USING A PARALLEL-T NETWORK FOR DEVELOPING QUADRATURE VOLTAGES AT VARIABLE FREQUENCIES.
NAVAL RESEARCH LAB WASHINGTON D C
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Two voltages phased in quadrature are developed at special junctions in a twin-T or parallel-T resistance-capacitance network. Heretofore, this network has been utilized for only its null transmission characteristics. Utilization of these properties remain essential when considering some complete circuits. The two voltages are produced with phase relation that is not sensitive to changes of the driving frequency however, the amplitude ratio of the two voltages is related to the null frequency. A variable frequency oscillator which generates two voltages phased in quadrature can be constructed using a symmetric parallel-T network. The operating frequency may be manually selected in somewhat the same manner as presently done with conventional Wien-bridge oscillators. This oscillator may be converted into a generator of voltages with arbitrary phase relations which may be simply controlled. By making connections to all junctions of the parallel-T network it is possible to construct frequency-selective amplifiers which operate through narrow bandwidths and produce well-filtered quadrature voltages. These voltages should be useful for producing undistorted circular time traces on oscilloscopes. With connections to all junctions in a parallel-T network it is possible to construct frequency discriminators with output voltages that vary in a predictable manner as the input frequency varies through a maximum-to-minimum ratio of four to one. The bandwidth together with the upper and lower limit of the output voltage can be altered by incorporating a frequency-selective amplifier as a part of the frequency discriminator. Author
- Electrical and Electronic Equipment