Output of the amplifier is higher than expected

Thread Starter

bessou55

Joined Oct 14, 2022
13
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:

IMG_9427.jpg

IMG_9390.jpg

IMG_9392.jpg
 

Ian0

Joined Aug 7, 2020
9,671
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?
 

Thread Starter

bessou55

Joined Oct 14, 2022
13
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?
 

ericgibbs

Joined Jan 29, 2010
18,766
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
 
Last edited:

Thread Starter

bessou55

Joined Oct 14, 2022
13
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
 

Ian0

Joined Aug 7, 2020
9,671
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!
 
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