Lena/Oct 2016: Difference between revisions

 

== 10/27/2016 ==

 

Implemented delta-sigma PDM (pulse-density modulation) for the FPGA. Now the FPGA can output "analog" control signals from the digital outputs, which our FPGA has plenty of. This would allow us to control every sensor shell coil on all three axis, and permit us to feedback on the field to keep all the sensors in average zero field and thus extend the dynamic range of our measurements. The signal to noise ratio in 0-1 kHz range is surprisingly good, and is around 100 dB. The VI is configured to output the "analog" levels with 16 bit precision. The switching rate is 20 MHz, with the CLK output.

 

It would be great to replace the analog inputs with digital signals as well. This would permit us to use a bigger FPGA (NI PXIe-7971R) that could drive as many as 25 sensors. Texas Instruments has Verified Designs section, that explains how to design and layout ADC circuits. [[File:TI ADC design ECG.pdf]]