Phase noise reduction in LC cross coupled oscillators using sinusoidal tail current shaping technique

Abstract

In this paper, using the concept of impulse sensitivity function (ISF) in Hajimiri's phase noise model, a novel circuit method for phase noise reduction in LC cross coupled oscillators is proposed. Based on the proposed technique, at outputs zero crossing points, where ISF is maximum, current supplying to the transistor pair is stopped by two added transistors. Due to the shaped effective ISF waveform and also reduction of its RMS value, phase noise is decreased. In addition, the cascode structure of the proposed technique leads to more phase noise reduction due to the suppression of the transistors noise power. The proposed circuit is designed for 10 GHz output frequency and inductor quality factor of 12, and simulated in a standard 0.18 µm CMOS technology with a 1.8 V supply. Compared to the simple cross coupled oscillator, phase noise at 1 MHz and power consumption are reduced by 8 dB and 26%, respectively. The phase noise and FOM for the proposed oscillator at 1 MHz offset frequency are ýý107.8 dBc/Hz and 186.2 dB, respectively.