Application Note
page 15 of 32
V1.0
2021-03-31
Distance2GoL (Software-Controlled FMCW) low-power radar shield using
BGT24LTR11 for range detection and human tracking
Hardware description: BGT24LTR11 Shield
4.3
Power supply
The Radar Baseboard XMC4700 is powered via micro-USB connector, external 7 V power supply or LiPo battery.
It also provides the supply for the BGT24LTR11 Shield via the connectors. An LDO (U6) is used on the
BGT24LTR11 Shield to supply all the components. Figure 7 shows the power supply concept used in the system.
LDO
VCC = 3.3 V
VCC1
IN
OUT
EN
4.7 µF
1 µF
C41
C42
C
o
n
n
ec
to
rs b
/w
B
a
se
B
o
a
rd
a
n
d
R
ad
ar
Sh
ie
ld
Micro USB /
External supply /
LiPo battery
R
shunt
Current sensors
VCC1
5 V
Figure 7
Block diagram
–
power supply concept
4.4
EEPROM
The BGT24LTR11 Shield contains an EEPROM (U7) to store data such as a board identifier. The Serial Data (SDA)
is a bi-directional pin that is used to transfer addresses and data into and out of the device. The Serial Clock
(SCL) is an input that is used to synchronize the data from and to the device.
When the Shield is plugged into the Radar Baseboard XMC4700
, the sensor’s supplies are initially deactivated.
Only the EEPROM is powered. The MCU reads the content of the EEPROM’s memory to determine which
Shield
is plugged into the
interface. Only when the board has been correctly identified are the sensor’s supplies
activated.
EEPROM
VCC
VCC
VSS
SCL
C
o
n
n
e
ctor
s
b
/w
B
as
e
B
o
ar
d
a
n
d
R
ad
ar
S
h
ie
ld
SDA
I2C_EEPROM.SCL
I2C_EEPROM.SDA
VCC
R83
R84
USIC
XMC4700
Figure 8
EEPROM block diagram
4.5
RF front end Shield
Figure 9 shows the top view of the RF front end. The RF front end has a cover with absorber material to get the
best RF performance. The transmitter and receiver inputs of the BGT24LTR11 are single-ended. The TX output
and RX input are connected over a matching structure, a DC block and a feed-through via to the antennas on
the other side of the board. The isolation between the RX and TX ports is improved by adding a grounded
length of line at the ground pins next to the TX output pin, as shown in Figure 9.
