Applied To The 2 G / 3 G Mobile Communication Digital Auxiliary Single Channel Multimode Receiver Research

With the popularity of3G communications and smartphones, the integration of RF chips has become increasingly demanding. Nowadays single-chip multi-mode transceiver using CMOS technology is the hot research topic. Multi-mode receiver can be realized in single-channel by circuit reconfiguration. As a result, the chip area can be saved and the receiver is more flexible to meet the upgrade of the standards. The scaling down of CMOS technology raises the integration level, but at the same time the supply voltage is getting lower and lower. It is more difficult to reach the specifications of some key performances, so digital assistance is needed to make up the shortage of the traditional RF and analog circuits and improve the key performances.Based on the above background, the requirements on the receiver structure and performance raised by the mainstream2G/3G standards are compared and summarized. A single-channel multi-mode receiver architecture for2G/3G mobile communications is raised. The whole receiver channel includes a RF frontend, an analog baseband, a two-channel ADC and a digital frontend. Digital assistance is used to support multiple modes and improve the key performances of the receiver.Digital assistance is used to calibrate the second-order distortion and IQ mismatch in the receiver, and the IIP2and IRR performances are improved. Firstly the second-order distortion generated by the threshold voltage mismatch of the mixer switches is quantized, and the feasibility of cancelling out the other second-order distortions by artificially introducing the threshold voltage mismatch is demonstrated. On the basis a wideband RF frontend with digital IIP2calibration is designed. An artificially introduced mismatch by controlling the bias of the switches is used to calibrate the IIP2, and the IIP2after calibration is raised to48dBm. Secondly, an adaptive digital calibration algorithm is raised. The algorithm can adaptively select the intermediate frequency (IF) and compensate the IQ mismatch according to the power ratio of the adjacent channel interference to the desired signal. It can overcome the shortages that compensation using a training signal is not suitable for online calibration and adaptive compensation is easily impacted by wireless fading. After implemented in a low-IF GSM receiver, the phase error is improved from6.78degree to3.23degree, and the IRR is improved from29.1dB to44.3dB. Targeting GSM and TD-SCDMA standards, a single-channel multi-mode receiver is designed and implemented in SMIC0.13um RF CMOS process. Advanced Design System (ADS) and Vector Signal Analysis (VSA) software are used to model and simulate the system. By using digital assistance, multiple modes are supported, and the key performances such as the IIP2and IRR are effectively improved. The whole transceiver configured in TD-SCDMA mode has been verified by connecting to a commercial baseband processor and the test bench has successfully accessed the TD-SCDMA network and established conversation connections.