Design Of A 38.4MHz Low Power And Low Phase Noise TC-DCXO

The X-tal(crystal) oscillator is used to supply local oscillation for RF communication system, or reference clock signal for digital circuit, so it is an important part of communication system. It is always composed by a X-tal, a circuit for starting oscillation and frequency modulation, so that it can oscillate steadily. With a small access coefficient and a high quality factor, the X-tal can get a very steady signal with a low phase noise if the outside circuit is well designed.The DCXO(digitally controlled crystal oscillator) is the main choice of the future applications for oscillators. Now the lower accuracy VCXOs are still used widely, and there are not enough efforts on DCXO in our country, so researches on DCXO will make lots of sense. In the issue, the theory of the oscillators and the performance index are introduced, and we also analyzed the sorts and the operational principle of oscillators. We got the way of frequency modulation and temperature compensation, and the power and the phase noise were discussed particularly. Form these, and with the supports of two country's magnitude items, we designed a low power and low phase noise Colpitts DCXO for TD-LTE application, which got over the differences of new structure, new technology and new standard, integrated the functions of amplitude control, frequency modulation and temperature compensation, and the work frequency was 38.4MHz. In this design, the amplitude control was used to reduce the power consumption, and the frequency could make sure the oscillator working steadily and accurately, then the temperature compensation extended the working temperature range to-25℃to 85℃.This design was implemented in TSMC0.13μm technology. For the analog circuit, the pre-simulation tool is Spectre of Cadence, and the layout tool is Virtuoso, and the post-simulation tool is Calibre and Assura. For the digital part, the verification tool is Modelsim, and the synthesizer is DC of Synopsis, and the layout tool is Encounter. The mix simulation tool is Spectre.This issue will follow this scheme:First, we will introduce the operational principle of the oscillators, and analyzed the performance index of TC-DCXO; Then, we will discuss the operational principles and the implementation detailed.Finally, we will give the simulation and test results.The low power and low phase noise TC-DCXO working at 38.4MHz of this issue got a low phase noise, that is:142dBc/Hz@1kHz,143dBc/Hz@10kHz. The frequency only moves 1.6ppm from-25°to 85°. The digital controlled capacitance array uses 12bit to control 255 capacitance cell, and a∑-A modulator controls another cell to get smaller frequency steps. And the power consumption is 3 mA.