通过改进电路结构,采用CMOS交叉耦合结构提供负阻,设计一种20 MHz的集成石英晶体振荡器.在该振荡器中,采用共模反馈使其输出稳定的直流电平,并增加RC高通滤波器和预抑制电路降低其相位噪声.基于NUVOTON 0.35 μm CMOS工艺,利用Cadence Spectre对电路进行仿真,结果表明,在电源电压为3.3 V,偏置电流约400 μA时,该振荡器的起振时间约为1.5 ms,输出波形峰-峰值为1.08 V,输出直流电平约为801.6 mV.输出信号频率为19.95 MHz,相位噪声分别可以达到-155 dBc/Hz@1 kHz,-164 dBc/Hz@10 kHz.%By improving the circuit structure and adopting the CMOS cross-coupled structure to provide negative resistance, a 20 MHz integrated quartz crystal oscillator was proposed.In this oscillator, the common-mode feedback was adopted to achieve stable DC output, and the RC high filter circuit and the pre-rejection circuit were designed to reduce the phase noise.With NUVOTON 0.35 μm CMOS process, the circuit was designed and simulated by the Spectre in Cadence.Under the supply voltage of 3.3 V and the bias current of 400 μA, the results indicated that start-up time of the oscillator was about 1.5 ms, the peak value of the output waveform was 1.08 V, the DC output was about 801.6 mV, the frequency of output was 20 MHz, and the phase noise reaches-155 dBc/Hz@1 kHz and-164 dBc/Hz@10 kHz, respectively.
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