Variable phase-shift circuit, phase interpolator including the same, and a digital frequency synthesizer incorporating such an interpolator

摘要

The variable phase-shifting circuit (40) comprises an input (A) for receiving an input signal (Sin) having a determined frequency of oscillations (Fin), an output (B) for delivering an output signal (Sout) having the same frequency of oscillations and a variable phase-shift with respect to the input signal, and at least one control input (C) receiving a signal (Is) for controlling the phase-shift of the output signal with respect to the input signal. The circuit comprises as the central part a synchronized oscillator (OS) having a synchronization inptu coupled to the input of the circuit, and at least one output coupled to the output of the circuit. The synchronized oscillator has the frequency of free oscillations (Fo) variable, which is controlled by the signal (Is). The synchronized oscillator (OS) comprises an astable multivibrator circuit having two branches connected in parallel between a positive supply terminal and a negative supply terminal or the ground, and a current source in each branch, where the stationary state currents are determined by the control signal (Is) in a manner to vary the frequency of free oscillations of the synchronized oscillator. The phase interpolator (claimed) comprises an output delivering an interpolated clock signal, at least one data input for a digital value representing the difference between the instant of effective switching of a pulse of a signal to interpolate and the instant of desired switching of the output signal, a set of N1, for example 8, variable phase-shifting circuits (claimed), each receiving a reference clock signal and delivering a signal phase-shifted according to the control signal, a multiplexer with N1 inputs for signals delivered by the variable phase-shifting circuits, a register, a digital-analog converter delivering an analog signal for the phase-shift correction which is directed to the control inputs of the variable phase-shifting circuits, a demultiplexer receiving the phase-shift correction signal and delivering N1 output signals to the control inputs of the variable phase-shifting circuits, a multiphase clock generator comprising a second set of N1 variable phase-shifting circuits connected in series and receiving the reference clock signal at one end of the series and delivering output signals to the inputs of the variable phase-shifting circuits of the first set, a phase comparator, a low-pass filter, and an adaptation module; and a calibration circuit comprising a third set of N2, for example 4, variable phase-shifting circuits connected in series, a second phase comparator receiving the reference clock signal, a second low-pass filter, and a second adaptation module whose outputs are connected to the control inputs of the third set. A digital frequency synthesizer (claimed) comprises a phase accumulator coupled to the phase interpolator.