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Controlled Linearity Phase Shifter

IP.com Disclosure Number: IPCOM000075539D
Original Publication Date: 1971-Oct-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Leighton, HN: AUTHOR

Abstract

The circuit of Fig. 1 includes a phase-shifting circuit 10, which can be controlled by a single variable resistance R(V) to shift the phase of the output signal e(0) over a range of more than 180 degrees with respect to an input signal e(1). Fig. 2 shows a diagram of the output voltage vector including its amplitude and phase with respect to the input voltage. In order to linearize the phase shift provided by phaseshifting circuit 10, a phase comparator circuit 30 is provided, to compare the relative phase different between the input signal e(1) and the output signal e(0) with phase-control signal E(c).

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Controlled Linearity Phase Shifter

The circuit of Fig. 1 includes a phase-shifting circuit 10, which can be controlled by a single variable resistance R(V) to shift the phase of the output signal e(0) over a range of more than 180 degrees with respect to an input signal e(1). Fig. 2 shows a diagram of the output voltage vector including its amplitude and phase with respect to the input voltage. In order to linearize the phase shift provided by phaseshifting circuit 10, a phase comparator circuit 30 is provided, to compare the relative phase different between the input signal e(1) and the output signal e(0) with phase-control signal E(c).

Phase-shifting circuit 10 has a preshifting circuit including resistors R1 and R2 and capacitor C1 to provide a downward shift to the vector diagram, as shown in Fig. 2, allowing the output voltage vector to swing through an arc greater than 180 degrees. The theoretical limits of rotation are from -45 degrees to 225 degrees, but this will result in an output voltage of zero amplitude at a phase shift of +90 degrees and, therefore, the range must be restricted to less than the theoretical maximum of 270 degrees. The downward shift will cause the amplitude of e(o) to vary with phase, but this can be compensated for by an automatic gain control in following amplifier stages. If a square wave output is acceptable, the signal e'(o) from square-wave converter 37 can be used. phase- shifting circuit 10 also has a voltage-divider circuit having resistors R3 and R4, which attenuate the input signal e(1) to a value e(3) that is equal to the real part of the preshifted signal e(2). Phase shifting circuit 10 also has a variable-phase shifter including operational amplifier I11 resistors 5 and R6, capacitor C2 and variable resistance RV in the form of a field-effect transistor controlled by resistors R7 and R8.

The variable resistance R(V) cannot, of course, be varied from zero to infinity if implemented using a field-effect transistor, but can be varied within the range of R(min) =500 ohms to R(max) =50,000 ohms. For symmetry of design, it is desirable to select C2 such that the center of the...