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Understanding of the Single ended to 'balanced' converter
Enginstud , 05-09-2023, 11:51 AM
Hi everyone,
I need help with understanding the schematic used in the course before feeding our single ended biased signal to the ADC differential inputs.
VCOM is the biasing voltage.
I understood that r306 and C307 form a low pass filter, but why not connecting the cap to GND ? I believe it has to do with the "balanced" conversion, we want the same common mode voltage on both lines I think, but it's still obscur to me.
Can you please help me understanding that circuit? I searched online but did not find responses.
And, what if we did not used that circuit, and directly connected the biased voltage to -IN, and the biased signal to +in of the ADC ?
Thank you very much.
I need help with understanding the schematic used in the course before feeding our single ended biased signal to the ADC differential inputs.
VCOM is the biasing voltage.
I understood that r306 and C307 form a low pass filter, but why not connecting the cap to GND ? I believe it has to do with the "balanced" conversion, we want the same common mode voltage on both lines I think, but it's still obscur to me.
Can you please help me understanding that circuit? I searched online but did not find responses.
And, what if we did not used that circuit, and directly connected the biased voltage to -IN, and the biased signal to +in of the ADC ?
Thank you very much.
qdrives , 05-09-2023, 02:41 PM
R306 and C307 alone are not a low pass filter.
You can consider R307 at as being in series with R306 for that filter and then the question is how low impedance is Vcom?
If you want a more direct low pass filter, C307 need to be connected to Gnd.
As it is now, when ADC_IN+ goes up, so does ADC_IN-, until R307 can lower it back to Vcom.
This also is not a differential signal as ADC_IN- is almost constant at Vcom. Transients on ADC_IN+ are the same polarity on ADC_IN- due to C307 as mentioned before.
You can consider R307 at as being in series with R306 for that filter and then the question is how low impedance is Vcom?
If you want a more direct low pass filter, C307 need to be connected to Gnd.
As it is now, when ADC_IN+ goes up, so does ADC_IN-, until R307 can lower it back to Vcom.
This also is not a differential signal as ADC_IN- is almost constant at Vcom. Transients on ADC_IN+ are the same polarity on ADC_IN- due to C307 as mentioned before.
Enginstud , 05-10-2023, 02:15 PM
To understand that subject I'll need more explanation, can you maybe redirect me to ressources on that subject ? I searched but did not find enough explanation on that, I am a still a beginner regarding analog stuff, I need to learn more.
qdrives , 05-11-2023, 03:37 PM
"...that subject..." I assume you mean the RC filter?
Well, you would need to start there ("RC filter") together with the basic circuit elements resistors and capacitors in this case.
Well, you would need to start there ("RC filter") together with the basic circuit elements resistors and capacitors in this case.
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