John Martin

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  1. The looper project says: 1.2) The XADC requires an input wave biased at .5V, .... in particular they used AD3P and AD3N. Their added circuit provides a 0.5V DC bias which I assume presents the 0.5/-0.5V waveforms from the guitar as 1.0/0.0V to AD3P. Are any of the Artix-7 ADC inputs configured to allow direct sampling of waveforms with 0V DC bias?
  2. For a school project using the Nexys 4 DDR I need to input audio from a single ended source (voltage+ground). This can be either directly from a guitar (1Vp-p) or the headphone output of a iPod Nano (2Vp-p). The Nexys 4 reference does not indicate how the Artix-7 JXADC differential inputs are configured, whether unipolar or bipolar mode. From the Xilinx doc "7 Series FPGAs and Zynq-7000 All programmable SoC XADC Dual 12-Bit 1 MSPS Analog-to-Digital Converter" it appears bipolar would be needed with the analog source voltage connected to a ADnP and the ground connected to ADnN. The desired output is 12-bit signed as either audio source is a 0DC with positive and negative values. Can I do this with the CON4 PMOD connected directly to one of the Nexus 4 DDR PMOD ports or must I use a AD1/AD2 PMOD (with a CON4 PMOD connected to the AD1/AD2 input)?