DAC5686

The DAC5686 is a dual-channel 16-bit high-speed digital-to-analog converter (DAC) with integrated 2´, 4´, 8´, and 16´ interpolation filters, a numerically controlled oscillator (NCO), onboard clock multiplier, and on-chip voltage reference. The DAC5686 has been specifically designed to allow for low input data rates between the DAC and ASIC, or FPGA, and high output transmit intermediate frequencies (IF). Target applications include high-speed digital data transmission in wired and wireless communication systems and high-frequency direct-digital synthesis DDS.

The DAC5686 provides three modes of operation: dual-channel, single-sideband, and quadrature modulation. In dual-channel mode, interpolation filtering increases the DAC update rate, which reduces sinx/x rolloff and enables the use of relaxed analog post-filtering.

Single-sideband mode provides an alternative interface to the analog quadrature modulators. Channel carrier selection is performed at baseband by mixing in the ASIC/FPGA. Baseband I and Q from the ASIC/FPGA are input to the DAC5686, which in turn performs a complex mix resulting in Hilbert transform pairs at the outputs of the DAC5686's two DACs. An external RF quadrature modulator then performs the final single-sideband up-conversion. The DAC5686's complex mixing frequencies are flexibly chosen with the 32-bit programmable NCO.

Unmatched gains and offsets at the RF quadrature modulator result in unwanted sideband and local oscillator feedthrough. Each DAC in the DAC5686 has an 11-bit offset adjustment and 12-bit gain adjustment, which compensate for quadrature modulator input imbalances, thus reducing RF filtering requirements.