Radio-frequency (RF) circuit comprising a voltage-controlled oscillator (VCO) and circuit for compensating effect of frequency drift by suppressing harmonic components

摘要

The RF circuit (RFCT) comprises a VCO delivering an RF signal (V1,F1), a phase-locked loop (PLL) for controlling the VCO, a modulation circuit (TXCT) receiving the RF signal and delivering a modulated signal (RFSx) comprising harmonic components, in particular H2 and H4, which can perturb the functioning of the VCO by the effect of frequency locking or pulling, a compensation circuit (COMPCT,COMPCT1,COMPCT2,COMPCT3) receiving the harmonic components and delivering a compensation signal (Bcomp), and means for injecting the compensation signal into the VCO. The compensation signal has an amplitude substantially equal to the amplitude of resultant parasitic signal and a phase opposite to that of the parasitic signal. The compensation circuit (COMPCT1) is non symmetric and delivers a single-component compensation signal which is injected at a point of the VCO. The compensation circuit (COMCT2) is non symmetric and delivers a two-component compensation signal which are injected at two points of the VCO. The compensation circuit (COMPCT3) is symmetric and delivers a compensation signal having two components in phase opposition which are injected at two points of the VCO. The compensation circuit receives a harmonic component (H2,H4) taken from the modulation circuit (TXCT), in particular from an RF amplifier (RFAMP), or a harmonic component is delivered by a generator circuit different from the modulation circuit. The compensation circuit comprises a phase-shifting circuit for modifying the phase of the harmonic component, or delivering two signals in phase quadrature, or signals in phase quadrature and opposition. The phase-shifting circuit comprises an equilibrated bridge of resistors and capacitors which is of low sensitivity to temperature. The compensation circuit comprises one or more attenuator circuits for modifying the amplitude of harmonic component, where the attenuator circuit comprises adjustable resistors and capacitors, or a combination of the two elements. The compensation circuit comprises at least two attenuator circuits whose outputs are added for controlling the phase and the amplitude of the compensation signal, or a group of attenuator circuits receiving the signals in phase quadrature or in phase quadrature and phase opposition, and whose outputs are added. An attenuator circuit comprises capacitors and resistors which are electrically adjustable by analog signals delivered by a digital-analog converter, where the digital data for adjustment are stored in a memory cell. The compensation signal (Bcomp) is injected to a terminal of an active component, or to a terminal of a passive component of the VCO, or the injection is by inductive coupling. A method (claimed) for stabilizing the functioning of the VCO controlled by the PLL is implemented by the RF circuit (claimed).