ourth-generation wireless and mobile systems are currently the focus of research and development. They will allow new types of services to be universally available to consumers and for industrial applications. Broadband wireless networks will enable packet-based high-datarate communications suitable for video transmission and mobile Internet applications.This article is based on a project that aims to develop a single-chip wireless broadband communication system in the 5 GHz band, compliant with the Hiperlan/2 [1] and IEEE 802.11a [2] standards. Both standards specify broadband communication systems using orthogonal frequency-division multiplexing (OFDM) with data rates ranging from 6-54 Mb/s. Depending on the desired data rate, the modulation scheme adopted can be either binary phase shift keying (BPSK), quaternary PSK (QPSK), or quadrature amplitude modulation (QAM) with 1-6 b/subcarrier. The bandwidth of the transmitted signal is 20 MHz and the symbol duration is 4 µs including 0.8 µs for a guard interval.To open a broad market for consumer products, low cost of the required hardware is essential. One way to realize lowcost systems is to reduce the system complexity and implement all functions in a single chip. A single-chip solution is also advantageous in terms of performance and power dissipation when compared with multichip implementations. Fewer wires have to be routed via slow and power-hungry pad drivers. In addition, short interconnections allow faster operation of the system. Our in-house 0.25 µm SiGe:C BiCMOS technology enables the integration of complex digital baseband and data link control (DLC) functionality together with the analog RF front-end (AFE). Since the complete design flow, from system simulation down to working silicon, is on hand and under one roof, fast feedback is possible during the complete design cycle.By simultaneously considering all layers of the protocol stack, we were able to optimize the system performance. The dynamic activation/deactivation of certain blocks during transmission and reception allows us to introduce efficient power reduction mechanisms.In our vision, this broadband modem forms the communication element for a single-chip wireless engine which in turn is the heart of a complete personal digital assistant (PDA). For that purpose we also intend to integrate a TCP/IP processor and a Java-based application engine as well as advanced power management and test engines.This article is structured as follows. We give a very rough estimation of the algorithmic complexity of various blocks in the baseband and DLC layer of the wireless modem. This allows a first evaluation of the computing resources required for the modem functionality. A discussion based on these results leads to the derivation of a suitable system architecture. Some aspects of the design flow used are highlighted. A set of required hardware and software tools is listed. Some results of our work are presented. Here we focus on the implementation of specific blocks within the digital baseband processor....
This brief presents a baseband automatic gain control (AGC) circuit for an IEEE 802.11a wireless local area network (WLAN) direct conversion receiver. The whole receiver is to be fully integrated in a low-cost 0.25-µm 75-GHz SiGe bipolar complementary metal-oxide-semiconductor (BiCMOS) process; thus, the AGC has been implemented in this technology by employing newly designed cells, such as a linear variable gain amplifier (VGA) and a fast-settling peak detector. Due to the stringent settling-time constraints of this system, a feedforward gain control architecture is proposed to achieve fast convergence. The proposed AGC is composed of two coarse-gain stages and a fine-gain stage, with a feedforward control loop for each stage. It converges with a gain error of below ±1 dB in less than 3.2 µs, whereas the power and area consumption are 13.75 mW and 0.225 mm 2 , respectively.
IndexTerms-Bipolar complementary metal-oxidesemiconductor (BiCMOS) integrated circuits, feedforward systems, gain control, peak detector, variable gain amplifier (VGA), wireless local-area network (WLAN).
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