Analysis and design of 2.3-GHz current-controlled oscillator using novel multiple-nested ring architecture and a 2-GHz PLL frequency synthesizer design

Abstract

A novel differential voltage-clamped current-mode delay cell is proposed and its advantages such as low supply sensitivity, wide tuning range and high speed operation are verified by a three-stage ring oscillator through fabrication and experiments. Due to the nature of current mode with voltage clamping and robustness against noise, experimental results show the supply sensitivity is very low about 0.1~0.2 %/V in the 500 ~ 800 MHz range having its tuning range over 1 decade up to 1.38 GHz. Based on the differential voltage-clamped current-mode delay cell, the novel multiple-nested ring (MNR) oscillator architectures are developed and four types of MNR oscillators are presented. Among them, two MNR oscillators are implemented using a 0.8 ($\mu$ nwell CMOS process. Since the operation of their delay cells is basically a voltage-clamped and current-mode, the experimental verifications of two MNR oscillators show such properties as wide tuning range, low supply sensitivity and high speed operation. Using the feedback theory, the loop gain analyses for the four types of MNR oscillators and conventional three- and four-stage ring oscillators are carried out. From the loop gain analyses, the oscillator characteristic parameters such as the oscillation frequency and minimum gain for oscillation are obtained for each type of oscillators. Throughout the analyses, we find that the oscillation frequencies of MNR oscillators can be made higher than those of conventional ring oscillators and obtain the functions which show ``how much the oscillation frequencies of MNR oscillators can be increased compared with those of conventional ring oscillators``. The noise analyses of MNR oscillators for the noise performance parameters such as thermal output noise power of the delay cell, noise spectral density function and total output noise power are performed. From these analyses, we obtain the functions which show ``how much the noise performance of MNR oscillators can be...