A 1.8dB NF 112mW Single-Chip Diversity Tuner for 2.6GHz S-DMB Applications

Abstract

Mobile TV" is recently emerging across the world. In Korean and Japanese markets, a next generation digital broadcasting service, S-DMB system, has been developed for automotive and handheld terminals. Because S-DMB service is mobile and personalized, the market demand is expected to be higher and broader than existing household-based broadcasting services. S-DMB service offers high-quality streaming videos and CD quality music at low cost [1]. S-DMB adopts the code-division multiplexing (CDM) technology and supports the ITU-R BO/1130-4 Digital System E standard. S-DMB service provides extended coverage using a satellite in most areas and gap fillers in shadow areas such as inside buildings and subways. To maximize the coverage with a satellite, a diversity architecture is strongly recommended for the S-DMB tuner by service providers.Main challenges of an S-DMB tuner are small size, low power consumption, low noise and wide dynamic range. At diversity operating mode, small gain difference and high path isolation between diversity paths are also important constraints over the wide dynamic range. In this paper, a fully monolithic diversity 2.6GHz S-DMB tuner IC is presented. The proposed solution has a die size of 2.3×2.3mm 2 , an NF of less than 1.8dB, a path isolation of more than 25dB, and a DR of over 100dB while it has a less than 4dB path-gain mismatch and a power consumption of 112mW.To reduce size and power consumption for use in battery-operated mobile-TV terminals, two signal path units for diversity architecture are integrated into a single chip with a shared common LO unit, as shown in Fig. 33.6.1. For both signal path units, direct conversion architecture is used to further reduce the size and power consumption. Over 100dB DR, to receive signals from both a satellite and gap fillers, is achieved by the mixed gain-control scheme: wide continuous gain control for the VGA and step gain control for the RF front-end. This step-gain-control scheme is used to achieve lower noise, smaller size, and lower power RF front-end design by eliminating requirements for RF VGA and associated control blocks.The RF front-end of both signal path units consists of a low-noise step-gain amplifier (LNSGA), a low-noise step-gain down-conversion I/Q mixer (LNSGDCM), and a quadrature LO generator as shown in Fig. 33.6.2. The LNSGA has two gain modes: a highgain mode and a low-gain mode. For the high-gain mode, an inductively degenerated cascode structure is used to achieve 17dB gain and 1.2dB NF while drawing only 4mA. For the lowgain mode, a digitally adjusted resistor (R1) and a MOS switch (Q3) are used for -13dB loss and over +25dBm IIP3. Coupling between two LNSGA via bonding wires and ground paddle of the package are main causes of degrading path isolation. The path isolation of over 25dB is achieved by reducing the bonding wire coupling factor by careful pin placements, reducing coupling through ground paddle by controlling degeneration amount, and reducing coupling through substrate by careful layout using trench hole. T...

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“…A temperature compensation for baseband VGA has been reported [7] . However, the β of the transistors Q3-Q6 in Fig.…”

“…The control voltage V GC in Eq. ( 1) is determined by the transistors Q3 and Q4 [7] , and is given by where n is the multiplicity parameter of transistor Q4 to transistor Q3. Substitute Eq.…”

“…However, there is another important specification that the VGA needs to fulfil, which is that the gain of the VGA should not drift with the temperature variation. Some works of the temperature compensation for the intermediate frequency (IF) and baseband VGA have been reported [6,7] , but are of the same importance as for the RF VGA.…”

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“…The temperature compensation can be done as shown in Fig. 2(c) [2] . Then, with the compensated voltage V gc generated by the AGC circuit, the temperature variations can be compensated.…”