Spannungsteiler zur Erzeugung analoger Ausgangsspannungen

摘要

865,171. Digital - to - analogue converters. DICK CO. A.B. July 23, 1959 [Aug. 4, 1958], No. 25370/59. Class 40 (1). A digital-to-analogue converter consists of a string of Zener diodes through which a constant current is passed to produce standard voltage steps, certain steps being cut out according to the digital input. In the form of Fig. 1, three diodes 30, 32, 34, producing steps of 40, 20 and 10 volts, are series connected with a cathode follower 10 arranged to give a constant current. Each diode is shunted by a normally non-conducting transistor 40, 42, 44 which, when conducting, shorts out the corresponding voltage step. Inputs to the transistors come from the secondaries 56, 66, 76 of transformers 52, 62, 72 to the primaries of which pulses are applied from the source 82 of digital input signals. A similar string of diodes 301, 321, 341 is connected to another constant current source 12 and each is shunted by a normallyconducting transistor 401, 421, 441. These are controlled by a further set of secondary windings 58, 68, 78 on the transformers 52, 62, 72. A signal applied to a transformer, say 52, cuts out the corresponding voltage step on the lefthand side and cuts it in on the right-hand side. The two sides are connected to the plates 84 of a cathode-ray tube so that a difference of deflection voltage of double the corresponding voltage is produced by each input signal. Thus with no signal the transistors 40-44 are non-conducting and those 401-441 are conducting so that B-70 volts are applied to the left-hand plate and B volts to the right-hand plate, a deflection voltage of 70 volts. When a pulse is applied to transformer 52, the plate voltages become B - 30 and B - 40 a difference of - 10 volts. A similar circuit produces horizontal deflection voltages so that a pattern of 64 possible deflections is available in a matrix of 8 X 8. In a second embodiment both sets of transistors are normally off, the second string of diodes being oppositely poled so that the voltage steps produced are opposite in polarity to those of the first string. The constant current sources include transistors connected as cathode followers.