Dual Digital-To-Analogue Converter Families Provide Best-In-Class Performance In Wideband Communications Applications

The AD974x and AD978x TxDAC devices offer best-in-class W-CDMA ACLR (adjacent-channel leakage ratio) performance of 80 dBc at 61.44 MHz, a 5-dBc improvement over the nearest competitive transmit DACs. ACLR is a measure of transmitter performance defined as the ratio of the transmitted power to the power measured after a receiver filter in the adjacent RF channel. The new TxDAC ICs are ideal for many wideband communications standards, including GSM, W-CDMA, CDMA2000, TD-SCDMA, WiMAX, LMDS/MMDS, and point-to-point wideband. They are also designed for instrumentation applications, such as RF signal generators, automated test equipment and ultrasound systems.

New Design Technique Eliminates IF Mixing Stage
The AD974x and AD978x 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.

The AD974x and AD978x families also 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 1.8-V and 3.3-V power supplies and have power dissipation of 315 mW.

The AD974x and AD978x TxDAC families are pin-compatible and interface to analogue quadrature modulators, such as Analog Devices’ ADL5370.