Adaptive Calibration Methods for an Image - Reject Mixer by Isaac Sever

The wireless communications market has grown substantially during the last decade. Recent advances in wireless technology have reduced the size and cost of mobile radios while improving performance. The increasing level of integration in wireless circuits has led to many of these improvements. However, increased integration is dependent on the development of novel transceiver architectures that allow the designer to eliminate many large discrete electronic components and to combine multiple circuit blocks on a single chip. At the same time, numerous wireless standards have been introduced which dictate the performance specifications of the hardware in wireless devices. Hardware requirements differ substantially between wireless communications applications. The implementation of multiple cellular standards in a single architecture also requires novel transceiver design approaches. Currently, most analog receiver front-ends use multiple integrated circuits fabricated in different processes. It is difficult to meet the requirements of multiple standards using discrete components and simultaneously reduce the size of a receiver.-4-A novel multi-standard image-reject receiver was proposed in [1,2]. In past, image-reject designs have focused on careful circuit layout and matching in order to achieve maximum performance. This design features a different approach-in order to allow the system to support multiple standards, the mixer has the capacity for self-calibration. The self-calibration procedure can be used to optimize system performance over a wide frequency range. This improves the system performance for each standard and allows hardware reuse. The increase in wireless networking with various wireless local area network (WLAN) protocols such as IEEE 802.11b (in the 2.4Ghz band) and 802.11a (in the 5Ghz band) [22] creates new opportunities for multi-standard receives. Migration from 802.11b to 802.11a will require a dual-band solution, and would be a good application of a multi-standard receiver. The fundamental limitations of an image-reject receiver and past attempts to minimize the effect of circuit mismatches will be explored. A digital signal processing algorithm will be proposed that can be used to calibrate image-rejection mixers. The algorithm and custom VLSI implementations, with the minimization of their power consumption and circuit area in mind, will be explored. An image-rejection mixer uses complex phase shifts to allow the signal and its image to be processed differently. In this system, the RF carrier is translated to baseband by two pairs of quadrature mixers, which exploit the relationship between the image and the desired signal. By summing the baseband channels, the image frequencies cancel-5-while the desired band adds constructively …