Abstract: An AC coupled amplifier system is protected from overloading input signals by means of a "bootstrap" circuit which provides a compensation signal substantially matching the overscale portion of such input signal and applies that compensation signal to the coupling capacitor as an offset in order to prevent excessive charge accumulation on that capacitor. A voltage controlled current source serves as a signal range limiter in the circuit and responds to overscale input signals by causing a circuit loop opening and forcing loop closure in a secondary feedback circuit from which the extent of input signal overscale is determined. The matching compensation signal is then derived from such determination. The protection circuit further provides a reset function to account for extended overscale input signal levels.

Abstract: Input pulses are coupled through a delay network to a pulse amplifier. The amplifier includes feedback circuitry for correcting its output to a particular baseline level, generally zero volts. Within the amplifier feedback path is a gate, which is normally closed. Input pulses are also coupled to a pulse detector; whenever an input pulse is detected, the baseline gate in the amplifier feedback path is open, and the dynamic feedback operation is temporarily inhibited. During this time, the most recent previous level of baseline correction is retained.

Abstract: A pre-amplifier for photomultiplier tubes includes means to compensate for the combined dark current and noise output of a photomultiplier tube without inducing a noise dependent offset voltage at the pre-amplifier output. A feedback amplifier and a compensating network, including a capacitor, cooperate to monitor the pre-amplifier output and during this time to maintain the feedback amplifier in a linearly responsive state while charging the capacitor to an amount necessary to clamp the average value of the most negative excursion of the pre-amplifier output to ground.

Abstract: A DC level clamping circuit comprising a differential amplifier circuit constituted by a pair of transistors, a signal source, a first capacitor connected between the signal source and a first input terminal of the amplifier circuit, a second capacitor connected between the ground and a second input terminal of the amplifier circuit and having substantially the same capacity as the first capacitor, a pulse generator, a DC power source and first and second switching elements. The first switching element is connected between the DC power source and the first input terminal of the amplifier circuit, and the second switching element between the DC power source and the second input terminal of the amplifier circuit. These switching elements are controlled by the pulses from the pulse generator in a similar manner.

Abstract: An improved fast-recovery circuit for ECG amplifiers and the like. The fast-recovery circuit includes threshold responsive circuitry connected in parallel with part of the resistance associated with the integrator in a feedback circuit of the amplifier. The threshold responsive circuitry operates to increase feedback frequency response of the integrator when the normally very low frequency output signal of the amplifier exceeds a certain threshold. The improved circuit prevents the threshold circuitry from responding to pulses or excursions in the output signal of a relatively higher frequency content and which exceed the amplitude threshold for less than a predetermined interval, as for instance caused by pacer spikes, large QRS complexes and the like. Preferably, the improved threshold responsive means comprises transistor means connected across the integrator's resistance and having capacitance means across the base-emitter circuit thereof for inhibiting response to certain short duration signals.

Abstract: A passing circuit for coupling a signal portion and suppressing a DC component included in a composite input signal, includes a transistor having a substantially constant output signal for a variable input signal at a predetermined operating point, and biasing means connected to the transistor and operable for substantially maintaining the predetermined operating point at a value defining a constant output of the transition corresponding to the DC component to be removed from the input signal.

Abstract: A clamping circuit in which a signal such as a line sequential color television signal is clamped to a reference, such as a black level by means of a corrective signal which is the integrated output of a current multiplier. The gain of the multiplier, which is fed with a signal corresponding to the difference between the signal that is to be clamped and the reference, varies from a maximum to a minimum during a period of clamping. Large initial error in the signal can be rapidly corrected and the final corrective signal corresponds to the average error during the period of clamping.