Datasheet

LMV710-N, LMV711-N, LMV715-N
SNOS519J –APRIL 2000–REVISED MARCH 2013 www.ti.com
Figure 44. Typical of GSM P.A. Control Loop
GSM Power Amplifier Control Loop
There are four critical sections in the GSM Power Amplifier Control Loop. The class-C R
F
power amplifier
provides amplification of the R
F
signal. A directional coupler couples small amount of R
F
energy from the output
of the R
F
P. A. to 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-N/LMV711/LMV715 are well suited as an error amplifier in this application. The LMV711/LMV715
have an extra shutdown pin to switch the op amp to shutdown mode. In shutdown mode, the LMV711/LMV715
consume very low current. The LMV711 provides a ground voltage to the power amplifier control pin V
PC
.
Therefore, the power amplifier can be turned off to save battery life. The LMV715 output will be “tri-stated” when
in shutdown.
Simplified Schematic
Figure 45. LMV711
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