Application Note
page 13 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 Shield demonstrates the features of the BGT24LTR11 RF front-end chip and gives the user a customizable
radar solution. The board enables implementation of different baseband settings, VCO control, etc. to get
closer to a custom-fit solution for the use case. It also makes it possible to quickly gather sampled radar data
that can be used to develop radar signal processing algorithms on a PC or implement target detection
algorithms directly on the microcontroller using DAVE™.
4.2
Block diagram
Figure 6 shows the block diagram of the Distance2GoL system. It consists of the highly integrated 24 GHz
transceiver IC BGT24LTR11 with 1 TX and 1 RX antenna. The hardware consists of two main parts: one Software-
Controlled FMCW BGT24LTR11 Shield and one microcontroller unit with XMC4700.
In order to keep the output frequency within the industrial, scientific and medical (ISM) band and generate the
frequency ramp, the tuning voltage (V_TUNE) is software-controlled via a Digital-to-Analog Converter (DAC) in
the microcontroller unit. The DAC output (V_TUNE_IN) is smoothed by two RC low-pass filters and fed to the
V_TUNE input of the BGT24LTR11. The IF outputs (I/Q signals) are first bandpass filtered by two stages of op-
amps and then sampled by four synchronized Analog-to-Digital Converters (ADCs), which are built into the
XMC4700 MCU. The user can select the output of the first amplification stage (low-gain output) for sampling for
low-range applications. The op-amps are also duty-cycled for a low power consumption using control signals
(BB1_EN and BB2_EN).
An initial RF within the ISM band at the start-up of the radar system is ensured by utilizing the built-in voltage
source V_PTAT (Proportional-to-Absolute Temperature). After enabling VCC_PTAT, the output voltage is
sampled by an ADC and set by the DAC as V_TUNE. The Capture-and-Compare Unit (CCU) of the XMC4700
measures the divider output (DIV_OUT) of the BGT24LTR11 MMIC to supervise the current RF and (re)calibrate
the start and stop frequencies if required. During this process, VCC_PTAT is also enabled to set the correct
divider frequency.
For optimizing the power consumption of the system, the BGT24LTR11 MMIC is duty cycled, along with the
building blocks of divider and PTAT using control signals from the MCU (VCC_BGT_EN, VCC_DIV_EN and
VCC_PTAT_OUT).
