Do you mean microamps not milliamps?IronaSona said:
The input resistance of a common emitter transistor tends to be around 1 k, so your figure of 95k does not sound correct. A useful website here: https://www.allaboutcircuits.com/textbook/semiconductors/chpt-4/amplifier-impedances/tech99 said:
Nope. That site has a common emitter with no emitter resistor, while the OP has a large emitter resistor. I get that the input impedance looking into the base of Q1 is much larger than 1k Ohm.tech99 said:
Perhaps I did the arithmetic wrong, but at 1 kHz a 50 nF capacitor has an impedance of about -i3185 Ohms, so at 1kHz you cannot treat it as a short.tech99 said:
milivoltstech99 said:
yes sorry milivoltsjasonRF said:
But if i change the resistor to anything else besides 90k to 96k , ill get smaller or bigger output voltage than i want right.?tech99 said:
When I did a back of the envelope calculation I recall getting something between 80k and 90k Ohms. It depends on the assumed gain of the transistor. The spec sheet says between 200 and 450 (that is what the ‘B’ designation means). What does your spice model use? It will be listed as ‘Bf=some number’ in the .model statement.IronaSona said:
Ive tried looking again but couldn't find anything ,but i did find somewhere in my notes which says that RS=RC1=8625 so that means that RS has to be 8625 too right ?jasonRF said:
No, that makes no sense to me.IronaSona said:
The input resistance of a BJT amplifier refers to the resistance seen at the input terminal of the amplifier. It is a measure of how much the input voltage changes for a given change in the input current.
The input resistance of a BJT amplifier is important because it determines the amount of signal that can be effectively transferred from the input to the output. A higher input resistance allows for a greater range of input signals to be amplified, resulting in a more versatile and efficient amplifier.
The input resistance of a BJT amplifier can be calculated by dividing the change in input voltage by the change in input current. It can also be calculated using the formula: Rin = (β + 1) * Re, where β is the current gain of the transistor and Re is the emitter resistance.
The input resistance of a BJT amplifier is affected by several factors, including the type and characteristics of the transistor used, the value of the emitter resistance, and the frequency of the input signal. Additionally, the biasing of the transistor and the configuration of the amplifier circuit can also impact the input resistance.
The input resistance of a BJT amplifier can be increased by using a transistor with a higher current gain, increasing the value of the emitter resistance, and using a common emitter configuration. Additionally, using negative feedback can also increase the input resistance of the amplifier.
