Help - Amplifier Frequency Voltage relationship

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Discussion Overview

The discussion revolves around the relationship between frequency and output voltage in amplifiers, particularly focusing on the reasons for voltage drop outside the amplifier's bandwidth. It includes technical explanations and conceptual clarifications related to impedance and component behavior in amplifiers.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant asks why the output voltage of an amplifier decreases when the frequency is outside its bandwidth.
  • Another participant suggests that the capacitance of amplifier components affects their ability to respond to high-frequency inputs, leading to a voltage drop.
  • A further explanation involves impedance analysis, noting that the impedance of capacitance decreases with increasing frequency, which contributes to the gain reduction in the frequency response plot.
  • One participant highlights the importance of inductance in amplifiers, suggesting it also plays a significant role in the frequency response.
  • A later reply acknowledges the role of impedance in affecting voltage output and expresses newfound clarity regarding the frequency-impedance relationship.

Areas of Agreement / Disagreement

Participants generally agree that impedance is a key factor affecting output voltage, but there are multiple views on the specific contributions of capacitance and inductance, indicating that the discussion remains somewhat contested.

Contextual Notes

The discussion does not resolve the complexities of how capacitance and inductance interact within amplifiers, nor does it clarify the specific conditions under which these effects become significant.

Simon M
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Can someone help me by describing why the output voltage drops away in an amplifier when the frequency is above or below the bandwidth?
 
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The easist explanation is that the components of the amplifier have capacitance, and that capacitance takes time to charge and discharge. Essentially, the amplifier is not able to swing its output fast enough to keep up with a high-frequency input.

- Warren
 
The in-depth explanation is that if you do an impedance analysis of the amplifier, and get the frequency response plot of the amplifier, you have the answer to your question. In amplifiers, there is always the capacitance effect, and capacitance impedance drops as the frequency of the input signal increases. (NB: Z=1/jwC where w=angular frequency of the signal) So the gain of the amplifier in the frequnecy response plot will fall to zero as w increases. The physical explanation of why the capacitance drops as frequency increases has been explained by chroot.
 
Last edited:
Don't forget inductance. It plays a large part in some amplifiers.
 
Hey...Thanks.

It was clear that impedance is a main contributing factor that effects voltage output but I was unsure about the relationship between frequency and impedance. Got it now!
 

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