How many degree phases have been shifted from input to output in common emitter configuration?
Common Emitter Configuration Phase Shift
The common emitter (CE) configuration is one of the most widely used transistor amplifier configurations. In this configuration, the input signal is applied between the base and emitter, and the output signal is taken between the collector and emitter. The emitter terminal is common to both the input and output circuits, hence the name "common emitter".
When a transistor is used as an amplifier in the common emitter configuration, there is a specific phase relationship between the input signal (applied to the base) and the output signal (taken from the collector).
Understanding the Common Emitter Phase Shift
Let's consider the operation of a transistor in the active region in a common emitter configuration. When a positive-going signal is applied to the base (increasing base current \(I_B\)), this causes an increase in the collector current \(I_C\) (since \(I_C \approx \beta I_B\)).
Now, consider the output circuit. The output voltage \(V_{out}\) is typically measured across a collector resistor \(R_C\) in series with the collector supply voltage \(V_{CC}\). The relationship is often given by \(V_{out} = V_{CC} - I_C R_C\).
- When the input signal goes positive, \(I_B\) increases.
- Increasing \(I_B\) leads to an increase in \(I_C\).
- According to \(V_{out} = V_{CC} - I_C R_C\), if \(I_C\) increases, \(V_{out}\) decreases (since \(V_{CC}\) and \(R_C\) are constant).
- Therefore, a positive change in the input signal results in a negative change in the output signal.
Conversely, when the input signal goes negative, \(I_B\) decreases, causing \(I_C\) to decrease. A decrease in \(I_C\) leads to an increase in \(V_{out}\). So, a negative change in the input signal results in a positive change in the output signal.
This inverse relationship between the input and output signals means that the output signal is 180 degrees out of phase with the input signal in a common emitter configuration.
Phase Shift in Common Emitter Amplifier
In summary, the common emitter configuration provides current gain and voltage gain, but it introduces a phase inversion between the input and output voltages. The output voltage waveform is effectively an inverted version of the input voltage waveform.
The amount of phase shift from the input to the output voltage in an ideal common emitter amplifier operating in its linear region is consistently 180 degrees.
Important Questions from Configuration of BJT
BC147 is the transistor used for:
- What is the relationship between the common-emitter current gain ($\beta$) and the common-base current gain ($\alpha$) of a bipolar junction transistor (BJT)?
Which of the following is NOT true for a common collector transistor?
The other name for the common collector amplifier is -
Match List I with List II:
List I
(Bias Configuration of BJT)
List II
(Stability factor equation)
(A) Fixed Bias Configuration (I) S(V BE ) = \(\rm −\frac{\beta/R_E}{\beta+R_{TH}/R_E}\) (B) Emitter Bias Configuration (II) S(V BE ) = −β/R E (C) Voltage Divider Configuration (III) S(V BE ) = \(\rm −\frac{\beta/R_C}{\beta+R_E/R_C}\) (D) Feedback Bias Configuration (IV) S(V BE ) = \(\rm −\frac{\beta/R_E}{\beta+R_B/R_E}\) Choose the correct answer from the options given below :
