GB1241454A - Maximum and minimum signal selectors - Google Patents

Abstract

1,241,454. Selecting the maximum or minimum signal. ENGLISH ELECTRIC CO. Ltd. 6 March, 1970 [6 Dec., 1968], No. 58083/68. Heading H3T. [Also in Division H2] The maximum or minimum amplitude signal of a number of input signals is selected by applying the signals to the input transistor of a respective transistor long-tail pair and applying negative feedback from the common output to the other side of the pairs. As shown the longtail pairs have respective input transistors TR1A-TR1C and a common transistor TR2, the output being fed back negatively via TR5 to the base of TR2. The one of transistors TR1 receiving the largest input signal robs the other TR1 transistors of their share of the constant emitter current provided by R3 and the feedback to TR2 maintains the current in TR2 almost equal to that in the conducting transistor TR1. If two or more signals are equal the current is shared by a corresponding number of the conducting transistors TR1 and the base emitter voltages are thus less than that of TR2 thereby introducing an error. This may be overcome by using independent long tail pairs (Figs. 2 and 3, not shown), Fig. 3, using transistors of the opposite conductivity type and thus selecting the minimum signal.