Apparatus for generating an oscillating signal in a desired phase relationship with an input signal, including a mixer arranged to receive a pair of reference signals oscillating at a common frequency and having a phase offset between them, and to mix the reference signals in variable proportions according to the value of input weighting signals to generate an output signal. A comparator is to compare the phase of the output signal with that of the input signal to determine whether the signals are in the desired phase relationship and, if not, to output one or more control signals indicative of the required adjustment in the phase of the output signal to achieve the desired phase relationship. An adjustable ring oscillator including a plurality of stages is connected in a ring and arranged to propagate oscillations around the ring. The ring oscillator is responsive to one or more control signals to propagate the oscillations in first and second directions around the ring and is arranged to provide the weighting signals to the mixer from outputs of ones of its stages.

An N-way Circular Phase Interpolator interpolates the N phases of a reference clock signal to generate a tunable clock. By using more than two phases for interpolation, high excess frequencies as well as high precision (i.e. small jitter) are achieved. The N-way Circular Phase Interpolator provides for analog filtering in the phase domain, which attenuates the out-of-band phase noises thus further reducing the output jitter.

A linear interpolator is provided that includes differential pairs of transistors biased such that a first input voltage may be multiplied by a factor r wherein 0.ltoreq.r.ltoreq.1 and such that a second input voltage may be multiplied by the complement factor (1-r). By combining the multiplied input voltages, a linear interpolation is provided based upon the factor r.

The present invention, generally speaking, provides a time shift angle demodulator that is of simple construction and has an extended linear range. Range extension is achieved by using the input signals directly, not simply post-processing the S-PFD outputs. In accordance with one embodiment of the invention, a method of measuring the phase or frequency of a periodic input signal uses a periodic reference signal and includes comparing the input signal to the reference signal to obtain a lead signal and a lag signal; changing the count of an up/down counter in dependence on the input signal, the reference signal, the lead signal and the lag signal; and using the lead signal, the lag signal and the count signal to produce a phase or frequency signal. In accordance with another embodiment of the invention, an apparatus for measuring the phase or frequency of a periodic input signal uses a periodic reference signal and includes a comparison circuit for comparing the input signal to the reference signal to obtain a lead signal and a lag signal; a logic circuit, including an up/down counter, responsive to the input signal, the reference signal, the lead signal and the lag signal to change the count of the up/down counter; and circuitry for using the lead signal, the lag signal and the count signal to produce a phase or frequency signal.

A steering current generator for a phase interpolator has a multiplicity of fine phase adjustment current sources, each of which is switchable to direct its current to one or other of two summing nodes. The current of each of those two summing nodes is supplemented by respective fixed always-on current sources. The steering current generator has four current outputs and a switching matrix is provided to switch the current from the summing nodes to first and second selected ones of those outputs. The switching matrix is also connected to switch bleed currents to the other two of the current outputs.