A fast and accurate phase noise measurement of free running oscillators using a single spectrum analyzer

This paper presents a practical phase noise measurement approach, which only requires a spectrum analyzer and a computer, featuring fast setups, accurate results and low cost. Not like the conventional methods using extra assistant circuits to get rid of the frequency drift problem, this approach takes advantage of modern spectrum analyzers to acquire IQ data to calculate phase noise. The low quantization noise of the instrument makes this approach suitable for most CMOS integrated oscillators. The IQ data sampling time can be made small enough so that the frequency drift is not so obvious to harm the measurement accuracy. The experimental results clearly demonstrates the accuracy and the effectiveness of this method through measuring phase noise of two voltage controlled oscillators (VCOs) in 180nm CMOS process at 2.6 GHz and 3.0 GHz respectively.