Switching RF Mixer with Embedded All-Digital Frequency Synthesizer
Nikolaos Stamatopoulos
Abstract
There has been an increasing interest in all-digital architectures in the RFIC industry over the past few years, mainly due to the higher challenge in the design and the extra cost of fabrication of RF analog and mixed-signal ICs versus standard digital ones in modern nano-scale IC technologies. Digital circuit designs offer the advantages of portability, reconfigurability, automated checking and verification. This thesis proposes a switching RF downconverting mixer whose Local Oscillator (LO) input is driven by an embedded all-digital frequency synthesizer, offering some of the aforementioned advantages compared to traditional analog mixer architectures. Switching mixers are popular blocks in discrete-component designs and have been implemented in RFICs. However, they are typically driven by classical PLLs or complex mixed-signal frequency synthesizers. The mixer architecture discussed in this thesis is based on digital transmission gates which are driven directly by the output stream of the embedded all-digital frequency synthesizer. Certain dithering techniques are also used to make the synthesizer’s spectrum sinewave-like and convert spurs to continuous noise floor. Chapter 1 discusses the theory behind 1-bit frequency synthesis using the optimal dithering sequence to eliminate spurs. Chapter 2 presents a simple switching mixer driven by an embedded single-bit frequency synthesizer with dithering. Finally, Chapter 3 presents a multi-bit switching multiplier/mixer using switched capacitors.