GB1127627A - Improvements in or relating to circuit arrangements for regulating the dynamic range of electrical signals - Google Patents

Abstract

1,127,627. Nonlinear circuits. SIEMENS A.G. 23 Sept., 1965 [24 Sept., 1964], No. 40527/65. Heading G4G. Non-linear circuit includes a four terminal network, one arm of which includes a control network having two inductively coupled parallel arms at least one of which contains a series connected non-linear impedance, e.g. a diode, and in which the signal appearing at the input terminals or the output terminals is applied across the inductive coupling element in one of the parallel arms so that the control network injects a dynamically modified signal into the four terminal network. Fig. 6 shows a forward control compressor or expander in which the control network includes resistors R 1 and R 2 , one of which is non-linear, connected in series with the respective inductively coupled elements in a parallel circuit between points B<SP>1</SP> and C<SP>1</SP>. Across one inductive element is applied the input signal via a cathode follower so that a voltage Ue.e-<SP>a</SP> is developed across the points B<SP>1</SP>C<SP>1</SP>, to be combined with the input voltage Ue, to provide the output voltage Ua to the output transformer U 2 . The function e<SP>-a</SP> is shown to be so that the circuit operates as a compressor if, with increase in signal applied to the network, R 2 decreases and R 1 remains constant, and as an expander if R 1 decreases and R 2 remains constant. In a backward controlled circuit the connections A<SP>1</SP>B<SP>1</SP> and C<SP>1</SP>D<SP>1</SP> of Fig. 6 are broken and connections made A<SP>1</SP>C<SP>1</SP> and B<SP>1</SP>D<SP>1</SP> so that the cathode follower is fed with the output signal and the voltage developed across the non-linear network combined with the input. In a modification of Fig. 6, incorporating the backward control connections set out above, the transformer U 2 is replaced by a cathode follower which allows the lower winding of transformer U 1 , and the balancing network R n to be omitted, Fig. 7 (not shown). A further modification, Fig. 8, includes an extra winding on transformer U 1 to feed, via cathode follower Rol, the non-linear circuit. The reciprocal circuit may be provided by exchanging the positions of R 1 and R 2 by links A<SP>11</SP>, B<SP>11</SP>, C<SP>11</SP>, D<SP>11</SP>. An equivalent circuit to Fig. 6, but which employs transistors operating on current rather than voltage, is described relative to Fig. 9 (not shown).