A direct-conversion receiver for DVB-H

Abstract

The European system for the fixed and portable reception of digital television, DVB-T, has been available for several years. Recently, companies have been developing solutions to receive DVB signals on mobile and handheld terminals, and integrating them into GSM or 3G convergence terminals. The existing standard has been augmented by an annex, DVB-H (handheld), enabling point to multipoint reception of digital television and IP content on mobile phones using the existing DVB-T network. A consortium of companies is collaborating to define the mobile and portable DVB-T/H radio access interface (MBRAI) specifications for mobile DVB-receivers [1].In the battery-powered environment of handheld devices, the constraints of small physical size and low power consumption require new tuner concepts that differ from classical superheterodyne receiver architectures. In this paper, a fully integrated low-power UHF tuner IC design for such applications is presented.A classical OFDM DVB-T receiver employs down-conversion from UHF to either a 1 st or 2 nd intermediate frequency (IF). Another current approach is the up-down conversion structure [2], obviating the input tracking bandpass filters. A/D conversion occurs at the 1 st or 2 nd IF, with the final down-conversion to the complex baseband signal occurring in the digital domain, thus avoiding mismatch errors between the I and Q channels that would degrade image rejection. Such classical architectures have the disadvantage of requiring external SAW filters.To overcome these limitations, a direct down-conversion from the RF band to baseband (zero-IF) is used. Channel selectivity is achieved by subsequent low-pass filtering. This architecture has the advantages of reduced complexity, fewer external components, and no need for image suppression filtering. DC offsets, flicker noise, and I/Q channel amplitude and phase imbalances need careful attention. Constant I/Q mismatch errors may be corrected by DSP in the demodulator [3], but frequency-dependent errors have to be minimised by careful circuit design and layout.The position of the tuner IC within the DVB-H receiver system is illustrated in Fig. 23.1.1. An external LNA precedes the IC. The output consists of differential analog I and Q baseband signals. Since reception will occur in the presence of other DVB-T/H and PAL signals, there are stringent linearity, sensitivity and selectivity requirements.This receiver design is implemented in a 0.35µm SiGe:C BiCMOS technology, using 10µm Cu top layer with 3-level AlCu interconnect, SiGe:C HBTs, graded channel MOS devices, and multiple resistor and capacitor types. The low-loss thick Cu top layer allows on-chip inductors with Q-factors in excess of 20.The UHF tuner IC (Fig. 23.1.2) consists of the following circuit blocks: broadband LNA, dual quadrature mixer, post-mixer amplifier (PMA), multiple bandwidth baseband filter and associated tracking loop, VCO, PLL, crystal reference, quadrature LO generator and an I 2 C interface. A wide-band detector (WBD) provides power-level informati...

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