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TI's fully-differential amps push ADCs to 100MHz

Posted: 27 Jan 2005 ?? ?Print Version ?Bookmark and Share

Keywords:texas instruments? ti? differential amplifier? ths4509?

Texas Instruments Inc.'s (TI's) next-generation differential amplifiers for driving high-speed ADCs up to 100MHz tout low noise and distortion and fast settling time.

Boasting one-third less settling time, 25 percent lower noise, and 10dB to 24dB improvement over competing amplifiers, the THS4509 is the company's first fully-differential amplifier manufactured using its BiCOM-III process, said Jim Karki, TI's strategic marketing manager for high-speed amplifiers and RF products. TI's SiGe process, which integrates complementary npn and pnp bipolar transistors, is also based on a 350nm CMOS process, he said.

The process has enabled TI to boost ADC performance from 50MHz to 100MHz. Essentially, TI is shooting to raise the standards bar for amplifier performance in all of the markets it addresses, Karki said.

ADCs are moving up the performance chain and the amplifiers that are driving them need to mirror their performance, Karki explained. "ADCs are becoming faster, offering lower noise and better precision, and the amplifiers used to drive them need to keep up with this progress. A lot of wideband applications, especially in test and measurement and communications are moving into higher frequencies," he added.

The fully-differential THS4509 amplifier can be used with other manufacturer's high-performance ADCs, as well as TI's ADS5424 14bit, 105Msps ADC, which is also being introduced today. Compared to TI's older ADS5500 14bit A/D converter, which is shown in the diagram above in combination with the THS4509, the ADS5424 is slower but provides lower noise and improved SFDR and SNR characteristics, Karki said. Based on the application, engineers can decide which is more importantmore speed or less noise.

The high-speed amplifier market will rise from roughly $715 million this year worldwide, to more than $1.3 billion by 2009, according to Databeans Inc. China represents the fastest growing region with high-speed amplifier sales expected to reach nearly $474 million in 2009.

Other players in this market include Analog Devices Inc., Intersil Corp., Linear Technology Corp., Maxim Integrated Products Inc. and National Semiconductor Corp.

Last month, National Semi also announced a high-speed amplifier, dubbed the LMH6550. With a fully differential VFB (voltage feedback) topology, it allows balanced inputs to ADCs and can be used as single-ended-to-differential or used as differential-to-differential. Harmonic distortion of -88dBc at 20MHz and high-speed (400MHz bandwidth and 3,000V/?s sampling rate) supports driving a variety of 10 to 14bit ADCs. It is available now in SOIC-8 and MSOP-8 packaging and is priced at $2.29 in 1,000-unit quantities.

- Bettyann Liotta

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