User guide

19
ATA5811/ATA5812 [Preliminary]
4689B–RKE–04/04
Figure 16. Power Setting and Output Matching
Output Power and TX
Supply Current versus
Supply Voltage and
Temperature
Table 8 on page 20 shows the measurement of the output power for a typical device
with VS1 = VS2 = VS in the 433.92 MHz and 6.2 dBm case versus temperature and
supply voltage measured according to Figure 16 on page 19 with components according
to Table 7. As opposed to the receiver sensitivity the supply voltage has here the major
impact on output power variations because of the large signal behavior of a power
amplifier. Thus, a two battery system with voltage regulator or a 5 V system shows
much less variation than a 2.4 V to 3.6 V one battery system because the supply voltage
is then well within 3.0 V and 3.6 V.
The reason is that the amplitude at the output RF_OUT with optimum load resistance is
AVCC - 0.4 V and the power is proportional to (AVCC - 0.4 V)
2
if the load impedance is
not changed. This means that the theoretical output power reduction if reducing the sup-
ply voltage from 3.0 V to 2.4 V is 10 log ((3 V - 0.4 V)
2
/(2.4 V - 0.4 V)
2
) = 2.2 dB. Table 8
on page 20 shows that principle behavior in the measurement. This is not the same
case for higher voltages since here increasing the supply voltage from 3 V to 3.6 V
should theoretical increase the power by 1.8 dB but only 0.8 dB in the measurement
shows that the amplitude does not increase with the supply voltage because the load
impedance is optimized for 3 V and the output amplitude stays more constant.
ATA5811/ATA5812
RF_OUT
10
C
1
L
1
RF
OUT
AVCC
C
2
C
3
R_PWR
PWR_H
R
1
VPWR_H
8
9
Table 7. Measured Output Power and Current Consumption with VS1 = VS2 = 3 V, T
amb
= 25°C
Frequency (MHz) TX Current (mA) Output Power (dBm) R1 (kΩ) VPWR_H R
Lopt
(Ω)L1 (nH) Q
L1
C1 (pF) C3 (pF)
315 8.5 0.4 56 GND 2500 82 28 1.5 0
315 10.5 5.7 27 GND 920 68 32 2.2 0
315 16.7 10.5 27 AVCC 350 56 35 3.9 0
433.92 8.6 0.1 56 GND 2300 56 40 0.75 0
433.92 11.2 6.2 22 GND 890 47 38 1.5 0
433.92 17.8 11 22 AVCC 300 33 43 2.7 0
868.3 9.3 -0.3 33 GND 1170 12 58 1.0 3.3
868.3 11.5 5.4 15 GND 471 15 54 1.0 0
868.3 16.3 9.5 22 AVCC 245 10 57 1.5 0