Patent GB-844304-A (GB)
Title: Improvements in signal translating apparatus
IPC: H03M1/00
Filed: 1956-12-28
Abstract: 844,304. Controlled non-linear inductors. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 28, 1956 [Dec. 30, 1955], No. 39532/56. Class 40 (9). [Also in Group XXXVIII] An electric digital-to-analogue code converter converts electric representations of a plurality of digit positions in a binary word into an A.C. analogue voltage and comprises a plurality of bi-stable devices, one for each order of said digit positions, each of said bi-stable devices including magnetic core means controlled by the associated digit representation to transmit or not to transmit an A.C. voltage proportional to the quantity represented by that digit position. As described for converting a representation in pure binary code of a number having three - binary digits plus a sign digit, to analogue form, Fig. 1, latches or triggers L2<SP>2</SP>, L2<SP>1</SP>, L2‹, LS are initially reset by pulses applied to RESET terminals to saturate magnetic cores 22, 21, 20, 33. For a digital input, for example, of 1010 where the three left-hand digits represent the number and the right-hand digit represents its sign (0 for positive, 1 for negative), the latches L2‹, L2<SP>2</SP> are turned on by inputs to the SET 2‹ and SET 2<SP>2</SP> terminals. This unsaturates the cores 20, 22 which act as transformers to allow windings 23, 29 to produce voltages in windings 24, 30 proportional to the respective turns ratios. The turns ratios for the cores 20, 21, 22 are in the ratio 1: 2: 4 so that the cores 20, 22 acting together produce a voltage proportional to five across the windings 31, 32. Since the latch LS remained reset, the core 33 remains saturated and an output in phase with the input A.C., and thus corresponding to a positive sign is produced across the output terminals 37, 38 by transformer action of the core 34. Had the digital input been 1011, the latch LS would have been set to saturate the core 34, and the output at terminals 37, 38 by transformer action of the core 33 would have been 180 degrees out of phase with the input A.C., corresponding to a negative sign. Cores 34, 39-41 are provided to maintain the source 25 under approximately constant loading. The latch circuit (Fig. 10, not shown) employs two transistors as bi-stable elements. Fig. 14 shows a circuit for setting the latches LS, L2‹, L2<SP>1</SP>, L2<SP>2</SP> and includes means whereby a " 1 " in any of the higher order digits of the digital input number incident at terminal 57 may set the latches L2‹, L2<SP>1</SP>, L2<SP>2</SP> simultaneously for use when the output of the converter represents the error signal in a closed loop servo system. The latches LS, L2‹, L2<SP>1</SP>, L2<SP>2</SP>, LS are initially reset at BG1 time. The sign digit appears at BG2 time, the 2‹ digit at BG3 time, &c. The AND gates 59 to 62 are opened at times BG2 to BG5 allow the latches LS, L2‹ to L2<SP>2</SP> to be set. At BG6 time, the latch 56 is set to open the AND gate 58 so that if a "1 " occurs in any digital position after the fourth from the right it will set any of the latches L2‹ to L2<SP>2</SP> not already set. A modification (Fig. 4, not shown) is adapted to provide an analogue output when the digital input is in a two-out-of-five code. A further modification (Fig. 5, not shown) provides an analogue output when the digital input is in coded decimal form. The transistor latch circuit may be eliminated if the bi-stable circuit of Fig. 7a employing two pairs 85, 86 and 87, 88 of magnetic cores. The terminals L, M are connected through serial input windings 81, 82, 83, 84, outputs from the sections 79, 80 being taken from the terminals N, P and S, T. The circuit is regarded as OFF when the cores 85, 86 are saturated, the cores being sent to this condition by a pulse applied to the RESET terminals Q, R. The source potential then appears across the windings 83, 84 to produce a D.C. voltage at the commoned cathodes of diodes 98, 99 which keeps the cores 85, 86 saturated by winding 100, and an A.C. output is produced across terminals S, T. A SET input to terminals U, W saturates the cores 87, 88 so that the windings 83, 84 become low-impedance paths and no potential is developed to keep cores 85, 86 saturated. An A.C. output from the windings 89, 90 then appears at the terminals N, P. Several of these circuits may be combined to produce a digital-to-analogue converter for a binary input (Fig. 8, not shown). An alternative bi-stable device, Fig. 9, employs only two magnetic cores 105, 106 with A.C. input windings 107, 108 and output windings 109, 111. Core 105 has a RESET winding 110 and core 106 has a SET winding 112. The windings 113, 114 provide cross connections to make the circuit bi-stable. A RESET input to the winding 110 saturates core 105 to allow the A.C. input potential to be developed across the winding 108, the winding 113 serving to saturate the core 105 and maintain it saturated when the RESET impulse ends. A SET impulse to the winding 112 changes the states of the cores.