Testing apparatus for voltage-variable capacitors employing phase-locked oscillators

Claim 2

Apparatus for testing the voltage-dependent capacitance characteristic of a voltage-variable capacitor, said apparatus comprising: reference oscillator means providing an output signal at a corresponding predetermined output frequency for each value of a respective control signal; a test oscillator which employs said voltage-variable capacitor as a frequency-determining element and which provides an output signal at a frequency which is a function of a control signal applied to said capacitor; a phase detector responsive to said oscillator output signals for providing an error signal which varies as a function of the phase difference between said oscillator output signals; means for providing to one of said oscillators a control signal which varies as a function of said error signal thereby to phase lock said oscillators to the same output frequency; and means for providing to the other of said oscillators a control signal which varies as a predetermined function of time thereby to correspondingly scan the common output signal frequency over a range of values whereby the amplitude of said error signal varies as a function of the voltage-dependent capacitance characteristic of said capacitor.

Claim 3

Apparatus as set forth in claim 1 wherein said reference oscillator is similar to said test oscillator and employs a standard voltage-variable capacitor as a frequency-determining element.

Claim 4

Apparatus as set forth in claim 2 wherein the amplitude of the reference oscillator control signal is variable and is applied to said standard voltage-variable capacitor for controlling the operating frequency of the reference oscillator.

Claim 5

Apparatus as set forth in claim 3 including means for generating a signal having an amplitude which is proportional to the difference between the amplitudes of said control signals.

Claim 6

Apparatus as set forth in claim 3 including means for generating a signal having an amplitude which is proportional to the ratio of the difference between the amplitudes of said control signals to the amplitude of one of said control signals.

Claim 7

Apparatus as set forth in claim 3 wherein said means for providing a time-varying control signal to the other oscillator includes a voltage ramp generator.

Claim 8

Apparatus for testing the voltage-dependent capacitance characteristic of a voltage-varIable capacitor, said apparatus comprising: a reference oscillator which employs a standard voltage-variable capacitor as a frequency-determining element and provides an output signal at a corresponding predetermined output frequency for each value of a control voltage applied to said standard capacitor; a test oscillator which employs the voltage-variable capacitor being tested as a frequency-determining element and which provides an output signal at a frequency which is a function of a control voltage applied to said capacitor; a phase detector responsive to said oscillator output signals for providing an error signal having an amplitude which varies as a function of the phase difference between said oscillator output signals; means for providing to one of said oscillators a control voltage which varies as a function of said error signal thereby to phase lock said oscillators to the same output frequency; and means for providing to the other of said oscillators a control voltage which varies as a predetermined function of time thereby to correspondingly scan the common output signal frequency over a range of values, whereby the amplitude of said error signal varies as a function of the voltage-dependent capacitance characteristic of said capacitor.

Claim 9

Apparatus for testing the voltage-dependent capacitance characteristic of a voltage-varIable capacitor, said apparatus comprising: a reference oscillator which employs a standard voltage-variable capacitor as a frequency-determining element and provides an output signal at a corresponding predetermined output frequency for each value of a control voltage applied to said standard capacitor; a test oscillator which employs the voltage-variable capacitor being tested as a frequency-determining element and which provides an output signal at a frequency which is a function of a control voltage applied to said capacitor; a phase detector responsive to said oscillator output signals for providing an error signal having an amplitude which varies as a function of the phase difference between said oscillator output signals; means for providing to one of said oscillators a control voltage which varies as a function of said error signal thereby to phase lock said oscillators to the same output frequency; and means for providing to the other of said oscillators a control voltage which varies as a predetermined function of time thereby to correspondingly scan the common output signal frequency over a range of values, whereby the amplitude of said error signal varies as a function of the voltage-dependent capacitance characteristic of said capacitor.

Claim 10

Apparatus as set forth in claim 7 including means for generating a signal which is proportional to the difference between the amplitudes of the two control voltages.

Claim 11

Apparatus as set forth in claim 7 including means for generating a signal which is proportional to the percentage difference in the amplitude between the two control voltages.

Claim 12

Apparatus for testing the voltage-dependent capacitance characteristic of a voltage-variable capacitor, said apparatus comprising: a reference oscillator which employs a standard voltage-variable capacitor as a frequency-determining element and provides an output signal at a corresponding predetermined output frequency for each value of a control voltage applied to said standard capacitor; a test oscillator which employs the voltage-variable capacitor being tested as a frequency-determining element and which provides an output signal at a frequency which is a function of a control voltage applied to said capacitor; a phase detector responsive to said oscillator output signals for providing an error signal having an amplitude which varies as a function of the phase difference between said oscillator output signals; means for applying said error signal to said standard capacitor thereby to phase lock said reference oscillator to the operating frequency of said test oscillator; and means for applying a ramp voltage to the capacitor being tested thereby to correspondingly vary the common oscillator output signal frequency as a function of time whereby the amplitude of said error signal varies as a function of the voltage-dependent capacitance characteristic of the capacitor being tested.

Claim 13

Apparatus for testing the voltage-dependent capacitance characteristic of a voltage-variable capacitor, said apparatus comprising: a reference oscillator which employs a standard voltage-variable capacitor as a frequency-determining element and provides an output signal at a corresponding predetermined output frequency for each value of a control voltage applied to said standard capacitor; a test oscillator which employs the voltage-variable capacitor being tested as a frequency-determining element and which provides an output signal at a frequency which is a function of a control voltage applied to said capacitor; a phase detector responsive to said oscillator output signals for providing an error signal having an amplitude which varies as a function of the phase difference between said oscillator output signals; means for applying said error signal to said standard capacitor thereby to phase lock said reference oscillator to the operating frequency of said test oscillator; and means for applying a ramp voltage to the capacitor being tested thereby to correspondingly vary the common oscillator output signal frequency as a function of time whereby the amplitude of said error signal varies as a function of the voltage-dependent capacitance characteristic of the capacitor being tested.