Temperature, supply and process-insensitive signal-controlled oscillators

Abstract

Signal-controlled oscillator structures are provided that are substantially insensitive to temperature, supply voltages and fabrication processes. They include a plurality of time-delay stages that are serially connected in a closed feedback ring and each of the stages includes an amplifier, at least one capacitor and at least one signal-controlled impedance element that couples the capacitor to the amplifier. Accordingly, the frequency of the oscillator is a function of a control signal applied to the impedance elements of the stages. In an oscillator embodiment, each of the amplifiers is a differential pair of transistors, the capacitor comprises first and second capacitors and the signal-controlled impedance element comprises first and second coupling transistors that each couples a respective one of the capacitors to a different side of the differential output. Preferably, first and second triode-biased load transistors are each coupled to a different side of the differential output and biased by a voltage reference which has a Vt-referenced source, a sensor and a summer. The source generates a source voltage and a feed-forward current, the sensor generates a feedback current that corrects the feed-forward current and the summer sums the feed-forward current and the feedback current into a sum current and generates a reference voltage that is responsive to the sum current. Accordingly, changes in the feed-forward current are corrected by changes in the feedback current so that the sum current and the reference voltage are substantially constant.