Digitally Programmable-Gain IF Amp Offers Low Distortion

Dec 18, 2008 11:16 AM, MD&D News Staff

With an output third-order intercept of 43 dBm at 200 MHz, the LT5554 broadband digitally programmable-gain IF amplifier from Linear Technology Corp. improves signal integrity performance. The amplifier also has excellent reverse isolation, making it well-suited for driving high-speed, high-resolution analog-to-digital converters, where the input sampling noise can double back to the RF and IF circuits.

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A 7-bit parallel word controls gains from 2 to 18 dB, producing 0.125-dBm steps, the best granularity available, according to the company. Settling time from a gain change is less then 5 ns, which allows very fast and accurate automatic gain control performance with low glitch noise. Gain accuracy is ±0.1 dB from –40°C to 85°C, which is five times better than the closest competition, said Linear.

The LT5554 is powered from a single 5-V supply, drawing a nominal supply current of 200 mA. The chip can be shut down via an Enable pin. When in shutdown, the device draws a typical supply current of 4 mA and a maximum of 5.1 mA. The amplifier is a full differential input and output device. Its differential outputs can drive directly into 50-Ω loads.

The device comes in a 32-lead, 5- by 5-mm plastic QFN surface-mount package. Prices for the LT5554 start at $4.40 each in 1000-piece quantities. The amplifier is available immediately from stock.