A Sub-1mm2 Dynamically Tuned CMOS MB-OFDM 3-to-8GHz UWB Receiver Front-End

Abstract

Ultrawide Band (UWB) Multi-Band OFDM (MB-OFDM) systems have been proposed as an emerging solution to wireless communication applications requiring high data rates (up to 400Mb/s) over short distances [1]. In one proposed version, the modulated carrier with a bandwidth of 528MHz can hop to one of fourteen channels (2904 + 528·nMHz, n = 1, 2…14), divided into four groups of three channels and one group of two channels. To assure the widest possible adoption, RF portions of these systems should consume little dc power and die area, and be implemented in a standard CMOS process. These last requirements argue against the use of on-chip inductors wherever possible.A dynamically tuned UWB OFDM receiver front-end is presented in a 0.18µm CMOS technology. The receiver uses no on-chip inductors and consists of a dynamically tunable low-noise amplifier (LNA), a downconverter and a tunable intermediate frequency (IF) bandpass filter. The receiver is designed to work for the lower three groups; however, the concept can easily be extended to include the higher groups.A direct-conversion UWB receiver, while attractive for power consumption and simplicity of local oscillator (LO) scheme [2], has the well-known problems of time varying dc offset and sensitivity to narrowband jammers. Since the LO can vary from 3.5 to 10.3GHz, the dc offset present at the mixer output can vary significantly with every frequency hop, and the offset calibration loop has to settle to its final value well within the guard interval of 9ns. A differential heterodyne architecture largely eliminates the dc offset issues and provides the additional advantage of reduced second-order distortion, reducing the dc power requirements. One of the drawbacks of a heterodyne receiver; the need for an interstage filter, has been overcome in this design by creating a passive band-pass filter entirely with bond wires and onchip capacitors.To avoid the classical heterodyne receiver image rejection problem, the frequency plan was carefully designed for an IF of 2.64GHz, so that all the images fall below 2.4GHz. An external bandpass filter with a lower cut-off frequency of 3GHz, which is standard in UWB receiver designs, therefore suppresses all the images, as shown in Fig. 6.8.1. In addition, the LNA provides some image rejection, eliminating the need for an image reject mixer.The LNA (Fig. 6.8.2) is a differential cascode amplifier (to enable operation at 2.3V without breakdown) with an LC load. To eliminate the use of on-chip inductors, the load is realized with bond wires and on-chip capacitors. Input matching is achieved via resistive feedback and optimized device sizing. The output device capacitance and mixer input capacitance resonate with the bond wires at 7GHz. The tank's Q is then reduced by a shunt resistor, broadening the bandwidth of the circuit. This provides for good LNA gain in Group 3 (6.3 to 7.9GHz). When the received signal is in the lower-band Group 2 or Group 1, extra shunt capacitance is switched in, by setting bits b 0 and b 1 "high" successively, ...

Ultra-Wideband RF Transceive

“…Both MB-OFDM (Ranjan & Larson, 2006;Zheng H et al, 2007;Bergervoet et al, 2007;Beek et al, 2008) and DS-UWB (Zheng Y. et al, 2007(Zheng Y. et al, , 2008 are carrier-modulated systems, where a mixer is used to up/down convert the radio frequency (RF) signal, therefore it requires local oscillator (LO) synthesis. On the other hand, IR-UWB (Yang, C. et al, 2005 ;) is a carrier-less pulse-based system, therefore, we can eliminate the fast hopping LO synthesis, thus reducing the complexity and power consumption of the entire radio.…”

Ultra Wideband RF Transceiver Design in CMOS Technology

“…Both MB-OFDM (Ranjan & Larson, 2006;Zheng, H. et al, 2007;Bergervoet et al, 2007;Beek et al, 2008) and DS-UWB (Zheng, Y. et al, 2007(Zheng, Y. et al, , 2008 are carrier-modulated systems, where a mixer is used to up/down convert the baseband (BB)/radio frequency (RF) signal, therefore requiring local oscillator (LO) synthesis. The main difference between these two systems is that MB-OFDM systems are dealing with continuous ultra-wideband modulated signals while DS-UWB systems are transmitting discrete short pulses which also occupy ultra-wide bandwidth.…”

“…The main architectures of MB-OFDM UWB transceivers can be categorized into superheterodyne transceivers (Ranjan & Larson, 2006;Zheng, H. et al, 2007) and directconversion transceivers (Bergervoet et al, 2007;Beek et al, 2008), which are quite similar as those traditional narrow-band RF transceivers.…”

A 0.8–6 GHz Wideband Receiver Front-End for Software-Defined Radio

“…The intuitive SDR receiver topology is to connect frontends of different standards in parallel as shown in Figure 1(a); nevertheless, the chip size of such topology would be too large. A wideband radio [2][3][4][5][6] and a tunable-band radio [7][8][9] (see Figure 1(b)) are good candidates for this purpose. The most challenging problem is how to design an LNA and a mixer that meet all the requirements in such a wideband from 800 MHz to 6 GHz.…”

“…Besides, the trade-off between noise figure and bandwidth remains an issue. Tunable-band receivers switching its frequency with tunable passive devices [7][8][9] would be promising, except that the size of passive devices is too costly to accept. Designs of mixers can be also challenging for SDR.…”