...every signal source?Almost every signal source is a fairly high resistance current source.
Yes - no surprise.Here is a common-emitter transistor with a sinewave voltage source. The input is a sinewave but the output isn't:
I don`t think that this is a good argument.. The collector of a previous transistor stage has the resistance of its collector resistor.
Here is a common-emitter transistor with a sinewave voltage source. The input is a sinewave but the output isn't:
Yes, negative feedback reduces gain and distortion.Audioguru - I have played a little with my simulator.
I have used your circuit for two different analyses.
Yes, negative feedback reduces gain and distortion.
With a gain of 1 like a piece of wire then the distortion is nice and low.
Your output is severely clipping. If your input is reduced to a peak of 85mV then the distortion is about half of it is without the 25k input series resistor. The 25k resistor makes a poor current source but it is better than a voltage source.Nevertheless, I hope you got the real meaning of my simulation results.
I have a little supplement:
If you increase the input signal from 25 to app. 120mV - with the series resistor of 25 kohms (as preferred by you) - we get about the same output swing as in your example (post#20) and about the same distortions!!
Question: Where are the advantages of a large source resistance?
Your output is severely clipping. If your input is reduced to a peak of 85mV then the distortion is about half of it is without the 25k input series resistor. The 25k resistor makes a poor current source but it is better than a voltage source.
The transistor is far from clipping (at the top of the waveform) caused by becoming cutoff. Instead it is showing that the base-emitter voltage change causes a logarithmic change in the collector current which is not linear. The bottom of the waveform is actually expanded which is the opposite of the top.Two comments:
1.) Surprisingly, the 2N3904 models in PSpice and LTC differ considerably. I didn`t observe such clipping effects during my simulations with PSpice as shown in your display (left figure).
No, the gain values are exactly the same. The circuit with the 25k series input resistor has its input attenuated by the 25k resistor so of course the input level to this resistor was increased.2.) The comparison of your simulation results as shown in the right-hand figure is rather meaningless. Because:
You are comparing two circuits with different gain values (about the same output, but left: 25mV input, right: 85mV input). The situation will change drastically if you reduce the gain of the left circuit to the same value of the right circuit using emitter feedback (as mentioned in my post#25).
No, the gain values are exactly the same. The circuit with the 25k series input resistor has its input attenuated by the 25k resistor so of course the input level to this resistor was increased.
Since the 25k resistor made a lousy current source I increased it to 470k but then my waveform was clipped at the bottom so I re-biased the transistor slightly to push the waveform up. Now the output levels are the same but the differences in distortion are obvious.
The THD numbers acording to LTspice are 7.4 % (current controlled) versus 1.9 % (voltage controlled with feedback). The original voltage controlled circuit from post #28 has 21.4 % THD.The series input resistor reduced the distortion a lot but the emitter negative feedback looks a little better.
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