Mumbai University > EXTC > Sem 3 > Analog Electronics 1

Marks: 10 M

Year: Nov 2013

• Parameters of CE configurations are as follows
• Input impedance$(h_{ie})$
• Output admittance$(h_{oe})$
• Reverse voltage gain$(h_{re})$
• Forward current gain$(h_{fe})$
• Input impedance(hie): It is the ratio of change in input or base-emitter voltage$(V_{EB})$ to change in base current $(I_B)$ at a constant output or collector-emitter voltage$(V_{CE})$ $$h_ie=\frac{∆V_{EB}}{∆I_B} , V_{CE}=constant$$
  • It is determined from input characteristics of diode
  • Input characteristics are $I_B$ vs. $V_EB$ at constant $V_{CE}$

Fig1 determining input impedance from Input characteristics

• Procedure

  1. Draw input characteristics curve at some positive value of output voltages
  2. Mark two points on that curve $(X_1,Y_1)$ and $(X_2,Y_2)$
  3. Take the slope of curve between these two points and the answer of slope of curve is input impedance $$h_ie=\frac{∆V_{EB}}{∆I_B} =\frac{Y_2-Y_1}{X_2-X_1 } , V_{CE} =constant$$

• Output admittance $(h_{oe})$: It is the ratio of change in output or collector current $(I_C)$ to change in output or collector-emitter voltage $(V_{CE})$ at a constant base current $(I_B)$. $$h_{oe}=\frac{∆I_C}{∆V_{CE}} , I_B=constant$$

  • It is determined from output characteristic of diode. Output characteristics are $I_C$ vs $V_{CE}$ at a constant $I_B$.

Fig2 determining output admittance from output characteristic

• Procedure

1. Draw output characteristics for some finite positive value of current $I_B$
2. Mark two point $(I_{C1},V_{CE1})$ and $(I_{C2},V_{CE2})$
3. Take slope of a curve between these two points $$h_{oe}=\frac{∆I_C}{∆V_{CE}} =\frac{I_{C2}-I_{C1}}{V_{CE2}-V_{CE1}}, IB=constant.$$
4. Reverse voltage gain $(h_{re})$: It is the ratio of change in base-emitter voltage$(V_{EB})$ to change in collector-emitter voltage$(V_{CE})$ at a constant base current $(I_B)$. $$h_re=\frac{∆V_{EB}}{∆V_{CE}} , I_B=constant$$
   • It is determined from input characteristics of diode

Fig3 determining reverse voltage gain from input characteristics

• Procedure
• Draw input characteristics curve for two different positive collector-emitter voltage

• Draw a constant $I_B$ current line passing through both the curve and mark corresponding base-emitter voltage points on $X-axis (X_1 and X_2)$

  Reverse voltage gain is given by $$h_{oe}=\frac{∆V_{EB}}{∆V_{CE}} =\frac{X_2-X_1}{V_{CE} (6V)-V_{CE} (0V)}, I_B=constant$$

• Forward current gain $(h_{ie})$: It is the ratio of change in collector current$(I_C)$ to change in base current $(I_B)$ at a constant collector-emitter voltage$(V_{CE})$ $$h_{ie}=\frac{∆I_C}{∆I_B} , V_{CE}=constant$$
  • It is determined from output characteristics

Fig4 determining forward current gain from output characteristics

• Procedure
• Draw output characteristics curve for two different finite positive value of voltage VCE

• Draw a constant VCE voltage line passing through both the curve and mark corresponding collector current points on $Y-axis (Y_1 and Y_2)$

  Forward current gain is given by $$h_{ie}=\frac{∆I_C}{∆I_B} =\frac{I_{C2}-I_{C1}}{I_{B2}-I_{B1}} , V_{CE}=constant$$