| 摘要 |
<p>1,269,046. Multiplying circuits. EMI Ltd. 28 April, 1969 [1 May, 1968], No. 20609/68. Heading G4G. The time delay inherent in the smoothing circuit of a time-division analogue multiplying circuit is compensated by phase-shifters in the circuits of the input voltages. Ideally, the output should be z = xy, but a delay t in the smoothing circuit results in z=xy-zt. According to the invention, the inputs are so delayed that the circuit performs the operation defined by z+zt=(x+xt)(y+yt) whereby it is found, on expressing zt in terms of the other variables, that the new equation for z includes no first order terms in t. In the multiplier shown, analogue voltage x is applied from terminal 1 through phase-advance circuit 6, 7 to integrating circuit 8, 9. A constant voltage k is applied to terminals 4, 5 which are connected to the input of the integrator 8, 9, respectively, through a resistance 10 equal to the resistance 6 and through a resistance 11 of half the value of resistances 6 and 10. Thus, depending upon the state of switch 12, the rate of change of the output of the integrator 8, 9 is proportional either to k+x or k-x. This output feeds a trigger 13 designed to operate the switch 12 when the output rises to a certain upper threshold value and thereafter to operate it again when the output falls to a certain lower threshold value. It can be shown that the switchoperating signal is a rectangular pulse having a mark/space ratio of (k+x) : (k-x). A summing amplifier 17 is connected to terminals 2, 3, respectively, supplied with analogue voltages y and -y, these signals being advanced in phase by circuits 15, 16 and 18, 19, both having the same time constant as circuit 6, 7, the value of resistor 18 being half that of resistor 15. The signal -y is applied to the amplifier 17 through switch 14 actuated by the same signal as switch 12. The pulse input to the amplifier has an amplitude equal to y and a mark/space ratio equal to (k+x) : (k-x). This signal is smoothed by the capacitance 21 which produces a phase change of the same magnitude as the compensating capacitances 7, 16, 19. The smoothed signal represents the desired product xy.</p> |
