I'm using an INA128 as an amplifier with a gain of 100 (Rg = 511 Ω) as in the schematic below (but without the filters.)

I use a signal generator for the input (3 mV.) The expected output is 3 mV × 100 = 0.3 V but I get 1.2 V. I don't understand what the problem is.

Here are the pictures of the schematic, the input from the signal generator, and the output:

 

hi niss,
Welcome to AAC.
Where is Vref connected
E

 

hi niss,
This is what LTspice shows for your circuit
E


Added image with Vref not connected.

 

You seem to have 200kHz input and 50Hz output.
Have you connected the same signal to both inputs?
Do you live somewhere that has a 50Hz mains supply?

 

hi niss,
This is what LTspice shows for your circuit
E
View attachment 278743

Added image with Vref not connected.

Thank you for your answer.
I connected the Vref to ground.
I dont understand why the waveform is different in the oscilloscope.
Also do I need to add the 10k in the output?

 

You seem to have 200kHz input and 50Hz output.
Have you connected the same signal to both inputs?
Do you live somewhere that has a 50Hz mains supply?

I grounded the Vin- and connected the Vin+ to the voltage generator (3mV)
Yes the mains supply is 50Hz.
do I need to change the frequency?

 

hi niss.
Added the 10k load as part of the simulation.
How are you connecting the signal generator to the two INA input resistors.?
E
BTW:
Do you have an input capacitor from the sig gen to the input, you may be injecting a DC component from your sig gen.


@nissafha
Please confirm the signal input frequency.???


Check the actual value of the 511R resistor with an Ohm-meter

 

If the circuit is built on a breadboard with messy long wires all over the place then the output is guaranteed to be 50Hz.

 

The ground clip of the signal generator is connected to the ground of power supply, and the other clip is connected to the resistor of Vin+ on the breadboard
Vin - is also connected to ground.
I changed the input frequency to 2kHz. im not sure which frequency to choose.
And no I dont have input capacitor.
511 Ohm is correct

 

hi niss,
Try this quick test,
Connect both inputs together and to 0v, what is the INA Vout level.?
E

 

The ground clip of the signal generator is connected to the ground of power supply, and the other clip is connected to the resistor of Vin+ on the breadboard
Vin - is also connected to ground.
I changed the input frequency to 2kHz. im not sure which frequency to choose.
And no I dont have input capacitor.
511 Ohm is correct

If it’s audio, you test it at 1kHz - everybody does!

 

This is the output of the scope and the multimeter when both inputs are 0 @ericgibbs

 

Hi niss.

3.3mV is typical, so thats OK.
Try this test circuit using a 100nF 100K and 1kHz Sine set for 3mV.

E

 

What supplies are you using for the plus and minus 5V.