BGT24MTR11
User's Guide
Transmitter Section
Application Note AN305, Rev. 1.0
2012-11-15
10 / 15
Figure 6
TX output power vs. frequency for different temperatures
4.1.1
Enabling and Disabling of the Output Power
The TX outputs are disabled by default after powering-up the IC. This is to make sure that the output frequency
can be stabilized before actually transmitting a signal.
Note: Disabling the TX outputs will not reduce power consumption as all IC-internal blocks will still be running.
TX outputs are switched to an internal load when disabled. This keeps the power dissipation at a constant
level and therefore keeps the chip temperature constant. Abrupt changes in temperature would cause the
VCO’s frequency to jump to a different value which might lead to violation of the band limits before the
frequency control loop can re-lock the frequency again.
There are two possibilities to turn on and off the TX ouput power. The first is via the SPI bus and the second is
using the TXOFF pin.
4.1.1.1
Enabling/disabling via the SPI bus.
To enable the power output SPI data bit 12 (DIS_PA) needs to be set to LOW and to disable the power it needs
to be set to HIGH. If you use this method, please connect the TXOFF pin to ground.
4.1.1.2
Enabling/disabling via the TXOFF pin.
Using the TXOFF pin (pin 26) for swiching on/off or generating transmit pulses allow considerably shorter
switching times compared to using the SPI bus.
In this mode it is necessary to first set SPI data bit 12 to LOW and thus generally activating the TX outputs. After
that applying a voltage below 0.5 V to TXOFF will enable the TX outputs and a voltage higher than 1.5 V will
disable the TX outputs.
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5
10
10.5
11
24
24.05
24.1
24.15
24.2
24.25
O
u
tp
u
t
P
o
w
e
r
/
d
B
m
Frequency / GHz
TX Output Power vs. Frequency and Temperature
-40°C
25°C
75°C
125°C
