[Question]Input referred noise voltage?

[GDF]

What is the input referred noise voltage of this circuit?
How to calculate it?

 

[Syukri]

Well at the first glance your transistor look matched, so I think all signal will be sent pretty good.

Seem like your Vout is at the horizontal 300ohm.
Looking at the cct, your voltage in will be divided equally between those 2 resistor.

Vo-Vin=0. Well there is no noise if it's like this?

If u are looking for the physics criterion, what is the temp, and all other factors if noise.

Soory if I'm wrong

 

[skal81]

1) Horizontal Resistor contribution
It is placed at the input so it's noise appears directly:
Vn1 = 4kTR (R=300Ω)

2) Vertical Resistor
I usually calculate the output noise using equivalent voltage/current, and convert to the input. Finally I put it square.
Consider the noise as a current source I. It sees 2 parallel resistors, so the output voltage is I*R/2. The gain is 1/2 therefore the input equivalent voltage is I*R.
Taking square for the noise I get: I*R², where I=4kT/R. Therefore the input noise is
Vn2 = 4kTR

3) Total
Vn_in = 2*4kTR

I think is you do a noise simulation you'll get a result that matches.

Remark about 2). For noise the input is grounded. So your circuit is symetric... Therefore it is easy to see that both resistor will have the same noise contribution. Sometimes you don't need to do all the calculation

 

[GDF]

1) Horizontal Resistor contribution
It is placed at the input so it's noise appears directly:
Vn1 = 4kTR (R=300Ω)

2) Vertical Resistor
I usually calculate the output noise using equivalent voltage/current, and convert to the input. Finally I put it square.
Consider the noise as a current source I. It sees 2 parallel resistors, so the output voltage is I*R/2. The gain is 1/2 therefore the input equivalent voltage is I*R.
Taking square for the noise I get: I*R², where I=4kT/R. Therefore the input noise is
Vn2 = 4kTR

3) Total
Vn_in = 2*4kTR

I think is you do a noise simulation you'll get a result that matches.

Remark about 2). For noise the input is grounded. So your circuit is symetric... Therefore it is easy to see that both resistor will have the same noise contribution. Sometimes you don't need to do all the calculation

So, you make the signal source open when you calculate input referred noise, right?

 

[skal81]

Not open, shorted.
In a general case, to calculate the noise, connect the input to ground and calculate the noise contribution of each device one by one (turning off the others) and do the sum. It is possible because the noise are uncorrelated (flicker / thermal noise).