Ip Software In Ubuntu

In the ideal model output V or is independent of the load as in R L always going to have AV i what we mean that the R or amplifier is zero.

The more accurate model would consider a Thevenin equivalent of V TH = AV i and R TH = R or in series. Depending on the values \u200b\u200bof R or the description given by the ideal case will be more or less adequate. In real amplifiers the value of R or typically of the order of tens of ohms, at worst it could reach the value some hundred ohms. The real value of R or depend on the type of amplifier. The catalogs listed the maximum values \u200b\u200bof R or . We will try now the importance that may be the fact that R or not null. If you look at the attached figure, R or introduces a voltage divider where

In this expression if Ro = 0 then we get the ideal case Vo = AVi also if RL>> same thing happens Ro and Ro + RL is RL and thus again we obtain Vo = AVi. The problem then occurs when Ro and RL are comparable in which case we find the real case, in which the output is far below the ideal. For example, assume that Ro = RL Vo output would be worth half of the ideal. Therefore, we will explore a new model how to modify the expression of the gain from having a Ro.

Consider an ideal inverting amplifier to which we added externally and series resistance R or to account character real.

Accordingly we have

Assuming the isolated circuit, we can say that the intensity I passing through Ro is the same as through R2. With this we have to ...

expression obtained in closed loop where the number appears in A, which generally has very high values \u200b\u200b(10 ⁵ - 10 ⁶ ) and the term Ro/R2 that has values \u200b\u200bless than 1 since in general Ro <

Compared with open loop expression V'o / Vd =- A note that the difference is in the denominator in the ratio Ro/R2 is not negligible compared to unity and this causes an effective reduction the open loop gain. A 'decreases with respect to A and depends on Ro and R2. The larger R2 Ro have less influence on profit. R2 also increase in an inverting amplifier means that R1 must also increase to achieve the same profit, which means increasing the input impedance is always desirable.

We obtained Vo / Vd which is the gain G we seek to obtain this gain from the expression of the intensity I in R1 and R2 ...

Putting you in terms of Vo by the expression Vd =-Vo / A 'obtained above We ...

Vo grouping the terms in one hand and the other get Vi ...

clearing the ratio Vo / Vi, multiplying and dividing by R2 and replacing A by its value ...

The term that appears in the denominator due to a decrease in Ro G and depends on the magnitude of A. If A increases the error produced decreases, the closed loop gain. Furthermore, if Ro increases an increase in the error, which also occurs if you increase the term (1 + R2/R1). Finally, if the error induced R2 increases will be smaller. Yet we come to the idea that the larger G greater the influence of Ro and the larger lower R2 that influence.

We can see the magnitude of this factor for an unfavorable case:

assume that

Ro = 10 ^{2 ohms}

A = 10 ⁵

(1 + R2/R1) = 100

R2 = 100 Kohm

the error is about 10 ^-6 which represents a very small error as that term is added to 1, which is totally negligible.

In most cases the errors of magnitude of resistance for both input and output are very small and therefore only be taken into account in cases in which required very high precision.