Application Note
page 21 of 32
V1.0
2021-03-31
Distance2GoL (Software-Controlled FMCW) low-power radar shield using
BGT24LTR11 for range detection and human tracking
Power consumption analysis
5
Power consumption analysis
The BGT24LTR11 Shield is designed for low power consumption.
•
The MMIC is turned on with TX enabled for all
N
C
chirps per frame and with TX disabled during frequency
checke and recalibration, while the influence of the TX status on the power consumption is neglectable.
In order to avoid out-of-band spurs, MMIC and TX are enabled and disabled for chirping only at center
frequency, for which reason the on-time per chirp
t
on
is larger than the pure up-chirp time
t
up
. If the pulse
repetition time (PRT) is smaller than or equal to 3 ms, the fast chirp mode is enabled and
t
on
is equal to
the PRT. If the PRT is larger than 3 ms, the power-saving mode is applied and
t
on
is 2.5 ms.
•
The PTAT and the divider are used for frequency checks and recalibration (with MMIC enabled). Each
frame a frequency check is performed, which requires around 1 ms. The recalibration is only performed
if the frequency fails takes around 2 ms. Thus, the mean total recalibration time per frame
t
calib
is 3 ms at
maximum.
•
The baseband section consists of the two stages of op-amps and the voltage divider. It is turned on
simultaneously with the MMIC and TX for chirping and is turned off shortly after the end of the up-chirp.
As shown in Table 5, the major contributors to the power consumption are the MMIC and the divider.
Table 5
Power consumption overview
Component
Current consumption (mA)
On-time per frame (ms)
MMIC (BGT24LTR11)
45
N
C
*
t
on
MMIC+ D PTAT
65.5 (45 + 19 + 1.5)
t
calib
(~3)
Baseband section
(op-amps and voltage divider)
0.335
t
up
+ 0.6
The Distance2GoL power consumption can be computed after calculating the current consumption of the
BGT24LTR11 for chirping, the frequency check and recalibration, and the duty-cycling of the baseband section.
Some exemplary power consumption calculations are shown in the table below:
Table 6
Power consumption calculation
Frame period
(ms)
Pulse
repetition time
(ms)
Chirps per
frame
Calibration
time (ms)
Current
consumption
(mA)
Power
consumption
(mW)
100 (default)
5
10
3
13.3
43.8
100
5
12
3
15.5
51.3
150
5
10
3
8.9
29.3
150
10
12
3
10.4
34.2
200
5
10
3
6.64
21.9
200
10
12
3
7.8
25.6
For more information about the power consumption calculation please refer to the
“Power_consumption_sFMCW_D2GL” Excel calculator file.