Electronic Design

Broadband Tuner Available In ICs And In Fully Configured RF Modules

Four distinct versions of a single-chip broadband tuner are capable of covering 48 to 860 MHz. Each is optimized for one of four specific requirements—set-top boxes, cable-modems, PC/TV convergence applications, and digital TVs. Their manufacturer, Microtune Inc. of Plano, Texas, also is introducing the MicroModules series. Devices in this line incorporate these new MicroTune ICs in fully tested RF subsystems.

The MT2030 series of single-chip broadband tuners can receive frequencies from 48 to 860 MHz while converting a selected channel to an IF. Close-in phase noise is low, so the tuners can be used for digital and analog signals. An AGC range of 50 dB in the low-noise amplifier (LNA) suits the chip for off-air as well as cable applications. Also, a dual-conversion architecture eliminates the need for a tracking bandpass filter for initial filtering. Instead, the entire input band is converted to the first IF. It's then fed to a fixed bandpass filter, which requires no manual adjustment and delivers higher performance at a lower cost.

After the LNA, the first mixer upconverts the input spectrum to 1.09 GHz. Next, an image-reject mixer downconverts the filtered IF spectrum to a standard IF output in the 36- to 44-MHz range. The mixer provides excellent image rejection, and it eases the first IF filter's performance requirements. A frequency synthesis system is included on the chip to derive the first and second local-oscillator frequencies from an external 5.25-MHz crystal. A serial interface enables programming and reads back the IC's status.

The frequency synthesizer system's PLLs and varactors are integrated. The chip requires a single 5-V supply and consumes just 2.5 W, which is 28% less than earlier versions. The noise figure referred to the input port is 8 dB. The phase noise for LO1 + LO2 at a 10-kHz offset is −84 dBc/Hz. At a 100-kHz offset, it's −105 dBc/Hz. The gain flatness from 55 to 860 MHz is ±3 dB, and the IF gain flatness is better than 0.75 dB.

Microtune also has announced the first releases in its MM8000 series of MicroModules for these four applications. About the size of a credit card, each module contains all of the functions necessary for an RF subsystem.

The MM8838 MicroModule is a complete, fully tested, turnkey RF subsystem intended for open-cable set-top boxes. It enables end-equipment compliance with FCC Part 15.118. In turn, set-top boxes and cable modems can be labeled "cable ready"and "cable compatible."

The heart of the MicroModule is the MicroTuner 2030-STB single-chip tuner (see the figure). This component provides the required IF flatness, low phase noise, and linearity. Meanwhile, the reverse data channel consists of a variable-gain, serial-port power amplifier that can transmit signals upstream in the 5- to 27-MHz range.

The forward application transport (FAT) comprises a dual-conversion, single-chip MicroTuner and band-limiting filters. The FAT can support analog NTSC signals as well as digitally modulated QAM-64 or QAM-256 signals in the 54- to 862-MHz range. At the same time, an external oscillator frequency is applied to the forward data converter. This feature downconverts a channel that's 2 MHz wide (in the 70- to 130-MHz range) to an IF of 36 MHz. The converter transports quadrature phase-shifting keying signals downstream.

The MT2030 ICs are available now with reference designs developing tuner-on-board solutions. The MT2030-STB (digital interactive set-top box) is $17.95 each. The MT2030-CM (cable modem) costs $15.95. The MT2032-PC (PC/TV) goes for $14.95. The MT2032-DTV (digital TV) is $17.95, and the MM8838 MicroModule for OpenCable set-top boxes is priced at $34.95. All prices are for 10,000-unit lots. Samples will be available in June.

Microtune, Inc., 2540 East Plano Pkwy., Plano, TX 75074; (972) 673-1600, (972) 673-1602; fax (972) 673-1602; www.microtune.com.

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