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-   -   Distortion through Early Effect - mainly low Order or high Order Components ? (http://www.diyaudio.com/forums/solid-state/159024-distortion-effect-mainly-low-components.html)

tiefbassuebertr 19th January 2010 06:46 PM

Distortion through Early Effect - mainly low Order or high Order Components ?
 
Jim Early first characterized this effect due to an effective decrease in the base width by BjT's because of the widening of the base-collector depletion region, resulting in an increase in the collector current with an increase in the collector voltage.
What kind of distortions are to expect, if the Early effect is very strong (large values of early voltage VA) ?
Is it rather even-numbered or odd-harmonic?
so as more low order or high order distortions?
Thank you for your comments.

here some informations from Mr. James M. Early:
James M. Early

darkfenriz 19th January 2010 06:51 PM

Mainly second harmonic, goes up with current a lot.

lineup 16th May 2018 07:04 AM

What can be done to reduce Early Effect in Wilson current mirror?
I want to see some examples, circuits.

mchambin 16th May 2018 07:30 AM

Quote:

Originally Posted by tiefbassuebertr (http://www.diyaudio.com/forums/solid-state/159024-distortion-effect-mainly-low-components-post2053803.html#post2053803)
Early effect is very strong (large values of early voltage VA)

it is the other way around.
About distortion: The Early effect doesn't induce distortion. From the look of Ic versus Vce where you can locate - Va that characterize the Early effect you can see it doesn't introduce non linearity in the curves.

Elvee 16th May 2018 08:22 AM

Typical misinterpretation: because the characteristics looks linear does not imply that E.E. is a linear effect: to qualify for this, the characteristics should remain parallel for different base currents, which they don't: they all converge towards a (hopefully) single point, which happens to be the Early voltage.
This implies that the output resistance varies with current.

Early effect is the main distortion cause in the low-power, voltage amplification stages of an amplifier

mchambin 16th May 2018 09:25 AM

I do ont agree. I see dV/dI = constant.
Distortion does not come from Early effect per se. This so called distortion is an indirect effect.

Elvee 16th May 2018 11:18 AM

In order to produce a voltage variation at its output, an amplifying stage needs to modulate its current; since the synthetic output resistance resulting from the Early effect varies with the level of current (as shown by the different slopes of the characteristics), it generates non-linearities... But you are entitled to your opinion...

mchambin 16th May 2018 03:21 PM

Forget my opinion.
It all depends, how one understands: "Distortion through Early Effect".

Mark Johnson 16th May 2018 03:43 PM

Easy enough to measure. Just connect a series RC between collector and emitter. The R is effectively in parallel with the transistor's hybrid pi "ro" (incremental signal Early effect), thus you have externally modified the Early effect. The series C is simply a DC blocking capacitor. Choose C >= 1/[(6 rad/sec)*R] and you'll be fine.

Measure distortion without and with the series RC. Does distortion go up, go down, or stay the same, when you increase the Early effect by decreasing "ro" ??

Elvee 16th May 2018 04:14 PM

Quote:

Originally Posted by mchambin (http://www.diyaudio.com/forums/solid-state/159024-distortion-effect-mainly-low-components-post5435070.html#post5435070)
I do ont agree. I see dV/dI = constant.
Distortion does not come from Early effect per se. This so called distortion is an indirect effect.

No matter how you turn the problem: to generate non-linearities, you need a source of non-linearity, ie. some parameter varying with the signal level, and the Early effect is the origin of this non-linearity, because it is a non-linear phenomenon.

If you model an amplifier using the small signal transistor model (current sources, resistances and conductances), there is no way to generate distortions.
Adding the Early effect makes the output conductance (or resistance) non-linear and causes distortions.

The Early effect can also be seen as a β increase when Vce increases, which is a non-linear effect, exactly like the voltage across a diode increases its conductance, just more subtle. Of course, you can try to argue that this too is an indirect effect...


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