A Wide Tuning Fully-swing Differential VCO with Improved Active Inductors for SERDES Application

Abstract

A new wide tuning fully-swing differential VCO delay cell with improved active inductor load is proposed in this paper. The proposed VCO adopts an N-latch topology and provides both rail-to-rail voltage swing and wide voltage tuning range. Simulation results of 4-stage ring VCOs with various loads implemented demonstrate that the I-V characteristic of the VCO cells with active inductor load is better than that of the VCO cells with current-source load, the output voltage swing of the cell in N-latch topology is larger than that of the cell in P-latch topology, the frequency tuning range of proposed VCO is larger than that of the VCO with conventional active inductor load. The proposed VCO is implemented and integrated into a SERDES (SERial and DESerial) chip by TSMC 0.13μm 1.5 V 8-metal CMOS technology, but the whole die size of the VCO and buffers are100*110um2. Test results of the SERDES chip show that the VCO works well.