- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Hello. First my post here, so may be I'm posting to wrong place, sorry of that.
I have ~3kHz signal with +-0.5V amplitude that i need to record and process on PSoC3. The signal have sinusoidal-like waveform. How should I configure delta-sigma ADC to get most accuracy and speed? How should i connect ADC to the signal source for correct processing of negative parts of signal? Lost in tons of parameters.
Thanks in advance.
- Labels:
-
PSoC 3
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Regarding accuracy and speed. You trade off resolution, speed.
Some questions -
1) What are you using digitized signal for ? Simple harmonic content determination
or magnitude scale is important. FFT for former, wavelet transform for latter.
2) How much T do you want to store signal, eg. how many samples do you need to accumulate.
3) If you want to preserve 3 Khz harmonic content, then meeting Nyquist will take care of
that. @ 6 Khz DelSig can generate 17 bit conversion.
Regards, Dana.
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Nyquist doesn't quite cut it.
An SAR converter has a frequency response of sin(x)/x. The Delsig converter in the PSoC3 has a frequency response of (sin(x)/x)^4, where x = PI*f/fsample. For the SAR case, the -3dB bandwidth is 0.44* fsample. For the Delsig case, the -3 dB bandwidth is 0.22*fsample. If you want accuracy = 10% at 3.0 kHz, the minimum sample rate is 24 kHz. This is a simple calculation. This is not a circuit design or implementation or software problem. It is a mathematical certainty of the topology of nth order delta sigma converters. It can be compensated with specifically designed digital filters.
---- Dennis
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Dennis its so much easier on calculations of we ignore the H(s) response of
other components in the signal path. Its a good thing I did not contribute to the
design on navigation systems to Mars, would have wound up crashing into alpha
centauri. I am glad you caught my error.
Question, in SAR is H(s) a simple sampler or a zero order hold response ?
Which leads me to a suggestion, encorporate either in config tool, or in a table,
1/2 lsb frequency response for all basic resolutions. Just a thought, maybe even
a graphic to remind us (me especially) response properties of the converter.
Regards, Dana.
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
The 1/2 LSB frequency response is an interesting idea, an interesting way to look at the problem.
We're looking at log(base2)(1/(1-abs((sin(x)/x))^n) where x = pi*f/fsample.The guaranteed accuracy is not as good as you might hope. See attached .xls, where series# = sinx/x order(n).
This is mathematical, entirely different from the settling problem, which is handled nicely by the settling time as specified in the component datasheet.
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
The spreadsheet attach missing.
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
@Dana
I can assure you it is quite more difficult to hit Alpha Centauri than to hit Mars, which tonight will be visible just right to and above the full-moon from your location. Alpha Centauri (proxima) is high up in the north while Mars and Moon traveling in the ecliptic. This means that any object started from Earth gets a huge V0-kick vectored in the ecliptic and it will be VERY hard (costing MUCH energy) to leave that trajectory
Bob
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Dennis, chrome has a problem with attachments, use IE or Firefox.....
Regards, Dana.