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.