Analogue to digital converters

Claim 1

An analogue to digital converter for converting to digital form an analogue input signal which input signal may be subject to a normal mode interfering signal of period P, the converter comprising integrating means having an input and an output, timing means for applying the input signal to the input of the integrating means for a sampling interval S + dS to cause the output level of the integrating means to deviate from a datum level, a source of a reference signal, a source of clock pulses, a pulse counter, means for applying the reference signal to the input of the integrating means in such a manner as to cause the integrating means output to return to the datum level during a digitizing interval and for simultaneously causing the pulse counter to count clock pulses, and means responsive to the return to the integrating means output level to the datum level for terminating the digitizing interval, the integrating means having first and second selectable transfer functions of the form 1/pT1 and 1/(1 + pI2) respectively, wherein T1 and T2 are preselected time constants and p is the differential operator d/dt, and control means for selectively causing the integrating means to have a transfer function of the first form during the digitizing interval and during a predetermined period S from the start of each sampling interval, and a transfer function of the second form during the remaining period dS of the sampling interval.