Complete Wireless Design
If you want to climb the learning curve with grace, and start designing what you need immediately, this easy-to-understand guide will help you design an entire radio system from the ground up.
TABLE OF CONTENTS Complete Wireless Design
3.9: Coupling/Decoupling of Amplifiers
3.9 Coupling/Decoupling of Amplifiers
3.9.1 Introduction
Amplifier coupling. To prevent DC biasing of consecutive amplifier stages from adversely affecting other stages, a method of coupling an AC signal into or out of another amplifier or another source and its load must be found. Unmatched RF amplifiers also demand a good impedance match for maximum power transfer and the reduction of reflections (decreased VSWR), as well as for supplying filtering for harmonic attenuation.
The actual type of coupling in a discrete circuit, sometimes combined with impedance matching, will depend on the sort of signal being amplified. DC, low-frequency AC, high-frequency AC, and wideband amplification, will all have specific requirements.
3.9.2 Design of decoupling/coupling circuits
Decoupling. RF must not enter an amplifier s power supply, and the power supply s voltage to the amplifier must not influence any circuits that are before or after the amplifier. Both occurrences would have a negative effect on system operation, as any alternating current into the amplifier s DC bias supply can cause circuit instabilities and noise throughout a system; while passing DC beyond the immediate amplifier stage area would affect the bias of any following amplifier or be sent to ground as a short. In performing as coupling and decoupling elements, capacitors and inductors prevent any of the above from occurring.
However, in order to function as desired, coupling and decoupling capacitors must not be near their parallel (high-impedance) resonant mode, while decoupling inductors must not be close to any series (low-impedance) resonant modes nor should...
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