Part Number: INA223
For correlating figure 28 “0.1Hz to 10Hz Voltage Noise”
We builds up active filter as TI verified design mentioned in document #SLAU522
And take OPA827 as DUT, briefly connecting and wiring without shielding can.
The resulting waveform is approximate and satisfied as the attachment (PK-Pk = 24.2mV) but not INA223 while using as DUT instead
According to figure 28 of INA223, the estimation should be
(1) Gain = 20
VOUTPK-PK = 200nV/ Div x 6 Div x 20 (Gain) X 100 (Filter Gain) = 2.4mV
(2) Gain = 300
VOUTPK-PK = 200nV/ Div x 1 Div x 300 (Gain) X 100 (Filter Gain) = 6mV
The resulting is 10 times more than expectation; we have no idea what dominate the measurement, and how to identify
We simply set VCM about 1V and VIN+ - VIN- is about 5mV via voltage divider (200 ohm and 1 ohm), tie VIN – to GND.
Thanks for recommendation and measurement guide!
Patrick Simmons, TI Sensing Products Applications Support
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In reply to Patrick Simmons:
Thanks for recommendation!
Actually the differential voltage developed across is from the dividing of linear power supply or Alkaline battery
VS = Linear power supply
VBUS = Linear power supply or Alkaline battery
Conventionally the output noise of OPA is measured by shorting the input to GND.
As understanding, the incorrect input common mode voltage will lead INA incorrect as well
Since INA is symmetrical and balanced, is it suitable to connect the both inputs to GND?
Or all I have to do is to find a clear source?
Is it possible to show how you measure the noise of INA?
In reply to Ben Huang1:
Can you set up the INA223 like shown below?
Also one test you could do is measure the noise of the output for the following configuration. This will show if these op amps are contributing more noise than expected.
Lastly, if you apply a 1mV sine-wave at the input here, do you see a 100mV sine-wave output?
At the moment having some difficulty tracking down the engineer and the test apparatus used for the noise measurements we took. Will let you know when I am able to track them down. Also I would not connect the inputs of the INA223 to ground for your measurement.
Thanks for the reminder and comment!
The transfer function and noise floor of BPF have been checked.
The corner frequency and gain are close to your design but I am not sure what the expectation of noise floor is. since there is no mention in this document # SLAU522
Noise floor of BPF
INA223 @ Shut voltage mode (Gain =20V/V)
According to the waveform, the pk-pk is much worse than expectation
Please refer to the set-up picture, is there anything required to have an improvement? Maybe I should not take something as granted!
Appreciate for paying much attention and effort on this case
Board Modification for INA223 20190110.pptxBoard Modification for INA223 20190110.pptxHi Patrick
Thanks for reply and sorry for not describing clearly!
When you say the gain is close, does that mean when you passed a 1mV signal at 1Hz and saw a 100mV output? If it was greater than 100mV, how big was it?
Yes! Where the close gain and corner frequency I mentioned is the active BPF (I am trying to matching the components as the design recommended as possible)
I noticed that your fabricated board is a little different than what is shown in SLAU522. Can you give me a list of the board modifications you made?
Please find the attached ppt for more details, Basically, the difference is for INA223 only and leave others unchanged.
As for your setup, could you this time include the INA223 and ground the inputs.
Does it mean tie both input to GND directly as conventional noise measurement of OPA? As memory, you would not connect the input to GND for this measurement, what is the intention for grounding the input to GND this time?
Also can you set the output mode to shunt voltage measurement in the configuration register if you have not already done so previously?
Also I am always configuring the measurement to shut voltage mode, thanks for reminder!
At the moment having some difficulty tracking down the engineer and the test apparatus used for the noise measurements we took. Will let you know when I am able to track them down
Is it possible to track them down?
I am planning to make a board revision, please find the same ppt for reference as well.
Any recommendations and ideas are welcome
Appreciate for continuing paying much attention on this measurement!
This item is the most critical in the precision measurement!
Much more time consumption is reasonable but it is worthy.
I am also studying anything possible to make this measurement better!
To make sure what I understand clearly and avoid any misleading, I may draw a simple schematic for discussing!
(1) Stimulus from battery
(2) Tie both inputs to GND
Does it also require? (Too much closer to GND)
I am going to follow your recommendation once the revised board is available.
Looking forward to your own measurement and another application report publication as SLAU522, that someone can easily Google it and get satisfied guide to the beginner as me
In reply to kai klaas69:
I made a brief ptt file to show how the measurement is taking
Since the revised board is not ready, I using the previous one still
INA223 Set up for noise measurement.pptx
Have you ever evaluated the shielding effectiveness of mental box?
I put a mobile phone inside the box and make a 3G/4G phone call,
but the ringtone is still perceived.
As you mentioned, properly shielding can dramatically improve the noise performance, I have no idea how to define the “properly”
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