What am I using? 3 stages of amplification. An input voltage of 10mV peak or 20mV pkpk into the first stage.

1st stage: NJFET Common Source. Using a voltage gain of 3.

2nd stage: NPN BJT Emitter Resister. Using a voltage gain of 30.

3rd stage: NPN BJT Emitter Resister. Using a voltage gain of 30.

What is my problem? I am getting bad clipping on my final output in multisim simulations. The first two stages simulated great. I got a voltage gain of around 68 from the first two stages with no clipping. I know these two stages work correctly. The last stage is where I'm getting my clipping.

Below I will include images of my circuit, my output/input values, as well as my calculations.

Why I need your help I need to get rid of this voltage clipping. Any suggestions would be great. Thanks!





1 Answer 1


I would start by saying that Vcc is not high enough for the amount a gain you are looking for with an amplitude of 0.010V in your input signal and your gains we have 0.010V x 3 x 30 x 30 = 27V of amplitude for your output signal but yet your Vcc its only 15V. The first 2 stages work because 0.010V x 3 x 30 = 0.9V which in Vcc is able to provide

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    \$\begingroup\$ Or, to put it another way, why in the world do you think it shouldn't clip? \$\endgroup\$ Apr 16, 2015 at 3:27
  • \$\begingroup\$ In addition, your choices of resistor values for the bias voltage dividers are bizarre. They should be equal above and below, and large, as they form part of the input impedance of each stage. Try 100k each. You need to bias each stage to about the midpoint of the supply rails. \$\endgroup\$
    – user207421
    Apr 16, 2015 at 8:30
  • \$\begingroup\$ Well I'm only a student so I'm learning, but in all the single stage amplifiers I've made, Rbias1 has always been about 20times smaller than Rbias2. Give or take of course. This has always gotten me a Qpoint on the center of the load line, a Vceq in the center, and pretty close to the maximum power efficiency. That's why I'm starting to think its what the reply above said about trying to exceed the Vcc voltage. I dont know why I over looked that. Thank you for your reply though, and I will take Rbias values into consideration when doing my new calculations. \$\endgroup\$ Apr 16, 2015 at 18:09

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