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RF and Microwave Transmitter Design by Andrei Grebennikov

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13

Control Circuits

This chapter discusses the circuit schematics and main properties of the semiconductor control circuits that are usually characterized by small size, low power consumption, high-speed performance, and operating life. Generally, they can be built based on the p–i–n diodes, silicon MOSFET, or GaAs MESFET transistors and can be divided into two basic parts: amplitude and phase control circuits. The control circuits are necessary to protect high power devices from excessive peak voltage or dc current conditions. They also used as switching elements for directing signal between different transmitting paths, as variable gain amplifiers to stabilize transmitter output power, as attenuators and phase shifters to changing the amplitude and phase of the transmitting signal paths in array systems, or as limiters to protect power-sensitive components.

13.1 POWER DETECTOR AND VSWR PROTECTION

In wireless communication systems based on GSM/EDGE, CDMA2000, WCDMA, or OFDM standards with nonconstant envelope signals, it is required that the power amplifier could operate with high power, high efficiency, high linearity, and high spectral purity simultaneously under significant load variation where the values of the load voltage standing wave ratio (VSWR) may be very high. For conventional power amplifiers, the performance degrades significantly with high VSWR when the entire active device sees the high impedance conditions corresponding to the device operation in a highly nonlinear ...

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