PCF5077T Просмотр технического описания (PDF) - Philips Electronics

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PCF5077T

Power amplifier controller for GSM and PCN systems

Philips Electronics 

Philips Semiconductors

Power amplifier controller for GSM and

PCN systems

Preliminary specification

PCF5077T

ADJUSTMENT OF THE HOME POSITION

The 6-bit DAC for VHOME determines the start point of the

burst in the time template. Curve 2 in Fig.8 shows what

happens when VHOME is too low. The burst starts too late

and the up-ramping of the power is too steep. The steep

up-ramping results in a wide transient spectra. The RF

input power shall be switched off when the TRIG signal is

LOW to keep the −70 dB margin before the burst.

The home position has to be adjusted for each mobile

phone because of DAC tolerances and individual PA

characteristics.

The temperature coefficients for VHOME (−2 and −4 mV/K)

are used to compensate the temperature shift of the PA

control curve. Therefore the PA and the controller shall be

placed nearby on the printed-circuit board. Additionally it

has to be considered that the temperature of the PA and

PCF5077T are different because the PA heats up itself.

Software may help to adapt VHOME to different

temperatures.

ADJUSTMENT OF VKICK

After the falling edge of HPA the integrator starts to

increase the control voltage up to the position of VKICK

where the PA should have reached its active region.

Increasing VKICK at high power level makes the up ramping

of the burst smoother and improves the transient spectra.

VKICK must be reduced for low level of VPL to avoid that

both voltages become equal. Setting VKICK to minimum

value for the lowest power level can be sufficient.

At low power level the burst will start later because of the

bend sensor curve (see Fig.7). The trigger pulse has to be

started up to 3 bits earlier for the lowest power level to

avoid that the power is ramped up too late for the first data

bits of the burst.

LIMIT FOR CORRECT DOWN-RAMPING

The maximum RF power that the power module in

saturation is able to deliver depends on RF input power,

transmit frequency, supply voltage, temperature and load

impedance. The maximum VPL must be matched to the

worst case output power and then reduced by 1 dB when

the PCF5077T is used in closed loop mode.

Curve 2 in Fig.9 shows what happens when the PA is

driven into saturation. The down-ramping of the power is

getting too steep and therefore the transient spectra will be

too wide. The 1 dB margin is necessary because of the flat

PA control curve at high power level. The loop needs more

time to reduce the power during the down-ramping and the

control voltage increases. The high control voltage forces

the power quickly down when the steep region of the

control curve is achieved. The steep down-ramping results

in a wide transient spectra.

1997 Nov 19

10

handbook, halfpage

VS

(V)

1

MGK915

10−1

10−2

−5 0 5 10 15 20 25 30 35

P (dBm)

Fig.7 Sensor voltage as a function of output power (diode BAT62).

16

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