GB1141952A - Improvements in or relating to electrical oscillators - Google Patents

Abstract

1,141,952. Frequency generating circuits. AIRMEC Ltd. 19 Jan., 1968 [19 Jan., 1967], No. 2979/67. Heading H3F. A frequency generating arrangement comprises an oscillator providing a first frequency, indicator means providing a measure of that frequency, and frequency-dividing means reducing the frequency to an accurate submultiple from which an output signal is produced, whereby the indicator means can be used to determine the output frequency without a full cycle of said output frequency having to be completed. A driving oscillator 10, preferably of sine wave output, produces a direct output on terminal 18 and also drives the first in a series chain of frequency dividers 12. Each of the dividers 12 comprises a cyclic counter type circuit and produces a second output signal whose amplitude at any given instant is proportional to the number of cycles counted since the preceding zero count. These second outputs from counters 12 are fed to an adding circuit 13 which generates a staircase waveform each step of which represents one count in the frequency dividers. Adder 13 feeds a phase inverter 14 producing an inverted staircase waveform which with that from adder 13 is fed to an electronic switch 15 which operates in synchronism with the frequency dividers to select alternate cycles of the two staircase waveform inputs to produce an essentially triangular waveform. The steps of this are smoothed and the waveform converted to sinusoidal form in a shaping circuit 16 which also renders the peak amplitude independent of frequency. Attenuator 17 enables the final output amplitude to be varied. The Specification also describes the use of the arrangement in measuring phase-shift in a circuit under test (Fig. 2, not shown).