slope of the output voltage of a variable-voltage generator 417 producing a trapezoidal waveform which is superimposed upon the charge on capacitor 49. In a fifth embodiment 517, Fig. 5, of period large compared with a cycle of timer 55 generates a triangular voltage under control of flip-flop 519 whose state of conductivity determines the sense of slope of the voltage curve. Frequency selector units 56, 56<SP>1</SP> are alternately connectible to coincidence gate 510 by a switch controlled by the flip-flop 510 in response to an identity signal from coincidence gate 510, the switch-over coinciding with a reversal of slope of voltage source 517. With unit 56 in circuit to establish the lower sweep frequency of oscillator 52, the determination by gate 510 of an identity between the count of counter 54 and the signal from unit 66 trips flip-flop 519 to establish a rising voltage in the output of source 57 and to connect unit 56<SP>1</SP> in lieu of unit 56, the next reversal occurring upon the registration of an identity between the output of counter 54 and the signal of unit 56<SP>1</SP> determining the upper frequency limit.