Maker Pro
Maker Pro

impedance of a constant current source

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
8,393
Joined
Nov 28, 2011
Messages
8,393
sabahan, I have attached your new posts to the existing thread that you created on this subject.

Did you learn anything from the reference that Steve linked to in post #16? Your first question on the new thread (post #18) seems to indicate that you didn't.

The schematic in post #20 won't do anything. It looks like you intend to use a current mirror at the bottom, but the bases of the transistors aren't connected to anything else. You need to connect them to the collector of one of the transistors.

Even then, the circuit won't work. You can't use a current source in both the emitter and the collector path. If you do, whichever current source passes the higher current will pull the amplifier transistor's voltages towards it and away from the other current source. At least, it would if the amplifier transistor had any bias on it!

You need to go back to explanations and tutorials, and build an understanding of how transistors work. Then progress to current sources, and current mirrors.
 

sabahan

Jul 14, 2013
31
Joined
Jul 14, 2013
Messages
31
Yes,I had build a Common emitter amplifier with only resistance load and a degeneration resistor,I know how to calculate them,I had try remove either one of them,both create a way to large amplification factor,even with a small input voltage of 50mV P-P and output wave form clip both ends.

if I replace the current mirror with a resistor,I need to increase the resistor to a very large value which make the amplifier useless,it do not have enough current to drive the output stage,same as with the zener diode active load

I have run the simulation in LT spice,but seems that the simulation result is not the same as the actual circuit.The simulation works well but when I buld then,it is a total difference story.

Yes I simulate the setup I post and the output is very small,I thought had did something wrong,I did study some amplifier circuit on the web,some do have the stup I post,I did not simulate or build them,only as a reference
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
8,393
Joined
Nov 28, 2011
Messages
8,393
OK. So what are you trying to do?

You want to build an amplifier circuit using a constant current source as the collector load?

You know that will give a pretty high voltage gain. So you need to feed a low signal level into it, otherwise it will clip, as you said.

In post #13 you said that using a constant current source for the collector load will reduce distortion due to the Early effect. I don't think that's right. Using a current source as the collector load will increase the voltage gain of the stage, but I don't see how it would affect the distortion due to the Early effect. Using a current MIRROR as the collector load WILL reduce distortion due to the Early effect. Is that what you want to do?

Instead of asking very specific questions, try describing what you want to do. Start with the big picture. What's the purpose of your experimentation?
 

sabahan

Jul 14, 2013
31
Joined
Jul 14, 2013
Messages
31
This is what I understand see is I'm correct
If I use only resistor,when I feed a sine wave in,when the wave reach it peak,let say 3V,with a amplification factor of 10,I get a 30 V out,with a collector resistor of 1 k,I get a collector current of 30ma,re will be 0.8 ohm,when the input signal at 0.1V,output signal will be 1V,with a collector current of 1ma,re will be 25 ohm.
If I have a degeneration resistor of 100 ohm,my amplification factor will vary from 9.9 to 9.2,this variation will create harmonic distortion,this is what I read from the book
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
8,393
Joined
Nov 28, 2011
Messages
8,393
I can't make sense of that last post at all.

What are you trying to achieve?

Are you a student?

Can you give me a link to the assignment you're working on?

Can you give links to the other material you have been reading?
 

sabahan

Jul 14, 2013
31
Joined
Jul 14, 2013
Messages
31
I read the book audio power amplifier design,I'm not a student ,just a hobbyist ,I have no background on electronic,or very limited
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
8,393
Joined
Nov 28, 2011
Messages
8,393
OK. As far as I can tell from your comments, especially in post #24, you do not understand how transistors, current sources, current mirrors, and common emitter amplifiers work. You can't just jump into amplifier design without learning the basics. That starts with understanding voltage, current, and resistance. Then you progress to discrete semiconductors - diodes, transistors, MOSFETs. Then you learn about circuit configurations - current sources, current mirrors, transistor amplifier configurations. You should be able to find a lot of what you need to learn on the net. Also, build up some kitsets or project designs (preferably not from instructables.com). If you don't learn all that stuff, you will never be able to understand these circuits or that book.
 

shumifan50

Jan 16, 2014
579
Joined
Jan 16, 2014
Messages
579
@Kris:
Electronics is being treated like programming. Read some book and you can do anything.
 
Top