20-bit DAC Simplifies MRI-signal Path

Analog Devices' new AD5791 DAC has better performance and uses fewer parts in MRI (magnetic-resonance-imaging) equipment than other methods targeting this application. It also finds use in process control; data-acquisition systems; source-measurement units; and general analog applications, such as digital gain and offset adjustment, programmable-voltage and -current sources, and programmable attenuators.

The device offers a maximum-relative-accuracy specification of ±1 LSB, guaranteed monotonic operation with a ±1-LSB-maximum DNL (differential-nonlinearity) specification, 0.025-ppm low-frequency noise, and 0.05ppm/°C output drift. The spectral-noise density is 9nV/√Hz, and settling time is 1 μsec. You can configure the output for standard unipolar 5V and 10V or bipolar ±5 and ±10V ranges. The device operates from a 33V bipolar power supply and consumes 4.2mA of current on the analog power pins and 800mA on the digital power pin. It directly drives a 60kΩ load, eliminating linearity and noise degradation that are the drawbacks of output-buffering op amps. The AD5791 uses a three-wire serial interface that operates at clock rates as high as 50MHz.

The part comes in 24-pin LFCSPs and 20-pin TTSOPs and operates over a -40°C to 105°C temperature range.

Analog Devices