Accurate frequency oscillators

An oscillator, including:

• a voltage supply variation reduction circuit configured to be coupled to a voltage source and to pass a first current when a voltage of the voltage source exceeds a selected value, the voltage supply variation reduction circuit including:
• a first zero temperature coefficient resistor coupled to the voltage source;
• a first stack of diode-connected NFETs having conduction channels coupled in series between the first zero temperature coefficient resistor and a reference potential;
• and
• an NFET coupled in a current mirror configuration to a diode-connected NFET in the first stack of diode-connected NFETs;
• and
• a bias generation circuit, coupled to the voltage supply variation reduction circuit and configured to be coupled to the voltage source, the bias generation circuit configured to pass a second current when the voltage of the voltage source exceeds the selected value, wherein the second current is essentially constant, the bias generation circuit including:
• a second zero temperature coefficient resistor coupled to the voltage source;
• and
• a second stack of diode-connected NFETs conduction channels coupled in series between the second zero temperature coefficient resistor and the reference potential, wherein the NFET coupled in the current mirror configuration has a conduction channel coupled between the reference potential and a node between the second zero temperature coefficient resistor and the second stack of diode-connected NFETs;
• a temperature-compensation circuit, coupled to the bias generation circuit and configured to be coupled to the voltage source, the temperature-compensation circuit configured to pass a temperature-compensated third current through a bias NFET, the temperature-compensation circuit including:
• a diode-connected PFET having a conduction channel coupled to the voltage source;
• the bias NFET having a conduction channel coupled to the conduction channel of the diode-connected PFET;
• and
• a third zero temperature coefficient resistor and a negative temperature coefficient resistor coupled in series between the conduction channel of the bias NFET and the reference potential;
• and
• oscillator circuitry coupled to the temperature-compensation circuit and configured to pass the temperature-compensated third current and generate an output comprising a periodic waveform.

A ring oscillator, including an odd number of inverter stages coupled in series, at least one inverter stage including:

• an output node;
• a PFET having a conduction channel configured to be coupled to a voltage source;
• an NFET having a conduction channel configured to be coupled to a reference potential;
• an input coupled to a gate of the PFET and a gate of the NFET;
• a first negative temperature coefficient resistor coupled between the conduction channel of the PFET and the output node;
• a second negative temperature coefficient resistor coupled between the conduction channel of the NFET and the output node;
• and
• a capacitor coupled to the output node and configured to be coupled to the reference potential.