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FROM EDN EUROPE: SiGe to boost op-amp performance

Texas Instruments has introduced a series of op amps
that extends the performance of its high-frequency and audio products. The
THS4271/5 voltage-feedback devices provide 1.4-GHz unity-gain bandwidth,
900V/src= "http://www.e-insite.net/articles/images/EDNE/20020808/17csq6.gif"> μsec slew rate and 2.8 nV/src="http://www.e-insite.net/articles/images/EDNE/20020808/17csq6.gif"> noise density. Output voltage swing is 2V p-p, and the distortion at 30 MHz is –84 dB relative to the carrier. These figures equate to true 14-bit performance at 30 MHz, TI says; the devices operate from a 5V line. They come in a small-outline leadless package that minimises parasitic-component losses.

TI also plans by year-end to introduce a complementary BiCMOS process using SiGe (silicon-germanium) gate structures that will allow manufacturers to build closely matched npn and pnp transistors on the same devices; npn and pnp devices will have f_Ts of 20 and 15 GHz, respectively. TI forecasts that devices using this technology will have half the noise levels of its current processes and will operate at 100 MHz with distortion of –100 dB. The CMOS aspects of the process will allow you to build a significant amount of logic in 0.5-micron dimensions on a die for mixed-signal applications with extensive use of dielectric isolation to control operating conditions.

In a different area of amplifier application, the TPA2005D1 allows you to design a power-efficient audio amplifier for use in battery-powered products with 1.1W output in Class D. The modulation scheme permits Class D operation without an output filter and requires only two resistors and a capacitor. A 78-dB power-supply-rejection ratio aids a clean audio output in a battery-powered environment. Prices for the audio chips start at 49 cents (1000).

Texas Instruments, +49 8161 80 33 11, www.ti.com.