RC/CR automatic quadrature network
First Claim
1. A phase shift circuit comprising:
- a first phase shifter having a first input that receives an input signal to be phase shifted, a first output at which appears a phase shifted first output signal having an amplitude that is related to the phase difference between the input signal and the first output signal, and a first control input that receives a first control signal to which the first phase shifter is responsive by varying the phase shift between the input signal and the first output signal;
a second phase shifter having a second input that receives the input signal, a second output at which appears a phase shifted second output signal having an amplitude that is related to the phase difference between the input signal and the second output signal, and a second control input that receives a second control signal to which the second phase shifter is responsive by varying the phase shift between the input signal and the second output signal;
a first amplitude detector, coupled to the first output signal, that produces a first level signal corresponding to the amplitude of the first output signal;
a second amplitude detector, coupled to the second output signal, that produces a second level signal corresponding to the amplitude of the second output signal;
a differential amplifier having inputs coupled to the first and second level signals and having an output; and
a circuit coupled to the output of the differential amplifier and having outputs coupled to the first and second control inputs, the circuit introducing a differential offset between the first and second control signals.
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Accused Products
Abstract
An IQ modulator incorporates a quadrature network that is responsive to a frequency dependent control signal and that has in-phase and quadrature signals that are of equal amplitude and in exact quadrature over a wide range of applied frequencies. The quadrature network includes RC and CR phase shifters whose C'"'"'s are fixed capacitors of equal value and whose R'"'"'s are made equal to each other and to the capacitive reactance of the C'"'"'s by the action of the frequency dependent control signal. The R'"'"'s may be FET'"'"'s. The frequency dependent control signal may be generated without express knowledge of the applied frequency by a servo loop that nulls out the amplitude difference between the in-phase and quadrature outputs from the quadrature network; it may also be generated from a look-up table as an express function of frequency. The frequency dependent control signal is split into separate instances that are applied to each R, and an offset may be introduced therebetween to provide extreme precision. The offset may be fixed or programmatically controlled as a function of frequency. Varactors may be used to provide variable C'"'"'s in cooperation with fixed R'"'"'s. The entire circuit may be fabricated as a GaAs IC for use in the frequency range of 200 MHz to 3 GHz.
56 Citations
7 Claims
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1. A phase shift circuit comprising:
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a first phase shifter having a first input that receives an input signal to be phase shifted, a first output at which appears a phase shifted first output signal having an amplitude that is related to the phase difference between the input signal and the first output signal, and a first control input that receives a first control signal to which the first phase shifter is responsive by varying the phase shift between the input signal and the first output signal; a second phase shifter having a second input that receives the input signal, a second output at which appears a phase shifted second output signal having an amplitude that is related to the phase difference between the input signal and the second output signal, and a second control input that receives a second control signal to which the second phase shifter is responsive by varying the phase shift between the input signal and the second output signal; a first amplitude detector, coupled to the first output signal, that produces a first level signal corresponding to the amplitude of the first output signal; a second amplitude detector, coupled to the second output signal, that produces a second level signal corresponding to the amplitude of the second output signal; a differential amplifier having inputs coupled to the first and second level signals and having an output; and a circuit coupled to the output of the differential amplifier and having outputs coupled to the first and second control inputs, the circuit introducing a differential offset between the first and second control signals. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification