Digital phase-locked loop circuit including a phase delay quantizer and method of use
A phase locked loop circuit in accordance with an embodiment implements a digital phase delay quantizer to replace the analog charge-pump and phase frequency detector in an analog PLL circuit. Therefore, the built-in loop filter can be a compact-sized, high order, high bandwidth, and high attenuation digital filter as well. The digital PLL circuit takes advantage of the deep sub-micron process technology which features high speed, high resolution, compact size, and low power.
1. A digital phase locked loop circuit comprising:
a reference clock generator for providing a reference clock signal;
a digital filter for providing filtered digital codes;
a digital controlled oscillator coupled to the digital filter to receive the filtered digital codes and provide an output signal;
a frequency divider coupled to receive the output signal and provide a frequency divided signal; and
a phase delay quantizer coupled to the frequency divider, reference clock generator and digital filter; the phase delay quantizer operable to quantize a phase delay and between the reference clock signal and the frequency divided and to provide digital codes to the digital filter based upon signals from the frequency divider and the reference clock generator, wherein the phase delay quantizer quantizes the phase delay between the reference clock and the divided frequency signals without the use of oversampling, wherein the phase delay quantizer comprises a plurality of interpolated delay stages, wherein an interpolated delay chain in the phase delay quantizer forms a circular ring so that the delay stages can be reused.
2. The digital phase locked loop circuit of claim 1 wherein the reference clock generator comprises a crystal oscillator.
3. The digital phase locked loop of claim 1 wherein the phase delay quantizer comprises a plurality of interpolated delay stages to achieve a shorter delay time than a gate delay.
4. The digital phase locked loop of claim 3 wherein the phase delay quantizer includes a code subtractor to subtract codes generated by the reference clock signal and the frequency divided signal to quantize the delay time between edges of the signals.
5. The digital phase locked loop of claim 3 wherein the phase delay quantizer includes a ring counter to memorize the number of full rings that are running between buffer stages in the digital phase locked loop circuit.