Abstract:
A modulator for generating a control code in response to a frequency control word is provided. The modulator includes an adder, an accumulator, a next state generation unit, and a code generation unit. The adder generates a frequency error signal by calculating a difference between the frequency control word and the control code. The accumulator generates a phase error signal by accumulating the frequency error signal. The phase error signal includes an integer part and a fractional part. The integer part of the phase error signal is a current state signal. The next state generation unit generates a next state signal according to a characteristic probability distribution determined by the fractional part of the phase error signal. The code generation unit generates the control code in response to the current state signal and the next state signal.
Abstract:
Spread spectrum generators and methods are disclosed. In one implementation, a spread spectrum clock generator includes a phase locked loop generating an output clock according to a first clock and a second clock; a delay line coupled between the first clock and the phase locked loop; a modulation unit providing a modulation signal to control the delay line thereby modulating phase of the first clock, such that frequency of the output clock generated by the phase locked loop varies periodically; a scaling unit scaling the modulation signal from the modulation unit according to a scaling ratio, and outputting to the delay line; and a calibration unit generating an output signal for controlling the scaling ratio.
Abstract:
A modulator for generating a control code in response to a frequency control word is provided. The modulator includes an adder, an accumulator, a next state generation unit, and a code generation unit. The adder generates a frequency error signal by calculating a difference between the frequency control word and the control code. The accumulator generates a phase error signal by accumulating the frequency error signal. The phase error signal includes an integer part and a fractional part. The integer part of the phase error signal is a current state signal. The next state generation unit generates a next state signal according to a characteristic probability distribution determined by the fractional part of the phase error signal. The code generation unit generates the control code in response to the current state signal and the next state signal.
Abstract:
A digitally controlled oscillator includes a ring oscillator and a first supplementary circuit. The ring oscillator is coupled to a supply voltage and generates a signal oscillated at an oscillating frequency. The oscillating frequency is controlled by a digital code and further varies with a supply voltage drift in a first direction. The first supplementary circuit is coupled to the ring oscillator and facilitates the oscillating frequency to vary with the supply voltage drift in a second direction reverse to the first direction.
Abstract:
A circuit for controlling a mixed mode controlled oscillator. The circuit comprises a charge pump, and a digital loop filter. The charge pump is coupled to the mixed mode controlled oscillator. The charge pump receives an up/down signal and sends a current signal to the mixed mode controlled oscillator. The digital loop filter receives the up/down signal and generates a digital code signal to the mixed mode controlled oscillator. An output frequency of the mixed mode controlled oscillator is controlled by the current signal and the digital code signal.