[Moved]: INA210 swing to GND limiting at GND+0.005 how can it realize this function

Hi, guys!
I am planning use the INA210 to do some design. INA210 is a difference amplifier shown in the pic1. It has two inputs IN+ and IN-, one output VOUT and one reference input Vref. And I asked the supporting team: what is the output of the amplifier when Vref is connected to GND. They replied me: since the amplifier can swing to GND with a offset (GND+0.005). So the output will always be Vin*Gain+0.005. I am very curious about this kind of "clamping" function. It stop the amplifier from saturation. How they design the output stage? (INA210 can have a wide input common mode voltage rang:-0.3-26V. If the common mode voltage is zero, Vref is also zero. Load resistor is connected to GND. These is no current flowing in the resistor at this moment, how can this amplifier can still have GND+0.005V output when input differential signal is zero ?)

Re: INA210 swing to GND limiting at GND+0.005 how can it realize this function

You discussing output stage saturation voltage which can be found with any amplifier, it has nothing to do with reference or differential input voltage level.

Re: INA210 swing to GND limiting at GND+0.005 how can it realize this function

FvM said:

You discussing output stage saturation voltage which can be found with any amplifier, it has nothing to do with reference or differential input voltage level.

Click to expand...

Thanks for your reply!
From your reply, my understanding is: since I tied the reference voltage to ground, Ideally, the output of the amplifier should be ground. However in this single supply amplifier, the output cannot swing to ture ground. It saturates and stay in GND+0.005V. Am I right?
And I want to know how to control the amplifier saturates at GND+0.005.

Re: INA210 swing to GND limiting at GND+0.005 how can it realize this function

Hi,

usually one avoids saturation of OPAMS.

Therefore you have some options:
* the simplest is to "add" some offset. just use a voltage didvider to feed about 20..50mV to the REF-signal. (20 ...50mV is the 5mV plus some headroom)
* or use a small negative supply instead of GND.

Saturation often causes increased supply current and often it causes some additional delay to leave the "saturation state". (some OPAMPs only microseconds, but others more than 100ms)

Both usually is not what you want.


Klaus

Re: INA210 swing to GND limiting at GND+0.005 how can it realize this function

Hi,

"...how can this amplifier can still have GND+0.005V output when input differential signal is zero?"

Maybe related to unavoidable mismatch between input devices, or similar type of mismatch like bias currents, internal resistors, etc., total device noise at output, something related to a Vce from an output device that will never swing lower than 5mV, some or all of the above in combination?

Re: INA210 swing to GND limiting at GND+0.005 how can it realize this function

It saturates and stay in GND+0.005V. Am I right?
And I want to know how to control the amplifier saturates at GND+0.005.

Click to expand...

The datasheet says 5 mV typical, 50 mV maximal saturation voltage. The variation is due to production tolerances and may be other parameters like supply voltage or temperature. You can't control it specifically.

If you want to understand what causes the saturation voltage, you need to analyze a transistor level amplifier circuit, which is unknown, unfortunately.

To achieve a linear amplifier output range down to zero input voltage, you can either use a negative supply voltage, or more practical, raise Vref to e.g. 100 mV.