Electronic Devices - Operational Amplifiers - Discussion

Which amplifier has open loop gain >1?

@Mayur.

Because of P proportional to V^2.
The power gain is 10 log (A).
Voltage gain is 20 log (A).

@Mayur.

The power gain is 10 log(A).
Voltage gain is 20 log(A).

@Amadi, you must carefully write the formula at least.
The power gain is 20log(A).
The voltage gain is 10log(A).

But the above formula for converting gain to decibel is only applicable for current gain 20log(A) and voltage gain 20log(A). While power gain is 10log(A).

20log(75,000/100) - 20log(75,000/1,000) = 20dB.

How? please explain.

An op amp has open loop gain that decreases at the rate of 20 db/decade.

We all know that Bandwidth-gain product is constant for op-amp.
Let us consider an op-amp with Bandwidth-gain product equal to 1MHz.

--> Bandwith-Gain = BW*Av(it is constant. In our case 1MHz).

--> Gain(in DB) = 20log|Av|.

(Below I have varied BW and noted corresponding gain, using the fact that Bandwidth-Gain product remains constant.)

BW(in Hz) : Av : Gain(in DB)
1M : 1 : 0
100K : 10 : 20
10K : 100 : 40.... so on.

It can be seen that Gain in DB decreases by 20DB for every Decade(Ten times the considered frequency)

So the option [C] is correct answer...!

(I hope I have analysed it correctly. If mistake please do correct it...).

I think 1DB = 20log(A); and frequency variations do not change the variations of the gain.

So, in this we are just converting the gain to decibels by using above formula.