Method and circuit arrangement for measuring AM to PM conversion

Claim 2

Method for measuring amplitude modulation to phase modulation (AM/PM) conversion of a system under test, including the steps of: generating a carrier frequency signal; generating a test-tone signal; phase modulating the carrier frequency signal in response to the test-tone signal; applying the modulated carrier frequency signal to the system under test via one and the other of two separate signal channels during periodically alternating time periods, said one channel including a selected transfer function and said other channel having a transfer function including selected group delay and amplitude parameters, where one of said group delay and amplitude parameters is frequency independent and the other is linearly dependent on frequency and the phase-modulated carrier frequency signal is amplitude modulated by the linearly frequency dependent parameter; demodulating the phase of the carrier frequency signal at the output of the system under test during periodically alternating time periods; and measuring the phase modulation produced in the system under test because of the amplitude modulation of the carrier frequency signal, from the different demodulated test-tone signals obtained during periodically alternating time periods.

Claim 3

Method as in claim 1, wherein in the step of applying the modulated carrier signal to the system under test, said other signal channel has a frequency independent amplitude response and a linearly frequency dependent group delay response and the difference in amplitude of the demodulated test-tone signals formed during periodically alternating time periods is measured.

Claim 4

Method as in claim 2 wherein in the step of applying the modulated carrier signal to the system under test, said one signal channel provides a direct connection.

Claim 5

Method as in claim 2, wherein in the step of measuring, the sensitivity of the measurement is increased by providing said one signal channel also with a frequency independent amplitude response and a linearly frequency dependent group delay response, and the linearly frequency dependent group delay responses of both signal channels have equal but opposite slope values.

Claim 6

Method as in claim 1, wherein in the step of applying the modulated carrier signal to the system under test, the phase modulated carrier signal is delayed during one half time period in said one channel and, in the other half time period, is passed via the other signal channel having a frequency independent group delay response and a linearly frequency dependent amplitude response, where the delay of said one signal channel compensates the delay introduced in the other signal channel by the phase modulation due to the frequency independent group delay response, and in the step of measuring, measuring the difference in phase of the demodulated test-tone signals during periodically alternating half periods.

Claim 7

Method as in claim 5, wherein in the step of applying the modulated carrier signal to the system under test, said other signal channel also has a frequency independent group delay response and a linearly frequency dependent amplitude response and the linear amplitude responses have equal but opposite slope values.

Claim 8

Apparatus for measuring amplitude modulation to phase modulation (AM/PM) conversion comprising: a carrier frequency oscillator; a test-tone oscillator; a phase modulator connected to both oscillators to provide a phase modulated carrier frequency signal; switching means having an input connected to the phase modulator output for applying said signal at its input in a periodically alternating sequence to each one and another of two signal channels; said one signal channel having a selected transfer function, and said other signal channel has a transfer function including selected amplitude and group delay parameters, one of said amplitude and group delay parameters being frequency independent, and the other of the parameters being linearly frequency dependent and causing amplitude modulation of the phase modulated carrier frequency signal; means coupling each of the signal channels to the system under test; detector means connected to the system under test for responding to the signals applied thereto from the system under test; and measuring means connected to the detector means to measure AM/PM conversion of the system under test from the difference in the demodulated test-tone signals obtained during both periodically alternating time periods.

Claim 9

Apparatus for measuring amplitude modulation to phase modulation (AM/PM) conversion comprising: a carrier frequency oscillator; a test-tone oscillator; a phase modulator connected to both oscillators to provide a phase modulated carrier frequency signal; switching means having an input connected to the phase modulator output for applying said signal at its input in a periodically alternating sequence to each one and another of two signal channels; said one signal channel having a selected transfer function, and said other signal channel has a transfer function including selected amplitude and group delay parameters, one of said amplitude and group delay parameters being frequency independent, and the other of the parameters being linearly frequency dependent and causing amplitude modulation of the phase modulated carrier frequency signal; means coupling each of the signal channels to the system under test; detector means connected to the system under test for responding to the signals applied thereto from the system under test; and measuring means connected to the detector means to measure AM/PM conversion of the system under test from the difference in the demodulated test-tone signals obtained during both periodically alternating time periods.

Claim 10

Apparatus as in claim 7 wherein said selected transfer function of said one signal channel has a frequency independent amplitude response and a linearly frequency dependent group delay response and the measuring means measures the difference in amplitude of the demodulated signals obtained during both periodically alternating time periods.

Claim 11

Apparatus as in claim 7 wherein said one channel includes a direct connection.

Claim 12

Apparatus as in claim 8 wherein said other signal channel also has a transfer function with a frequency independent amplitude response and a linearly frequency dependent group delay response and both group delay responses have equal but opposite slope values.

Claim 13

Apparatus as in claim 7 wherein said one signal channel includes delay means and said other signal channel has a frequency independent group delay response and a linearly frequency dependent amplitude response and the delay means compensates for the delay caused by the phase modulation because of the frequency independent group delay response, and the measuring means measures the difference in phase of the test-tone signals obtained during periodically alternating half time periods.

Claim 14

Apparatus as in claim 7, wherein said one signal channel has a frequency independent group delay response and a linearly frequency dependent amplitude response and said other signal channel also has a transfer function including a frequency independent group delay response and a linearly frequency dependent amplitude response, and the slope values of the amplitude responses have equal but opposite slope values.