GB895201A - Improvements relating to electrical function generators - Google Patents

Abstract

895,201. Cathode-ray tube circuits; non- linear vilve circuits; waveform generating circuits. ELECTRICAL & MUSICAL INDUSTRIES Ltd. July 24, 1958 [Aug. 3, 1957], No. 24665/57. Classes 40(6) and 40(7). A function generator comprises a matrix of electrical impedances of selected magnitudes, a series of gates respectively associated with different combinations of the impedances, means for operating one of the gates thereby to select the respective combination of impedances, and means for pulsing the impedances of at least the selected combination in sequence to generate an electrical function of which successive ordinates are determined by the magnitudes of the impedances of the selected combination, the gates being so arranged that operation of a gate is required to condition the connections to the respective combination of impedances in such a way that operation of the pulsing means can produce an output from the function generator. Two such generators are provided to afford the X, Y deflections for character writing on a cathode-ray tube (C.R.T.) screen, Fig. 9 (not shown). Pulses from a delay unit D Fig. 1 appear sequentially on conductors P 1 . .P N connected by an impedance matrix C to output conductors B 1 . . B M each of which thereby carries a quantized approximation to a predetermined waveform, Fig. 3 (not shown), the desired function being selected by switch S. The impedance matrix may comprise resistors Fig. 2 or transformers, Fig. 10 (not shown). In the quiescent state leads C Fig. 2 are biased below amplifier A o cut-off and diodes BW are switched off. For function e.g. M-1 selection a positive potential is applied to lead C M-1 , for a time equal to that of the pulse train from the delay unit, and switches off diode CW M-1 , the function ordinate voltages passing to amplifier A o via diode BW M-1 . The delay unit may be a delay line, a circuit as described in Specification 647,950 or a ring counter as described in Specification 766,987 or 766,988. In a modification the rate of change of output during successive intercolumn intervals is controlled by replacing the amplifier feedback resistor Rs by a capacitor, Figs. 4 and 11 (not shown). In a further embodiment a sawtooth waveform from generator G s Fig. 5 is applied to subtraction circuit E directly and via non-linear amplifier A 1 . Non-linear amplifiers, Fig. 7. Cathode resistors R 0 is connected to a network N M comprising diodes D 1 . . D N resistors R 1 . . R N and bias sources -v. . -Nv. A negativegoing sawtooth input to the control grid of valve V 1 causes the diodes to switch over successively to the reverse condition to give discrete variations of effective cathode resistance. To afford greater distortion additional diodes and resistors are provided, Fig. 8 (not shown). To generate multiple functions, either separate non-linear amplifiers or networks N M are used, switching being effected to choose a desired function as described above. For spacing characters formed on the C.R.T. screen, a shift generator synchronized with the initial pulse generator is provided. Specification 761,853 also is referred to.