Sheng-Fuh Chang

A dual-band RF transceiver for multistandard WLAN applications

A new dual-band RF transceiver is presented for 2.4- and 5.2-GHz multistandard wireless local area networks. The proposed dual-band RF transceiver integrates a concurrent dual-band front-end, a triple-band frequency synthesizer, and a band-sharing in-phase/quadrature modulator/demodulator to maximize component and power reuse. The design is started with the examination of an enhanced dual-band heterodyne architecture and then the optimal circuit partition to satisfy the multistandard requirements. Key dual-band circuits are designed and integrated with other building blocks for experimental demonstration. The measurement shows that eight 5-GHz channels and 13 2.4-GHz channels can be synthesized within 130 /spl mu/s with phase noise less than -98 dBc/Hz at 100-kHz off carrier and spur suppression greater than -65 dBc. The transmitted P/sub 1 dB/ power is 25/20 dBm at 2.4/5.2 GHz, respectively, with the modulation accuracy error-vector magnitude (EVM) values varying from 3.57% to 7.19%. The receiver gain is 20/31 dB at 2.4/5.2 GHz front-end and 70 dB at IF back-end with EVM within 2.32% to 10% from -70- to -17-dBm received power range.

Design of a Reflection-Type Phase Shifter With Wide Relative Phase Shift and Constant Insertion Loss

reflection-type phase shifter with constant insertion loss over a wide relative phase-shift range is presented. This important feature is attributed to the salient integration of an impedance-transforming quadrature coupler with equalized series-resonated varactors. The impedance-transforming quadrature coupler is used to increase the maximal relative phase shift for a given varactor with a limited capacitance range. When the phase is tuned, the typical large insertion-loss variation of the phase shifter due to the varactor parasitic effect is minimized by shunting the series-resonated varactor with a resistor Rp. A set of closed-form equations for predicting the relative phase shift, insertion loss, and insertion-loss variation with respect to the quadrature coupler and varactor parameters is derived. Three phase shifters were implemented with a silicon varactor of a restricted capacitance range of Cv,min = 1.4 pF and Cv,max = 8 pF, wherein the parasitic resistance is close to 2 Omega. The measured insertion-loss variation is 0.1 dB over the relative phase-shift tuning range of 237deg at 2 GHz and the return losses are better than 20 dB, excellently agreeing with the theoretical and simulated results.

New high-directivity coupler design with coupled spurlines

A new high-directivity coupler using coupled spurlines is proposed. The effective capacitances of coupled spurlines generate an isolation zero at any desired frequency due to their equalization effect on the odd-mode and even-mode phase velocities. The measurement results demonstrate an improved performance over the conventional parallel-line coupler in terms of the isolation and the coupling flatness.

A high stopband-rejection LTCC filter with multiple transmission zeros

A low-temperature-cofired ceramic (LTCC) bandpass filter with high stopband rejection is presented for multistandard coexisted wireless communication applications, such as the integrated wireless local area network (WLAN)/wavelength code-division multiple access handset, the dual-band triple-mode WLANs, and the global system for mobile communications/global positioning system receivers. By improving the filter cell structure, 2n transmission zeros can be generated to achieve wide-band suppression from cascading n filter cells. The presented method provides the design flexibility of locating these transmission zeros distributed in the lower and upper stopbands. An LTCC bandpass filter with four transmission zeros has been implemented for experimental demonstration. The measured insertion loss is less than 1.5 dB at 2500 MHz, and four transmission zeros are obtained at 1.64, 1.88, 4.36, and 5.32 GHz, respectively. These result in 48-59 dB for lower stopband suppression and 38-55 dB for higher stopband reduction. This paper demonstrates that the proposed filter is extremely suitable for the multiband RF transceivers where the cross-band interference must be adequately reduced.

2.45-GHz CMOS Reflection-Type Phase-Shifter MMICs With Minimal Loss Variation Over Quadrants of Phase-Shift Range

CMOS reflection-type phase shifters with minimal insertion-loss variation over quadrants of phase-shift range are presented. Two performance enhancement techniques are proposed. First, the 3-dB quadrature hybrid is designed with a phase-compensated inductively coupled hybrid. Second, an impedance-transformed pi-resonated varactor network is presented to provide a full 360deg phase range, using a MOSFET varactor with limited reactance variation range. The design considerations and simulation are described. Two experimental 2.45-GHz phase shifters were implemented in 0.18-mum CMOS technology. One has a measured phase-shift range of 120deg with the insertion loss of 5.6 plusmn 1.2 dB in 2.33-2.60 GHz and the other has a phase range larger than 340deg with the insertion loss of 10.6 plusmn 2 dB in 2.44-2.55 GHz. Both chips are extremely compact with sizes of 0.72 and 0.66 mm2, respectively, and consume zero dc power.

