Transistor bypass capacitor for specific frequency

In summary, the equation fl=1/2πC(r_i+R_L) is applicable to both single and two-stage amplifiers and can be used to calculate the value of the capacitor needed for the amplifier in Fig. 4.14a to amplify signals down to 30 Hz. It is important to consult your textbook or professor for more information on this topic.
  • #1
oddjobmj
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Homework Statement



To circumvent the negative feedback needed for thermal stability and to avoid the accompanying reduction of gain, a bypass capacitor CE needs to be placed in parallel with an emitter resistor RE, such as in Fig. 4.14a, cf. Fig. 18a. Determine what capacitor needs to be used for the amplifier in Fig. 4.14a if the amplifier is to amplify signals down to 30 Hz.

Fig 4.14a:

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Homework Equations



fl=[itex]\frac{1}{2πC(r_i+R_L)}[/itex] (?)

The Attempt at a Solution



The equation above is the only seemingly relevant equation I can find in the book. The main issue I have with it is that it is used with a two-stage amplifier whereas the question is asking about a single stage. Can this work for both? If so, I'm not sure what my equivalent ri and RL are.

Am I even on the right track? We haven't covered this in class, I can't find it in the book, and my google searches aren't yielding anything.
 
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  • #2


Thank you for your question. I understand your confusion about the equation and its applicability to a single stage amplifier. Let me clarify a few things for you.

Firstly, the equation you have mentioned is indeed applicable to both single and two-stage amplifiers. The only difference is that in a single stage amplifier, the input resistance ri will be the resistance of the input source, while in a two-stage amplifier, it will be the combined resistance of the first stage and the input source.

Secondly, the equation is used to calculate the lower cut-off frequency, which is the frequency below which the signal will be attenuated. This is important in your case because you need to amplify signals down to 30 Hz. So, based on the equation, you can calculate the value of the capacitor needed to achieve this frequency.

Lastly, I would recommend consulting your textbook or your professor for more information on this topic, as it seems to be a crucial concept in your course. I hope this helps clarify your doubts. Good luck with your studies!
 

FAQ: Transistor bypass capacitor for specific frequency

What is a transistor bypass capacitor?

A transistor bypass capacitor is a type of electronic component that is used in circuits to filter out unwanted high frequency noise. It is placed in parallel with the collector-emitter junction of a transistor to provide a low impedance path for high frequency signals to the ground, effectively bypassing the transistor.

Why is a bypass capacitor necessary for specific frequency?

A bypass capacitor is necessary for specific frequency because it helps to reduce the high frequency noise that may be present in the circuit. This is particularly important for sensitive electronic devices, as high frequency noise can interfere with the proper functioning of the circuit or cause distortion in the output signal.

How do I choose the right bypass capacitor for a specific frequency?

Choosing the right bypass capacitor for a specific frequency depends on the desired frequency range of the circuit and the capacitance value of the capacitor. Generally, a larger capacitance value is required for lower frequencies, while smaller capacitance values are suitable for higher frequencies. It is also important to consider the voltage rating and tolerance of the capacitor.

Can I use any type of capacitor as a bypass capacitor for a specific frequency?

No, not all types of capacitors can be used as bypass capacitors for a specific frequency. Ceramic capacitors are typically preferred for high frequency applications due to their low inductance and high frequency response. Electrolytic capacitors, on the other hand, are better suited for lower frequencies and have a higher tolerance for voltage fluctuations.

What happens if a bypass capacitor is not used for a specific frequency?

If a bypass capacitor is not used for a specific frequency, high frequency noise can pass through the circuit and cause interference or distortion. This can lead to malfunctions or incorrect readings in electronic devices. Additionally, without a bypass capacitor, the transistor may not function properly and could potentially overheat or fail.

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