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Variable gain amp sets new performance standard

Posted: 08 Feb 2008 ?? ?Print Version ?Bookmark and Share

Keywords:programmable variable gain amplifier? low impedance?


Analog Devices Inc. has introduced a digitally programmable variable gain amplifier (VGA) with transmit driver claimed to set a new standard of performance for driving signals over power lines, cables and other applications with low impedance.

The AD8260 operates on a single 3.3V power supply and has a transmit driver that produces 200mA output up to 100kHz, and greater than 100mA above that frequency. This is an improvement over competing solutions using a discrete VGA, output driver and pre-amp, which consume 90 percent more board space, and require multiple power supplies.

The AD8260 VGA operates at -3dB bandwidth of 200MHz and includes a 30dB gain range digitally adjustable in 3dB gain steps providing the headroom needed for losses introduced in various cabling systems. The VGA features 2.4nV/rtHz input voltage noise and driver with a built-in gain of 1.5, which is suitable for converting DAC differential output signals to a voltage that can directly drive very low impedances. The AD8260 can fully drive a 10 load with 2Vpp at 10MHz. The chip dissipates just 93mW of power, which is less than half that of competing devices.

The AD8260 includes a high-current driver, usable as a transmitter, and a low-noise digitally programmable VGA, which is useable as a receiver, combined in a 5mm x 5mm chip-scale package. The receiver section consists of a single-ended input preamplifier and linear-in-dB, differential-output VGA. The differential output facilitates the interface to modern low-voltage, high-speed ADCs. Versatile single- and dual-supply operation allow gain control of negative-going pulses, such as generated by photodiodes or photo-multiplier tubes, and allows for the processing of band-pass signals on a single supply. The AD8260 preamplifier is user-configurable with external resistors for gains greater than 6dB. The driver is set-up to be driven by modern current output DACs.

The AD8260 is sampling now, with full volume production scheduled for March. The chip is available in a 32-Lead LFCSP over the extended industrial temperature range -40C to 105C and is priced at $3.79 in 1,000-unit quantities.

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