US 4,399,409 A · Apparatus for testing the linearity of a frequency modulated oscillator

Abstract

A linearity test signal generator alternately provides a burst of a modulation frequency and no modulation to the modulation input of the frequency modulator oscillator (FMO) under test. A programmable divider is connected to the output of said frequency modulated oscillator to produce a binary output signal which is applied to the automatic phase control circuit. This circuit in turn develops a DC control signal which is applied to the control input of said frequency modulated oscillator to maintain the average oscillator frequency constant. This DC control voltage gives an indication of the shift in the average free running frequency of the oscillator while being modulated, caused by oscillator non-linearity. The voltage is first sampled when the oscillator is unmodulated to produce a reference voltage which is stored and then compared to a sample of the DC control voltage when the oscillator is being modulated. The difference between the two voltage samples is used to generate an error signal proportional to the amplitude and the sign of the difference. A zero center meter is employed to indicate the magnitude of the error and to permit rapid adjustment to obtain a minimum error indication.

Claims8

Dependent claims

Apparatus for testing the linearity of a frequency modulated oscillator comprising:

timing means generating first and second synchronizing signals and a first timing signal;
logic means responsive to said first timing signal for applying short bursts of a modulating test signal to the oscillator so as to alternately obtain a carrier alone and a deviated signal at the output of the oscillator;
first means responsive to an output signal of the oscillator for alternately generating a first DC control signal voltage derived from the carrier signal and a second DC control signal derived from the deviated signal;
second means responsive to said first and second synchronizing signals and sequentially responsive to said first and second control signals for providing at an output terminal an error signal representative of the magnitude and sign of the difference between the magnitudes of said first and second control signals;
and
third means responsive to the error signal at said output terminal of said second means for measuring the magnitude and sign of the error signal so as to determine when the difference has been set to a minimum.

3 more elements

Dependencies are inferred from the claim text.

Apparatus for testing the linearity of a frequency modulated oscillator

Life of this patent

Apparatus for testing the linearity of a frequency modulated oscillator

Life of this patent

Abstract

Claims8