Rainbow Electronics ATA5812 - Manual (Page 20)

20
ATA5811/ATA5812 [Preliminary]
4689B–RKE–04/04
Table 9 shows the relative changes of the output power of a typical device compared to
3.0 V/25°C. As can be seen a temperature change to -40° as well as to +105° reduces
the power by less than 1 dB due to the bandgap regulated output current. Measure-
ments of all the cases in Table 7 on page 19 over temperature and supply voltage have
shown about the same relative behavior as shown in Table 9
RX/TX Switch The RX/TX switch decouples the LNA from the PA in TX mode, and directs the received
power to the LNA in RX mode. To do this, it has a low impedance to GND in TX mode
and a high impedance to GND in RX mode. To design a proper RX/TX decoupling
a linear simulation tool for radio frequency design together with the measured device
impedances of Table 1 on page 10, Table 7 on page 19, Table 10 and Table 11 on page
22 should be used, but the exact element values have to be found on board. Figure 17
on page 21 shows an approximate equivalent circuit of the switch. The principal switch-
ing operation is described here according to the application of Figure 4 on page 6. The
application of Figure 5 on page 7 works similarly.
Table 8. Measured Output Power and Supply Current at 433.92 MHz, PWR_H = GND
VS = 2.4 V 3.0 V 3.6 V
T
amb
= -40°C
10.19 mA
3.8 dBm
10.19 mA
5.5 dBm
10.78 mA
6.2 dBm
T
amb
= +25°C
10.62 mA
4.6 dBm
11.19 mA
6.2 dBm
11.79 mA
7.1 dBm
T
amb
= +105°C
11.4 mA
3.8 dBm 12.02 mA
5.4 dBm
12.73 mA
6.3 dBm
Table 9. Measurements of Typical Output Power Relative to 3 V/25°
VS = 2.4 V 3.0 V 3.6 V
T
amb
= -40°C -2.4 dB -0.7 dB 0 dB
T
amb
= +25°C -1.6 dB 0 dB +0.9 dB
T
amb
= +105°C -2.4 dB -0.8 dB +0.1 dB
Table 10. Impedance of the RX/TX Switch RX_TX2 Shorted to GND
Frequency Z(RX_TX1) TX Mode Z(RX_TX1) RX Mode
315 MHz (4.8 + j3.2)
Ω
(11.3 - j214)
Ω
433.92 MHz (4.5 + j4.3)
Ω
(10.3 - j153)
Ω
868.3 MHz (5 + j9)
Ω
(8.9 - j73)
Ω