Design Of Analog Baseband Chain For Integrated Ultra Wideband Receiver

As one of the WPAN technologies, Ultra-wideband (UWB) is characterized by its high data rate and low-power. Intended for chip-level ultra-wideband RF transceiver, analog baseband was designed for the receiver in this work. Applied orthogonal frequency division multiplexing technology, the system required analog baseband to be in charge of gain controlling and channel filtering within bandwidth of 264MHz, as UWB standards support a channel bandwidth of 528MHz. According to the architecture of receiver, designing goals of analog baseband circuit were derived. In this design, current-mode programmable gain amplifier (PGA) and channel selection filter (CSF) were presented to meet the unique system requirements. Also voltage-to-current conversion stage, current-to-voltage conversion stage and DC offset cancellation circuit were included for the whole system.Firstly, in the section of programmable gain amplifier, the optimal number of the cascade gain block for the PGA was discussed, and next comprehensive analysis of conventional PGA structure was presented. Taking the requirements of high bandwidth and high gain range into account, current mode PGA structure was presented. On the shoulder of the prior works, a detailed analysis of the current mode PGA was investigated, including optimization methods for input and output impedance, means for bandwidth extension, and the way to get adjustable gain. Also noise performance of PGA gain block was given, and finally simulation results of PGA were presented.In the section of channel selection filter, advantages of Gm-C structure over Active-RC structure were explained and Gm-C structure was selected as it’s more suitable for high-frequency applications. Then basic circuit characteristics, system considerations and design methods of Gm-C filter were systematically expounded, including the cascade design method, considerations for cascade of second-order integrator units, trade-off between SNR and power consumption, and non-ideal effect of operational transconduct amplifier(OTA). Based on the sixth-order Chebyshev low-pass prototype, parameters of the second-order integrator units were determined, and the dual-output OTA for Gm-C filter applied super source follower structure. Also the local feedback technology applied in super source follower structure was analyzed concretely. The sixth-order low-pass filter employed only six OTAs. Finally, the simulation results were given.Next, illustration of mechanism of the DC offset, its deterioration and method to remove DC offset were given, and the configuration of the DC offset cancellation circuit was investigated. To complete the analog baseband, voltage-to-current conversion stage, current-to-voltage conversion stage, output buffer, and the digital gain-control circuit were needed. In this thesis, circuit implementations of voltage-to-current conversion stage, current-to-voltage conversion stage and the output buffer were also analyzed concretely. Finally, the complete analog baseband chain was given.All the circuit blocks in analog baseband were verified through post simulation and layout of each module was carefully designed. Then integration of the entire analog baseband was completed, including two layout versions. The analog baseband chain implemented in commercial TSMC 0.13μm RF CMOS process has been taped-out. The post-simulation results show that the analog baseband chain has a gain range of 0-60dB with 2dB gain step, noise figure of 22dB, the input 1dB compression point of -54dBm, and in-band IIP3 of -41dBm all at 60dB gain mode, which meet the requirements.