GB1060991A - Improvements in or relating to phase shifting circuits - Google Patents

Abstract

1,060,991. Impedance networks. NORTH ATLANTIC INDUSTRIES Inc. Feb. 18, 1964, No. 6753/64. Heading H3U. A 90-degree phase-shift circuit giving substantially constant attenuation and relatively slowly varying phase-shift over an operative frequency band comprises phase-lead and phase-lag networks 2 and 3 excited in antiphase from an A.C. source 1 and combining means, shown as an adding network 4, to which the outputs of the networks 2 and 3 are applied to deliver a resultant equal to the mean of the outputs, and the networks being chosen to have equal attenuations and produce equal phase changes of opposite sign at the centre frequency of the said frequency band. Networks 2 and 3 may comprise simple resistancecapacitance networks, Figs. 2 and 3 (not shown) respectively, but Fig. 5 shows a preferred form of circuit in which the phase-lag network is composed of two sections R 3 , C 3 , R 4 and R 5 , C 4 , R 6 while the phase-lead network is composed of sections R 7 , C 5 , R 8 and R 9 , C 6 , R 10 . Curves 9 and 10, Fig. 6, show the response curves for the two halves of the circuit, curve 10 being drawn in the third quadrant to indicate excitation in antiphase. The centre frequency w 0 is chosen to correspond to points 12, 13 at which the tangents to the curves are perpendicular to the axis of the exciting voltage e. The mean of the outputs e 1 , e 2 , taken from output point 11 is then in quadrature with the input e and it can be seen that there is little change in amplitude and phase of the output as the operative points move in opposite directions round their respective curves 9 and 10 as the frequency is altered. In Fig. 8 (not shown), the R-C branches C 3 R 4 and C 5 R 7 of Fig. 5 are each replaced by a single capacitor; as a result the curves of Fig. 5 are modified slightly with the result that the amplitude of the output remains substantially constant over the operative frequency band but the phase changes slightly. Fig. 10 shows a network having a similar response to that of Fig. 8 (not shown), but in this the phase-lag and phase-lead networks are partly combined, resistance Ra and the shunt branches Rx Cx, Ry Cy functioning as the phase lag network and the capacitance Cb and the same shunt branches functioning as the phase-lead network. The values are chosen so that Rx, Cy=Ry, Cx=Ra, Cb=<SP>1</SP>|w 0 .