High gain from a BJT CE amp with no bypass cap

Thread Starter

automagp68

Joined Nov 13, 2011
81
Is this possible?

I am restricted from using caps for an on chip device

How do i get some gain out of a common emitter without a bypass cap

Obviously the presence of RE in my AC model kills my gain given its multiplex by Beta in the AC model
 

#12

Joined Nov 30, 2010
18,210
The ratio of collector resistor to emitter resistor gives a gain figure. The reason for the capacitor is to make the impedance of the emitter seem to disappear at higher frequencies. Sometimes that means higher than 2 or 3 HZ. It's very negotiable with a capacitor. Very predictable without a capacitor.
 

Thread Starter

automagp68

Joined Nov 13, 2011
81
The ratio of collector resistor to emitter resistor gives a gain figure. The reason for the capacitor is to make the impedance of the emitter seem to disappear at higher frequencies. Sometimes that means higher than 2 or 3 HZ. It's very negotiable with a capacitor. Very predictable without a capacitor.
Yes i understand that. Thats why in my original post i stated that RE without a capacitor for Vo/Vin is multiplied by beta giving you a large denominator hence a small gain.

I can't have a large difference in RC and RE giving me the typical ratio to rely on given the fact that I'm restricted to a 15V supply and need a 7.5 +- swing.

So what do i do. Any thoughts
 
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Thread Starter

automagp68

Joined Nov 13, 2011
81
Typically, something drives design requirements. The aren't supposed to be arbitrary. Good luck.
These are the specifics i was given. What more do you want me to say about it?
I was told no bypass caps do to It being ON chip
As i said in the above post #1

I was asking for assistance given these parameters. I wasn't asking for someone to come on and question why the parameters are what they are?????
 

KL7AJ

Joined Nov 4, 2008
2,225
Is this possible?

I am restricted from using caps for an on chip device

How do i get some gain out of a common emitter without a bypass cap

Obviously the presence of RE in my AC model kills my gain given its multiplex by Beta in the AC model
You can eliminate the emitter resistor entirely, but you will need to devise some other form of thermal stabilization.
 

Brownout

Joined Jan 10, 2012
2,390
You can eliminate the emitter resistor entirely, but you will need to devise some other form of thermal stabilization.
That can be done with a long tail pair. The emitter AC load is the grounded base transistor.
 
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Thread Starter

automagp68

Joined Nov 13, 2011
81
That can be done with a long tail pair. The emitter AC load is the grounded base transistor.
Can you explain in a little more depth?

I thought a long tailed pair was a diff amp?

Here is what i got so far which isn't much obviously.
The bottom bjtis just a 1mA current source as I'm sure you all have seen before




This circuit is yielding a gain of 80 on paper and around 60 or so in the sim

Any suggestions on where to go form here are much much appreciated.
 

Bordodynov

Joined May 20, 2015
2,632
See Gain=1500
This gain for small signals (less than 0.1 mV). By increasing the signal going soft limit. When the signal amplitude 20 mV gain of approximately to 150.

Joke.png

Plot change the output amplitude and the gain on the input amplitude

Plot1.png
 
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