JPS5574469A - Frequency measuring device for frequency modulated wave - Google Patents

Abstract

PURPOSE: To enable measurement in high accuracy that the variation of the parameters of elements used is little possible without being subject to the effect of the discriminating sensitivity of a used frequency discriminator, by forming this device lest frequency discriminating sensitivity should be contained as a parameter when counting frequency.

CONSTITUTION: A reference signal generator 31 generates signals in frequency fR₂ different from frequency fR₁ that a reference signal generator 13 generates. A high-frequency switch 12 repeatedly draws the signals to be measured of FM waves and the reference signals fR₁, fR₂ in order in the timing of a control signal generating circuit 14. Meanwhile, the circuit 14 generates the control pulses of an A/D converter 32 besides the control pulses of A/D converters 18, 19 during the time when the switch 12 selects the reference signals fR₂, converts voltage, which is proportional to the reference signals fR₂ supplied from a low-pass filter 17 through a frequency discriminator 16, into A/D 32, and forwards output aR₂₁. The output aS_i-_aR_1i of a subtraction circuit 20 is divided 34 by output aR_1i-aR_2i obtained by subtracting 33 the output aR_2i from the output of the converter 19. Measurement is not subject to the variation of the divided output because discriminating sensitivity Kd is not included in the divided output, and frequency can accurately be measured.

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