| Summary: | 碩士 === 逢甲大學 === 通訊工程所 === 94 === The maturity of the electromagnetic wave theory and Maxwell’s equation has been derived. In addition, the computer skills and communication technology which have also quickly brought up the development of present communication industry. From low power transmission system of PHS to 3G system or the forth generation wireless communication system, it has already been inevitable trend that frequency band up to 5 GHz. Standard CMOS process making RF frond-end is a interested topic for industries and schools. However, the inaccuracy of the component model and the parasitism affection keep challenging the RF designers’ ability. And to manufacture the device characteristics in high frequency also are big challenge for the engineer. Even through design RF circuit in the CMOS process has above drawback; it still gives us a chance to challenge.
In this paper, we utilize TSMC 0.18 μm process to analyze a differential CMOS LC Voltage-Controlled Oscillator (VCO) and design a quadrature CMOS LC-VCO. In these two kinds of circuit structures, we use LC resonators design concept to achieve higher spectral purity and lower phase noise than other types such as ring oscillators, etc. Then, we employ one way to provide negative resistance or conductance is by using complementary cross-coupled transistors that re-uses the current with an additional pMOS pair and hence provides extra gm. For that reason it needs only a half the current of nMOS-only structure for the same total gm. The oscillation amplitude of this structure is approximately twice as large as that of nMOS-only structure.
For the above kind of VCO structure, we begin to design and implement two complementary cross-coupled LC QVCO, both use current reuse method to decrease the power consumption. The power consumption of the QVCO core in the first structure is 27.18 mW and the second structure is 23.73 mW (without buffer). The phase noise of the first QVCO is about lower than -111 dBc, and the second QVCO is lower than -108 dBc (offset at 1 MHz). The frequency tuning range is from 7.911 GHz to 10.58 GHz in the first one, the other is from 7.530 GHz to 9.789 GHz, that is satisfied the group no. 4 and group no. 5 of UWB-MBOA system. The group no. 4 and no. 5 includes five center frequencies, which are 8.184 GHz, 8.712 GHz, 9.240 GHz, 9.768 GHz and 10.296 GHz. The both circuit structures can be applied to direct conversion system, low IF system, UWB-MBOA system.
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