Patent GB-937908-A (GB)
Title: Improved ball-or-roller bearings
IPC: H03K4/501
Filed: 1961-01-02
Abstract: 937,908. Pulse modulation circuits. G. S. BAHRS, D. W. MARTIN, and M. M. McWHORTER. Jan. 2, 1961 [Nov. 25, 1959], No. 118/61. Class 40 (5). In an apparatus for converting a variable voltage to a variable pulse rate the input signal e in , Fig. 1, is supplied via terminals 11 and resistor R in  to charge a capacitor C I . A D.C. amplifier 13 presenting a high impedance to the capacitor C 1  amplifies the voltage appearing on the capacitor, Fig. 3C, and controls a multivibrator 14 which develops a control pulse of period T, Fig. 3D, whenever the applied voltage reaches a predetermined level, e.g. zero. A charging circuit 15 and charge-dispensing circuit 16 provide a standard pulse having a constant current times time product each time a pulse is applied from the multivibrator. The average current I scd  from the charge dispenser is therefore proportional to the pulse repetition frequency. The standard pulse is fed back to the point 12 and lowers the voltage e n  below zero as indicated at 18, Fig. 3B, and the input signal, Fig. 3A, charges the capacitor C I , as shown at 19, until it reaches zero volts and the multivibrator 14 is triggered again to activate the circuits 15, 16, and withdraw another standard charge from the capacitor C I . The circuit operates at such a frequency as to maintain the voltage e n  across the capacitor C 1  very near zero, the capacitor being neither charged nor discharged by any appreciable amount, and the average current flowing into the capacitor being maintained substantially at zero. Thus the current i in  is approximately equal to e in /R in . A current I os  derived from a reference source E  ref  via a resistor R os  sets the operating point of the apparatus for zero input. Initially with the current i c  positive, the voltage e p  at point 21 is equal to the voltage E ref . When the current i c , Fig. 3E, reverses as at 22 due to a pulse 23, Fig. 3D, from the multivibrator 14 a capacitor C p  discharges and the voltage e p , Fig. 3F, falls linearly until it is clamped at zero potential by the diode D2 and Cp ceases to discharge as shown at 26. When the current i c  reverses, as at 27, and is again positive, Cp is charged, as shown at 28, and the voltage e p  increases linearly until it is clamped at the reference voltage E ref  by the diode D1 Each time the charging circuit 15 operates, e p  swings between E ref  and zero and back to E ref , the discharge current I SCD  from Cp, Fig. 3G, being passed via diode D4 to the capacitor C I  and charging current being passed via diode D3 to earth, and in this way a standard charge is dispensed once per cycle. With no input current the device will operate at a frequency # 0  dependent upon I os  and input voltages of either polarity will cause a corresponding deviation from this centre frequency. The diodes D3, D4, introduce some non-linearity into the voltage change across the capacitor Cp, as shown at 29, 30, Fig. 3H, and this may be minimized by connecting a correctly damped inductive network in series with Cp giving the waveform I, Fig. 3. Alternatively two inductive networks in series with the diodes D3, D4, respectively, may be used. A transistorized circuit for effecting the necessary operations is described, Fig. 2 (not shown).