Class A Common Emitter Amplifier

This amplifier circuit can be used to enlarge small signals (possibly from a sensor or receiver). This may enable the circuit designer to power a larger device with a weak input signal. Additionally, the output is technically DC and will therefore be suitable for use with speakers and audio systems. This is due to the amplifier being biased at approximately half of the supply voltage(does not cross 0V). The design parameters of this circuit are as follows: Voltage gain = -5 Maximum output voltage swing = 10V pk-pk (before clipping) Vcq = 6.5V Icq = 1mA To design your own CE amplifier you can follow these steps. -Decide on your supply voltage (Vcc) I chose 12V here as it is a common supply voltage. -Decide how much voltage gain you require for the signal I chose 5x here but it really depends on the application. The CE amplifier will invert the output signal, so it is really -5x gain. -Determine the maximum output voltage swing. If using a sinusoidal signal this will be the pk-pk output value. This must be smaller than the supply voltage Vcc. -Once you have decided on the above parameters, simply use the following equations to work out the resistor values. Vcq(bias point of output signal) = Vcc-(half of maximum output voltage swing) Vc(collector voltage) = Vcc-Vcq Rc(collector resistor) = (Vcc-Vc)/Ic Ic=collector current = any value(1mA is good) Re(emmitter resistor) = Rc/gain Ve(emmitter voltage) = ic*Re Vb(base voltage) = Ve+0.7 R2(bottom left) = 10*Re R1(top left) = [R2*(Vcc-Vb)]/Vb The capacitors are just there to block the DC voltage and isolate AC signals. I hope that the above helps. Should be an easy enough process if you follow the equations through from start to end. Otherwise, there are plenty other guides on how to do this. Enjoy!

published 4 years ago