Multi-Stage Amplifier Project

Thread Starter

bigyanengi

Joined Feb 24, 2024
37
Before you add the third stage, you need to add the cascode (it's pointless, all it will do is reduce the output voltage, but it's in the assignment). Then you needs to add the emitter followers.
Look up "Complementary emitter follower".
Then you need to check you have enough gain and bandwidth before proceeding to part 2 in which you add feedback (as @ericgibbs said in post #38)
What time zone are you in? Perhaps you could fill in the details. Some of us might have been outside enjoying the Spring sunshine!
Hello Ian,
I am in GMT +5:45 hours time zone. The cascode added with the output of what I have?1708875148174.png
 

Thread Starter

bigyanengi

Joined Feb 24, 2024
37
Yes. What have you learned so far about the cascode circuit?
Cascode is a 2 stage common emitter stage where the output is realized from the common collector. The schematics where you told me to delete Q6 and Q7, they were in cacode mode.
 

ericgibbs

Joined Jan 29, 2010
19,026
Hi Ian,
I do find it confusing, there are a number of 'parameters' defined in the original specification which are ambiguous IMO.
I would use a common emitter stage for the 2nd stage.

E
 

Ian0

Joined Aug 7, 2020
10,079
Hi Ian,
I do find it confusing, there are a number of 'parameters' defined in the original specification which are ambiguous IMO.
I would use a common emitter stage for the 2nd stage.

E
I agree with you, but it might need a common base stage attached to it in order to collect the marks!
 

Ian0

Joined Aug 7, 2020
10,079
You have lost the benefit of the current mirror load for the input long-tailed pair. By loading one side only, you have unbalanced the long-tailed pair. Didn't it say you couldn't use resistor loads?
If you connect the emitter of Q2 to the collector of Q1, and replace R1/R2 by constant current sources, you have a folded cascode, but then it's getting really (and unnecessarily) complicated. Save that one for another day.
 

Thread Starter

bigyanengi

Joined Feb 24, 2024
37
But not correctly! Emitters go to the positive supply!
Don't forget the the OUTPUT of the common emitter stage goes to the INPUT of the common base stage.
@Ian0
I feed the first stage output to the base of the Q7, and move to bias the Q6? or feed the first stage output to the common nodeof Q6 collector and Q7's emitter? I am sorry I am getting a little bit confused here.
 

Ian0

Joined Aug 7, 2020
10,079
If you start with the post #41 circuit which has a common emitter output.
The cascode is a common emitter driving a common base - so the output of the common emitter circuit, goes to the INPUT of the common base circuit. The final output is from the output of the common base circuit (which connects to a constant-current load)
 

Thread Starter

bigyanengi

Joined Feb 24, 2024
37
If you start with the post #41 circuit which has a common emitter output.
The cascode is a common emitter driving a common base - so the output of the common emitter circuit, goes to the INPUT of the common base circuit. The final output is from the output of the common base circuit (which connects to a constant-current load)
@Ian0
DO I need to add another pnp transistor to do this modification? If I add lets say pnp Q9, and bias the base and connect the collector to 5v then what should I do with the emitter? I cant connect the emitter with the output coming from Q8 collector.
 
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