20-bit DAC simplifies MRI-signal path
Paul Rako, Technical Editor -- EDN, June 10, 2010
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 0.05-ppm/°C output drift. The spectral-noise density is 9 nV/√Hz, and settling time is 1 μsec. You can configure the output for standard unipolar 5 and 10V or bipolar ±5 and ±10V ranges. The device operates from a 33V bipolar power supply and consumes 4.2 mA of current on the analog power pins and 800 mA on the digital power pin. It directly drives a 60-kΩ 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 50 MHz.
The part comes in 24-pin LFCSPs and 20-pin TTSOPs, operates over a -40 to +105°C temperature range, and has a suggested retail price of $38 (1000). Samples are available now, and production quantities will become available in August 2010.
Analog Devices
