Anadigics patents circuit to protect GSM PAs
"This active clamping circuit is simple and compact yet protects PAs by reducing the gain of the amplifier when output voltage becomes too high," said Charles Huang, executive vice president and chief technical officer at Anadigics. "This patent provides another example of how we are continuing to develop innovative technology to further strengthen our portfolio of power amplifier solutions.
"Our line of GSM PAs continues to grow market share by providing customers with exceptional efficiency, while ensuring that the product remains reliable, even under extreme operating conditions."
PAs in mobile phones can be subjected to extreme operating conditions which can lead to problems including amplifier failure. For example, a mismatch between the impedances of the mobile phone antenna and the amplifier circuit can cause the voltage standing wave ratio (VSWR) to increase. If in turn this causes the voltage level at the output of the amplifier to increase to a dangerous level, the result can be failure of the PA, rendering the mobile phone useless.
To prevent amplifier failure, active control circuits may be added to the PA that can adjust its gain to keep it within safe operating conditions. Many previous control circuits are highly complex, expensive and take up valuable space on the IC or printed circuit board.
Anadigics active clamping circuit for multi-stage PAs includes a feedback circuit which affects the gain of the amplifier. The feedback circuit feeds an output via a filter and a clamping transistor to an input of at least one stage of the power amplifier. The output fed to the filter and clamping transistor may be tapped from one or more diodes belonging to a diode stack connected to the PA s output.
