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Distortion through Early Effect - mainly low Order or high Order Components ?
Distortion through Early Effect - mainly low Order or high Order Components ?
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Old 19th January 2010, 06:46 PM   #1
tiefbassuebertr is offline tiefbassuebertr  Germany
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Default 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
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Old 19th January 2010, 06:51 PM   #2
darkfenriz is offline darkfenriz  Poland
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Mainly second harmonic, goes up with current a lot.
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Old 16th May 2018, 07:04 AM   #3
lineup is offline lineup  Sweden
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What can be done to reduce Early Effect in Wilson current mirror?
I want to see some examples, circuits.
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Old 16th May 2018, 07:30 AM   #4
mchambin is offline mchambin  France
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Quote:
Originally Posted by tiefbassuebertr View Post
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.
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Old 16th May 2018, 08:22 AM   #5
Elvee is offline Elvee  Belgium
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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
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Old 16th May 2018, 09:25 AM   #6
mchambin is offline mchambin  France
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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.
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Last edited by mchambin; 16th May 2018 at 09:28 AM.
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Old 16th May 2018, 11:18 AM   #7
Elvee is offline Elvee  Belgium
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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...
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Old 16th May 2018, 03:21 PM   #8
mchambin is offline mchambin  France
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Forget my opinion.
It all depends, how one understands: "Distortion through Early Effect".
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Old 16th May 2018, 03:43 PM   #9
Mark Johnson is offline Mark Johnson  United States
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Distortion through Early Effect - mainly low Order or high Order Components ?
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" ??
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Old 16th May 2018, 04:14 PM   #10
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by mchambin View Post
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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