How many clock pulses are needed for an 8 bit ADC's mid-signed range?

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Discussion Overview

The discussion revolves around determining the number of clock pulses required for an 8-bit Analog-to-Digital Converter (ADC) to achieve an exact mid-signed range. Participants explore various types of ADCs and their characteristics, including the implications of signed versus unsigned representations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that for an 8-bit ADC, 4 clock pulses may be needed for the mid-signed range.
  • Another participant calculates that an 8-bit unsigned ADC has 256 values, while a signed ADC has 128 values, but expresses uncertainty about the clock pulses required.
  • There is a discussion about the representation of signed numbers, including two's complement and sign and magnitude, with some participants questioning the correctness of earlier claims.
  • A later reply indicates that the type of ADC significantly affects the number of clock cycles, noting that flash ADCs are instantaneous and do not require clock cycles, while successive approximation ADCs require clock cycles equal to the number of bits.
  • Another participant mentions that most modern ADCs are of the flash type or sigma-delta type, which may influence the clock pulse requirement.

Areas of Agreement / Disagreement

Participants express differing views on the type of ADC and the corresponding clock pulse requirements, indicating that there is no consensus on the exact number of clock pulses needed for the mid-signed range in an 8-bit ADC.

Contextual Notes

The discussion highlights ambiguities in the original question regarding the type of ADC and the relationship between clock cycles and input voltage, which may affect the interpretations and responses provided by participants.

BIGEYE
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Missed some class notes due to being sick. Anyway have a tutorial question I
need some help with as I missed out on the subject.
For an 8 bit ADC, how many clock pulses are required for an exact mid-signed
range.
I think 4, appreciate if someone can advise.

TIA
 
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8 bit = 2^8 = 256
i don't know what clock pulses. but if its 8 bit unsigned it is 256. if its signed then it becomes 128
ie: 1 111 1111 -- > +
0 111 1111 -- > -
typically last bit/MSB to indicate polarity. I may be wrong
 
thanks

thanks for that
 
edmondng said:
8 bit = 2^8 = 256
i don't know what clock pulses. but if its 8 bit unsigned it is 256. if its signed then it becomes 128
ie: 1 111 1111 -- > +
0 111 1111 -- > -
typically last bit/MSB to indicate polarity. I may be wrong

Oh I don't think i did something like this but.

If its Signed :
and Minus ..then the MSB bit 7 is a 1. Indicating - is on right?
Then again it could be a Two's Compliment or a Sign and Magnitude.
Unsigned
+128 64 32 16 8 4 2 1
0 0 0 0 0 0 0 0
2s compliment
-128 64 32 16 8 4 2 1
0 0 0 0 0 0 0 0
Sign and Mag
-/+ 64 32 16 8 4 2 1
0 0 0 0 0 0 0 0
I don't think edmongd is right. My opinion.
Although the 8 bit indicating 256 location is correct.

Clock pulses are orginating from the System clock diagrammatically speaking on the outside of the cpu into the Control Unit of the CPU or Inside the Control Unit.
They send clock cycles of 1-0-1 into the cpu something like that..
 
BIGEYE said:
Missed some class notes due to being sick. Anyway have a tutorial question I
need some help with as I missed out on the subject.
For an 8 bit ADC, how many clock pulses are required for an exact mid-signed
range.
I think 4, appreciate if someone can advise.

TIA

What is an ADC? Clock pulses come in cycles of 1 0 1 if I'm not mistaken but probably am.
mid-signed range? do you mean sign and magnitude ? boq.

Isn't a clock pulse 1/0 ?
Which then becomes a clock pulse cycle of 101 or 010 ermm ******

Wheres the Expert whos doing a Degree in Computing...lol
I've only done it till advanced!
 
It depends on what kind of ADC.

Pretty much all ADC's today are the flash type, which means it is instantaneous (asynchronous)--zero clock cycles. However, the fact that the question implies there are clock cycles suggests its either a counter (nobody makes those--they're more for teaching first-years the basic idea of ADC) or a successive approximation. So from the context it looks like we are to assume its a successive approximation ADC. A SA ADC always takes as many clock cycles as the number of bits. So it takes eight clock cycles no matter what. But then, since we're having to make presumptions because the question is ambiguous, I'm wondering why the question would imply the clocks are related to the input voltage--which, as I said, is not the case with a successive approximation ADC.

There are also hybrid ADCs, which might, for example, make every pair of bits a flash-type, and successively approximate through each pair--essentially its a base-four ADC instead of a base-two ADC.
 
Last edited:
fleem said:
It depends on what kind of ADC.
yup.
Pretty much all ADC's today are the flash type,
certainly all 8-bit A/D converters today are flash. but i might think that most A/D converters today are what they put on sound cards and are almost certainly of the "sigma-delta" type. sometimes called a "1-bit converter".
 

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