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Dual DACs enhance quality of wideband cellular signals

Posted: 13 Sep 2007 ?? ?Print Version ?Bookmark and Share

Keywords:DAC? wideband communication application? W-CDMA?

AD974x and AD978x

Analog Devices Inc. (ADI) announced the AD974x and AD978x, the latest additions to its TxDAC portfolio of DACs optimized for the transmit signal path of communications systems.

The new two-channel, high-speed DACs include the AD974x family of 8-, 10,-, 12-, 14-, and 16bit devices with sample rates up to 250MSPS using low-voltage CMOS inputs; and the AD978x family of 12-, 14-, and 16bit DACs, which use LVDS inputs to achieve sample rates as fast as 600 MSPS. Both families of TxDAC devices feature low noise and low intermodulation distortion to enable the high-quality synthesis of wideband cellular signals.

The AD974x and AD978x TxDAC devices offer W-CDMA adjacent-channel leakage ratio performance of 80dBc at 61.44MHz, a 5dBc improvement over the nearest competitive transmit DACs. The new TxDAC ICs are designed for many wideband communications standards including GSM, W-CDMA, CDMA2000, TD-SCDMA, WiMAX, LMDS/MMDS and point-to-point wideband. They are also suited for instrumentation applications, such as RF signal generators, automated test equipment and ultrasound systems.

The new DAC families integrate a new mixer function that provides designers with a usable output beyond Nyquist frequency. In the "normal mode," the signal in the first Nyquist zone is strongest. In the "mixer mode," the DACs can directly generate RF signals by boosting the signal power in the second and third Nyquist zones. This allows designers to eliminate a mixing stage, reducing component count and design complexity in direct-RF applications.

In addition, the AD974x and AD978x families integrate two auxiliary DACs that can be used to compensate for TxDAC device or mixer offset errors without adding external components. The new DACs operate from 1.8V and 3.3V power supplies and have power dissipation of 315mW.

The AD974x and AD978x TxDAC families are pin-compatible and interface to analog quadrature modulators, such as ADI's ADL5370. The AD974x (AD9741/42/45/46/47) and AD978x (AD9780/81/83) TxDAC families are available in full production quantities for $14.59 per unit in 1,000-unit quantities and are available in a 72-lead LFCSP.

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