A Gilbert Cell Mixer with Digitally Controlled Performance Space

In today’s world, new wireless communication standards evolve fast, putting a significant burden on set makers and RF IC design houses to have integrated and cheap solutions quickly on the market place. Hence there is a strong need for flexible circuit topologies that can support a range of applications via adjustability and configurability. However, this concept makes only sense if the reuse count (how many times the circuit is used while having a minimum amount of design effort) of the flexible circuits justifies the investment. This in turn, is strongly related to the performance space (the set of specifications that can be covered with one circuit, which is a sub-set of the total design space) that can be covered by the adjustable circuit. In order to assess this performance space, the Gilbert cell is considered as an example. The Gilbert cell is the most common switching mixer topology, and it is used as a basis for a digitally controlled Gilbert cell. Hence, design equations of the Gilbert cell are determined and a full design procedure is developed. DC limitations and design parameter limitations of the Gilbert cell are considered. The design space of the Gilbert cell for CMOS 0.25um technology, is determined. Following assessment of its limitations and its design space, a digitally controlled Gilbert cell is derived starting from the basic Gilbert cell. Some general solutions how the digitally controlled Gilbert might be used as a sheared component in multi-standard terminals, are mentioned. Advantages and drawbacks of these solutions in comparison with the fixed solutions are discussed.