Multimode Transmitter's Variable Gain Analog Low-pass Filter Design

With the development of wireless communication and CMOS technology, it becomes realistic to integrate different communication protocols on single chip. Realizing multi-standard transceivers with maximum hardware reuse is of great importance to minimize the manufacturing cost. Therefore, reconfigurability is a key point in the design of the analog baseband circuits. In addition, the reduction of power consumption and off-chip components is also a key design issue in enhancing portability and battery operation. This work focuses on the circuit theory and implementation method of baseband filter in multi-mode transmitters. Circuit optimization methods are presented in this thesis to improve some key performances of baseband filter.Firstly, this work analyses the performance requirements of GSM, TD-SCDMA and WCDMA multi-mode transmitters.Secondly, different types of analog filters are compared and the design flow of analog filters is presented. The linearity performance of Tow-Thomas biquad is analysed.Further, this paper describes a low-pass reconfigurable baseband filter for GSM, TD-SCDMA and WCDMA multi-mode transmitters. The baseband filter incorporates -40 to 0 dB programmable gain control. An automatic frequency tuning (AFT) circuit is adopted to compensate the cut-off frequency variation. The filter's cut-off frequency can be reconfigured for GSM/TD-SCDMA/WCDMA multi-mode transmitter. The out-of-band noise performance and in-band linearity performance are optimized.Finally, the layout considerations are presented. The basic circuit theory and design method are verified. An optimization design is put forward to improve the filter's concerned performance. Measurement results show that the design meets demands of the system.