GSM POWER AMPLIFIER CONTROL LOOP

There are four critical sections in the GSM Power Amplifier

Control Loop. The class-C R

plification of the R

small amount of R

an envelope detector diode. The detector diode senses the

signal level and rectifies it to a DC level to indicate the signal

strength at the antenna. An op-amp is used as an error

amplifier to process the diode voltage and ramping voltage.

This loop control the power amplifier gain via the op-amp

and forces the detector diode voltage and ramping voltage to

be equal. Power control is accomplished by changing the

ramping voltage.

The LMV710, LMV711 and LMV715 are well suited as an

error amplifier in this application. The LMV711 and LMV715

have an extra shutdown pin to switch the op-amp to shut-

down mode. In shutdown mode, the LMV711 and LMV715

consume very low current. The LMV711 provides a ground

voltage to the power amplifier control pin V

power amplifier can be turned off to save battery life. The

LMV715 output will be “tri-stated” when in shutdown.

10132506

FIGURE 9. Typical of GSM P.A. Control Loop

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