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Balanced Amplifiers in RF Design

Balanced amplifiers have been in existence for several decades and continue to provide an excellent solution for many RF and microwave applications.

Some of the advantages of balanced amplifiers which make them attractive to designers and users include their excellent impedance match (in and out ports), higher output power, higher third order intercept point, excellent noise figure and wide bandwidth.

A balanced amplifier consists of a pair of identical 2-way, 90° splitters (also called 3-dB couplers) and a pair of single ended amplifiers. Two of the balanced amplifier’s ports are terminated in its characteristic impedance Z0.

Figure 1 shows the block schematic of this type of amplifier design. In order to understand the benefits of balanced amplifiers, we need to examine the properties of 2-way, 90° splitters first.

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