Patent GB-1524527-A (GB)
Title: Circuit arrangments
IPC: H03M1/00
Filed: 1975-08-20
Abstract: 1524527 Analogue-to-digital and digital-to-analogue conversion SIEMENS AG 20 Aug 1975 [20 Sept 1974] 34554/75 Heading H3H In an analogue-to-digital or digital-to-analogue converter, an integrated circuit comprises a plurality of field effect of bipolar transistors 2, 3,... 5, whose gate electrodes are connected to respective tapping points of a resistive line 1, one other electrode of each transistor being connected to a common line 10, the other electrodes being connected to respective loads 6, 7, 9 (e.g resistors, capacitors or diodes). The resistive line may be continuous or comprise discrete resistors. The resistances between consecutive tapping points may be equal or unequal for non-linear conversions. Analogue-to-digital conversion.-In Fig. 1, the input analogue is applied through amplifier 16 to line 10, the ends 19, 20 of the resistive line are connected to different potentials, and the digital output is taken from terminals 23, 33, 53. In a modification, Fig. 3 (not shown), line 10 is at a constant potential, e.g. earth, the input analogue being applied via an amplifier (30) to one end (19) of the resistive line, the other end (20) of which is connected to a constant current source or sink (300). In another modification, Fig. 5, a common reference voltage is applied via gates 512, 513 to both ends of the resistive line during the first part of a clock pulse from 550. For the remainder of the clock pulse and afterwards gates 512, 513 are disabled and gates 510, 511 enabled to connect the input analogue and a constant current source of sink 540 to the resistive line. At the end of the clock pulse a number of the transistors 2-5 will conduct, discharging respective capacitors 60, 70, 90, a digital output being obtained at terminals 23, 33, 53. Digital-to-analogue conversion.-In Fig. 7 the digital input is applied to terminals 811, 821, 841 and a sawtooth voltage to one end 19 of the resistive line, the other end 20 of which is connected to a constant current source or sink 85. A voltage step appears at 871 when the first one of the transistors 2, 3, 5 that has a zero voltage digital input is rendered conductive and a pulse generator 87 enables a gate 88 to sample the sawtooth voltage to obtained the analogue output at terminal 891. In another arrangement, Fig. 8 (not shown), the ends of the resistive line are connected to respective potentials, one of the digital inputs (811-814) receives a zero voltage thus selecting a tapping point (11-14) on the resistive line, the analogue output being obtained across a resistor (96) connected to the common line (10). Temperature compensation.-A temperature compensating resistor (3021) and transistor (301) may be connected to one end of the resistive line, Fig. 13 (not shown); inverting amplifiers (303, 304) may be connected to respective ends of the resistive line, their inputs being connected to a common voltage source (U 1N ), which may be a reference source of an analogue input, via respective resistors (305, 307), Fig. 14 (not shown); or a single differential amplifier (3034) may be connected across the resistive line, with appropriate feedback and input resistances, Fig. 15 (not shown).