Phase-locked loop circuit having linear voltage-domain time-to-digital converter with output subrange

A sub-range controlling circuit to be disposed between a charge pump and an analog-to-digital converter (ADC) in a phase-locked loop (PLL) circuit, comprising:

• a plurality of capacitor banks each comprising:
• a plurality of capacitor units each having a first terminal coupled to an output of the charge pump and coupled an input of the ADC and having a second terminal;
• and
• a plurality of switch units each having a first terminal coupled to the second terminal of a corresponding capacitor unit and having a second terminal selectively coupled to one of a reference voltage and a ground level;
• and
• a control logic circuit, coupled to the plurality of capacitor banks, for limiting a voltage level corresponding to the output of the charge pump in a voltage range by respectively controlling states of switch units in at least one capacitor bank to dynamically adjust down the voltage level for one time or multiple times to generate an adjusted voltage level for the ADC.

A method of a phase-locked loop (PLL) circuit, comprising:

• using a phase detector to generate a charging current signal according to an input frequency signal and a feedback signal which is generated from a feedback circuit;
• limiting an analog voltage level, provided for an analog-to-digital converter of the processing circuit and corresponding to the charging current signal, in a voltage range according to a prediction signal to generate a digital output;
• using a loop filter to perform a low-pass filter operation according to the digital output;
• using a digital controlled oscillator (DCO) to generate a DCO frequency signal according to an output of the loop filter;
• using the feedback circuit to generate the feedback signal according to the DCO frequency signal;
• using a sigma-delta modulator (SDM) to generate a phase signal, which indicates accumulated phase shift information, according to information of the feedback circuit and fractional frequency information;
• and
• generating the prediction signal according to the phase signal.