Wide frequency range CMOS relaxation oscillator with variable hysteresis

A variable frequency oscillator which produces an output signal, the oscillator comprising:

• a ramp circuit including:
• a controlled current source, responsive to a frequency control signal for providing a first current signal which varies in magnitude in proportion to the frequency control signal;
• a controlled current sink, responsive to the frequency control signal for providing a path for a second current signal to a source of reference potential;
• and
• a capacitor, coupled to receive the first current signal from the controlled current source and to provide the second current signal to the current sink;
• wherein a potential developed across the capacitor in response to the first current signal represents a positive-going ramp signal and the potential developed across the capacitor in response to the second current signal represents a negative-going ramp signal;
• a hysteresis circuit which, responsive to the frequency control signal being in first and second states, generates a hysteresis signal having a relatively high value and a relatively low value, respectively, the relatively high value and relatively low value defining a hysteresis range, wherein the hysteresis circuit is responsive to a first control signal to change the hysteresis range;
• and
• a comparator which compares the ramp signal to the hysteresis signal to generate the output signal of the oscillator and the frequency control signal, the frequency control signal being in the first state when the ramp signal is less than the hysteresis signal and being in the second state when the ramp signal is greater than the hysteresis signal.

A phase-locked loop comprising:

• A variable frequency oscillator which produces an output signal, the oscillator comprising:
• a ramp circuit which generates a ramp signal having a rate of change defined by a first control signal, the ramp circuit being responsive to a second control signal being in first and second states to generate a positive-going ramp and a negative-going ramp, respectively;
• a hysteresis circuit which, responsive to the second control signal being in the first and second states, generates a signal having a relatively high value and a relatively low value, respectively, the relatively high value and relatively low value defining a hysteresis range, wherein the hysteresis circuit is responsive to the first control signal to change the hysteresis range;
• and
• a comparator which compares the ramp signal to the hysteresis signal to generate the output signal of the oscillator and the second control signal, the second control signal being in the first state when the ramp signal is less than the hysteresis signal and being in the second state when the ramp signal is greater than the hysteresis signal;
• a phase comparator, coupled to receive the output signal of the variable frequency oscillator and a reference signal, the phase comparator generating a first pulse signal when the output signal leads the reference signal in phase and generating a second pulse signal when the reference signal leads the output signal in phase;
• and
• charge pump means, responsive to the first and second pulse signals for generating the first control signal.