Patent ID: 7532079

Claim:
A method for making a digitally tuned crystal oscillator circuit, the method comprising: coupling an input of a digital modulator to receive a multi-bit input signal, wherein the digital modulator is configured to modulate the multi-bit input signal by oversampling, or by noiseshaping and oversampling, to produce a digitally-modulated output signal, at an output of the digital modulator, which has a lower number of bits than the multi-bit input signal; coupling a tuning capacitor with the crystal oscillator circuit; coupling a varactor with the tuning capacitor in the crystal oscillator circuit; and coupling the output of the digital modulator to the crystal oscillator circuit and the tuning capacitor, wherein: the oversampling or noiseshaping comprises dithering of the multi-bit input signal, a number of bits from the digitally-modulated output signal comprises a lower number of bits than the multi-bit input signal, and a capacitance of the varactor is configured to be set by controlling the capacitance of the varactor with a control voltage of (Kav*VREF 1 +(1−Kav)*VREF 2 ), wherein Kav is an average value of the digitally-modulated output signal, VREF 1 is a first reference voltage, and VREF 2 is a second reference voltage.