BGT24MTR11
User's Guide
Transmitter Section
Application Note AN305, Rev. 1.0
2012-11-15
9 / 15
4
Transmitter Section
This chapter describes the functionalities of the main power amplifier (PA in the block diagram) that provides the
ouput for transmitting the actual radar signal at the TX output as well as the medium power amplifier (MPA) that
provides the signal at the LO output.
4.1
TX Section
The TX output signal is provided via TX and TXX pins (pin 22 and 23). It is a differential output signal with a load
impedance of 100
, given that the off-chip compensation structures, shown in the data sheet, are in place.
Ideally the TX outputs can be used directly with an antenna that has differential 100
inputs. In case of single-
ended antennas it will be necessary to use a balun. If the antenna is single-ended 50
then there is also the
option to terminate one of the TX outputs with 50
and use the other one directly as a 50
output port.
However, this will reduce the available output power by 3 dB.
Note: It is not recommended to create a 100
single-ended output signal by grounding one of the TX pins.
The TX output power level can be adjusted via settings in the SPI data register as shown in the table below.
Table 1
Output power reduction
SPI Data Register
Reduction of output power relative to
maximum output power / dB
Bit 2
Bit 1
Bit 0
0
0
0
0
0
0
1
0.4
0
1
0
0.8
0
1
1
1.4
1
0
0
2.5
1
0
1
4
1
1
0
6
1
1
1
9
To mitigate the roll-off of output power at high temperatures it is possible to set SPI data bit 3 (PC1_BUF, High
TX buffer output power) to HIGH. This buffer is not explicitily shown in the block diagram in Figure 1 on page 5.
At room temperature there is only an increase of 0.2 dB in the maximum TX output power.
Output power plotted versus frequency for different temperatures can be found in the figure below. The TX
buffer was in high output power mode during this measurement.
