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loop123:

--- Quote from: ebastler on April 04, 2024, 06:50:18 am ---
--- Quote from: loop123 on April 04, 2024, 01:24:59 am ---For direct 10uV mapping into the ADC like in the case of the g.USBamp which doesnt have amplifier. It may be true but when the output is 0.5V (after 10uV x 50000 gain in main amp). What would be wrong for the 0.5V at audio Adc? would it make it like 0.4V or 0.6V?? How about the chip shown in spec in my last 2 messages used by the E1DA? does it keep stable reference voltage?

--- End quote ---

It would be really helpful if you clarify for us -- and for yourself! -- what your requirements are.

* What frequency range do you need to capture (lower and upper limit)?

* Do you need to capture only low-level signals, say in the 10 µV range -- in which case you could and should use an analog pre-amplifier, and then can work with an ADC with low resolution?

* Or do you need to pick out a 10 µV signal sitting on a 1 V background, as implied by your original questions in this thread -- in which case you need an ADC with correspondingly high resolution, if you want to use digital signal processing techniques to pick out the weak signal?

* Why do you think precise, absolute voltage levels are so critical for you to control or measure? I understand that you intend to study some EEG-like brain/computer interface -- won't the physiological differences and drifts, day-to-day and run-to-run variations of contacting the electrodes etc. be dominant by far?  Given your limited budget, there is no room for an approach like "I'd rather get something that covers all the bases and all potential future needs". If there is any chance to establish a solution for $200, it will need to be tailored to your specific needs. Hence, until you have a clear and consistent picture of what your signals are and how you need to control and measure them, there is not much point in equipment discussions.

--- End quote ---

I already have a 50,000 gain amplifier to work with 10uV (100Hz to 2400Hz) signal. The CWE BMA-200. Since the output of the amplifier is 0.5V to 2 V. Then even audio ADC can work with it, right?  When you talk about stable reference voltage. Can it make the output vary between say 0.5V to become 0..4V or does it only occur in micro or millivolt signal?

I already have the E1DA ADC as well as a 16 channel amp that doesn't have any amplifier inside. The 16 channel g.USBAmp has this description I shared earlier. My question concerns its last sentence.

https://www.gtec.at/product/gusbamp-research/

"g.USBamp uses wide-range DC-coupled amplifier technology in combination with 24-bit sampling. The result is an input voltage range of +/- 250 mV with a resolution of < 85,7 nV! This means that any physiological signal can be recorded directly, without additional hardware. Neither high electrode offset voltage nor large artifacts resulting from electrical or magnetic stimulation will saturate the amplifier inputs. This feature is an important requisite for various artifact treatment and correction techniques"

"Each of the 16 analog to digital converters operates at 2.4576 MHz. Oversampling 64 times yields the internal sampling rate of 38,400 Hz (per channel and for all channels!). In addition, a powerful floating point Digital Signal Processor performs oversampling and real-time filtering of the biosignal data (between 0 Hz – 2,400 Hz). Therefore, a typical sampling frequency of 256 Hz yields an oversampling rate of 9,600. This results in a very high signal to noise ratio, which is especially critical when recording evoked potentials (EP) in the EEG or identifying small amplitude changes in high-resolution ECG recordings. You are measuring far below the noise-range of conventional amplifiers.""


Today due to JeremyC comments that I only knew about nV/Sqrt(Hz) noise formulas. I researched for hours about bits, how to compute for dynamic range in dB and even to relate to nV/Sqrt(Hz). Now I know. But I still can't totally comprehend the above description "You are measuring far below the noise-range of conventional amplifiers."? How so? What is typical noise-range of conventional amplifiers and how could it be measuring far below? Please give actual figure as examples. Thank you.
gf:

--- Quote from: loop123 on April 04, 2024, 01:24:59 am ---It may be true but when the output is 0.5V (after 10uV x 50000 gain in main amp). What would be wrong for the 0.5V at audio Adc?

--- End quote ---

My understanding of the problem is that you consider your BMA-200 pre-amplifier too noisy, so you are looking for an alternative solution. And as far as I understood (in the other thread), one of your requirements is a high input impedance, which is not particularly helpful either if you want low noise on the other hand.


--- Quote ---You are measuring far below the noise-range of conventional amplifiers

--- End quote ---

This is just meaningless marketing :blah:
Do you have numbers? E.g. plot of the (input referred) noise spectral density up to 1 kHz (which seems to be your ROI)? Did you ask the manufacturer to provide some data?
ebastler:

--- Quote from: loop123 on April 04, 2024, 07:16:36 am ---...

