Broadband gain amplifier has best distortion characteristics in class

June 21, 2004 – A new 850 MHz programmable gain, broadband amplifier from Linear Technology has the best distortion characteristics of any amplifier in its class. The LT5514 exhibits an output third-order intercept (OIP3) of 49dBm at 70MHz, and has 2nd and 3rd order distortion products lower than -87dBc, while delivering 2V peak-to-peak output into a 200-Ohm load. Its combination of low noise and high spurious-free output capability makes it ideal for 12- and 14-bit, 65Msps or faster A/D converters in high performance communication systems. The LT5514 is designed for a range of applications, including ADC drivers, IF amplifiers for cellular basestation receivers, amplifier/drivers for basestation transmitter distortion correction loops, and amplifiers for cable headend upstream receivers.

The LT5514's variable gain is adjusted by means of an on-chip, digitally controlled attenuator in combination with a fixed gain amplifier. A 4-bit parallel input word provides accurate gain control, ranging from 10.5dB to 33dB, with a 1.5dB incremental step.

The LT5514 has a differential input and output topology, providing a balanced drive to an A/D converter, while preserving its very low distortion characteristics. Even with 50 Ohm loads, the amplifier output can swing more than 3Vp-p to match any A/D converter's input voltage range. As an amplifier, the LT5514 has a gain flatness of +/- 1dB over a 450MHz bandwidth. Meanwhile it introduces very little group delay, reducing phase distortion over a wide operating frequency.

The LT5514 contains two output amplifiers connected in parallel. Optimal distortion performance is achieved when both amplifiers are operating. However, the device can operate in a reduced power mode by selectively turning off one of the internal amplifiers, reducing the supply current by about 50%, yet still providing 43dBm OIP3 at 70MHz.

The LT5514 comes in a 20-pin plastic TSSOP package. The price in 1,000 piece quantities is $5.20. The product is available from stock.

The datasheet for the LT5514 is available here.

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