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why we are taking 3 db for calculate the frequency response

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Mkanimozhi

Mkanimozhi

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frequency response 3db

Hi,
why we are taking 3 db in as a point to calculate gain factor in all circuits why can't we take 5 db or 10 db or 20 db and not doing calculations, or where we take 3 db as reference or where we use 5 db.

regards
kanimozhi.m
 

3db frequency response

Mkanimozhi said:
Hi,
why we are taking 3 db in as a point to calculate gain factor in all circuits why can't we take 5 db or 10 db or 20 db and not doing calculations, or where we take 3 db as reference or where we use 5 db.
regards
kanimozhi.m
Click to expand...

Please, feel free to use 4, 7 or how many dB`s you want.
But in this case, it will be problematic to compare the performance of your circuit with other solutions. Therefore, there was a common international agreement to use the 3 dB point (half power point) - if it makes sense !!
However, there are some exceptions from this rule: Normally, the bandwidth of a Tschebycheff like filter response is NOT determined by -3-dB-points. It´s given by the ripple factor.
 

3db points

Most people can hear a 3dB change in sound level. 2dB is a very small change in loudness that some people cannot hear the difference.
4dB is a very noticeable change in loudness.
 

3db in frequency response

Because the 3db point is a convienent point to use. It represents the point at which the output power has dropped to 50%. It is also useful because the 3db point represents a 45 degree phase shift which is a nice number to understand what is going in regards to the bode plot.

The 3db point just works out to nice values. You can use for example, the -5db point. However, it is not clear what that represents without doing math. If someone gives you the 3db point, you can figure out simply how the amp is behaving in a matter of seconds. You can't do that with any other db point. So it is just a convienence to use the -3db point as opposed to any other point.
 

frequency response db

haff99 said:
........... It is also useful because the 3db point represents a 45 degree phase shift which is a nice number to understand what is going in regards to the bode plot.
Click to expand...

Yes, but remember: only for first order circuits !
 

how we calculate db

In the ancient past when hand calculations were used, it was very convenient to get the 3 dB point because the reactance of a series or shunt element had the same magnitude as the real part of the circuit impedance at that point.

In bandpass filter design in the ancient days the 6 and the 60 dB points were frequently used. The bandwidth ratio of these two points was called "shape factor." I can still remember one common example of a Butterworth BPF with eight poles that had a shape factor of 2.
 

bode plot: half power point

"Yes, but remember: only for first order circuits ! "

Thats true but it is a pretty good estimate unless you are really pushing the bandwidth way out.
 

calculate 3db

the reason for this lies in bode plot.bode plot is linearized of the actual curve. the maximum error lies at a point where the two slope curve (say horizontal and -20db slope line) meet. the error b/w ideal and bode plot at this point is maximum and is -3db.

thus 3db point denotes the frequency at which the roll over stats.

hock
 

3db point

if I can remember well, if a signal is halved, a 3 db reduction in the signal amplitude takes place
 

3db point frequencies and bandwidth

at 3db we get half of double of signal power,exectly .7, thats y we consider 3db
 

3 db factor

concerning to gain factor at 3db point ,we will get a stabilized gain .that is the range of frequencies for which gain is constant is more at 3 db point that is why we took 3 db point
 

what is 3db point and how to calculate it?

jerins said:
concerning to gain factor at 3db point ,we will get a stabilized gain .that is the range of frequencies for which gain is constant is more at 3 db point that is why we took 3 db point
Click to expand...

Does anybody understand this contribution ?
At the 3-dB-frequency the gain is only 70% of the maximum gain value. Neither is the gain "stabilized" nor is it "constant".
 

how to calculate 3db

70% of the voltage causes the current also to have a 70% reduction. Then the output power is voltage times current (70% x 70%)= half.
 

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