# In-amp output signal clipped

#### fbp

Joined Aug 9, 2023
30
Hi,
I am using the INA849 IC. My goal is to use 8V power rails, with a mid supply (4V) reference input to the in-amp. While simulating the circuit, my output waveform gets clipped.

Please guide me. Is there a particular connection I am not doing correctly?

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• 3.6 MB Views: 27

#### ericgibbs

Joined Jan 29, 2010
18,268
Hi fbp,
What value of Rg resistor do have in circuit??

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#### fbp

Joined Aug 9, 2023
30
I am using the in-amp as a unity gain amplifier for now.

#### fbp

Joined Aug 9, 2023
30
Do we have the give an offset of 4V to the input for the in-amp?

#### ericgibbs

Joined Jan 29, 2010
18,268
hi,
Check the datasheet for the resistor value you need for your required Gain.
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#### fbp

Joined Aug 9, 2023
30
Do we have the give an offset of 4V to the input of the in-amp or directly give the input without an offset?

#### fbp

Joined Aug 9, 2023
30
I want to have it as a unit gain amplifier, and I am using an in-amp sicke it has good CMRR. While simulating the circuit, do I have to put a resistor of 1 ohm?

hi,
Check the datasheet for the resistor value you need for your required Gain.
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View attachment 300958

#### ericgibbs

Joined Jan 29, 2010
18,268
hi,
If you want the Vout to be centred around +4v, use a Vref voltage,
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#### fbp

Joined Aug 9, 2023
30
Yes I did give 4V as the reference input to the INA849 through the LT6231 opamp.

#### ericgibbs

Joined Jan 29, 2010
18,268
Hi,
Look at that table for gain of unity, the Gain figure is not available.
What is the Input signal?
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#### ericgibbs

Joined Jan 29, 2010
18,268
Hi,
You could use a 2:1 resistive voltage divider on the Input and set the Gain for 2, 6.04k resistor.
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#### ericgibbs

Joined Jan 29, 2010
18,268
Hi,
Like this option.
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#### fbp

Joined Aug 9, 2023
30
The input signal is a 5Vpp signal with 500kHz. I am just not sure if a 4V offset is required at my input as well.

I am not able to access the link you shared in the previous message

#### fbp

Joined Aug 9, 2023
30
Sorry, I was able to view the image, it took time to load. I was wondering why a voltage divide at the input?

#### BobTPH

Joined Jun 5, 2013
8,142
You need to treat the mid voltage as your signal ground.

Connect the sine generator ground and the + input to the mid point voltage, not to the the battery negative.

#### fbp

Joined Aug 9, 2023
30
Is it to compensate for the gain of 2?

#### fbp

Joined Aug 9, 2023
30
You need to treat the mid voltage as your signal ground.

Connect the sine generator ground and the + input to the mid point voltage, not to the the battery negative.
I have to set the input as mid supply as well?

#### BobTPH

Joined Jun 5, 2013
8,142
I have to set the input as mid supply as well?
Yes, it is the signal ground. If you connect an input to the battery negative, it is at -4V with respect to the reference voltage.

Think of the voltages this way: The midpoint is 0V, the supply positive is +4V and the supply negative is -4V.

#### fbp

Joined Aug 9, 2023
30
Yes, it is the signal ground. If you connect an input to the battery negative, it is at -4V with respect to the reference voltage.

Think of the voltages this way: The midpoint is 0V, the supply positive is +4V and the supply negative is -4V.
My input was actually already set to mid-supply. Am I doing something wrong in the connections or n the schematic?

#### ericgibbs

Joined Jan 29, 2010
18,268
hi fbp,
This is what I see with your circuit.
What do you want the Vout to be ???

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