The gain fall off due to the fact that the coupling capacitors and the bypass capacitors no longer behave as a short circuit and thus gain becomes as a function of frequency:. When f increases X c decreases hence no short circuit.
Thus to improve the response both the coupling and bypass capacitor should be very high. Mid-Band frequency:. In this frequency, over which the amplification is reasonably constant and equal to A 1 , and over which the delay quite remains constant. High frequency:. The ratio of Gain A 2 at high frequency to the mid-band gain A 0. Start Learning. This question was previously asked in. Attempt Online. Increasing the value of the coupling capacitor only Increasing the values of the bypass capacitor and coupling capacitor Increasing the value of bypass capacitor only Decreasing the value of the coupling capacitor.
Answer Detailed Solution Below Option 2 : Increasing the values of the bypass capacitor and coupling capacitor. Start Now. Low Frequency 2. Mid-frequency 3. Note: Mid-Band frequency: In this frequency, over which the amplification is reasonably constant and equal to A 1 , and over which the delay quite remains constant. Get Started for Free Download App. More Frequency Response Questions Q1.
In the above circuit the optimum low frequency compensation is obtained when. The inductance LF and resistance RF in the above circuit is used for. In an RC coupled transistor amplifier 1. Low-frequency response is determined by coupling capacitors. High-frequency response is determined by junction capacitances. However, if the frequency increases, more signal passes through them instead of going in the base branch of the transistor, therefore decreasing the voltage gain.
A very important formula is given in Equation 3 and links the cutoff frequency of a RC filter :. First of all we consider the input high-pass filter R in C 1.
As explained in previous tutorials, R in is the total input impedance of the amplifier. The low cutoff frequency of the bypass structure is thus :. One last thing we need to understand before plotting the Bode graph is about the slope out of the midrange values.
This value means for high-pass filters resp. When multiple filters are blocking the same range of frequencies, the roll-off is enhanced. This information can be synthesized in a Bode plot showing the low frequency response of the CEA in asymptotic representation :.
High frequency response As stated previously, it is the internal transistor capacitors that will limit the gain at high frequencies acting as low-pass filters. It can be shown that the equivalent circuit of Figure 2 at high frequency can be drawn such as presented in Figure 5 :.
We can note that the coupling capacitors are not represented since they behave as short circuits at high frequencies. Moreover, the emitter branch is shorten to the ground for the same reason applying to the bypass capacitor. The information given here is summarized in a Bode plot representing the high frequency response of the CEA in asymptotic representation :. Conclusion We have presented some key-concepts such as the decibel unit and the cutoff frequency in order to understand the idea of frequency response.
We have seen that many different types of capacitors influence both the low and high frequency response of amplifiers. Coupling and bypass capacitors indeed limit the low frequency response whereas the internal transistor capacitors limit the high frequency response. In the two last sections, we show a step by step method to determine separately the low and high frequency response of a typical CEA configuration. By merging the two Bode graphs obtained for the low and high frequency responses in Figure 4 and 6 , we can now plot the overall frequency response of the CEA configuration :.
Frequency Response of Amplifiers Boris Poupet bpoupet hotmail. Introduction As such for any electronic circuit, the behavior of amplifiers is affected by the frequency of the signal on their input terminal. Definitions Before defining in details the frequency response, we need to present the unit of decibel dB and the logarithmic scale related to it.
A simplified Bode graph of an amplifier is shown in the Figure 1 below : fig 1 : Typical Bode graph of an amplifier. More tutorials in Amplifiers. Connect with. I allow to create an account. When you login first time using a Social Login button, we collect your account public profile information shared by Social Login provider, based on your privacy settings. We also get your email address to automatically create an account for you in our website. Once your account is created, you'll be logged-in to this account.
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