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Analog to Digital Converter

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jeyes56

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Hi there folks,

My instructor ask us to create an analog to digital converter,
im searching for the circuit of it,
it just convert the analog signal (sine wave) to an digital signal (square wave)..

can anyone help me, or show me an circuit for this?

Thanks.
 
Well, there are a lot of things to look at !

- Determine the input voltage range
- Determine digital format (number of bits, two's complement or not)
- Determine the bandwidth (frequencies) you want to sample, then determine the sampling frequencies (look for the Nyquist frequency)
- Then detemrine the all-in-one chip that you might use.
- Of if you need to build it from ground-up, then you need to look for
- Some filtering circuit to remove unwanted frequencies
- A sample-and-hold circuit to "hold the voltage" still while you digitize it
- A successive aproximation circuit with a DAC and a comparator (or some other technique if you whish)
- A digital "interface" to retrieve the result.

Tell us more about the requirements and what you have planned so far and we can point you to doc/circuits.
 
its just an introduction for us on digital circuit..
our instructor told us to create an analog to digital converter,, he did not mentioned anything from the things you've presented. Only, that statement.

well then, its up to us what to do,,
i'll think of it for now, thanks.

by the way, can you suggest what to do from the input until the output?
 
its just an introduction for us on digital circuit..
our instructor told us to create an analog to digital converter,, he did not mentioned anything from the things you've presented. Only, that statement.

well then, its up to us what to do,,
i'll think of it for now, thanks.

by the way, can you suggest what to do from the input until the output?

Probably the simplest for you at beginner level is a 'flash' converter that uses a resistor stack reference for a bunch of comparitors. You then use a digital decoder that take the comparitor weighting levels to a binary output. The simple implemention will slew digital output as analog input changes but it is an ADC.
 
Two things :

  1. Another simple way would be with the use of a DAC (digital to analog) circuit. Have you covered that topic ? If you did use a DAC, you would just need to generate a voltage from the minimum to the maximum, linearly, and use a comparator that would tell you when the DAC voltage reaches the signal voltage. You would then have your digitized value. As opposed to the 'flash' method suggested above, which can be accomplished without a MCU, this method I'm proposing would required one.
  2. As for the steps one would normall follow, here they are (key words are italic). I put more than you probably need but that gives you a big picture :
    • Characterize the signal you want to digitize
      • What is the maximum frequency to want to sample ? From there, by the Nyquist law, you would find your sampling rate (e.g. 44.1kHz for CDs)
      • How sensitive your sampling will be (what's the smallest variation in voltage amplitude can be sampled) ? That will give you the resolution (in bits) you need. (e.g. for a singal 5V p-p, using 8 bits, the smallest interval would be 1/256 * 5V ≈ 20mV. the equivalent dynamic range is then -20 * log (1 / 256) ≈ 48dB; for 16-bit, ≈ 96dB)
    • Design a filter to remove undesirable frequencies (to prevent aliasing)
    • Design a sample and hold circuit. Because the sampling period has a finite length, the signal must remain constant during the conversion. That's why you have to sample the signal at the beginning of every sampling period and hold it still while the conversion takes place.
    • Decide which sampling technique you need. We've mentionned 3 so far, there are a few others. Most of them, in a way or another, require to compage a known voltage to the held signal voltage in order to find out the bits representing the signal.
    • Determine what you do with the result...
 
My instructor ask us to create an analog to digital converter,
im searching for the circuit of it,
it just convert the analog signal (sine wave) to an digital signal (square wave)..
Sounds like he may be talking about a 1-bit A/D converter, which is a comparator (Google comparator).
 
just convert the analog signal (sine wave) to an digital signal (square wave)
If that's all the brief is then just apply the sine-wave (amplified or attenuated as necessary) to a (preferably Schmitt) logic gate.
 
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