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safwatonline
Joined: 19 Nov 2005
Posts: 1347
Helped: 164
Location: EGYPT
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 23 Apr 2008 20:22 CT SD ADC |
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i was wondering what are the limiting factors for high resolution CT SD ADC?
i.e. why i cannot find some 20bit or more CT SD ADC
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tekno1
Joined: 26 May 2005
Posts: 85
Helped: 5
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| 28 Apr 2008 4:19 CT SD ADC |
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I am not an expert on this but answer to your question is: Oversampling converters samples the input signal many times so oversampling and averaging results high resolution at the end. CT SD are used in RF frequencies and oversampling clock needs to be too high in order to oversample enough to get higher resolution. Process dependent clocking speed limits the resolution. Also for RF applications often 6 to 10 bits of resolution is enough.
I hope this helps.
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safwatonline
Joined: 19 Nov 2005
Posts: 1347
Helped: 164
Location: EGYPT
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| 28 Apr 2008 4:57 CT SD ADC |
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| actually, i don't agree. why are u limiting the use of CT ADC to RF freq.
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MikeR
Joined: 16 Dec 2006
Posts: 77
Helped: 5
Location: Belarus
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| 28 Apr 2008 8:32 CT SD ADC |
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| I think a basic limiting factor there is unideality of components: key, opamp ;noise in MOS, CAP, RES; unideality C(V) character capacitance; you can get more than 20 bit of monotony but not linear.
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elbadry
Joined: 06 May 2005
Posts: 355
Helped: 62
Location: Egypt
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| 30 Apr 2008 13:30 Re: CT SD ADC |
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| There are continuous-time implementations which achieve 118 dB of DR and are used in FM Rx
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caosl
Joined: 26 Mar 2006
Posts: 197
Helped: 15
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| 30 Apr 2008 15:21 Re: CT SD ADC |
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| I think SD adc is not appropriate in low frequency application such as instrument measurement which require very high resolution(18bit more), since the resistor's thermal noise is quite large at low clock frequency. The CT sd ADC's dominant application is in high bandwidth communication and the oversampling ratio is low.Also, the audio can use CT sd ADC.
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elbadry
Joined: 06 May 2005
Posts: 355
Helped: 62
Location: Egypt
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| 30 Apr 2008 15:54 Re: CT SD ADC |
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I disagree Casol
In SC, you would need a very large Cap to decrease thermal noise ( kT/C ). Likewise, in a continuous-time implementation, you can use a large Cap with smaller resistance to get the same goal.
I might be wrong, but that's what I guess
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re007972
Joined: 31 Mar 2007
Posts: 8
Helped: 1
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| 01 May 2008 15:45 Re: CT SD ADC |
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| I think it apply on the DAC's clock jitter.
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