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Direct Coupling AC multi-stage Amplifier

Direct Coupling AC multi-stage Amplifier

Direct Coupling AC multi-stage Amplifier

(OP)
Total gain = 500
Power supply = 15 V single ended
Input impedance > 1 Meg Ohm
Output impedance < 15 Ohm

direct-coupled AC using the chips:
2N7000 npn MOSFET
2N2907 pnp BJT
MJE3055 npn BJT Power Transistor

I'm having huge problems with this design.  I'm not sure where to start making assumptions so that I can begin the design process.  If you guys know of any books and/or links that I could go to to get some help it would be great.  Also if you have any suggestions I would appreciate those as well.

Thanks

RE: Direct Coupling AC multi-stage Amplifier

RE: Direct Coupling AC multi-stage Amplifier

md2ece,
  Without meaning to sound like a smart**s - start at the start then work thru the cct.
  Take your 2700 and set it up for a 1 meg input impedance.
Then calc what the gain (Av?) you would have for this cct. This will tell you  what you need the gain of the bjt cct to be. Now the choice is yours, put most of your gain on the 2907 and use the 3055 as the final power drive with an output impdance of 15 ohm.   

RE: Direct Coupling AC multi-stage Amplifier

try with any other npn transistor like bc100. test the circuit with the bc100 transistor.calculate all the parameters Av,Ai,bandwidth, Ri, Ro.try using other feedback paths.voltage series ,voltage shaunt, current series,current shaunt feedbacks.calculate first the gain bandwidth product it should be in the order of MEGA.try then using without feedback & again calculate gain bandwidth product. these two products should be almost same.then try for ratio of voltage gain with and without feedback and ratio of band widths with and without feedback
these two ratios should be almost same.
for all these testing keep your input voltage 20mV.this is the general proceedure of designing any multistage amplifier
try for single stage and then try for two stage at the beginning.
for more theoritical information you can consultthe following book:

ELECTRONIC DEVICES AND CIRCUITS by MILLMAN & HALKIS
TATA-McGRAW HILL PUBLICATION

RE: Direct Coupling AC multi-stage Amplifier

Suggestion:
1. When you look into multistage amplifiers, it makes a big difference whether or not there is an over all amplifier stages feedback loop. Typically, an odd stage amplifier (1-, 3-, 5-stage) with the overall feedback loop has the negative feedback with a tendency to be stable. If you happen to have an even stage amplifier (2-, 4-, 6-stage) with overall positive feedback loop, then this multistage amplifier tends to be unstable. What is sometimes done, one inserts an inverter between the even stage amplifiers with positive overall feedback to stabilize the even-multistage amplifier with the feedback.
2. This used to be a well-known fact during the era of analog computer modeling/programming.

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