Voltage gain: at least 20 dB at mid-band into 600 ohms

Frequency response:

Lower cut-off frequency: 40 Hz

Upper cut-off frequency: 1 MHz

Input impedance: 600 ohms ± 10%

Output impedance: 600 ohms ± 10%

DC supply voltage: 12 V

DC supply current: not more than 15 mA

Output power: not less than 2.0 mW into 600 ohms at mid-band.

The circuit should be based on a 2N2222A bipolar transistor

The circuit is to be fed from a source that has an output impedance of 600 ohms

load of 600 ohms

I have decided on the following setup

I've done a design, but I feel several things are wrong because my resistances are tiny.

First I assumed a quiescent input current ~ 8mA = IC (are these reasonable and how to improve on them??)

quiescent collector Voltage ~ 7V = VC

VCC - DC supply voltage

VE - quiescent emitter Voltage

VBE - voltage of base relative to emitter ~ 0.7V

Rc - collector resistor

Re - Emitter resistor

RL = load resistance = 600 ohms

RS = Source resistance = 600 ohms

VC = VCC - IC*Rc

giving me RC = 625 ohms - so i would use RC = 680 ohms

VC = 6.6v

then I considered the gain, decided on a gain of 10. Including the RL in the gain calculation:

voltage gain = -(Rc//RL)/(Re)

therefore

Re = (Rc//RL)/10 = ((680^-1)+(600^-1))^-1 /10 = 31.9 ohms (this value seems very small to me, so i can tell i've done something wrong). following the calculation I would use a 12 ohm resistor because 10 is the minimum gain, therefore:

voltage gain = -(Rc//RL)/(Re) = -(((680^-1)+(600^-1))^-1 /12= 26.6 gain

next I try and find values for Rb1 and Rb2.

VE = IE*Re= 0.008*12 = 0.1 V

Biasing the base: VE + VBE = 0.1+0.7 = 0.8 V

using the general rule Rb2 ~ 10*Re = 120 ohms

VCC*Rb2/(Rb1+Rb2) = 0.8

Rb1 = (Rb2*(VCC-0.8))/0.8 = (120*(12-0.8))/0.8 = 1680 ohms, use 1.5kohm resistor

I can't help feeling I'm making silly mistakes... how do I check the amplifier meets the specification? I have spent so much time trying to understand this, I really need your help, Thank you...

Stonecrow