Looking for '0' values in this ASK wave

Thread Starter

aaron_m

Joined Apr 27, 2014
13
Related to: https://forum.allaboutcircuits.com/threads/looking-for-adc-for-cochlear-implant-signal.175340/ - yes, I'm still working on this.

According to this section in the documentation 1), the 0 values should be "off" portions of the signal, but if you look at the wave as captured on a scope (displayed in octave), I don't see any breaks in the wave to suggest a 0 value. It's possible I'm capturing the wave incorrectly, though the packet examples in the documentation look equally filled with unbroken sine waves. Even if you were to rectify this wave, it looks like a series of unbroken, positive pulses. Can someone cure me of my ignorance?

1) Cochlear implants: system design, integration, and ...National Institutes of Health (NIH) (.gov)https://pubmed.ncbi.nlm.nih.gov › ...
2) One captured packet, including sync, active electrode, mode, amplitude, phase 1, phase 2
3) zoom-up of active electrode portion, showing series of waves
 

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Ya’akov

Joined Jan 27, 2019
9,230
Welcome to AAC.

Figure 9 from the paper shows 12 bits:

1710178976172.jpeg
three bits with a value of 1, then one 0, then four of 1, then one zero, then three of one
Your captured waveform doesn’t look like ASK modulation at all, and it looks very different from this. ASK is a very simple form of modulation, and it is just a signal with a fixed frequency and amplitude being turned on for a particular interval to indicate 1 and off for the same interval to indicate 0.

I am not sure what you captured but first, the attack decay envelope is very severe and could easily interfere if it as intended to be a digital modulation, and second, there is no time oriented structure in your extracted example.

The only way this could be right is if they only encoded the values of your labeled entities as a number of ones, and the zeros are exclusively field separators. So that, for example, Active Electrode might consist of n bits on providing a maximum number of possible values equal to n.

Then, it is followed but n bits off as a combination of field separator and redundant encoding (i.e. 111 followed by 000 so they can be checked against each other, and if they don’t match, it is discarded.)

But, a brief look at the paper says they use a total of 12 tokens consisting of very specific bit patterns, and including redundant bits for FEC (Forward Error Correction). I haven’t read beyond a small excerpt.
 

Thread Starter

aaron_m

Joined Apr 27, 2014
13
I am not sure what you captured
A brief methodology: I took the coil from the back of my head and put it up to a coil of wire wrapped around a pill bottle with the ends of the wires connected to the probes of the 'scope. I then captured a series of frames on the scope and uploaded a particularly good looking one to my Mac; I used Octave to present it on screen, and zoom in. So what's displayed should be directly what's being broadcast to the receiver literally implanted in my head. Unless I'm doing something wrong, there.

For completeness, I connected the probes to the pins leading to the coil to capture another packet, and it looks pretty similar. The moire pattern (in purple this time) looks a little different, but the series of unbroken waves are the same. Leading to my question: is this an actual ASK packet, or is the documentation incorrect?

Also, examples of captured packets shown in other parts of the documentation look pretty similar to what I've captured, but they're overviews instead of working examples, so I can't zoom in on those.

second, there is no time oriented structure in your extracted example.
I don't quite understand this. Do you mean there's no X value on the timeline? Or the spacing between the packets?
 

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