Comparator circuit

1,035,322. Transistor pulse circuits. ADAGE Inc. Jan. 10, 1963, No. 1254/63. Heading H3T. [Also in Division G4] A comparator suitable for use in an analogue to digital converter comprises two " Selector circuits" 112, 114 (Fig. 5, not shown) to respective ones of which is applied a reference voltage and the input signal and to both of which a ramp signal is applied from generator 110. When the ramp voltage reaches the voltage at the nearer of the two inputs the corresponding selector operates to produce an output at 98 or 100 and which operates a corresponding " Level sensing switch " 122, 124 to inhibit operation of the other selector. Accordingly, an output pulse occurs at 98 or 100 depending on whether the input signal is larger or smaller than the reference signal. In the embodiment a feedback path is provided through a diode 126 to balance out any unwanted feedback to the input signal source which might cause false operation. The Specification describes a basic complementary type multivibrator which is the subject of Specification 1,035,323 and how this may be modified to form a self-oscillating version of the present invention. In the basic multivibrator (Fig. 1) a capacitor 34 charges through resistor 40, resistor 36 (if provided) and a conducting clamping diode 46. The rising voltage on the upper plate of the capacitor causes transistor T 1 to become more conducting and thus, through a connection to the collector electrode, the base of transistor T 2 to become more negative. At the end of the timing period transistor T 2 becomes conducting, effectively clamping the potential at the collector of T 1 . The current through T 2 rises but the collector remains at a constant potential until its current exceeds the current through clamping diode 46 whereupon the potential rapidly rises. This causes the potential at the upper electrode of the capacitor to rise correspodingly until it is clamped by diode 44. This rise is communicated through the emitter-base path of T 1 to point 18. The potential at the lower plate of 34 continues to rise, though more slowly until the capacitor is discharged when the potential rises above that at the emitter of T 1 allowing diode 37 to conduct so that the emitter potential is carried positive until transistor T 1 is cut off. This is aided by regeneration from the collector of T 1 to the base of T 2 , the latter transistor being driven to cut-off during the process, allowing a new cycle to commence. Thus transistor T 1 remai