Offering the industry's highest performance for high data rate digital communications applications, Texas Instruments Incorporated (TI) today introduced a new high-speed, high-resolution and LVDS compatible digital-to-analog converter (DAC). The new 14-bit resolution DAC enables transmission of 3G multi-carrier wideband CDMA (WCDMA) and supports additional major wireless standards such as CDMA2000, IS-95, GSM, GPRS, EDGE and IS-136, as well as other digital applications based on QAM and QPSK modulation techniques. (See www.ti.com/sc/msds7257u.)

TI's DAC5675 maintains excellent dynamic performance at high output frequencies at up to 400 MSPS of data throughput. The high speeds enable direct digital intermediate frequency (IF) transmission at high intermediate frequencies, thus eliminating a mix-up stage from the signal chain and enabling the support of up to four WCDMA carriers in a single channel. Moreover, the DAC5675 features a 68 dB WCDMA adjacent channel power ratio (ACPR) at 150 MHz IF. For multi-carrier narrow-band applications, the DAC5675 provides a low intermodulation distortion (IMD3) of -82 dBc at 100 MHz IF. The high dynamic range of the new DAC5675 allows developers of cellular base transceiver stations, broadband wireless access and point-to-point microwave equipment, cable modem head ends and high-end test equipment to reduce system cost by relaxing filter specifications and reducing component count.

"The DAC5675 data converter demonstrates TI's commitment to providing leading analog and mixed-signal solutions for wireless base stations and other high-performance transceiver applications," said Robert Remmers, systems engineering manager of TI's Wireless Infrastructure Business Unit. "TI has leveraged its design and process expertise to create high-performance solutions that enable systems developers to reduce costs and simplify designs."

The DAC5675 is the first DAC to offer a low-voltage differential signaling (LVDS) interface, typically an option in ASIC and FPGA libraries, capable of providing a high-data rate direct interface to on-board ASICs and FPGAs. In addition, the LVDS interface of the DAC5675 lowers electromagnetic interference (EMI) in the system.

Texas Instruments Incorporated, Semiconductor Group, SC-01218, Literature Response Center, PO Box 954, Santa Clarita, CA 91380. Tel: 800-477-8924, ext. 4500. Web: www.ti.com

There are other companies that make high-speed digital-to-analog converters (DACs) but none that have such impressive performance credentials as the recently introduced TI DAC5675 data converter. It's targeted at the wireless infrastructure market and addresses the needs of the market for multi-carrier and high speed applications.

Using a DAC for these applications means that you must have a high update rate in the final output frequency, unlike designs that use analog-to-digital converters (ADCs) that can apply sampling techniques to get appropriate results. Wireless infrastructure requires more than a high update rate, it also needs a high output frequencies from 70 to 100 MHz. However, the technical wizardry to accomplish this is still not enough - an interface is needed to handle the update and output. To get these results from a DAC requires something other than a CMOS-based data bus because of potential electromagnetic interference. TI could have used interpolating filters to reduce the interface data rate between the DAC and the ASIC or a digital upconverter, or they could use a different type interface. The possible interfaces available that could handle the speeds TI needed include emitter-coupled logic (ECL), Pseudo ECL, and Low Voltage Differential Signal (LVDS). TI chose LVDS and it was a good fit because it is very widely used in backplane drivers and high-speed links. It's also available as core I/O blocks in ASICs and FPGAs. Don't despair if your designs require something other than LVDS, TI has plans for you as well.

This DAC isn't the only one on the market but it does have some of the most impressive performance specs at high output frequencies. There are other 400 MSPS DACs on the market but none at 70 MHz and above. These qualities are what make this DAC such a good fit for the wireless market.

And while we're talking about specs, let's look at the needs of service providers and how this DAC measures up. For a wideband CDMA carrier transmitting in one band and another carrier transmitting in an adjacent carrier it is important to not have excessive leakage in the adjacent bands. This adjacent channel power ratio (ACPR) typically needs to be about 68 dB. Impressively, TI is able to transmit not only one but multiples of these carriers at equivalent ACPR levels.

Support for system development includes an evaluation module (EVM) and documentation. For interfacing to other types of logic, such as digital signal processors (DSPs), TI offers the SN65LVDS387 CMOS-to-LVDS translator.

Samples of TI's 14-bit DAC5675 high-speed data converter are available now, with volume production scheduled for January 2002. The device is packaged in a 48-lead high-temperature quad flatpack (HTQFP) with PowerPad(TM). Planned pricing in quantities of 1,000 is $34.50.

Product folder with data sheet