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Forum: FPGA, VHDL & Verilog analogue-to-digital decoder


Author: hossam (Guest)
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hello
please I am looking for a VHDL description, for analogue-to-digital 
decoder, with analog input, and an output of 8 bits. if someone have 
information . thanks

Author: Lothar Miller (lkmiller) (Moderator)
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What do you need this "converter" for? What is a "analog value"? You 
know that you cannot synthesize such a description on a FPGA?

Author: hossam (Guest)
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hello
thank you for your help. Therefore the analog value is a voltage between 
40 and 200 mV. I'm not really a profissionnel in the field.
I want this converter to find two numerical values for comparison, if 
not. can I compare two voltage without converting them.

Author: Lattice User (Guest)
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hossam wrote:
> hello
> thank you for your help. Therefore the analog value is a voltage between
> 40 and 200 mV. I'm not really a profissionnel in the field.
> I want this converter to find two numerical values for comparison, if
> not. can I compare two voltage without converting them.

Yes you can, all what you need is an OPAMP with sufficient gain.

You can't implement an analog circuit directly with VHDL in a FPGA.

Some FPGA come with a low speed ADC (just like the one in many 
microcontroller) which you can access from VHDL.
You can also implement a sigma delta ADC in a FPGA using VHDL, but this 
also requires an external comparator (OPAMP).

Author: Lothar Miller (lkmiller) (Moderator)
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hossam wrote:
> can I compare two voltage without converting them.
With a comparator you can easily determine, which one of two voltages 
is higher...

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