Single tone technique for measuring IM distortion

Claim 3

The method according to claim 1 wherein said detecting step comprises: filtering the output of said active device in a bandpass filter centered about the frequency of said test-tone; synchronously detecting the output of said bandpass filter with reference to in-phase and phase-quadrature versions of said test-tone signal; filtering said synchronously detected signals in bandpass filters which are centered about the frequency of the amplitude-modulation priorly imposed on said multi-frequency signal; and then selecting the larger of two filtered signals as the signal which is directly proportional to the non-linearity of the device under test.

Claim 4

The method according to claim 1 wherein said detecting step comprises: filtering the output of said active device in a bandpass filter centered about the frequency of said test-tone; synchronously detecting the output of said bandpass filter with reference to in-phase and phase-quadrature versions of said test-tone signal; filtering said synchronously detected signals in bandpass filters which are centered about the frequency of the amplitude-modulation priorly imposed on said multi-frequency signal; squaring each of the two filtered signals; and then summing the squared signals to produce a combined signal which is directly proportional to the non-linearity of the device under test.

Claim 5

Apparatus for measuring the non-linearity of an active device having a given passband comprising: means for amplitude modulating a multi-frequency input signal at an angular frequency ω m ; a constant amplitude test tone generator of fixed angular frequency ω, where ω>>ω m and falls within said passband; means for coupling the outputs from said modulating means and said generator to the input of said active device; and means, connected to the output of said active device for detecting the resultant non-linear components of the test-tone signal, the amplitude of said non-linear components being directly proportional to the non-linearity of the device under test.

Claim 6

Apparatus for measuring the non-linearity of an active device having a given passband comprising: means for amplitude modulating a multi-frequency input signal at an angular frequency ω m ; a constant amplitude test tone generator of fixed angular frequency ω, where ω>>ω m and falls within said passband; means for coupling the outputs from said modulating means and said generator to the input of said active device; and means, connected to the output of said active device for detecting the resultant non-linear components of the test-tone signal, the amplitude of said non-linear components being directly proportional to the non-linearity of the device under test.

Claim 7

The apparatus according to claim 4 wherein said detecting means comprises: a first bandpass filter having its passband centered about ω, the angular frequency of said test-tone; first and second synchronous detectors each having a first input connected to the output of said first bandpass filter and a second input connected to said test-tone generating means; a phase-shifting network interposed between the output of said test-tone generating means and the second input of said first synchronous detector; and means for selecting the larger of the two outputs from said first and second synchronous detectors, said larger output being directly proportional to the non-linearity of said active device.

Claim 8

The apparatus according to claim 5 further including: third and fourth bandpass filters respectively interposed between the outputs of said first and second synchronous detectors and the input to said output selecting means, each of said bandpass filters being centered about ω m , the angular frequency of said amplitude-modulating means.

Claim 9

The apparatus according to claim 5 further comprising: means for tapping a portion of the output signal from said active device; a square-law detector connected to the output of said tapping means; and a comparator having one input connected to the output of said square-law detector and another input connected to the output of said output selecting means, the output of said comparator comprising a signal which is proportional to the non-linearity of the active device.