Patent GB-1068131-A (GB)
Title: Electronic analogue multiplier and divider
IPC: G06G7/163
Filed: 1962-11-13
Abstract: 1,068,131. Electric analogue calculating. REGISTRAR, JADAVPUR UNIVERSITY, INDIA, P. KUNDU, and S. BANERJI. Oct. 31, 1963 [Nov. 13, 1962], No. 42880/62. Heading G4G. [Also in Division H3] An electric analogue multiplier and divider comprises a logarithmic amplifier stage coupled over a linear amplifier to an exponential amplifier stage; an A.C. signal being supplied to the logarthmic stage ; separate first and second D.C. analogue signals being applied to the log ariithmicand exponential stages, and the output of the exponential stage representing the input multiplied by the first D.C. analogue signal and divided by the second. The amplifier stages may be transistorized, and it is then shown by mathematics that the collector current i c2  of the exponential stage is given by where i e 1  = input current, I eq 2  is the input junction current of the exponential stage due to the second D.C. analogue signal, and I eq 1  is the input junction current of the logarithmic stage due to the first D.C. analogue signal. In Fig. 1 an alternating input voltage V in  is applied to terminals AB, and high resistance R 1  in series therewith conducts a proportional A.C. into the emitter of transistor TR 1  operating as a logarithmic resistor, and a direct voltage VY at terminals CD causes a proportional polarizing D.C. to flow into the emitter over high resistance R 3 ; the D.C. amplitude being always in excess of the superimposed A.C. amplitude in the emitter circuit. The transistor base is grounded and the collector connected to a negative supply line, while the emitter is capacitance coupled to the base of a linear emitter follower connected transistor TR 2  presenting a high impedance to the logarithmic stage and a low impedance to the succeeding exponential stage, whose collector is capacitance coupled to the emitter of transistor TR 3  of the exponential stage, whose base is grounded and whose collector is connected to negative supply over R 2 . A direct voltage V x  is applied to terminals EF to cause a proportional direct current to flow into the emitter over high resistance R 4 ; the direct voltage between emitter and base being in excess of the corresponding alternating voltage. The output across collector load resistance R 2  represents the product of the input voltage V in  and the ratio x/y The coupling between the logarithmic and exponential stages may be reduced to capacitor C 2  if the input impedance of the exponential stage is greatly in excess of the output impedance of the logarithmic stage. In Fig. 2 (not shown), a square root law signal compressor circuit comprises a multiplier and divider whose output is amplified, linearly rectified, and applied to the y input of the multiplier divider; a polarizing voltage being applied to the x input. Similarly in Fig. 3 (not shown) a square law signal expander comprises a multiplier/divider whose input signal is linearly rectified to energize the x input; the y input being supplied with a polarizing voltage. In Fig. 4 (not shown) an amplitude stabilizing circuit comprises a multiplier/divider whose input signal is linearly rectified and applied to the y input; the x input being supplied with a polarizing voltage. In Fig. 5 (not shown) an input signal is applied to a multiplier/divider whose output is linearly amplified, linearly rectified, and applied to a non-linear function generator having a variable exponent N, whose output is applied to the y input. The multiplier/ divider output for an input A sin wt is Similarly (Fig. 6, not shown) the input signal is linearly rectified and applied to a variable exponent function generator whose output is applied to the x input of the multiplier/divider whose output is then A<SP>N+1</SP> sin wt for an input of A sin wt. In each case the remaining input of the multiplier/divider circuit is supplied with a polarizing voltage. The multiplier/divider circuit may also be employed as a linear amplitude modulator (Fig. 7, not shown) or as a linear variable gain amplifier in which the ratio of the x and y input voltages is varied. The linear rectifiers referred to may comprise (Fig. 8, not shown) a diode in series with a capacitor across the input, with the capacitor shunted by a resistor in series with an ohmic resistor and a non-linear resistor or semiconductor diode; the output being taken across the latter ohmic and non-linear resistors.