**CE Circuit with Unbypassed Emitter Resistor:**

**h-parameter Equivalent Circuit –** When an CE Circuit with Unbypassed Emitter Resistor (R_{E}) as shown in Fig. 6-25(a), it is also present in the ac equivalent circuit, [Fig. 6-25(b)].

R_{E} must also be shown in the h-parameter circuit between the transistor emitter terminal and the circuit common input-output terminal, (Fig. 6-26). As with the previous h-parameter circuit, the current directions and voltage polarities shown are those that occur when the instantaneous input voltage is positive-going. The presence of R_{E} without a bypass capacitor significantly affects the circuit input impedance and voltage gain.

**Input Impedance:**

An equation for the input impedance at the transistor base can be determined from υ_{1} and I_{b}. From Fig. 6-26,

Equation 6-20 gives the input impedance at the transistor base terminal. The circuit input impedance is again given by,

Examination of Eq. 6-20 shows that it is possible to very quickly estimate the input impedance at the transistor base in a CE Circuit with Unbypassed Emitter Resistor. For example, a circuit with R_{E} = 1 kΩ and h_{fe} = 100, has Z_{b} ≈ 100 kΩ.

**Output Impedance:**

The output impedance at the transistor collector can be shown to be substantially increased (above 1 / h_{oe}) by the presence of the CE Circuit with Unbypassed Emitter Resistor. Consequently, the circuit output impedance should be taken as,

**Voltage Gain:**

From the derivation of the input impedance equation,

The voltage gain of a CE Circuit with Unbypassed Emitter Resistor can be quickly estimated using Eq. 6-22. For the circuit in Fig. 6-25(a), with R_{C} = 4.7 kΩ, R_{E} =1 kΩ, and R_{L} ≫ R_{C}, A_{υ} ≈ -4.7.

**Performance Summary for CE Circuit with Unbypassed R**_{E}

_{E}

The most significant feature of the performance of a CE Circuit with Unbypassed Emitter Resistor is that its voltage gain is much lower than it would be normally. Its input impedance is also much higher than Z_{i} for a CE circuit that has R_{E} bypassed.