题目/Title：A Mixed-Loop CMOS Analog GFSK Modulator With Tunable Modulation Index

作者/Author：
                        Shuguang Han,Baoyong Chi,Zhihua Wang

期刊/Journal：IEEE Transactions on Circuits and Systems II-Express Briefs

年份/Issue Date：2007June

卷（期）及页码/Volume（No.）&pages：Vol.54, No.6, pp. 547 - 551

摘要/Abstract：
A new low-power analog Gaussian frequency-shift keying (GFSK) modulator is proposed and implemented in 0.18-CMOS process based on an analog computer implementation of the FM differential equation. The mixed-loop modulation approach is proposed to achieve high data rate and stable carrier frequency. The core of the GFSK modulator is a tunable harmonic oscillator consisting of two Gm-C integrators, whose center frequency can be adjusted by using the on-chip tunable phase-locked-loop (PLL) technique. A simple nonlinear resistor is used to maintain the constant output amplitude. The modulator operates at the center frequency of 2 MHz with the 0.1-0.55 tunable modulation index at 1-Mbps data rate. The modulator draws about 1.8 mA from the 1.8-V power supply and could achieve 2-Mbps data rate with the total harmonic distortion less than 3%.