Patent ID: 7839220

Claim:
A circuit, comprising: a phase-locked loop, comprising: a loop filter, providing a filtered control voltage; and a voltage-controlled oscillator, coupled to said loop filter, to receive said filtered control voltage and provide an output clock signal; said circuit further comprising: a runaway detector, coupled to said phase-locked loop, to provide a discharge control signal for adjusting said filtered control voltage in response to a predetermined condition of said phase-locked loop, said runaway detector includes a comparator to compare first and second input voltages and to output said discharge control signal based on said comparison, said first input voltage being based on a fixed voltage and said second input voltage being based on said output clock signal; wherein said runaway detector adjusts said filtered control voltage when said predetermined condition exists, thereby enabling said phase-locked loop to return to a lock condition; and wherein said runaway detector further includes: a first circuit branch, including a first plurality of resistors coupled to said fixed voltage and a ground, for generating said first input voltage; and a second circuit branch, including a second plurality of resistors, coupled to said fixed voltage and said ground, for generating said second input voltage; wherein, in response to a first state of said comparator, said runaway detector outputs a first signal to adjust said filtered control voltage, and in response to a second state of said comparator, said runaway detector outputs a second signal which allows said filtered control voltage to pass to said voltage-controlled oscillator.