bandwidth of unity gain amplifier?

ugb amplifier

suppose my opamp has open loop gain of 100dB and UGB of 5MHz.if i use this opamp as an unity gain amplifier,what would be the bandwidth of signal it can handle?and how?
thanks in advance.

what is unit gain bandwidth

signal from 0 to 50Hz can be handle without large distortion.

But , from 50Hz to 5Meg Hz can also handle with some distortion.

when the frequency of signal is larger than 5M Hz, the signal can not be handle.

unity-gain bandwidth

I believe you know that,

prodct of gain and bandwidth remain constant, this wil answer your question.

As frequency increases for a given load, amplifier is not capable to change the voltage in a given duration of time, hence swing decreses, this will reduce the gain.

As gain falls down swing decreses and hece the band width increases


regards

avinash said:

suppose my opamp has open loop gain of 100dB and UGB of 5MHz.if i use this opamp as an unity gain amplifier,what would be the bandwidth of signal it can handle?and how?
thanks in advance.

Click to expand...

The bandwidth will be equal to the UGB in a configuration as follower or buffer, this in the condition that your feedback factor is one. If it is less than one (example of an inverting amplifier) the resulting bandwidth will be equal to the feedback factor times the UGB.

Bastos

Your bandwidth will be 5MHz. That is because the gain-bandwidth product is a constant after the dominant pole. So, BW=UGB/Gain=5MHz/1=5MHz.
In fact, that is why you call it the Unity gain bandwidth, the bandwidth with a gain of 1.

dear VVV,
according to you my opamp should pass the signal of 5MHz bandwidth.but when i perform a transient analysis on unity gain buffer by providing a sinusoid of time period = 1/5MHz i.e 200ns and amplitude of 1Vpp centered at analog ground,o/p is not the replica of input i.e. o/p is distorted .even i am getting some triangular waveform at the o/p.what might be the reason?

You are probably going over the slew rate of your op-amp.

Please check your datasheet that your opamp can handle this fast signal.

If you are using LM741 you may not go over 0,5V/µS!!! otherwise you get an distorted signal.

It could be that you are indeed exceeding the slew rate of the opamp.
The GBW tells you the bandwidth for small signal. But GBW and slew-rate are two different parameters, each of which must be met.

thanks everybody specially VVV

but dear VVV,if i apply a sinusoid of amplitude 0.1mVpp and frequency of 5MHz , will my unity gain opamp be able to work properly ,provided my slew rate is 2V/us.if yes how?

,The right way to determine the slew-rate limted bandwidth, or the power bandwidth, as it's called, is to find the limiting effect of the slew-rate.

Slew-rate, SR, is the maximum possible rate of change of voltage per unit time:

SR=dv/dt.

If you have a sinusoidal signal of amplitude Vpk, you can write it like this:

v=Vpk*sinωt.

The voltage has the highest rate of change around 0, Π, 2Π and so on. This rate of change is found by differentiation:

dv/dt=Vpk*ω*cosωt. Its maximum occurs then for t=0, Π,...
For t=0 we get: dv/dt=Vpk*ω=Vpk*2*Π*f

This is the maximum rate of change of voltage, for a signal of amplitude Vpk and frequency f.
So, this rate of change must be lower than the slew-rate of the opamp, else the opamp will not be able to follow and distortion will occur.

In the limit, SR=Vpk*2*Π*fmax, where fmax is the maximum frequency of a signal of amplitude Vpk that an opamp having slew-rate SR will amplify without distortion:

fmax=SR/(Vpk*2*Π).

In your case, SR=2V/us and Vpk is 0.5V, so fmax=0.63MHz (for 1Vpp). That means at 1Vpp you can amplify a signal of only 0.63MHz. That is amolst 10 times less than your unity gain bandwidth, although the gain is still 1.

To get the full 5MHz, you need an amplitude of less than:

Vpk ≤ SR/(2*Π*5MHz)=0.063 V, that is a signal of less than 0.127 Vpp

I hope this helps.
Make sure you use the minimum SR in the datasheet.

Hi VVV
ur derivation is very clear! Really a heavyweight designer.