# [SOLVED]Op amp basic question

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#### Miltaridis

##### Newbie level 6
Why does an op amp bandwidth depend on vout pp ?

that is the maximum voltage source to your op amp

Vout pp is limited by Vs pp.
Hence Vout pp can only go up to Vs pp.
Vout pp = Vin pp x Max Gain

Since Gain Bandwidth Product, GBP = Gain x Bandwidth, we can say Bandwidth = GBP/Gain

Why does an op amp bandwidth depend on vout pp ?

Well i am using ada4817-1 and my datasheet says
−3 dB Bandwidth VOUT = 0.1 V p-p 1050MHZ
VOUT = 2 V p-p 200MHz

Why does an op amp bandwidth depend on vout pp ?

Because the output has an upper limit of slew rate (SR=dV/dt).
For sinusoidal signals, the highest slope occurs near zero which is proportional to Vp and the frequency.
V=Vp*sin(w*t)
dV/dt = Vp*w*cos(w*t)
where w= 2*pi*F
And
dV/dt max = ± Vp*2*pi*F

So for the output to give the expected Vp the following inequality should be satisfied:
Vp * 2 * pi * F < SR
F < SR / (Vp * 2 * pi)
So the lower Vp we accept at the output (by decreasing Vin), the higher the frequency we can get.

Edited:
If we let Vp_in constant and we increase the frequency, Vp, at F = SR / (Vp * 2 * pi) where Vp=Vp_in*Gv, will start to decrease as if it is Gv decreasing. The new Vp tries to satisfy:
Vp = SR_max/(2*pi*F)

Last edited:
• Miltaridis

### Miltaridis

Points: 2
Your datasheet already specifies Gain Bandwidth Product VOUT = 0.1 V p-p ≥410 MHz
With the info you have provided, it has already proven it.

If an op-amp doesn't comply to GBP, you better be worried!

Well i am using ada4817-1 and my datasheet says
−3 dB Bandwidth VOUT = 0.1 V p-p 1050MHZ
VOUT = 2 V p-p 200MHz

Well i am using ada4817-1 and my datasheet says
−3 dB Bandwidth VOUT = 0.1 V p-p 1050MHZ
VOUT = 2 V p-p 200MHz

Recommendation: Try to become more familiar with data sheet information.
The given voltage values (pp) are not maximum values but measurement conditions- as indicated at the top of the relevant columns in the data sheet.
Nevertheless, the answer from KerimF regarding slew rate influence is valid and is the reason for not driving the opamp at its thresholds during these measurements.

Thank you all for your help

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