NONPHASE SENSITIVE SYNCHRONOUS DETECTOR

1,187,516. Detectors. TEXTRON Inc. 19 April, 1968 [1 May, 1967] No. 18639/68. Heading H3Q. [Also in Divisions G1 and G6] A signal proportional to the magnitude E of that component of a complex electrical signal which has the same frequency as a reference signal, but unknown phase displacement # relative thereto, is obtained by producing from said reference and complex signals first and second signals V 1 , V 2 , proportional in magnitude to Ecos# and Esin# respectively, and from these producing a signal at least approximately proportional to V 1 cos# + V 2 sin#. In the embodiment described a signal in phase with the reference is induced in a centretapped secondary 18 of a transformer 13, a signal proportional to the complex signal is induced in a secondary 26a of transformer 35, and from these phase-sensitive diode detector circuit 31 produces at 44 a D.C. voltage proportional to Ecos#. A second similar circuit 32 produces at 47 a D.C. voltage equal to that at 44 but of opposite polarity and a diode OR gate 43, 46, selects that one of the voltages at 44, 47 having required polarity to constitute V 1 . A similar arrangement, supplied by a transformer 17 whose primary is excited 90 degrees out of phase with the reference, produces at 451 a second D.C. voltage V 2 proportional to Esin#. The signals V 1 , V 2 are applied to at least two summing circuits, each comprising a pair of input resistors, as 48a, 48b, connected to a summing junction, as 51. As shown, three summing circuits 48-50 are provided, the conductances of their input resistors being the ratios cos 15 degrees: cos 75 degrees, cos 45 degrees: cos 45 degrees and cos 75 degrees: cos 15 degrees. It is stated that the signal at the summing junction having the highest potential will, to a good approximation, be proportional to V 1 cos# + V 2 sin#. This signal is selected by diode gate 54-56 to provide Ecos2# + Esin2# at the output 57.