Patent ID: 7236058

Claim:
A frequency doubling circuit, comprising: a phase shifting circuit for generating from an input signal a pair of output signals having waveforms that are separated in phase by approximately 90°; a pair of hysteresis buffers, operative to enhance the waveforms of the pair of output signals, such that the waveforms have desirably steep transitions and are separated more precisely by a 90° phase difference, each of the hysteresis buffers comprising: a differential pair of transistors to which one of the pair of output signals is applied as an input, the transistors having two possible switching states in which one or the other of the transistors is latched in a conductive condition; and first and second feedback circuits cross-coupling the outputs of the transistors to their inputs, wherein a gradual change in input signal level results in rapid latching of the pair of transistors in one of its two switching states; and an exclusive OR (XOR) gate, for logically combining the enhanced pair of output signals to produce a single output signal of double the frequency of the input signal.