DC Gain of an Op-Amp!!

[snoop835]

dc gain op amp

Anyone has comments on WHY in practice the dc gain gain as low as 31dB (for example) may not be ideal for operational amplifier aplications? If the op-amp is connected in unity-gain configuration, does the dc gain matter?

cheers

 

[electronrancher]

op amp dc gain

It does matter - the accuracy of the follower is dependant upon the gain.

We can run through it. Here, the gain of the amp is denoted Av, and the feedback factor (=1 for a follower) is denoted B. So the real equation for the output of a follower is:
Vout = Vin*(1/(1 + B/Av))

So for a 1v input, and gain of 35 (31dB) the output of the follower would be 0.97v. Increase the gain to 60dB (Av=1000V/V) and the same follower would give an output of .999, much closer to the expected 1v.

 

[sunking]

yes, it depond on your system accuracy.
if the system requirement is not critial, the 30dB is OK

 

[cliffj]

30dB is pretty low for an opamp, besides it's DC value.
Without a large open loop gain, many close loop configurations
could not be form ( or virtual ground). Even for a unity-gain buffer,
you can't actually say that it's unity gain since there is no virtual
short characteristic at the input nodes. It depends on your accuracy
required.