A reconfigurable CMOS analog baseband for compact TDD wireless radio transceivers

In this paper, we propose a novel compact wireless radio transceiver architecture reusing a baseband chain so as to significantly reduce the die area. The proposed architecture employs a direct conversion architecture with a shared baseband chain and is suitable for wireless standards based on time-division duplexing (TDD) air interface. In direct conversion architectures, baseband filters and variable gain amplifiers (VGAs) are placed in the receive path as well as in the transmit path. Here, we propose to use the same baseband filters and VGAs in both the receive path and the transmit path to reduce the die area. To implement a baseband filter, we design a sixth-order Sallen-Key low-pass filter which can be shared for both the transmit path and the receive path. For VGAs, attenuators are designed for gain control with the gain range of -16 dB to 38 dB in this paper. In addition, DC feedback loops are added to cancel the DC offset. The analog baseband circuits proposed are designed using a standard 0.5 μm CMOS process and verified through simulations.