On Tue, 22 Mar 2016 11:46:54 -0700 (PDT), makolber@yahoo.com wrote:>On Tuesday, March 22, 2016 at 2:18:31 PM UTC-4, Tim Wescott wrote: >> On Fri, 18 Mar 2016 22:15:57 -0400, Randy Yates wrote: >> >> > Dear comp.dsp, >> > >> > Our recent "daily quiz" thread has caused me to think more about ADC >> > converter measurements, especially about the suitableness of using the >> > dynamic range measure to quantify converter performance. I would like to >> > bounce some of these thoughts off the group. >> > >> > First of all, for the purposes of this thread, let us assume we have a >> > theoretically perfect ADC, i.e., one with no non-linearities other than >> > the quantization process itself. >> > >> > Also let us define dynamic range as follows: >> > >> > DR = 10 * log(P_Strongest / P_Weakest) [dB], >> > >> > where P_Strongest is the power of the strongest signal the ADC can >> > convert and P_Weakest is the power of the weakest (non-zero) signal the >> > ADC can convert, at the output of the converter. I will purposely leave >> > the terms "signal" and "can convert" loosely defined at this point. >> > >> > Part I, Measuring DR Without Dither ----------------------------------- >> > >> > If we use a sine wave for the input signals, then one issue that comes >> > up is the "sine'edness" of the resulting ADC output at the lowest >> > possible input sine wave amplitude, e.g., q/2 * cos(omega * t), where q >> > is the converter's quantization step. Namely, that's just going to be a >> > square wave. >> > >> > 1. How does one get off referring to this as a sine wave? >> > >> > 2. How does one handle the fact a square wave has more power than the >> > sine wave? >> > >> > Part I, Measuring DR With Dither ----------------------------------- >> > >> > For this part we use the theoretically perfect non-subtractive dither >> > Robert Wannamaker outlined in his PhD thesis, namely uncorrelated TPDF >> > with endpoints at -q/2 and +q/2. >> > >> > In this case the output is perfectly linearized and the dynamic range is >> > INFINITE since, no matter how small the input sine amplitude is, it can >> > be "detected" at the output (detection method unspecified). >> > >> > Conclusion ---------- >> > >> > Dynamic range is NOT the right parameter to use for ADC resolution >> > measurement! SNR (or SINAD) is mo' better. >> >> Objection: If properly qualified (spurious-free, 3rd-order intermod, >> etc.), dynamic range is a _good_ parameter to use to qualify an ADC for a >> specific task. >> >> I agree that it's not a good method for ADCs in general. >> >> > >OK to continue the daily quiz > >in the context of receiver front ends.... > >what is generally meant when one refers to the INSTANTANEOUS dynamic range? > >MarkI'm not sure I've heard that term used before. Is there a context for it? Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
Dynamic Range as a Measure of ADC Converter Resolution and Accuracy
Started by ●March 18, 2016
Reply by ●March 22, 20162016-03-22
Reply by ●March 22, 20162016-03-22
On Tuesday, March 22, 2016 at 11:46:57 AM UTC-7, mako...@yahoo.com wrote:> ... > > OK to continue the daily quiz > > in the context of receiver front ends.... > > what is generally meant when one refers to the INSTANTANEOUS dynamic range? > > MarkOne example would be in a system with an automatic gain control (AGC), what is the dynamic range under a condition that does not allow the AGC to change gain. Dale B. Dalrymple
Reply by ●March 22, 20162016-03-22
On Tue, 22 Mar 2016 11:46:54 -0700, makolber wrote:> On Tuesday, March 22, 2016 at 2:18:31 PM UTC-4, Tim Wescott wrote: >> On Fri, 18 Mar 2016 22:15:57 -0400, Randy Yates wrote: >> >> > Dear comp.dsp, >> > >> > Our recent "daily quiz" thread has caused me to think more about ADC >> > converter measurements, especially about the suitableness of using >> > the dynamic range measure to quantify converter performance. I would >> > like to bounce some of these thoughts off the group. >> > >> > First of all, for the purposes of this thread, let us assume we have >> > a theoretically perfect ADC, i.e., one with no non-linearities other >> > than the quantization process itself. >> > >> > Also let us define dynamic range as follows: >> > >> > DR = 10 * log(P_Strongest / P_Weakest) [dB], >> > >> > where P_Strongest is the power of the strongest signal the ADC can >> > convert and P_Weakest is the power of the weakest (non-zero) signal >> > the ADC can convert, at the output of the converter. I will purposely >> > leave the terms "signal" and "can convert" loosely defined at this >> > point. >> > >> > Part I, Measuring DR Without Dither >> > ----------------------------------- >> > >> > If we use a sine wave for the input signals, then one issue that >> > comes up is the "sine'edness" of the resulting ADC output at the >> > lowest possible input sine wave amplitude, e.g., q/2 * cos(omega * >> > t), where q is the converter's quantization step. Namely, that's just >> > going to be a square wave. >> > >> > 1. How does one get off referring to this as a sine wave? >> > >> > 2. How does