Hey everyone! So, in my analog electronics class we just finished CE Amp analysis... and it seems easy enough to calculate gain when you have all the resistors (voltage divider biased). So I decided to implement CE amp in my project... and got in trouble... what resistors should I use?!

My signal source is going to be an RCA-output sound from my XBox. Somewhere on your forum I found that maximum Vrms for RCA-plug sound is 775mV. Converting it to Vpp = 1.096V. I'd like to crank it up to 5Vpp, so gain should equal to 4.899, also it'd be great to "put" that signal on top of a 2.5VDC to have resulting voltages go from 0V to 5V with respect to ground.

The only available Vcc I have is 5V, so I prefer that to stay that way. I can get any transistors, resistors, and capacitors, so I can choose any. Also I plan to feed the output to the Analog-to-digital converter of a microcontroller. I looked in the datasheet, but couldn't find resistance of ADC, so i don't know RL, however I found that "The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or less."

Can you please give me some ideas to start with choosing resistors? I looked online for quite a while, found a bunch of CE amp analysis, but no where - design.

 

You won't get 5V pp out with a 5V power supply. The transistor would have to swing from saturation to cutoff.

 

Well maybe not exaclty from 0V to 5V, maybe from 0.01V to 4.99V, isn't that what Large Signal Amplifier does?

 

Your micro may have a selectable or reference max voltage input for the ADC, lowering this to 1.096v + some offset may be a much simpler option if available. What micro are you intending to use?

 

If you want near rail-to-rail swing from an amplifier, your best bet is to use an op amp with rail-to-rail output capability. With a single transistor amplifier, you will be lucky to get 4V p-p out before the amplifier goes into hard limiting (saturation and cutoff). With 3V p-p out, you will still get over 1% distortion.

 

I simulated a single transistor with a gain of about 5.
Its positive swing is extremely distorted and almost reaches +4.5V.
Its negative swing clips at slightly less than +1V.

Use a rail-to-rail opamp instead.