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Open Loop Characteristics of 741 Op-Amp

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barrica

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Hello all

I wonder if anyone can help me,

Im starting out in the world of digital electronics as part of a work based learning course. As part of an assignment have been asked to investigate the “open loop characteristics of a 741 op-amp”.

Using Multisim I constructed a basic circuit using the 741 op amp and obtained a bode plot very similar to figure 4 in the following link.

**broken link removed**


The question being asked is to “explain the significance of this bode plot”.

Basically the only thing I can gather from this is that as the frequency is increased, the gain decreases, but what I don’t know is the significance of this or an example of where it may be used.

Apologies for the naivety of the question, of which im sure some of you would smirk at :), however any help would be much appreciated in explaining this to me.

Many thanks in advance.
 
Interestingly enough ....the main slope of the graph will appear as either one form or another. The slope shown here seems to be that of the -10 db per decade class. The other common version is a steeper slope, known as -20 db per decade. ... The abscissa is marked in multiples of 10 ... known as decades. If you were to convert the ordinate to a logarithmic equivalent, you would be able to read decibels.

The other notable characteristic of the graph is the point at which the slope of the initial line breaks, or starts to decrease. Generally, this point is taken at the location on the decreasing slope which is 3 db down from the original line...using the decibel format on the ordinate axis.


The -10 or -20 db per decade slope of the negative going graph segments is indicative of the nature of the mathematical transfer function of the component. A single pole in the denominator of the transfer function will generate the -10 db slope, whereas a double pole will have the -20 db slope.
 
Figure 5 is wrong. The frequency where the gain is 1 should be 1MHz, not 100kHz.
Then the slope would be correct at 6dB/octave or 20dB/decade.

The high frequency rolloff is called "frequency compensation". The gain is reduced to less than 1 at high frequencies where the phase shift of the circuit approaches 180 degrees so that the circuit does not oscillate when negative feedback is applied.
 
Hello all

I wonder if anyone can help me,

Im starting out in the world of digital electronics as part of a work based learning course. As part of an assignment have been asked to investigate the “open loop characteristics of a 741 op-amp”.

Using Multisim I constructed a basic circuit using the 741 op amp and obtained a bode plot very similar to figure 4 in the following link.

**broken link removed**


The question being asked is to “explain the significance of this bode plot”.

Basically the only thing I can gather from this is that as the frequency is increased, the gain decreases, but what I don’t know is the significance of this or an example of where it may be used.

Apologies for the naivety of the question, of which im sure some of you would smirk at :), however any help would be much appreciated in explaining this to me.

Many thanks in advance.


Well let me break it down for you:

OpAmps are a way to amplify a very small signal to large proportions. So for example if I have a sine wave that is 10 miliVolts i can amplify it as much as I want within some constraint.

The image, i.e., Bode (pronounced bow-dee) plot shows the amplitude of the output of a freqency inputted to the amplfier.

Ideally an amplifier, no matter what the frequency, can provide as much amplification as desired. That is not the case, reallistically the amplifier can only provide a finite amount of gain, because it cannot "keep up" with higher frequencies. This can be seen by the downward slop indicating a loss of gain.

the Gain Bandwidth Product (GBP on plot) is a fixed constant that defines the 0db Bandwidth of the signal. GBP = gain * frequency.

There are other things to beware of for OpAmps: Input Bias current, Total Harmonic Distortion, Input Voltage and current noise and saturation voltage.



Sources: My Senior Electrical Engineering Project.
 
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