# Building 3 Stage amplifier, Couple Questions

General question, how can I improve it? or make it more efficient? mabye there is something im missing...

Questions:

1. How can I deliver more dc voltage to the load? how do I improve my swing, im getting around 5.5volt
2. How can I improve the voltage distortion when increasing voltage input?
3. My phase is shifted in the output? tried to increase C7 didnt help.
4. How to improve BW and CMRR?
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• I'd lightly bias those emitters (of Q2 and Q4) to +6volts; use two resistors, each of 10Kohms. By the way, with only one input, CMRR is meaningless. – analogsystemsrf Jan 2 at 16:02
• Your bandwidth limitation is probably R29 and the Miller Input capacitance of that high-gain common-emitter stage. – analogsystemsrf Jan 2 at 16:05
• Why isn't global NFB applied to $Q_{11}$?? – jonk Jan 2 at 19:07

Maybe something like this

simulate this circuit – Schematic created using CircuitLab

You have to decide if the entire amplifier (gain of 10,000) is viable.

1) Can the non-Darlington Q1/Q2 be a light enough load that Q5 (transconductor) and Q7 (stiff current source/load) will provide 100X gain?

2) can you achieve another gain of 100X in a diffpair, if the load is D1+R4

3) how to achieve negative feedback

4) how to generate a BODE plot, so you can examine the gain margin and the phase margin

5) how to compensate the entire amplifier, even if the load (not shown) happens to be a reactive (inductive, capacitive) loud speaker load of 16 ohms?

6) does the output swing around GROUND (so you need +- 12volts, or you need a large output DC_blocking cap (not shown))

7) how to bias the input?

8) is base of Q3, or of Q4, the input?

9) what is the low-end rolloff, if C2 and R9 set that highpass response?

If you use a resistive load on a common-emitter stage, the most gain you can get in one stage is VDD/0.026 volts. Thus 26volts allows a gain of 1,000. Your use of two gain stages, assuming resistive loads, seems reasonable, indeed mandatory.

But with current-source "active" loads, the gain can be much higher, limited by EarlyVoltage and/or the "hie" feedback from collector-to-base.

Something like this can produce massive gain in just one stage

simulate this circuit – Schematic created using CircuitLab

Probably need a BIG capacitor across R9, to get highest gain. And will not be precise gain.