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Application NoteTransmitter Back Off and Receiver Gain Recommendation
for xWRL6432AOP

Radar Systems and Applications
ABSTRACTThis application report provides information on how to select the transmitter power backoff and the receiver gain
setting in the xWRL6432AOP radar device based on the end application and use case to avoid the increased
receiver noise figure and the risk of receiver ADC saturation, and correctly program them on TI’s xWRL6432AOP
radar devices.

Table of Contents
1 Introduction.............................................................................................................................................................................2
2 Increased Receiver Noise Figure.......................................................................................................................................... 23 Risk of Receiver ADC Saturation.......................................................................................................................................... 44 TX Backoff and RX Gain Recommendations........................................................................................................................45 Chirp Configuration Recommendations Using Sensing Estimator................................................................................... 66 Summary................................................................................................................................................................................. 77 References.............................................................................................................................................................................. 78 Revision History......................................................................................................................................................................7

List of Figures
Figure 2-1. EINF With Single TX on Across Frequencies............................................................................................................2
Figure 2-2. Average EINF With Single TX on Across Frequencies............................................................................................. 3
Figure 4-1. Maximum Allowed RX Gain Setting.......................................................................................................................... 4Figure 4-2. Minimum TX Backoff for 57 to 64GHz....................................................................................................................... 5Figure 4-3. Minimum TX Backoff for 61 to 64GHz....................................................................................................................... 5Figure 5-1. Sensing Estimator With Chirp That Causes ADC Saturation.................................................................................... 6Trademarks
All trademarks are the property of their respective owners.

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Introduction

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1 Introduction
When determining overall system performance with FMCW radar sensors, many factors affect the range ofdetection. Range of detection is determined by chirp slope, IF bandwidth, and the signal-to-noise ratio (SNR) ofthe reflected energy from a detected object. The SNR in turn depends on EIRP (combination of TX power andTX antenna gain), EINF (combination of RX antenna gain and RX noise figure) and RCS of the target object.
With the xWRL6432AOP device, there is limited isolation between transmit and receive antennas due to theclose proximity of the antennas on the antenna-on-package (AOP) device.
This impacts the receiver performance in two ways:••Impact 1: Increased receiver noise figure– Due to the noise riding on the TX- RX coupled signal the noise figure is increased.
Impact 2: Risk of receiver ADC saturation– The TX - RX coupling causes a low frequency signal at the RX output which can be large enough tosaturate the ADC if precautions are not taken.

2 Increased Receiver Noise Figure
The noise riding on the coupled signal can increase the noise figure of the receiver. Increased noise figure
reduces the SNR of the detected object, leading to reduced detection range and accuracy. The effective isotropic
noise figure therefore depends on two things:
1. TX Backoff
2. TX - RX Isolation
The TX - RX isolation depends on two factors:••Transmit and Receive combination
RF frequency

Figure 2-1 shows the dependencies of the effective isotropic noise figure (EINF) across different transmit andreceive combinations and across different RF frequencies. The EINF is shown for two different TX backoff
settings (0dB and 6dB). The change in noise figure between the two TX backoff settings show the impact ofTX-RX coupling on noise figure for different RF frequencies.

Figure 2-1. EINF With Single TX on Across Frequencies

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Increased Receiver Noise Figure

These effects across transmit and receive pairs can be combined to show a total effect of all transmit andreceive antennas across RF frequency. Figure 2-2 shows the noise figure averaged across different TX-RX
combinations.

Figure 2-2. Average EINF With Single TX on Across Frequencies
NoteDue to the increased noise figure at 60GHz, TI recommends avoiding narrow bandwidth chirps(< 0.5GHz) around 60GHz.
Maximizing detection range (or minimizing required integration time for a particular detection distance) relies on
maximizing detection SNR. Based on the previously-mentioned noise figure profiles, this can be achieved inseveral ways.
••••

Reducing TX power (increasing power backoff) lowers the noise figure by reducing the amount of coupling
between TX and RX antennas. This varies between TX and RX combination and across output frequency.
However, the benefit by lowered noise figure is outweighed by the reduction in transmitted power, lowering
the detection range.
Choosing start and stop frequencies (bandwidth) of the FMCW chirp can help reduce coupling and lower thenoise figure. As Figure 2-2 shows, the 61 to 64GHz band has lower coupling than the 57 to 61GHz band.
Designing a chirp to utilize the 61 to 64GHz portion of the frequency band can help lower the noise figure.
Local regulations and other considerations can drive frequency choice of the end application, but the previousgraphs can be used for expected noise figure in different frequency bands.
For applications which do not need all 6 virtual channels (TX and RX combinations), using TX2 can help
reduce noise figure. The coupling is lowest for TX2 in the 59 to 64GHz band. For single TX applications need,use TX2 over TX1 to get best performance and maximum range.
For two TX applications, use TDM MIMO mode instead of BPM MIMO mode.

