Abstract:
A clock data recovery circuit (CDR) extracts bit data values from a serial bit stream without reference to a transmitter clock. A controllable oscillator produces a regenerated clock signal controlled to match the frequency and phase of transitions between bits and the serial data is sampled at an optimal phase. A phase detector generates early-or-late indication bits for clock versus data transition times, which are accumulated and applied to a second order feedback control with two distinct feedback paths for frequency and phase, combined for correcting the controllable oscillator, selecting a sub-phase and/or determining an optimal phase at which the bit stream data values are sampled. The second order filter is operated at distinct rates such that the phase correction has a latency as short as one clock cycle and the frequency correction latency occurs over plural cycles.
Abstract:
A circuit includes a capacitive-load voltage controlled oscillator having an input configured to receive a first input signal and an output configured to output an oscillating output signal. A calibration circuit is coupled to the voltage controlled oscillator and is configured to output one or more control signals to the capacitive-load voltage controlled oscillator for adjusting a frequency of the oscillating output signal. The calibration circuit is configured to output the one or more control signals in response to a comparison of an input voltage to at least one reference voltage.