Timeline for Using a fully differential amplifier as a differential ADC driver
Current License: CC BY-SA 4.0
19 events
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| Feb 16, 2019 at 4:07 | comment | added | analogsystemsrf | You may also want a CMRR trimpot. | |
| Feb 15, 2019 at 21:00 | comment | added | user1999 | This is the daq I use mccdaq.com/usb-data-acquisition/USB-1616HS-BNC.aspx But for other reasons sources I can only use 5V or 10V range thats why I need to amplify the signal. | |
| Feb 15, 2019 at 21:00 | comment | added | DKNguyen | Differential inputs is NOT the same as bipolar inputs. Differential just means that the difference between the two inputs is the signal and either can go above or below each other in voltage. They could be centered on 2.5V and be limited between 0-5V. Bipolar implies that the signal can actually drop below 0V. I forgot to add that you should see Figure 14 in the OPA1632 datasheet. You probalby want those filter capacitors in the feedback loop. | |
| Feb 15, 2019 at 20:59 | comment | added | user1999 | ADC is diff ended inputs in real. That one in schematic is just a symbol. | |
| Feb 15, 2019 at 20:59 | comment | added | DKNguyen | Also, your ADC is not bipolar. That's a big problem. You'll have to bias both signal source and amp around the ADC's Vocm, not 0V. | |
| Feb 15, 2019 at 20:58 | comment | added | user1999 | Thanks a lot, my freq of interest is between DC and 150Hz. So thosecap values might be different. Transdures is for force not audio so Im not sure this amplifier suits fine. | |
| Feb 15, 2019 at 20:52 | comment | added | DKNguyen | 1. Your gain is not going to be 10. It's going to be 11 (I assume R5 and R6 are not resistors but is the signal output impedance). 2. electronics.stackexchange.com/questions/263424/… 3. ADC Common mode and noise filtering (also anti-alias): Look at Figure 46-49 of the ADC datasheet for the common-mode filters on the ADC input. 4. Use C0G capacitors in the signal path. Others types have DC-bias and microphonic effects. | |
| Feb 15, 2019 at 20:52 | comment | added | user1999 | I have found this uk.rs-online.com/web/p/resistor-networks/1680068 | |
| Feb 15, 2019 at 20:43 | comment | added | user1999 | Thanks one last question do you think the topolgy in my scematic is correct? I will add 100nF decoupling caps to supply rails. | |
| Feb 15, 2019 at 20:41 | comment | added | DKNguyen | Yeah, they come in all sorts of combinations of values pairs. They also exist in more than just pairs. They can also be very expensive. Search mouser or Digikey. I think you would have to be very lucky and pay a pretty penny to find a single array that has everything you need though. | |
| Feb 15, 2019 at 20:40 | comment | added | user1999 | I see, very informative. Are there such arrays including for example two 1k and two 10k in the same array? | |
| Feb 15, 2019 at 20:39 | history | edited | DKNguyen | CC BY-SA 4.0 |
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| Feb 15, 2019 at 20:35 | comment | added | DKNguyen | I won't provide an image but I shouldn't really need to since it's not difficult. Just look at both signal legs of your circuit. Each resistor in the same position should be matched and in the same array with the other. Note that pairing like this only helps CMRR. For example, pairing R1/R2, R3/R4, R5/R6 into their own arrays would help with CMRR. But then R1 and R3 can still drift which would make your gain vary over temperature. Thus ideally, you want EVERY resistor there to be in the same array but that is often just not possible. | |
| Feb 15, 2019 at 20:32 | comment | added | user1999 | Thanks could you also show or draw/sketch how such matched resistors will be placed in the circuit? Its a bit confusing since they are not seperate. There are four resistors in my circuit. I never used matched resistors before. | |
| Feb 15, 2019 at 20:32 | history | edited | DKNguyen | CC BY-SA 4.0 |
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| Feb 15, 2019 at 20:31 | history | edited | JYelton | CC BY-SA 4.0 |
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| Feb 15, 2019 at 20:26 | history | edited | DKNguyen | CC BY-SA 4.0 |
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| Feb 15, 2019 at 20:20 | review | First posts | |||
| Feb 15, 2019 at 22:59 | |||||
| Feb 15, 2019 at 20:15 | history | answered | DKNguyen | CC BY-SA 4.0 |