# Power Amplifier and Ramp Up/Down Sequence

The power amplifier (PA) bias supply is provided by VDDPA or VDDRF. The output power provided by the PA is determined by the voltage value of the selected regulator and the RF_REG1A_PA_PWR_PA_PWR field of the RF_REG1A register. The maxim output power is achieved when the RF_REG1A_PA_PWR_PA_PWR field is set to 0x0C. The effect of RF_REG1A_PA_PWR_PA_PWR on output power is shown in the "Relative Output Power" table relative to the maximum output power corresponding to the value 0x0C.

Table: Relative Output Power
RF_REG1A_PA_PWR_PA_PWR value | Relative output power (dB)
--- | ---
0x1D | -41
0x1E | -27 to -41
0x1F | -31
0x00 | -18.5
0x01 | -17
0x02 | -15.2
0x03 | -13.7
0x04 | -12.2
0x05 | -10.7
0x06 | -9.2
0x07 | -7.8
0x08 | -6.3
0x09 | -4.9
0x0A | -3.3
0x0B | -2
0x0C | Maximum

To reduce the spectral regrowth of the PA during power-up, a ramp-up and a ramp-down can be activated. The ramp-up works on the power back-off of the PA and additional ultra-low power output mode. The PA ramp-up is activated by setting the RF_REG31_PA_RAMPUP_EN_PA_RAMPUP bit of the RF_REG31 register to 1. The ramp-down is activated by setting the RF_REG31_PA_RAMPUP_EN_PA_RAMPDOWN bit of the same register to 0. The ramp-down only works if the ramp-up is activated. The ramp-up does not start with the activation of the PA. If the ramp-up is enabled, the PA back-off is set to the minimum as soon as the activation command reaches the PA. Then a variable counter controlled by the RF_REG31_PA_RAMPUP_DEL_PA_RAMPUP[2:0] field of the RF_REG31 register waits for the PA to be on. The values of the delay are (in μs units):

- 0b000: 0.25
- 0b001: 0.31
- 0b010: 0.5
- 0b011: 0.81
- 0b100: 1.5
- 0b101: 2.1
- 0b110: 2.8
- 0b111: 4.1

The steepness of the ramp-up is controlled by the parameter in the RF_REG31_PA_RAMPUP_TAU_PA_RAMPUP[1:0]field of the RF_REG31 register. The ramp-up duration depends on the final value of the PA back-off field RF_REG1A_PA_PWR_PA_PWR from the RF_REG1A register. In the case of the maximum final value of the PA back-off and starting from step 0 , the conversion listfollows (in μs units):

- 0b00: 6.0
- 0b01: 3.0
- 0b10: 2.0
- 0b11: 1.5

The PA ramp-down takes exactly the same amount of time.

The general behavior of the PA ramp-up is shown in the "Ramp-up sequence" figure.

Figure: Ramp-up sequence