Apparatus for detecting noise in the measurement of very small resistance

Abstract

A pair of a first and a second R-C integrating circuits connected in series. A first switch S.sub.1 supplies a first combined voltage E.sub.1 +E.sub.3 of a first positive threshold voltage E.sub.1 and a positive initial set up voltage E.sub.3 to a first capacitor in the first R-C circuit, and a second switch S.sub.2 supplies a second capacitor with a second combined voltage of a second positive threshold voltage E.sub.2 with a negative initial set up voltage -E.sub.4. The switches S.sub.1 and S.sub.2 are closed before the input of the signal to be measured. The switches are opened after the input of the signal. A first comparator compares a first discharged voltage output from the first capacitor and the first threshold voltage E.sub.1, and a second comparator compares a second discharged voltage output from the second capacitor and the second threshold voltage E.sub.2. A logic circuit is connected to the output terminals of the first and second comparators, respectively, and determine in conjunction with a timing circuit whether the first and second discharged voltages are within a range between the first threshold voltage E.sub.1 and second threshold voltage E.sub.2 within a predetermined time period of the input of the signal to be measured, so as to provide an indication to judge the right time for resistance measurements.