Question

Effect of feedback connection on input and output impedance :
• [A.] Input impedance increases in voltage-series configuration
• [B.] Input impedance increases in current-series configuration
• [C.] Input impedance increases in current-shunt configuration
• [D.] Output impedance decreases in voltage-shunt configuration
• [E.] Output impedance decreases in current-series configuration Choose the correct answer from the options given below :

• A. B, C, D only
• B. A, B, D only
• C. A, B, E only
• D. B, D, E only

Hint:

Remember:
• Series mixing \(\rightarrow\) increases input impedance
• Shunt mixing \(\rightarrow\) decreases input impedance
• Voltage sampling \(\rightarrow\) decreases output impedance
• Current sampling \(\rightarrow\) increases output impedance

Answer 1

The Correct Option is B

Concept: Feedback amplifiers are classified according to:
• Method of sampling at output
• Method of mixing at input The four basic feedback topologies are:
• Voltage-Series
• Voltage-Shunt
• Current-Series
• Current-Shunt Important rules:
• Series mixing increases input impedance.
• Shunt mixing decreases input impedance.
• Voltage sampling decreases output impedance.
• Current sampling increases output impedance.

Step 1: Analyze statement A. Statement A: \[ \text{Input impedance increases in voltage-series configuration} \] Voltage-series feedback uses:
• Series mixing at input Series mixing increases input impedance. Hence: \[ A \text{ is correct} \]

Step 2: Analyze statement B. Statement B: \[ \text{Input impedance increases in current-series configuration} \] Current-series feedback also uses:
• Series mixing at input Therefore input impedance increases. Thus: \[ B \text{ is correct} \]

Step 3: Analyze statement C. Statement C: \[ \text{Input impedance increases in current-shunt configuration} \] Current-shunt configuration uses:
• Shunt mixing at input Shunt mixing decreases input impedance. Hence: \[ C \text{ is incorrect} \]

Step 4: Analyze statement D. Statement D: \[ \text{Output impedance decreases in voltage-shunt configuration} \] Voltage sampling causes output impedance to decrease. Hence: \[ D \text{ is correct} \]

Step 5: Analyze statement E. Statement E: \[ \text{Output impedance decreases in current-series configuration} \] Current sampling increases output impedance. Therefore: \[ E \text{ is incorrect} \]

Step 6: Determine correct combination. Correct statements are: \[ A,\ B,\ D \] Hence correct option is: \[ \boxed{(B)} \]