Certain aspects of the present disclosure provide a relatively compact frequency-locked loop (FLL) using a discrete-time integrator. For certain aspects, the FLL also includes a supplemental oscillator and other circuitry that allows for saving the FLL frequency when a reference clock will be disconnected, maintaining a similar frequency during disconnection, and restoring the FLL frequency when the reference clock is reconnected. One example FLL circuit generally includes: an encoder; a combiner comprising a first input coupled to an output of the encoder; a digital-to-analog converter (DAC) comprising an input coupled to an output of the combiner; a discrete-time integrator comprising an input coupled to an output of the DAC; a voltage-controlled oscillator (VCO) comprising a control input coupled to an output of the discrete-time integrator; and a counter comprising an input coupled to an output of the VCO and comprising an output coupled to a second input of the combiner.

A signal reproduction circuit includes: an oscillator generating first clock and second clock having a same frequency but different phases; and a feedback circuit to control the oscillator in accordance with a phase relation and a frequency relation between input data and the first clock, wherein the feedback circuit includes: a frequency-phase detection circuit to compare a clock phase control signal and a clock phase detection signal and generate a frequency phase signal indicating the frequency relation between the input data and the first clock, a state detection circuit to detect a lock state in which falling edges or rising edges of the input data and the first clock synchronize and a frequency difference state in which frequencies of the input data and the first clock are different, and a selector to supply the frequency phase signal to the feedback loop only in the frequency difference state.

The present application provides a clock switching method, a clock switching apparatus, an electronic device, and a readable storage medium, the clock switching method includes: in a case where a first reference clock is determined to be in a locked state, determining an average control word according to a preset duration and an obtained real frequency tuning word; in a case where the first reference clock is determined to be in an invalid state, determining a compensation phase difference by using the average control word as a frequency control word of a digital phase locked loop; performing a phase compensation on a second reference clock according to the compensation phase difference to obtain an updated second reference clock; and switching the first reference clock to the updated second reference clock.

A phase-locked loop (PLL) circuit generates an output clock signal and includes: a selection circuit that selects one of a plurality of clock signals as a reference clock signal of the PLL circuit; and a control circuit that when a switch is made for the selection of the reference clock signal, temporarily reduces a division ratio used by a frequency divider that generates a feedback clock signal to be compared with the reference clock signal.