In transistor amplifier theory, compare the input–output phase relationship of two classic single-transistor stages: the common-collector (emitter follower) and the common-base amplifier. Considering a small-signal sinusoidal input, what overall phase shift exists between input and output for these configurations?

Introduction:
The phase relationship between an amplifier's input and output is a foundational concept in analog electronics. It determines whether a stage inverts the signal or preserves its polarity. This question focuses on two important single-transistor configurations—the common-collector (emitter follower) and the common-base—and asks you to identify their net input–output phase shift under small-signal sinusoidal operation.

Given Data / Assumptions:

• Bipolar junction transistor (BJT) operated in its linear region (active mode).
• Small-signal sinusoidal excitation so that incremental models apply.
• Common-collector (input at base, output at emitter) and common-base (input at emitter, output at collector) topologies.
• Biasing is correct so the device does not clip, saturate, or cut off within the signal swing.

Concept / Approach:
For small signals, we analyze the instantaneous relationship of input and output voltages. A stage is noninverting if the output rises when the input rises (0-degree phase shift) and inverting if the output falls when the input rises (180-degree shift). The common-emitter is the classic inverting amplifier. By contrast, the common-collector and common-base stages are noninverting in their usual voltage transfer sense and therefore exhibit approximately 0-degree phase shift.

Step-by-Step Solution:
Common-collector: input at base, output at emitter ≈ base minus a nearly constant V_BE. When the base voltage increases slightly, the emitter follows that increase (emitter follower). Hence the output and input move in phase, implying ~0 degrees.Common-base: input current enters the emitter, and the output is taken at the collector. For a small increase in emitter input voltage (raising emitter current), collector current increases and the collector voltage also moves in the same direction once load effects are considered in voltage gain; the configuration provides noninverting voltage transfer (small-signal output voltage is in phase with the effective input signal).Therefore, both stages are effectively noninverting for voltage, yielding an overall 0-degree phase shift between input and output.

Verification / Alternative check:
Small-signal hybrid-pi analysis confirms that the common-collector has voltage gain slightly less than 1 with positive sign, while the common-base has voltage gain typically greater than 1 with positive sign. Positive sign indicates noninversion, i.e., ~0-degree phase shift.

Why Other Options Are Wrong:
180 degrees: describes the common-emitter, not common-collector or common-base.90 degrees and 270 degrees: phase quadrature does not apply to these real-valued voltage transfer stages.

Common Pitfalls:
Assuming all single-transistor stages invert. Only the common-emitter reliably inverts; the common-collector and common-base are noninverting for voltage transfer.

Final Answer:
0 degrees