Patent GB-873509-A (GB)
Title: Improvements relating to dividing circuits
Inventor: JAMES IVANHOE JOHN PENFOUND
IPC: G06G7/161
Filed: 1956-11-15
Abstract: 873,509. Quotient analogue systems. ELECTRIC & MUSICAL INDUSTRIES Ltd. Nov. 15, 1957 [Nov. 15, 1956], No. 34959/56. Class 37. A dividing circuit produces an output proportional to the ratio of two applied voltages or currents A, B. In the embodiment of Fig. 2 of the drawing accompanying the Provisional Specification, B is the modulating potential and A is kept constant. The embodiment comprises a multivibrator consisting of valves 1, 2 and resistors and capacitances 4, 6 and 3, 5 and the variable potential B is applied at 19 so that the anode current of a pentode 18 (corresponding to R) and therefore the cathode current of valves 1, 2 varies with input so that the time taken to charge or discharge between the critical potentials of the multivibrator normally determined by diodes 15, 16 is proportional to the input at 19 and the frequency of the multivibrator output will be modulated by the reciprocal of the signal input. In the embodiment of Fig. 1 potentials A and B are both varied so that a B A signal of the form - or - may be derived A B dependent on whether frequency or period is measured. A multivibrator circuit is again used, catch diodes 62, 63 linearizing the potentials of saw-tooth waveforms applied to 50, 51. The modulating potential A is applied to the grids of valves 56, 57 the anodes of which are connected to the grids of valves 50, 51, potential A thus determining the charging current of capacitors 52, 53, while potential B which is applied to a constant current valve 54 modulates the cathode currents of valves 50, 51 and therefore the amplitude of the potential pulses at their anodes. The period of the pulses will therefore vary linearly with potential B and the frequency of the multivibrator linearly with potential A so that simultaneous variation of A and B causes the frequency of the multi- A vibrator to vary linearly with the ratio -. B The output is derived from terminal 66 and by detecting the frequency or period variations a A smoothly varying analogous-potential of - or B B - respectively can be derived. By a modifica- A tion of Fig. 2, the potential B may be applied to the control electrode of valve 60 so as to modulate the minimum potential for the grids of valves 50, 51. The constant current valve 54 must in this case however be replaced by a high value resistor. To derive an output A analogous to - a frequency discriminator is B employed (Fig. 2, not shown), while an output B analogous to - is derived by measuring the A period of the oscillations as already referred to. (It is stated in the Provisional Specification A B<2> A that an output of the form - or - or - or B<2> A BC BC -may be derived by using the additional A input at B' for applying different modulating potentials and that a phantastron or saratron may replace the two valve multivibrator.) The invention may be applied to deriving a signal representative of the chromaticity for use in colour television, the X, Y, Z signals representative of the colour components of a colour being added and applied as the modulating signal B and the signal X as the modulating potential A so that by using a frequency discriminator the desired chromaticity signal X output - is derived. Specification X+Y+Z 847,795 is referred to.