one handle the fact a square wave has more power than >> > the sine wave? >> > >> > Part I, Measuring DR With Dither ----------------------------------- >> > >> > For this part we use the theoretically perfect non-subtractive dither >> > Robert Wannamaker outlined in his PhD thesis, namely uncorrelated >> > TPDF with endpoints at -q/2 and +q/2. >> > >> > In this case the output is perfectly linearized and the dynamic range >> > is INFINITE since, no matter how small the input sine amplitude is, >> > it can be "detected" at the output (detection method unspecified). >> > >> > Conclusion ---------- >> > >> > Dynamic range is NOT the right parameter to use for ADC resolution >> > measurement! SNR (or SINAD) is mo' better. >> >> Objection: If properly qualified (spurious-free, 3rd-order intermod, >> etc.), dynamic range is a _good_ parameter to use to qualify an ADC for >> a specific task. >> >> I agree that it's not a good method for ADCs in general. >> >> >> > OK to continue the daily quiz > > in the context of receiver front ends.... > > what is generally meant when one refers to the INSTANTANEOUS dynamic > range? > > MarkDunno; like Eric, I've never heard of it. -- www.wescottdesign.com
Reply by ●March 23, 20162016-03-23
On Tuesday, March 22, 2016 at 4:58:13 PM UTC-5, Tim Wescott wrote:> On Tue, 22 Mar 2016 11:46:54 -0700, makolber wrote: > > > On Tuesday, March 22, 2016 at 2:18:31 PM UTC-4, Tim Wescott wrote: > >> On Fri, 18 Mar 2016 22:15:57 -0400, Randy Yates wrote: > >> > >> > Dear comp.dsp, > >> > > >> > Our recent "daily quiz" thread has caused me to think more about ADC > >> > converter measurements, especially about the suitableness of using > >> > the dynamic range measure to quantify converter performance. I would > >> > like to bounce some of these thoughts off the group. > >> > > >> > First of all, for the purposes of this thread, let us assume we have > >> > a theoretically perfect ADC, i.e., one with no non-linearities other > >> > than the quantization process itself. > >> > > >> > Also let us define dynamic range as follows: > >> > > >> > DR = 10 * log(P_Strongest / P_Weakest) [dB], > >> > > >> > where P_Strongest is the power of the strongest signal the ADC can > >> > convert and P_Weakest is the power of the weakest (non-zero) signal > >> > the ADC can convert, at the output of the converter. I will purposely > >> > leave the terms "signal" and "can convert" loosely defined at this > >> > point. > >> > > >> > Part I, Measuring DR Without Dither > >> > ----------------------------------- > >> > > >> > If we use a sine wave for the input signals, then one issue that > >> > comes up is the "sine'edness" of the resulting ADC output at the > >> > lowest possible input sine wave amplitude, e.g., q/2 * cos(omega * > >> > t), where q is the converter's quantization step. Namely, that's just > >> > going to be a square wave. > >> > > >> > 1. How does one get off referring to this as a sine wave? > >> > > >> > 2. How does one handle the fact a square wave has more power than > >> > the sine wave? > >> > > >> > Part I, Measuring DR With Dither ----------------------------------- > >> > > >> > For this part we use the theoretically perfect non-subtractive dither > >> > Robert Wannamaker outlined in his PhD thesis, namely uncorrelated > >> > TPDF with endpoints at -q/2 and +q/2. > >> > > >> > In this case the output is perfectly linearized and the dynamic range > >> > is INFINITE since, no matter how small the input sine amplitude is, > >> > it can be "detected" at the output (detection method unspecified). > >> > > >> > Conclusion ---------- > >> > > >> > Dynamic range is NOT the right parameter to use for ADC resolution > >> > measurement! SNR (or SINAD) is mo' better. > >> > >> Objection: If properly qualified (spurious-free, 3rd-order intermod, > >> etc.), dynamic range is a _good_ parameter to use to qualify an ADC for > >> a specific task. > >> > >> I agree that it's not a good method for ADCs in general. > >> > >> > >> > > OK to continue the daily quiz > > > > in the context of receiver front ends.... > > > > what is generally meant when one refers to the INSTANTANEOUS dynamic > > range? > > > > Mark > > Dunno; like Eric, I've never heard of it. > > -- > www.wescottdesign.comHere's one definition for instantaneous dynamic range http://www.ittc.ku.edu/~jstiles/622/handouts/Instantaneous%20Dynamic%20Range.pdf Clay
Reply by ●March 23, 20162016-03-23
On Tuesday, March 22, 2016 at 4:00:32 PM UTC-4, dbd wrote:> On Tuesday, March 22, 2016 at 11:46:57 AM UTC-7, mako...@yahoo.com wrote: > > ... > > > > OK to continue the daily quiz > > > > in the context of receiver front ends.... > > > > what is generally meant when one refers to the INSTANTANEOUS dynamic range? > > > > Mark > > One example would be in a system with an automatic gain control (AGC), what is the dynamic range under a condition that does not allow the AGC to change gain. > > Dale B. Dalrymplecorrect... relates to how strong unwanted signals a front end can tolerate at a given desired input signal level which sets the AGC.
