For a lab class we were assigned a final project where we have to design an amplifier using BJTs, diodes, and capacitors (MOSFETs are not allowed) in order to drive an 8-ohm speaker. The requirements given are as follows:
- that we were to be able to have gain adjust control for a certain range
- use 9 volts VCC and must not use voltage dividers, instead use current mirrors
- we must attain at least a certain voltage for a certain peak to peak sine wave input for a certain frequency range when gain adjust control is set to maximum, therefore there must be a minimum gain for the range of frequencies that our amplifier will support
- we are not allowed to use any op-amps, except to invert signals should we choose to use differential amplifiers
- there must be no clipping for a certain peak-to-peak sine wave input when gain adjust control is set to maximumm
I didn't include the exact specs for our final project in this question, since I think that isn't allowed isn't it? But our group's problem is how to approach this from a design perspective.
Our idea is to use a CE-CC configuration, but obviously this is a too basic thought.
I think it just so happened that all three of us always just thought of it from an analysis perspective. Or we all need to study more haha, which is actually true too.
We don't even know about A-B power supply configurations (is my terminology right)? Since it hasn't been discussed yet. Maybe in another class. I'm not sure if we were supposed to come up with a similar thing on our own using diode connected transistors or something, since we didn't cover using diodes in this class. This class is mainly about analyzing BJT and MOS configurations by the way, and their frequency responses.
So a guide on how to approach doing this would be great! So that we would at least know how to start doing this. Maybe we're also lacking insight on how does one actually drive an 8 ohm speaker... I mean we've already done this in lab, but how does it actually manage to emit sound? Is it because of the varying voltage due to the small-signal voltage introduced to the circuit? What would happen if a DC voltage is what's passing through the speaker? (We tried simulating a configuration in SIMetrix, and we made a mistake somewhere where the output voltage (the one across the speaker), is a constant DC level, so obviously we made a mistake somewhere). A clarification on how this actually works would be nice too :D Thanks to anyone who'll help!
[EDIT: Since people are commenting that I should include the requirements from the specs, I'll do so. I was hesitant to include these because it's classwork. But I suppose I really am being vague, and you guys are good judges on how to help me since you know what to do about this. Sorry for the oversight :(]
- must drive an 8 ohm speaker
- BJTs allowed: 2n3904, 2n3906, 2n4401, 2n4403
- gain adjust control must be 50 to 250
- 9V VCC and don't use voltage dividers
- peak to peak voltage across the speaker must be at least 1v for a 20mV peak-to-peak sine wave input, for frequencies ranging 500Hz to 20kHz when gain adjust control is set to maximum. So the amp must have a gain of at least 50 for frequencies ranging from 500Hz to 20kHz
- the amplified signal must be free of clipping for a 20mV peak-to-peak sine wave input when gain adjust control is set to maximum]