LMV715MF NSC [National Semiconductor], LMV715MF Datasheet - Page 14

• Manufacturer Part Number: LMV715MF
• Description: Low Power, RRIO Operational Amplifiers with High Output Current Drive and Shutdown Option
• Manufacturer: NSC [National Semiconductor]

www.national.com
Application Note
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.
F
F
energy from the output of the R
signal. A directional coupler couples
F
(Continued)
power amplifier provides am-
FIGURE 9. Typical of GSM P.A. Control Loop
F
P. A. to
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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.
PC
. Therefore, the