Basic Electronics Paper 2, WASSCE (PC), 2016

 

  • Question 5

    (a) State the class of power amplifiers preferred in the following ranges:
          (i) 20 Hz to 20kHz;
          (ii) 88MHz to 108MHz.

    (b) State two:
    (i) types of coupling used in multistage amplifiers;
    (ii) properties for each of the coupling types in (b)(i).
    (c) State one application of each of the coupling types in b(i).

  • Observation

          The expected answers were;

     

     

    (a)        (i)         Class A, B or AB                             
                (ii)        Class C                                                                                                  
    (b)        (i)         Types of coupling:
                            -  RC coupling                                                            
                            -  Transformer coupling                                                   
                          -  DC coupling                                                 
                (ii)        Properties – RC

    • Uses capacitor for coupling
    • Couples a.c.
    • Wide bandwidth/good frequency response
    • d.c. isolation between stages/blocks d.c.
    • Cheap                                                    

                            Transformer coupling

    • Coupling is by transformer
    • Low power loss/high efficiency
    • d.c. isolation
    • High gain
    • Impedance matching                    

                           Direct Coupling (DC)

    • Does not isolate d.c. signals
    • Stages are coupled directly
    • Amplifies d.c. signals/low frequency signals
    • Circuit is simple and cheap
    • Not suitable for high frequency      

                                
    (c)        Application:
    RC coupling
    -  as voltage amplifier
    -  as pre-amplifiers                                           
                Transformer coupling
    -  Power amplifiers
    - Impedance matching                             
    D.C. Coupling
    - low frequency amplification
    - d.c. amplification
    - differential amplifiers                                
    Many candidates could not state the types of coupling in multistage amplifiers; hence, failed to state their properties.                  

    (a)        (i)         Class A, B or AB                             
    (ii)        Class C                                                                                                  
    (b)        (i)         Types of coupling:
    -  RC coupling                                                            
    -  Transformer coupling                                                   
    -  DC coupling                                                 
    (ii)        Properties – RC

    • Uses capacitor for coupling
    • Couples a.c.
    • Wide bandwidth/good frequency response
    • d.c. isolation between stages/blocks d.c.
    • Cheap                                                    

                            Transformer coupling

    • Coupling is by transformer
    • Low power loss/high efficiency
    • d.c. isolation
    • High gain
    • Impedance matching                    

                           Direct Coupling (DC)

    • Does not isolate d.c. signals
    • Stages are coupled directly
    • Amplifies d.c. signals/low frequency signals
    • Circuit is simple and cheap
    • Not suitable for high frequency      

                                
    (c)        Application:
    RC coupling
    -  as voltage amplifier
    -  as pre-amplifiers                                           
                Transformer coupling
    -  Power amplifiers
    - Impedance matching                             
    D.C. Coupling
    - low frequency amplification
    - d.c. amplification
    - differential amplifiers                                
    Many candidates could not state the types of coupling in multistage amplifiers; hence, failed to state their properties.                  

    (a)        (i)         Class A, B or AB                             
    (ii)        Class C                                                                                                  
    (b)        (i)         Types of coupling:
    -  RC coupling                                                            
    -  Transformer coupling                                                   
    -  DC coupling                                                 
    (ii)        Properties – RC

    • Uses capacitor for coupling
    • Couples a.c.
    • Wide bandwidth/good frequency response
    • d.c. isolation between stages/blocks d.c.
    • Cheap                                                    

                            Transformer coupling

    • Coupling is by transformer
    • Low power loss/high efficiency
    • d.c. isolation
    • High gain
    • Impedance matching                    

                           Direct Coupling (DC)

    • Does not isolate d.c. signals
    • Stages are coupled directly
    • Amplifies d.c. signals/low frequency signals
    • Circuit is simple and cheap
    • Not suitable for high frequency      

                                
    (c)        Application:
    RC coupling
    -  as voltage amplifier
    -  as pre-amplifiers                                           
                Transformer coupling
    -  Power amplifiers
    - Impedance matching                             
    D.C. Coupling
    - low frequency amplification
    - d.c. amplification
    - differential amplifiers                                
    Many candidates could not state the types of coupling in multistage amplifiers; hence, failed to state their properties.