Analog & Digital Electronics

← Back to document page

Analog & Digital ElectronicsCourse No: PH-218Lec-12: frequency Response of BJT AmplifiersCourse Instructors: Dr. A. P. VAJPEYIDepartment of Physics, Indian Institute of Technology Guwahati, India1High frequency Response of CE Amplifier Athighfrequencies,internaltransistor junction capacitances docome into play, reducing an amplifier'sgain and introducing phase shift asthe signal frequency BJT, Cbeis the B-E junction capacitance, and Cbcis the B-C junction capacitance. (output to input capacitance)(output to input capacitance) At lower frequencies, the internal capacitances have a veryhighreactance because of their low capacitance value (usually only a few pf)and the low frequency value. Therefore, they look like opensand haveno effect on the transistor's performance. As the frequency goes up, the internal capacitive reactance's godown, and at some point they begin to have a significanteffect on the transistor's gain. When the reactance of Cbebecomes small enough, a significant amount of the signal voltage is lost due to a voltage-divider effect of the source resistance and the reactance of frequency Response of CE Amplifier 3 When the reactance of Cbcbecomessmallenough,asignificant amount of outputsignal voltage is fed back out ofphase with the input (negativefeedback),thuseffectivelyreduci ng the voltage Miller effect occurs only in inverting amplifiers it is the inverting

When the reactance of C be becomes small enough, a significant amount of the signal voltage is lost due to a voltage-divider effect of the source resistance and the reactance of C be. High frequency …

  Electronic, Frequency, Analog, Effect, Digital, Analog amp digital electronics