Testing the transfer function linearity of analogue input circuits

Claim 1

Apparatus for testing the linearity of the transfer function of an analogue input circuit under test which includes an analogue to digital converter, comprising: connection means for applying an analogue signal to, and for receiving a digitised signal from, the analogue input circuit; digital test signal generating means for generating a plurality of test signals in digital form; digital to analogue conversion means for converting said digital test signals simultaneously into analogue test signals of predetermined duration; analogue processing means responsive to said analogue test signals for providing from a predetermined combination of said analogue test signals a combination test signal; storage means for receiving from the input circuit and for storing digitised output signals corresponding to each of said analogue test signals and said combination test signal; timing means for causing the digital test signals to be generated repetitively, for causing the analogue and combination test signals to be applied sequentially to the connection means, and for causing the digitised output signals to be applied to the storage means; digital processing means including sampling means for sampling at a plurality of corresponding points each of the stored digitised output signals combination means for combining the digitised output signal samples corresponding to said analogue test signals in said predetermined combination to form a digital combination signal; differencing means for determining at each sample point a difference in magnitude between the digitised combination test signal and the digital combination signal; and summation means for summing the magnitude differences determined by the differencing means for each of the sampling points to provide an indication of the departure from linearity of the transfer function.

Claim 7

A method of evaluating a level of non-linearity in the transfer function of an analogue input circuit which includes an analogue-to-digital converter (ADC), comprising generating a plurality of digital test signals of predetermined duration, converting the digital test signals to analogue test signals, processing the analogue test signals to produce from a predetermined combination thereof a combination test signal, feeding the analogue test and the combination test signals to the input circuit one at a time, storing digitised forms of each signal from the ADC, sampling the stored signals at corresponding ones of a plurality of points thereof, defining at each sample point a digital combination signal by combining in said predetermined combination samples of the digitised test signals, determining the difference in magnitude between the digitised combination test signal and the digital combination signal, and summing the difference values obtained for each of the sample points.

Claim 8

A method of evaluating a level of non-linearity in the transfer function of an analogue input circuit which includes an analogue-to-digital converter (ADC), comprising generating a plurality of digital test signals of predetermined duration, converting the digital test signals to analogue test signals, processing the analogue test signals to produce from a predetermined combination thereof a combination test signal, feeding the analogue test and the combination test signals to the input circuit one at a time, storing digitised forms of each signal from the ADC, sampling the stored signals at corresponding ones of a plurality of points thereof, defining at each sample point a digital combination signal by combining in said predetermined combination samples of the digitised test signals, determining the difference in magnitude between the digitised combination test signal and the digital combination signal, and summing the difference values obtained for each of the sample points.