GB1048093A - Improvements relating to negative impedance converter circuits - Google Patents

Abstract

1,048,093. Negative impedance converters. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Feb. 2, 1965 [Feb. 5, 1964], No. 4890/64. Heading H3T. To correct for parasitic impedances and offset voltagers or currents in a negative impedance converter, the two-port converter circuit of the invention is provided with one or more of (a) a source of D.C. potential connected to a terminal of the second port to render the potentials at each terminal the same, (b) a correcting element, of similar value to the series parasitic impedance and/or offset voltage appearing at the first port, which is connected in series with the second port, ((c) a correcting element, of similar value to the shunt parasitic impedance and/or associated offset current appearing at the second port, which is connected in parallel with the first port. In the circuit of Fig. 7 the correcting impedance is resistor R 11 and resistor R 5 in the collector circuit of transistor T 1 serves as an extra D.C. source to correct the offset current appearing at the second source. At the second port the series correcting impedance is resistor R 7 and the output port terminal potentials are rendered equal by Zener diode ZD. The conversion ratio of the circuit, preferably - 1, is determined by the ratio of R 1 to R 2 and may be altered by the resistors R 8 , R 9 , R 10 acting to alter the effective impedance of R 2 . R 9 is altered to maintain the potential charge across R 8 equal to zero. A simplified version of the circuit of Fig. 7 is illustrated in Fig. 8 (not shown). In Fig. 9 (not shown) the resistors R 3 , R 4 of Fig. 7 are replaced by transistors T 3 , T 4 and the current and voltage correcting elements comprise transistors T 5 , T 6 . The single transistors of the circuits may be replaced by Darlington compound transistors (Fig. 10, not shown). A further alternative (Fig. 13, not shown) is a circuit based on a bridge arrangement (Fig. 11. not shown).