# What's the difference between successive approximation A/D and regular A/D converter?

PF Gold
P: 2,551
Wiki says:

 A successive approximation ADC is a type of analog-to-digital converter that converts a continuous analog waveform into a discrete digital representation via a binary search through all possible quantization levels before finally converging upon a digital output for each conversion.
Isn't this exactly what every A/D converter does?

For a graph of Vin to digital output it basically approximates the nearest digital value to the continuous signal ->

So I don't see the difference between them.
 HW Helper P: 6,189 Yes, that is what every A/D converter does. The difference is in how the A/D converter works internally, which has an implication on the performance it can give. A successive approximation ADC uses 1 comparator and counts towards the signal. This means a long conversion time. And it won't be able to follow a signal that makes "jumps" correctly. A direct-conversion ADC uses a bank of comparators to instantaneously convert the signal. This implies a short conversion time, and it can follow jumps. But it will be more expensive.
 P: 1,494 There is no such thing as a 'regular' ADC. Each has its pros and cons depending on if you want speed of conversion, cost or resolution, etc. If you look at this site on DAC and ADC it describes the many types. http://www.faqs.org/docs/electric/Digital/DIGI_13.html
P: 3,904
What's the difference between successive approximation A/D and regular A/D converter?

 Quote by 256bits There is no such thing as a 'regular' ADC. Each has its pros and cons depending on if you want speed of conversion, cost or resolution, etc. If you look at this site on DAC and ADC it describes the many types. http://www.faqs.org/docs/electric/Digital/DIGI_13.html
Yes, there are different type of ADC, bottom line is speed vs simplicity.
PF Gold
P: 2,551
 Quote by I like Serena A successive approximation ADC uses 1 comparator and counts towards the signal. This means a long conversion time. And it won't be able to follow a signal that makes "jumps" correctly. A direct-conversion ADC uses a bank of comparators to instantaneously convert the signal. This implies a short conversion time, and it can follow jumps. But it will be more expensive.
So a successive approximation is basically less accurate than direct-conversion ADC?

Is it essentially the cheaper junk of the ACD market since it uses more cheap and archaic methods?
HW Helper
P: 6,189
 Quote by Femme_physics So a successive approximation is basically less accurate than direct-conversion ADC? Is it essentially the cheaper junk of the ACD market since it uses more cheap and archaic methods?
Yep. :)
 Sci Advisor PF Gold P: 3,739 in real world environment a dual slope integrator with integration period of one power line cycle offers some benefits wrt line frequency noise rejection. But it's painfully slow.
 PF Gold P: 2,551 Well, I am supposed to explain the principle of how successive approximation works. And I need to demonstrate this explanation. I'm sorry it appears like a HW is intruding, but that's what sparked it all. I am tempted to just quote ILS. Problem is, even if I do, I need to demonstrate this successive approximation explanation based on the following A/D converter There are no comparators and no counters that I can see...
PF Gold
P: 2,551
Thanks :)

 Quote by I like Serena Yep. :)
According to the link "jim hardy" provided:

 One method of addressing the digital ramp ADC's shortcomings is the so-called successive-approximation ADC. The only change in this design is a very special counter circuit known as a successive-approximation register. Instead of counting up in binary sequence, this register counts by trying all values of bits starting with the most-significant bit and finishing at the least-significant bit. Throughout the count process, the register monitors the comparator's output to see if the binary count is less than or greater than the analog signal input, adjusting the bit values accordingly. The way the register counts is identical to the "trial-and-fit" method of decimal-to-binary conversion, whereby different values of bits are tried from MSB to LSB to get a binary number that equals the original decimal number. The advantage to this counting strategy is much faster results: the DAC output converges on the analog signal input in much larger steps than with the 0-to-full count sequence of a regular counter.
Why would they compliment this successive approximation method if it sucks so much?