Abstract: A voltage controlled oscillator (VCO) provides an output signal with an output frequency that varies only minimally for any given input control voltage despite variations in the manufacturing process, temperature and supply voltage. The VCO also includes a multistage ring oscillator which includes a plurality of series-connected current-starved inverter stages. The VCO utilizes a first current source to provide a substantially constant current independent of process, temperature and supply voltage and a second current source to provide a variable current that varies in response to process, temperature and supply voltage. Both current sources generate a respective current signal independent of the input signal to the VCO. An attenuator, responsive to the VCO's input voltage signal (typically from a phase-locked loop filter) provides a control current signal to the ring oscillator.

Abstract: A power on reset circuit that incorporates a voltage divider, and current reference generator and a switching circuit. The voltage divider generates an output voltage which is a predefined fraction of the supply voltage. The current reference generator generates a reference current which controls a first current mirror in the switching circuit. The switching circuit, which has a sharply sloped voltage transfer characteristic, includes a first transistor that is gated by the voltage divider output and coupled to the first current mirror at a first circuit node. The first transistor draws current from the first current mirror only when the voltage divider output exceeds a threshold voltage, causing the switching circuit to develop a first reset voltage on the first circuit node. The power on reset circuit may also include an inverter having an input coupled to the first circuit node and producing a second reset voltage on a second circuit node.