--- End quote ---

You claim to respond to my post, but have not really answered a single of my questions, right?  ::)

If you need to capture low-level signals only, rather than small signals sitting on top of a large fluctuating signal, then the CWE BMA-200 looks like a pretty capable pre-amplifier. And the g.USBAMP looks like a very plausible AD-converter -- probably a better choice than an audio amplifier since it is DC-coupled. (It better be good, given that it costs closer to $20000 than $200...)

What functionality do you find lacking in your current setup?
loop123:

--- Quote from: gf on April 04, 2024, 08:05:40 am ---
--- Quote from: loop123 on April 04, 2024, 01:24:59 am ---It may be true but when the output is 0.5V (after 10uV x 50000 gain in main amp). What would be wrong for the 0.5V at audio Adc?

--- End quote ---

My understanding of the problem is that you consider your BMA-200 pre-amplifier too noisy, so you are looking for an alternative solution. And as far as I understood (in the other thread), one of your requirements is a high input impedance, which is not particularly helpful either if you want low noise on the other hand.


--- Quote ---You are measuring far below the noise-range of conventional amplifiers

--- End quote ---

This is just meaningless marketing :blah:
Do you have numbers? E.g. plot of the (input referred) noise spectral density up to 1 kHz (which seems to be your ROI)? Did you ask the manufacturer to provide some data?

--- End quote ---

The following is the noise spec of my BMA-200. Noise Wideband Referred to Input <7uV P-P, < 3uV RMS, Wideband is 50kHz



The following is the noise spec of my USBamp.



Noise mentioned is 0.4uV RMS at 1 to 30 Hz. about 2.64uV Peak to Peak? According to Netech. Their simulator output is 10uV peak to peak. If you will extrapolate it. At 1000Hz. The g.USBamp will be so noisy the noise can reach 10uV? 

I mean if at 1 to 30Hz, the g.USBamp has noise of 2.64uV P-P, what is your estimate of the noise at 1000Hz? How do you compute the estimate? However their demo software still has the Netech simulator 10uV, 50Hz resolvable (see below). Shouldn't it be one big blur? 




I still haven't bought the software of the g.USBamp which costs more than $3000. Note major R&D centers used the g.USBamp. Including one with sigma 5 result I'm trying to replicate, one with the potential to produce 5 times the revolution caused by the discovery of DNA by Watson, etc. and will advance humanity a century ahead.


loop123:

--- Quote from: ebastler on April 04, 2024, 06:50:18 am ---
--- Quote from: loop123 on April 04, 2024, 01:24:59 am ---For direct 10uV mapping into the ADC like in the case of the g.USBamp which doesnt have amplifier. It may be true but when the output is 0.5V (after 10uV x 50000 gain in main amp). What would be wrong for the 0.5V at audio Adc? would it make it like 0.4V or 0.6V?? How about the chip shown in spec in my last 2 messages used by the E1DA? does it keep stable reference voltage?

--- End quote ---

It would be really helpful if you clarify for us -- and for yourself! -- what your requirements are.

* What frequency range do you need to capture (lower and upper limit)?

* Do you need to capture only low-level signals, say in the 10 µV range -- in which case you could and should use an analog pre-amplifier, and then can work with an ADC with low resolution?

* Or do you need to pick out a 10 µV signal sitting on a 1 V background, as implied by your original questions in this thread -- in which case you need an ADC with correspondingly high resolution, if you want to use digital signal processing techniques to pick out the weak signal?

* Why do you think precise, absolute voltage levels are so critical for you to control or measure? I understand that you intend to study some EEG-like brain/computer interface -- won't the physiological differences and drifts, day-to-day and run-to-run variations of contacting the electrodes etc. be dominant by far?  Given your limited budget, there is no room for an approach like "I'd rather get something that covers all the bases and all potential future needs". If there is any chance to establish a solution for $200, it will need to be tailored to your specific needs. Hence, until you have a clear and consistent picture of what your signals are and how you need to control and measure them, there is not much point in equipment discussions.

--- End quote ---

In my last message to you. I answered the 1st and 2nd question. About the third. It's small signal sitting on top of others. You said "Or do you need to pick out a 10 µV signal sitting on a 1 V background, as implied by your original questions in this thread -- in which case you need an ADC with correspondingly high resolution, if you want to use digital signal processing techniques to pick out the weak signal?".

But digital filters using oversampling with moving averages can only do brick wall filter above the cutoff frequency. How can digital signal processing techniques pick up the weak signal among the noises??  Is it not both the BMA-100 and USBamp outputs need to be pass through intensive Mathcad analysis?  Or can digital signal processing somehow remove further noises below the cutoff? if not, how can it pick up the weak signal? What techniques is this called?
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