METHOD AND A CIRCUIT FOR MEASURING A DC SIGNAL HAVING A VERY HIGH NOISE LEVEL

摘要

1473726 Measuring D C voltage COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT-ALCATEL 6 Aug 1974 [16 Aug 1973] 34628/74 Heading G1U In measuring a D.C. signal accompanied by noise, an integrator comprising a capacitive feedback amplifier is used, where the amplifier has a finite gain, A. The input signal S + N is integrated for a predetermined time t, during which the voltage or capacitor 3 and storage capacitor 4 rises exponentially towards a final value V o = A.S, reaching at time t, a value V 1 = V o (1-e-t1/#)+E, where T is the integrator time constant and E is the noise level, A.R.C. At this time, switches 5, 9, 10 are reversed, applying to the integrating capacitor a voltage KV 1 via the multiplier 6, 7, 8. By arranging the constant K to be 1-e-t1/#, a new signal V a is produced which differs from the value V o by KE. After a short time, switches 9, 10 are switched back and the integration proceeds. The portion KE now decreases exponentially and the final value V o is approached. After a predetermined time t 2 , the signal level (without noise) has approached within an acceptable range e.g. Π1% of its final value, and this is then measured 16, from which the value S can be determined. By choosing K = 2, the total measuring time t 1 + t 2 is reduced to minimum, being about 1.8T, as compared to about 5.3T for a simple RC integrator. The system is said to be used for measuring low-level test signals received from repeaters in submarine cable systems.