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Abstract

A novel and useful apparatus for and method of improving the quantization resolution of a time to digital converter in a digital PLL using noise shaping. The TDC quantization noise shaping scheme is effective to reduce the TDC quantization noise to acceptable levels especially in the case of integer-N channel operation. The mechanism monitors the output of the TDC circuit and adaptively generates a dither (i.e. delay) sequence based on the output. The dither sequence is applied to the frequency reference clock used in the TDC which adjusts the timing alignment between the edges of the frequency reference clock and the RF oscillator clock. The dynamic alignment changes effectively shape the quantization noise of the TDC. By shaping the quantization noise, a much finer in-band TDC resolution is achieved resulting in the quantization noise being pushed out to high frequencies where the PLL low pass characteristic effectively filters it out.

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