IMPROVED BASE-LINE STABILIZATION FOR PULSE AMPLIFIERS

The base-line of the output of a dc-coupled pulse amplifier can be held within narrow limits, if a regulator is used, that provides a high degree of negative dc-feedback from the output to the input via a low-pass filter. Base-line shifts following a CR-coupling network at the input can be avoided for duty cycles up to 40%, if the regulator-amplifier limits at very low amplitudes. In this case the stabilization circuit reacts not on the arithmetic mean value of the output-signal, but practically on the undisturbed baseline that can be stabilized therefore. A further improvement using a gate within the feedback-path, that closes during each input pulse is discussed. The circuit is given in detail: coupled with an amplifier with an output range of ± 10 V, the mean value of the baseline is held within ± 2 V at a pulse rate of 10 000 pps (from a NaI-detector) the statistical fluctuations go up to ± 5 mV. The dc-shift without signal is less than 5 mV/day (non cumulative). © 1968.