Application Note
page 19 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
The offset of the low-gain signal equals the static offset of the BGT output signals. Due to the DC block at the
beginning of the second stage, the offset of the high-gain signal matches the reference voltage of 1.65 V. As
shown in Figure 14, the first gain stage provides a gain of up to 30 dB (low-gain stage) and both the stages
together provide a gain of up to 57 dB (high-gain stage).
Figure 14
Baseband frequency response for low-gain and high-gain stages
Figure 14 shows the frequency response of the low- and high-gain stages. The BGT24LTR11 Shield allows the
user to select either the low-gain (first stage only) or high-gain (first stage + second stage) mode depending on
the target RCS and distance to be detected. The low-gain output is referenced to the individual mixer output
bias voltage (1.6 to 2.0 V), and the high-gain stage is AC coupled and referenced to V
CC
/2 = 1.65 V.
Table 2 lists the MCU pins (on the Radar Baseboard XMC4700) associated with each of the gain stages. Use the
graphical pin select tool in the
DAVE™ software to select the appropriate pins for
signal processing.
Table 2
Baseband amplifier to MCU pin connections
XMC4700
–
port pin
Pin label
Pin function
P14.6 (VADC.G0CH6)
IF.I1
IFI
–
high gain
P14.7 (VADC.G0CH7) / P14.3 (VADC.G1CH3)
IF.Q1
IFQ
–
high gain
P14.14 (VADC.G1CH6) / P15.3 (VADC.G2CH3)
IF.I2
IFI
–
low gain
P14.15 (VADC.G1CH7) / P15.9 (VADC.G3CH1)
IF.Q2
IFQ
–
low gain
The gain and bandwidth of the IF stages can be manually configured by the user by changing the resistor and
capacitor values specified in Table 3.
Table 3
Baseband amplifier components and settings
IF stage
Designator Gain
Configurable components
–
I section
Configurable components
–
Q section
Stage 1
(low gain)
U5A
30 dB
C16, R33, C17, R36
C37, R65, C35, R61
