System and circuit design techniques for WLAN-enabled multi-standard receiver.

摘要

As previous second generation (2G) digital cellular standards, such as GSM, were only oriented to the delivery of speech and low bit-rate data services, the need to support broadband multimedia services over wireless infrastructure (with data rates of up to 2 Mbits/sec) is driving the development of third generation (3G) W-CDMA air-interfaces. With the increasing popularity of Wireless Local Area Networks (WLAN), such as Bluetooth and IEEE 802.11b standards, a WLAN-enabled mobile phone, which will not only transfer voice and multimedia data but also access Internet wherever possible, outlines the scenario of the fourth generation (4G) mobile systems. In addition, WLAN-enabled cell phones are also expected to contain multimode cellular capability. An exploration of WLAN-enabled multi-standard wireless receiver is described in this dissertation. The standards under consideration in this proposal are GSM-900, WCDMA and WiFi (IEEE 802.11b).; A GSM/WCDMA/WiFi triple-standard receiver is proposed and analyzed. In this triple-standard receiver, a low-IF (100 kHz) architecture has been used for GSM to reduce the DC offset problem and relax the image rejection requirement while a Zero-IF architecture has been used for the other two standards. Three RF filters have been used to select appropriate signal bands. Due to the proximity of WCDMA and WiFi bands, LNA and mixer have been shared between them, but a second LNA and mixer is necessary for GSM operation. However, when one set of LNA and mixer is operational, the other set is powered down to reduce power consumption. Baseband components in I and Q paths include a DC-notch filter, poly-phase filter, VGA and ADC and these are shared among the three standards. The system level design specifications for these three standards are derived and then distributed among the building blocks in the receiver chain. The block level specifications form the guideline for the design of each building block.; To use a single ADC to cover multiple cellular and WLAN standards is a challenge, since the channel bandwidth are widely spread in those standards (channel bandwidths are 200kHz, 3.84MHz and 22MHz in GSM, WCDMA, WLAN 802.11b respectively). A multi-standard switched-capacitor (SC) SigmaDelta modulator is proposed. According to the different signal bandwidth and Dynamic Range specifications, this SigmaDelta modulator can be reconfigured to achieve the required dynamic range with less power consumption. This SigmaDelta modulator employs cascade 2-1-1-1 structure with multi-bit quantizer as a backbone. Zeros of the noise transfer function are reconfigured in WiFi mode to further suppress the in-band quantization noise. The prototype is designed and implemented in TSMC 0.18-mum CMOS process with 1.8V power supply. It achieves SNDR of 82dB for GSM mode, 75dB for WCDMA and 58dB for WiFi. It can also be used for other standards (e.g. Bluetooth and IEEE 802.11a) without any modification.