LT Spice simulation of a simple AD-converter (quantisation)

Thread Starter

nfh

Joined Jul 6, 2019
2
Hi there, I currently try to design an AD converter as simple as possible (for didactical reasons). It should be able to act as a 3bit converter on a time-dependent signal. It should preferably output a quantised signal (blue) from an analogue input (red)
3-bit_resolution_analog_comparison.png

If possible I only want to use opamps, resistors and (maybe And/Nand gatter). I started with a basic flash converter and feel that if I could sum the outputs of all comparators properly I would get the desired blue curve. Nevertheless my idea to just add an opamp summing amplifier didn't work at all.

AD_comp.png

Any idea how I could go on from here? I would appreciate any help.
 

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eetech00

Joined Jun 8, 2013
2,162
Try using comparator(s) to convert the analog signal to digital output.
You'll need to use window comparators as well.

I would use arbitrary behavioral devices to do the conversion.
 
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Thread Starter

nfh

Joined Jul 6, 2019
2
I took Ron's schematic and converted it using all a devices.
See attached.

Files attached below.

View attachment 223613

Thanks eetech00,

that's actually beautiful.
I recognise the three OR-gates to the right as a normal 8-(7)-3 binary encode. But what's the job of the XORS? Is it only to prove that at one time only one input at high might enter the OR-gates? I do not really catch it.
 

eetech00

Joined Jun 8, 2013
2,162
Thanks eetech00,

that's actually beautiful.
I recognise the three OR-gates to the right as a normal 8-(7)-3 binary encode. But what's the job of the XORS? Is it only to prove that at one time only one input at high might enter the OR-gates? I do not really catch it.
Yes. During an input signal transition, the first input high of an XOR gate will get precendence.
 
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