CE Amplifier
- Thread starter eis4497
- Start date
You'll get more appropriate answers if you show us the schematic for the circuit so we can see where those numbers are coming from.
Sorry. meant to show you the schematic.
Oh. And the output wave starts in a weird place. Like at -120 mV instead of zero.
your voltage gain calculation, seems wrong
Where did these numbers come from? How did you get 3.52? As written, the result is 27.45.
Hi Dennis:
I got the formulas from this electronic tutorial. But the actual schematic is from a textbook.
https://www.electronics-tutorials.ws/amplifier/amp_2.html
Thanks,
John
This is how I arrived at the gain.
r'e = 25 mV / IE = 25 mV / 1.13 mA = 22.1Ω
Gain = RL / (RE + r'e) = 3.6KΩ / (1KΩ + 22.1Ω) = 3.52 This is a far cry from 120.
How did you get 27.45?
r'e = 25 mV / IE = 25 mV / 1.13 mA = 22.1Ω
Gain at low frequencies = RL / (RE + r'e) = 3.6KΩ / (1KΩ + 22.1Ω) = 3.52
Gain at high frequencies = RL / r'e = 3.6KΩ / 22.1Ω = 162.90
What would the threshold be for low vs high frequencies, given an audio range
of 20Hz to 20Khz?
Gain at low frequencies = RL / (RE + r'e) = 3.6KΩ / (1KΩ + 22.1Ω) = 3.52
Gain at high frequencies = RL / r'e = 3.6KΩ / 22.1Ω = 162.90
What would the threshold be for low vs high frequencies, given an audio range
of 20Hz to 20Khz?
This is what you wrote in your original post.
That's different than what y0u later posted.
You didn't label all values or group the operations correctly.
The 1k ohms emitter resistor is bypassed with a 10uF capacitor so they result in 16 ohms at 1kHz. Since re is 22.1 ohms then the total emitter load impedance is 38.1 ohms and the gain at 1kHz should be 3600/38.1= 94.5 times.
At 20Hz, the reactance of the 10uF emitter capacitor is 800 ohms so the gain will be 3600/822= 4.38 times.
At 20kHz the stray capacitance of the circuit is low but a shielded audio cable capacitance might reduce the level of the high audio frequency.
At 20Hz, the reactance of the 10uF emitter capacitor is 800 ohms so the gain will be 3600/822= 4.38 times.
At 20kHz the stray capacitance of the circuit is low but a shielded audio cable capacitance might reduce the level of the high audio frequency.
Thanks.
When I use a directive to modify the 2N3904 transistor specs, Spice says that there is a duplicate definition for the
2N3904. I thought that the directive would override the original definition.
A simulation software "guesses" on the exact spec's of a transistor and picks an average or typical one, not one with minimum or maximum spec's.
But you are supposed to know that the reactance of a capacitor at high frequencies is very low, almost a short circuit to the AC.
But you are supposed to know that the reactance of a capacitor at high frequencies is very low, almost a short circuit to the AC.
What?
Pick a transistor like a 2N3904. Its datasheet shows a range of hFE is from 100 to 300 at a current of 10mA and the hFE might be only 40 at lower or higher current.
You can bias it at the typical hFE of 200 and a simulation (guessing that the typical hFE is 200) will show it working well, but one you buy with a lower or higher hFE will be totally messed up.
You need to design the transistor circuit so it works well when its hFE is low or is high, not just the typical number that a simulation program shows.
The voltage gain at high frequencies is increased when the reactance of the emitter capacitor is in parallel with the emitter resistor.
You can bias it at the typical hFE of 200 and a simulation (guessing that the typical hFE is 200) will show it working well, but one you buy with a lower or higher hFE will be totally messed up.
You need to design the transistor circuit so it works well when its hFE is low or is high, not just the typical number that a simulation program shows.
The voltage gain at high frequencies is increased when the reactance of the emitter capacitor is in parallel with the emitter resistor.
OK Thanks.
