5.5 Timing Diagram

To meet the time mask specifications for GSM, a good timing between the control signals and the RF signal

is essential. According to the specifications the PA RF output power needs to ramp within 28μs with minimum

overshoot. To achieve this, ramp the output of the PA controller at the same time as the RF signal from the

baseband. The ramp signal sets the controllers output to the required value, where the loop requires a certain

time to set this output. Therefore, set the VRAMP pin to the desired value some time before the desired output.

How much time depends on the setup and the PA used. If the controllers shutdown functionality is used, then set

the shutdown high about 6μs before the ramp is set high.

The control loop can be configured by the following variables:

• Lead time TX_EN event vs start GSM burst

• Lead time VRAMP vs start GSM burst

• Ramp profile

• Loop compensation

RF SIGNAL

TX_EN

VRAMP

OUT

6µs

Minimum

Figure 5-1. Timing VRAMP vs RF Signal

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SNWS014D – MARCH 2004 – REVISED JUNE 2025

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