Compact Millimeter-Wave CMOS Bandpass Filters Using Grounded Pedestal Stepped-Impedance Technique

This paper presents compact CMOS millimeter-wave bandpass filters based on a new stepped-impedance technique by incorporating a grounded pedestal into the microstrip line. The characteristic impedance of a microstrip line can be effectively changed by varying both the height of pedestal and the width of line. Therefore, the stepped-impedance resonators and stubs can be realized in the compact three-dimensional forms in CMOS. Two millimeter-wave bandpass filters were designed by using the new stepped-impedance resonators and stubs. Their chip sizes are significantly miniaturized to 0.37 x 0.2 mm2, equivalently 0.012 λg2 . The first chip filter has the insertion loss of 3.1-3.4 dB in 59-71 GHz and the second filter has the insertion loss of 3.5-3.8 dB in 53-64 GHz. Both chip filters have good stopband suppression attributed from the existence of transmission zeros.

Design of Stepped-Impedance Combline Bandpass Filters With Symmetric Insertion-Loss Response and Wide Stopband Range

An enhanced stepped-impedance combline bandpass filter employs an array of stepped-impedance resonators with tapped-transformer coupling at input and output is presented in this study. This filter has enhanced performance, including symmetric insertion-loss response around the passband and wider stopband range. The structure is compact and suitable for multilayer realization because it is free of lumped capacitors and has fewer via-hole grounds. The circuit is investigated with the characteristic mode theory of coupled lines to prove the existence of multiple transmission zeros around the passband. Numerous diagrams are given for circuit design purposes. The second- and fourth-order bandpass filters at 2.45 GHz were designed, measured, and compared with the conventional combline structure to demonstrate their performance enhancement.

Novel Design of a 2.5-GHz Fully Integrated CMOS Butler Matrix for Smart-Antenna Systems

This paper presents a novel design of monolithic 2.5-GHz 4times4 Butler matrix in 0.18-mum CMOS technology. To achieve a full integration of smart antenna system monolithically, the proposed Butler matrix is designed with the phase-compensated transformer-based quadrature couplers and reflection-type phase shifters. The measurements show an accurate phase distribution of 45plusmn3deg, 135 plusmn 4deg, -45 plusmn 3deg, and -135 plusmn 4deg with amplitude imbalance less than 1.5 dB. The antenna beamforming capability is also demonstrated by integrating the Butler matrix with a 1 X 4 monopole antenna array. The generated beams are pointing to -45deg, -15deg, 15deg, and 45deg, respectively, with less than 1deg error, which agree very well with the predictions. This Butler matrix consumes no dc power and only occupies the chip area of 1.36 times 1.47 mm2. To our knowledge, this is the first demonstration of the single-chip Butler matrix in CMOS technology.

A 24-GHz CMOS Butler Matrix MMIC for multi-beam smart antenna systems

A 24-GHz 4-way Butler matrix MMIC in 0.18-mum CMOS technology is presented. The multi-layer structure of CMOS process is utilized to monolithically realize the bulky Butler matrix on silicon substrate. Particularly, the multi-layer bifilar transformer is introduced to miniaturize the circuit and reduce the signal loss. The implemented CMOS Butler matrix MMIC only occupies a chip area of 0.41 mm2 (excluding I/O pads). The experimental results show that insertion losses are 2.2plusmn0.6 dB from 23 to 25 GHz and the phase errors are within 6deg. Therefore, by connecting this Butler matrix to a linear array antenna, four orthogonal beams, pointing to -49deg, -15deg, 15deg, and 49deg, respectively, are generated within 0.3deg error.

A reconfigurable bandpass-bandstop filter based on varactor-loaded closed-ring resonators [Technical Committee]

In this article, a novel reconfigurable bandpass-bandstop filter based on the varactor-loaded closed-ring resonators is presented, where the bandpass and bandstop characteristics can be easily controlled by tuning the varactor bias voltage. This reconfigurability results from the perturbation effect on the degenerated even and odd modes of the closed-ring resonator. When the perturbation varactor is at the series resonance, its reactance vanishes, so a bandstop characteristic is formed. When the perturbation varactor is changed to be capacitive, the bandpass characteristic is generated. Additional varactors, incorporated at input and output ports, are tuned along with the perturbation varactors to maintain good return losses.