Design Information

MMM6035 Advance Information, Rev. 2.4

16

Freescale Semiconductor

two-pole Sallenkey filter included in the VRAMP path to remove DAC noise and to provide VRAMP

signal smoothing.

7.2

Anti-Saturation Detection Feature

The MMM6035 prevents degradation of switching transients, regardless of battery conditions, due to an

internal anti-saturation detection feature. The goal of this block is to maintain the RF output power ramp

within the power versus time mask and to maintain acceptable spectral limits at specified offset

frequencies.

The anti-saturation detection feature is implemented by a feedback loop inside the power control loop

which detects when the power controller PMOS goes into the linear region. The feedback loop reduces

VRAMP to maintain the pass device in its saturation region, even under low battery voltage conditions.

Figure 6. Anti-Saturation Detection

7.3

Recommended Power Control Calibration Procedure

Power control calibration is carried out at two points. The procedure first requires the measurement of

output power (Po) calibration points at two values of Vramp (Vramp(1) and Vramp(2)). Figure 5 shows

these points, after conversion (*), plotted on the RMS RF output voltage (Vrf) against the control voltage

(Vramp) characteristic. Using these points, the Vramp voltage (Vramp(E)) can be estimated for any desired

output power level. In order to meet the transmitted power level versus time requirement of GSM05.05

Specification, at the lowest power level, it is also necessary to determine the Vramp pedestal voltage (see

Figure 4 and Figure 5) required to reach an acceptable power level when the controller section feedback

loop has stabilized after wake-up.

As a reminder:

Eqn. 1

where Po is in dBm into 50

Ω and Vrf is in Vrms.

-15

-10

-5

0

5

10

15

20

25

30

35

40

0

2

4

6

8

10

12

14

16

18

20

Time (us)

Time Mask

VBATT = 3.0V

Antisat off

VBATT = 3.0V

Antisat on

VBATT = 3.5V

Antisat on

Vrf

10

Po 13

–

() 20

⁄

=