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?

 

Hello Ian,
I am in GMT +5:45 hours time zone. The cascode added with the output of what I have?View attachment 316151

Yes. What have you learned so far about the cascode circuit?

 

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.

 

• Second stage: common-base to realize, with the output of the first stage, a cascode stage with
current < 1mA

Hi big,
The problem states that the 2nd Stage is a Common Base cascode.
E

 

Yes. What have you learned so far about the cascode circuit?

Would this cascode be dieal? However, My waveform is square spikes.

 

Hi big,
The problem states that the 2nd Stage is a Common Base cascode.
E

Hi Eric,
Should I remove the Q8 and Q6 and with state 1 output add the cascode and then cascode output to the emitter follower?

 

Hi big,
The problem states that the 2nd Stage is a Common Base cascode.
E

@ericgibbs , do you find that either confusing or tautologous? A cascode is, by definition, a common emitter stage driving a common base stage (originally common cathode driving common grid).

 

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

 

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!

 

The lower end of Rb and R1 should go to the negative supply, not ground. The top of Ra should go to ground.
How did you calculate R1? Isn't it supposed to have 5mA through it?
Then do the same for Q8, to set the output current.

Ian & @ericgibbs
How about this one?

 

Go back to post #41 and add another 2N3906 (plus a couple of resistors to bias it) to make a cascode.

 

Ian & @ericgibbs
How about this one?
View attachment 316164

 

Go back to post #41 and add another 2N3906 (plus a couple of resistors to bias it) to make a cascode.

@Ian0 , this is what I get.

 

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.

 

@Ian0 , this is what I get. View attachment 316166

Wrong way round! The common emitter stage drives the common base stage: Q6 collector goes to Q7 emitter.
But you will still have a squarewave, because you are inputting 10mV and expecting a gain of 5000!

 

Wrong way round! The common emitter stage drives the common base stage: Q6 collector goes to Q7 emitter.
But you will still have a squarewave, because you are inputting 10mV and expecting a gain of 5000!

@Ian0
I amended the design.

 

@Ian0
I amended the design. View attachment 316168

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.

 

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.

 

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)

 

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.