Patent GB-1009498-A (GB)
Title: Analogue multiplier
IPC: G06G7/163
Filed: 1964-05-28
Abstract: 1,009,498. Electric analogue calculating. NORTH AMERICAN AVIATION, Inc. May 28, 1964 [May 28, 1963], No. 22185/64. Heading G4G. An electric analogue multiplier comprises signal sources supplying a first multiplicand signal and a second reference signal to a gain controlled amplifier, a feedback loop responsive only to the reference signal and maintaining the amplification at a predetermined level, a signal source supplying a third multiplier signal to the feedback loop to vary the amplification, and a combining circuit receiving the amplifier output and at least one of the first and second signals to produce a signal proportional to the product of the first and third signals. Fig. 4 shows a voltage sensitive amplifier 15 energized over summation resistors 11, 17 by an input multiplicand signal e 1  at D.C. or L.F. and a reference H.F. signal E c (# 1 ); the frequencies of e 1  and E c (# 1 ) lying within the passband of the amplifier which is gain controlled by element 16 (which may be a field effect transistor or other voltage sensitive impedance) responsive to a multiplier signal e 2  at D.C. or L.F. combined over summation resistors with the rectified output of a band pass filter 18 tuned to w c  and connected to the amplifier output, which is also applied over a band stop filter 20 tuned to w c  for combination with signal e 1  over summation resistors at the input of amplifier 19. The gain of amplifier 15 varies inversely as the amplitude of E c (# 1 ) and may be thereby adjusted to, e.g. unity in the absence of e 2  to produce a phase inverted signal - e 1  so that the output e 0  of amplifier 19 is then (e 1 -e 1  = 0. The introduction of signal e 2  varies the gain of amplifier 15 to (I + K 2 e 2 ) and its output to - e 1 (1 + K 2 e 2 ) so that e 0  = e 1  - e 1 (1 + K 2 e 2 ) = K 2 e 1 e 2  and the sense of the product is responsive to the senses of the multiplier and multiplicand. Fig. 5 shows a modification wherein a reference signal E 2 (# 1  is applied over a quadrature phase shift feedback amplifier 26 to variable gain amplifier 10 over summation resistor 17 and to feedback amplifier 19a over summation resistor 29; a multiplicand signal E 1 (# 1 ) is applied to amplifier 10 over summation resistor 11 and to amplifier 19a over summation resistor 28; and a multiplier signal E 3 (# 1 ) is applied to the input of amplifier 19a over a quadrature shift capacitor 27; the signals being initially of like phase and frequency. The output of amplifier 10 is applied to the input of amplifier 19a over summation resistor 30, and the latter output energizes phase sensitive detector 31 also energized from the output of amplifier 26 to produce a control signal applied over a low pass filter and amplifier 16 to a field effect transistor or other voltage sensitive impedance 13 in the feedback path of amplifier 10. In the absence of multiplicand and multiplier signals E 1 (# 1 ) and E 3 (# 1 ) the gain of amplifier 10 is adjusted to unity, since the quadrature coded reference signals E c  |#90 from the outputs of amplifier 26 and of amplifier 10 combine to a quadrature coded difference signal at the output of amplifier 19a, which is detected at 31 to regulate the impedance of 13 and the gain of amplifier 20 to zeroize the difference. Application of multiplicand signal E 1 (# 1 ) applies inputs E 1  0 and E c  90 to amplifier 19a of which only the quadrature coded signal affects the gain of amplifier 10, since detector 31 produces zero output in response to in-phase signals. Variations of the multiplicand signal produce zero variations in the output of amplifier 19a since its input receives the sum of any variation #E 1  and a corresponding phase inverted variation - #E 1 . Application of a multiplier signal E 3 (# 1 ) in phase with E 1 (# 1 ) produces a corresponding quadrature signal at the input of amplifier 19a over capacitor 27, so that phase detector 31 responds to the corresponding output and varies the gain of amplifier 10, and also reduces any residual quadrature component in the output of 19a due to the response of amplifier 10 to E c . It is shown that the in-phase output e o  of amplifier 19a = E 1 E 3 ; the output sense being responsive to the senses of the inputs. A mathematical analysis is given.