In radio frequency (RF) circuits used for portable applications, power efficiency is extremely important. For this reason, Class C power amplifiers are used wherever practical. There are some limitations in using Class C amplifiers, as we discussed in class. Identify these issues. Another consideration for a power amplifier is efficient coupling of energy from the amplifier to the load. This generally requires an impedance matching network. Shown in the attachment are two circuits that could be used to match the amplifier output impedance to the load impedance. Ignoring tunability or component sizes, which is likely to be the best choice for a Class C amplifier? Why?
See attached for the circuit diagrams© BrainMass Inc. brainmass.com December 24, 2021, 11:24 pm ad1c9bdddf
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Disadvantages of using Class C amplifiers
• Poor dynamic range, typically dynamic range lies between 0 to 6 dB
• Unsuitable for certain types of signal modulation especially AM signals
• High output distortion but usually with operation at a single carrier frequency this is controlled to some extent by use of tuned output load
In order to couple the Class C amplifier to a load an impedance matching network is required. Another requirement is that this network should be a Low Pass Filter (LPF) design which then reduces the amount of output distortion from the design. Of the two coupling networks the one with the 2 grounded and parallel capacitors and the series inductor would be chosen for the coupling impedance matching network. This design would thus offer the LPF characteristic minimizing output distortion. The other design, whilst potentially matching the amplifier output impedance to the load would represent a High Pass Filter characteristic and produce far higher output distortion.© BrainMass Inc. brainmass.com December 24, 2021, 11:24 pm ad1c9bdddf>