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Broadband amp fuses programmability, ultra-low distortion

Posted: 22 Jun 2004 ?? ?Print Version ?Bookmark and Share

Keywords:linear technology? broadband? adc? lt5514? adc driver?

Striving to be a choice for communication systems applications such as basestation receivers and ADC drivers, Linear Technology announces the release of its 850MHz programmable gain, broadband amplifier LT5514. The company claims that the amplifier has the best distortion characteristics among amplifiers in its class. Applications for the LT5514 include ADC drivers and amplifiers for cellular basestation receivers, basestation transmitter distortion loops and cable head-end upstream receivers.

LT5514's combination of low noise and spurious free output makes it a good choice for 12- and 14-bit ADCs operating at a 65MSps or faster speeds, used in high performance communication systems. An on-chip, digitally-controlled attenuator combined with a fixed gain amplifier enables the chip gain adjustment. The amplifier is controlled with a 4bit parallel input word, allowing 1.5dB increments in gain. The device gain ranges from 9.5- to 32dB. At maximum gain, the device offers an 8dB noise figure.

"The target applications are in communications such as cellular basestations that cover CDMA and wideband CDMA standards," said James Wong, product marketing manager at Linear Technology's High frequency Business Unit. He added that cellular receivers as well as cable systems applications also benefit from the new amplifier.

"All of these communication receivers need some gain control to drive the A/D converter. The LT5514 fits right in there," said Wong. He asserted that cellular receivers ought to have mechanisms to regulate power as well.

The low distortion characteristic of the amplifier is preserved while providing drives on ADCs with its differential input and output topology. At 50-ohm loads, the amplifier output can swing more than 3Vpp to match the ADC's input voltage range. The gain flatness of the device as an amplifier is at 1dB at 450MHz bandwidth. Phase distortion in the device is reduced with its minimal introduction of group delay.

According to Wong, high linearity, low noise and high LO suppression are key features for wireless communication systems. Linearity and noise have a direct impact on spurious-free dynamic range of a radio system; LO, when leaked into the airwave, is an interference signal.

Optimal distortion performance is attained in LT5514 when the two output amplifiers connected in parallel are operating. An option is also available to run the device at a reduced power mode by turning off one of these amplifiers which would cut the supply current by half, but still providing 43dBm OIP3 at 70MHz.

Wong emphasized that with the low distortion at a wide bandwidth of the amplifier, it can enable high performance, more robust radios, and thus higher data throughput rates in communication systems.

Customer support

Linear provides support, evaluation boards and layouts for its products such as the LT5514. The company has set up a sample center for customers in China and has extended its reach in Asia through support centers in Japan, Taiwan and Korea.

"The Asian communication market is potentially huge and very important to the regional economy. High performance in this system will greatly enhance the region's global commerce and competitiveness. So we believe Linear Technology's products can play a key role," said Wong.

Other applications that could benefit from the device include radar systems, ultrasound or medical imaging systems, video systems, optical systems, industrial laser systems and automotive systems.

The LT5514 comes in a 20-pin TSSOP package and is priced at $5.20 in 1,000 piece quantities.

- Reden Mateo

Electronic Engineering Times - Asia





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