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ADC circuit - Analog to Digital Fixed Point

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hani nik

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I need to convert readings from sensor in analog voltage to binary fixed point Q2.13 format. (I hope this is the right place to ask...)

Is this something easy to do with discrete ADC on stripboard? Any suggestions on components?

Thank you.
 

Hello,

you apparently didn't consider, that a fractional part with fixed point numbers is just a matter of interpretation. There is effectivly no difference between signed integer and a Qm.n in number format except for an additional implicite scaling factor of 2^n.

ADC usually have an offset binary representation, many can be switched to two's complement (just another term for signed integer). But the difference between the two formats is only an inverted most significant bit, you can do this easily in postprocessing.

Regards,
Frank
 

Hello Frank.
Thanks. It sounds awfully simple for you but I am feeling a bit lost with so much to pick up from Matlab to Verilog, mathematics to electronics to digital design.
Could you please kick me in the right direction i.e. suggest me the right kind of books/links/ref for this issue of converting analog signals to fixed point numbers. I am missing some basic fundamentals here I believe. I will read up but I need some directions.

Thanks again for the info.
 

Hello,
I don't know a particular book or paper, but I guess there's a lot. Digital signal processing textbooks usually have a chapter for this topic. I just checked with U. Meyer-Baese Digital Signal Processing with Field Programmable Gate Arrays which I have near to my desk.

If dealing with physical quantities, e. g. voltages, it's useful to define a scaling factor either full scale or LSB. Then you can always calculate what a value means.
Another remark. I said, that it doesn't matter for an ADC value if you consider it as a fractional or integer number. This is different e. g. with filter coefficients, that have to be multiplied with the signal, cause the fractional part length implies the shift applied in a multiplication.

Regards,
Frank
 

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