Phase noise measurement techniques using delta-sigma TDC

Abstract

This paper describes two techniques for measuring phase noise of a clock using a delta-sigma time-to-digital converter (TDC). One technique uses a reference signal (which has only very small phase noise), and the other does not use a reference signal. Both proposed techniques can be implemented with relatively simple circuitry, due to the following: (i) The clock under test (CUT) is a repetitive signal. (ii) The time resolution with CUT and a reference clock can be increased by using longer measurement time with the delta-sigma TDC. (iii) The phase noise power spectrum can be calculated from the delta-sigma TDC output data using FFT. Costly high-performance spectrum analyzers which average several-time phase measurement results over a long measurement time (about 10s order), are not needed for phase noise measurement with the proposed technique. The other technique, which differs in that it uses a self-referenced clock rather than a reference signal, has potential wide applications.