Patent GB-1246396-A (GB)
Title: Ac-dc function generators
IPC: G06G7/28
Filed: 1969-09-23
Abstract: 1,246,396. Function generators. BENDIX CORP. 23 Sept., 1969 [1 Oct., 1968], No. 46812/69. Heading G4G. In an electronic function generator for approximating a prescribed function of an A.C. or D.C. input voltage by a plurality of straight line segments, each segment generator includes a threshold voltage source, an operational amplifier responsive to the input voltage and the threshold voltage, and gating means for the operational amplifier output which includes a field effect transistor (FET). The arrangement shown in Fig. 1 may produce at terminal 6 the function Eo, shown in Fig. 2, of the alternating input E I  applied to terminal 2, the signals corresponding to segment S 1  and S 2  for segment S 2 , and to S 1 , S 2 , and S 3  for segment S 3 , being summed in operational amplifier 5, the inversion of phase thereby produced being corrected by a subsequent operational amplifier 31. Segment S 1  is formed by the signal e 1  produced in the branch containing resistor 17, the slope being determined by the ratio of resistors 17 and 4. Segment S 2  is produced by the addition to e 1  of a signal e 2  produced in a branch containing FET's 29a and 30a which act as switches, diodes 23a and 16a limiting the negative voltage of source element 26a and the positive voltage of source element 18a, respectively, to a value of approximately 0À7 volts. A square wave reference signal from terminal 7, in phase with signal E I , is applied via diode 21a to the gate 20a of FET 30a, and is of sufficient amplitude to keep the gate closed during the negative half cycles. A first alternating threshold signal Eb 1 , in antiphase with the input signal E I  and the reference signal from terminal 7, is applied with signal E I  to the S 2  branch, the resultant signal being in antiphase or in phase with the reference square wave according as the input signal E I  is less than or greater than the first threshold signal Eb 1 . If E I  is less than Eb 1 , therefore, the resultant signal applied to source element 18a of FET 30a, twice phase-inverted by passage through operational amplifier 12a and 15a, is negative during the positive half cycles of the reference square wave, during which half cycles gate 20a is open, so that capacitor 25a, and hence gate element 28a of FET 29a, is charged negative, to keep gate 28a closed. When the input signal E, exceeds threshold signal Eb 1 , the resultant signal applied to source element 18a is positive during the positive half cycles of the reference square wave, so that gate element 28a of FET 29a is not closed, and the resultant signal from amplifier 12a passes to the summing amplifier 5, the single inversion of phase provided by amplifier 12a ensuring that signal e 2  is in antiphase with e 1 , to give a reduction of slope of segment S 2  compared with segment S 1 . If an increase in slope is required, the non-inverting rather than the inverting inputs of the operational amplifiers in the S 2  segment branch are employed. The branch for segment S 3  is similar to that for S 2 ; if the prescribed function does not pass through the origin in Fig. 2, the branch for segment S 1  is also replaced by one similar to that for segment S 2 . For a D.C. input signal E I , the reference square wave signal and the FET 30a and components 21a, 24a, and 25a may be dispensed with, the output of amplifier 15a being connected to gate element 28a through the diode 22a.