V-Band Multiport Heterodyne Receiver for High-Speed Communication Systems

Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2007, Article ID 34358, 7 pages doi:10.1155/2007/34358 Research Article V-Band Multiport Heterodyne Receiver for High-Speed Communication Systems Serioja O. Tatu and Emilia Moldovan Institut National de la Recherche Scientifique, Ènergie, Matériaux et Télécommunications (INRS-EMT), 800 de la Gauchetière Ouest, R 6900, Montréal, Canada H5A 1K6 Received 20 April 2006; Revised 10 October 2006; Accepted 11 October 2006 Recommended by Kiyoshi Hamaguchi A V-band receiver using a MHMIC multiport circuit is presented in this paper. The millimeterwave frequency conversion is performed using a passive circuit, the multiport, and related power detectors, avoiding the conventional millimeter-wave active costly mixers. Basically, the multiport circuit is an additive mixer in which the resulting sum of millimeter-wave signals is nonlinearly processed using millimeter-wave power detectors. This multiport heterodyne receiver is an excellent candidate for the future lowcost high-speed millimeter-wave wireless communication systems. The operating principle of the proposed heterodyne receiver and demodulation results of high-speed MPSK/QAM signals are presented and discussed in this paper. According to suggested datarate of 100–400 Mbps used to prove the operating principle, the IF of this receiver was chosen at 900 MHz. Therefore, this receiver is a possible alternative solution for WPAN applications Copyright © 2007 S. O. Tatu and E. Moldovan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. INTRODUCTION The modern communication receivers are more and more exigent in terms of wide-band, datarates, size, and costs [1]. The millimeter-wave technology has received increased attention in both academia and industry for very high-datarate wireless personal area network (WPAN) applications such as wireless data bus for cable replacement, high-speed wireless Internet access, wireless direct communication between notebooks and related devices, and wireless high-resolution TV and videoconferencing. The IEEE 802.15.3c industrial standard based on millimeter-wave technology has been recently introduced for WPAN. The use of millimeter-wave frequencies enables the design of compact and low-cost wireless millimeter-wave communication front-ends, which can offer convenient terminal mobility and high-capacity channels. This wide range of applications requires low-cost equipment operating at hundreds of megabits per second. In the last decade initial research has been made, especially in terms of designing new millimeter wave components operating over the V-band [2–5]. In order to improve overall performances of the communication receivers, alternative wide-band architectures for high-speed wireless communication systems have been explored in the past years [6–10]. This paper presents MPSK/QAM demodulation results of a V-band multiport heterodyne receiver suitable for very high-datarate WPAN applications. 2. THE MULTIPORT MIXER The main purpose of this paper is to demonstrate that the multiport circuit together with related power detectors and two differential amplifiers can successfully replace a conventional mixer in a low-cost millimeter-wave heterodyne or homodyne architecture. The multiport equivalent circuit of the heterodyne receiver uses four power detectors and two differential amplifiers operating at IF frequency. The multiport block diagram is shown in Figure 1. The circuit is composed of four 90Æ hybrid couplers and a 90Æ phase shifter. Let us assume that there are two input normalized waves, a5 from the LO and a6 from the RF input, having different amplitudes and frequencies. The MPSK/QAM modulated signals can be expressed using the phase and the amplitude variation of the RF input signal, α(t) and ϕ6 (t), 2 EURASIP Journal on Wireless Communications and Networking i 3 b3 8 7 a5 5 6 4 Zo 2 5 π/2 a6 Figure 2: Equivalence between the conventional I/Q mixer and the multiport mixer. 50 Ω Figure 1: The multiport circuit block diagram. 1 6 respectively,   3 RF  a5 = a exp j ω0 t + ϕ5 , q + LO 2 b2   2 4 i + LO 4 b4 π/2 RF 6 q 1 b1 Zo 1 3 RF  a6 = α(t) a exp j ω t + ϕ6 (t) . (1) 4 The output detected signals can be calculated based on the multiport block diagram and using the quadratic characteristic of the power detectors:  2 vi (t) = K bi (t) , v1,3 (t) = K v2,4 (t) = K (2) a2  1 + α(t)2  / + 2 α(t) 4   cos  Δω t + Δϕ(t) , (3) a2  1 + α(t)2  / + 2 α(t) 4   sin  Δω t + Δϕ(t) . (4) In the previous equation, Δω = ω0  ω represents the frequency difference between the multiport inputs (superheterodyne), and Δϕ(t) = ϕ6 (t)  ϕ5 is the phase difference between the same signals. Considering the sinusoidal antiphase signals in each equation (3) or (4), the DC offset is eliminated using a differential approach. Therefore the output I/Q signals are     i(t) = v3 (t)  v1 (t) = K α(t) a2 cos Δω t + Δϕ(t) , q(t) = v4 (t)  v2 (t) = K α(t) a2 sin Δω t + Δϕ(t) . (5) The previous equations show that the multiport circuit with four power detectors and two differential amplifiers can successfully replace a conventional mixer. Therefore the equivalence between the conventional I/Q mixer architecture and the multiport mixer, as presented in Figure 2, has been demonstrated. It must be noted that conventional superheterodyne approach using a down-converter does not have a direct equivalence with the proposed multiport approach. This conventional receiver can be implemented using a V-band downconverter mixer (a balun and two Schottky diodes, e.g.) and a IF I/Q mixer. In practice, for a multiport heterodyne receiver, the carrier frequency ω is close to the local oscillator frequency ω0 . 2 50 Ω 5 LO Figure 3: Layout of the V-band multiport circuit. Therefore, these receivers are low IF heterodyne receivers. However, if ω0 = ω, I/Q direct conversion is obtained in a homodyne architecture. This aspect can be considered as an important advantage of the proposed receiver compared to the conventional V-band down-conversion receiver. The same multiport front-end can be used for both heterodyne and homodyne architectures. In addition, signal to noise ratio is improved using a multiport circuit. The cost of additional hybrids and two Schottky diodes is compensated by the reduced cost of the IF stage (IF mixers instead of the conventional IF I/Q mixer). A V-band multiport circuit was designed in MHMIC technology using a 125 μm ceramic substrate having a relative permittivity of 9.9. Figure 3 shows the layout of the circuit having a size of approximately 3 mm by 3 mm. The circuit is composed of four 90Æ hybrid couplers connected by 50 Ω microstrip transmission lines. In or (...truncated)