Comparisons of sige active downconversion mixers and a high performance sige active mixer design for s-band applications

In wireless systems, frequency conversion is widely utilized to transmit and receive low frequency signals. These conversions are fulfilled by mixer circuits which are driven by a large local oscillator signal and an input signal. A mixer multiplies these signals and output of the circuit includes two frequency components as sum and difference of frequencies of input signals. In downconversion applications, frequency differences of input signals are acquired at the output of the circuit and frequency of the signal is reduced. SiGe transistors provide high performance especially in non-portable applications because they have higher fT, lower noise and may fed by higher supply voltage in order to obtain high performance, compared to MOS transistors in the same process corner. S-Band applications such as basestations, radars, wireless modems etc. also need to high performance mixer; therefore, there are several commercial mixer products in order to implement frequency conversion for these applications. In this thesis, Chapter 1 gives general information about thesis. SiGe transistors, BiCMOS process and general RF performance metrics in mixer design such as conversion gain, IIP3, noise figure etc. are explained Chapter 2. Chapter 3 is related to active mixer design considerations. LO amplification circuit, and IF amplifier are utilized in the design of the mixers in order to obtain higher performance. In Chapter 4, firstly, these peripheral circuits used in mixer comparisons are described in detail. After this, Gilbert Cell, Micromixer, Caprio's Quad Based Mixer and Gilbert Cell Class AB mixer topologies are presented. Topology informations, hand analyzes, circuit elements, performance metrics, input matching, performance trade-offs of the circuits are examined in detail. At the end of the chapter, all mixers are compared according to determined performance metrics. Furthermore, figure of merit of the mixers in entire S-Band are given to easily understand performance of the mixers. In Chapter 5, Gilbert Cell Class AB Mixer is chosen, designed and laid out. The mixer which is described in previous chapter is reconfigured according to bondwire inductors and pad capacitances. Moreover, another high performance IF amplifier is designed. The whole mixer circuit is designed for 2 – 3 GHz RF frequency differently from comparison sections due to wireless applications. After design information, schematic and parasitic extraction results of the circuit are presented. Finally, future works and possible enhancements in the circuit are discussed. In Chapter 6, all study is summarized.