Application Note
page 20 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
IF stage
Designator Gain
Configurable components
–
I section
Configurable components
–
Q section
Stage 1 + Stage 2
(high gain)
U5A + U4A
57 dB
All components as
mentioned for Stage 1 +
R49, R50, R32, C23, C24
All components as
mentioned for Stage 1 +
R55, R56, C34, R63, C33
4.8.1
IF section and FMCW ramp settings
The bandpass characteristics of the IF section are also determined from the FMCW ramp parameter settings.
Different ramp settings result in different IFs for targets at different distances. The baseband section is
designed to meet the required IF cut-offs. Table 4 gives an example of IFs produced by stationary targets at
particular distances corresponding to different sawtooth-type ramp parameters. These IFs ar
e also called “beat
frequencies”. T
he beat frequencies calculated in the table do not include the Doppler shift.
The
𝐵𝑒𝑎𝑡 𝐹𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 (𝐹𝑏)
is calculated from the following formula:
𝐵𝑒𝑎𝑡 𝐹𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 (𝐹𝑏) =
2 ∗ R ∗ ∆f
c ∗ 𝑇
𝑟
Where
R
= target distance in meters (m)
∆f
= ramp bandwidth in Hertz (Hz)
𝑇
𝑟
= ramp time in seconds (s)
c
= speed of light in meters/second (m/s)
Table 4
IF vs. FMCW ramp parameters vs. target distance
Ramp duration
(T
r
) (µs)
Ramp
bandwidth
(Δf)
(MHz)
Beat frequency (Fb) (kHz)
Target at 50 cm (R)
Target at 10 m (R)
Target at 30 m (R)
1000
180
0.60
12.00
36.00
1000
200
0.67
13.33
40.00
1500
180
0.40
8.00
24.00
1500 (default)
200
0.44
9.00
26.70
2000
180
0.30
6.00
18.00
2000
220
0.33
6.70
20.00
