Delay stage circuitry for a ring oscillator

Abstract

A ring oscillator includes an even-numbered plurality of ring coupled delay stages. Each delay stage includes a differential amplifier, a voltage clamping circuit, and a current source. The differential amplifier receives first and second input signals from a preceding delay stage. The differential amplifier provides a first output signal and a complementary second output signal at first and second nodes, respectively. The voltage clamping circuit is coupled between the first and second nodes to limit a peak-to-peak voltage swing of each of the first and second output signals. The current source is coupled to the differential amplifier and varies a bias current in accordance with a delay bias voltage.

Description

FIELD OF INVENTIONThe present invention relates to clock synchronization circuitry including a cascaded phase locked loop. In particular the present invention relates to a delay stage for a ring oscillator and a fine phase tuning circuitry, both used in the cascaded phase locked loop.BACKGROUND OF THE INVENTIONClock synchronization in integrated circuits is typically performed by a phase locked loop (PLL).Some prior PLLs use a ring oscillator as a voltage controlled oscillator. A ring oscillator is a chain of inversion elements coupled together in a negative feedback fashion, with each element contributing a delay amount which adds up to half an oscillation period. Some prior phase locked loop implementations using ring oscillators suffer phase offset and deadband problems, which are difficult to minimize without compromising one or the other.One disadvantage of prior ring oscillators is that the number of phase signals that can be generated are limited by the number of inversion el...

AI Technical Summary

Problems solved by technology

Some prior phase locked loop implementations using ring oscillators suffer phase offset and deadband problems, which are difficult to minimize without compromising one or the other.

One disadvantage of prior ring oscillators is that the number of phase signals that can be generated are limited by the number of inversion elements contained in the ring oscillator.

The number of inversion elements is, in turn, limited by the length of time dela

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