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Risk of Receiver ADC Saturation

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3 Risk of Receiver ADC Saturation
The TX - RX coupling causes a low-frequency signal at the RX output which can be large enough to saturate thereceiver ADC if precautions are not taken. The strength of the receiver ADC saturation depends on:
1. Coupled signal level at RX input:• TX backoff• RF frequency• Transmit and receive combinations under consideration
2. RX Gain setting
3. HPF attenuation:• Chirp slope and HPF cutoff frequency configurations
To mitigate this risk, the swing at the receiver output needs to be reduced. This is achieved by therecommendations in the following section.

4 TX Backoff and RX Gain Recommendations
Figure 4-1 and Figure 4-2 give the maximum allowed RX gain setting and minimum TX back off restrictions
based on chirp slope (X-axis) and HPF setting (different colors). These are recommendations which minimize
the effects of increased receiver noise figure and risk of receiver ADC saturation.

Figure 4-1. Maximum Allowed RX Gain Setting

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TX Backoff and RX Gain Recommendations

Figure 4-2. Minimum TX Backoff for 57 to 64GHz
TX backoff restriction can be relaxed as shown in Figure 4-3 for the following cases:••

Chirps contained within 61 to 64GHz for two TX applications
Chirps contained within 59 to 64GHz for single TX applications (using TX2)

Figure 4-3. Minimum TX Backoff for 61 to 64GHz
Using the previously-shown constraints makes sure that the best possible SNR is achieved and also the receiver
ADC is not saturated.

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5Chirp Configuration Recommendations Using Sensing Estimator

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5 Chirp Configuration Recommendations Using Sensing Estimator
If there is doubt about whether the chirp configuration is following the proper recommendations mentioned in thisapplication note, use the sensing estimator to check the chirp settings. The Advanced Chirp Design and Tuning
tab can check a chirp configuration to see if the settings comply with the graphs the previous sections. See
Figure 5-1 for an example of the warnings given in the sensing estimator.

Figure 5-1. Sensing Estimator With Chirp That Causes ADC Saturation
To evaluate the chirp configuration manually, consider the following settings:
1.
2.
3.
4.

TX Backoff
RX Gain
HPF settingFrequency SlopeFirst, look at the HPF setting and Frequency Slope to make sure the requirements for RX gain are met. In theexample pictured in Figure 5-1, HPF setting = 1400kHz and Frequency Slope, S (MHz/μs) = 240. This means
the maximum RX gain is 36 (see Figure 4-1). In this case, the decision is made to change the RX gain to 36 or
below to make sure that the maximum receiver gain constraint is met.
Next, look at the TX backoff for the frequency range. Here the frequency range is 57–63GHz so use the data inFigure 4-2. This shows the minimum TX backoff as 3. In this case, the decision is to change the TX backoff to 3
or above to make sure the minimum back off constraint is met.
With the changes of RX gain from 40 to 36 and the TX backoff from 0 to 3, there is little or no risk of ADC
saturation and the errors in the sensing estimator are cleared.

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Summary

6 Summary
The receiver ADC saturation can significantly impact radar functionality and leads to the loss of crucial
information from the reflected signal of the target object. Additionally, a higher noise figure degrades theoverall performance of the radar by reducing the SNR, which consequently affects both the range and angleresolution. The recommendations provided for selecting transmitter power backoff and receiver gain settings
for the xWRL6432AOP radar device are intended to create the best possible performance. These guidelines
address how improper settings can result in higher EINF due to noise in the TX-RX coupled signal and the risk ofreceiver ADC saturation from low-frequency signals at the RX output. Recommendations are provided to achieve
the most favorable settings on xWRL6432AOP radar devices based on the end application, thus enhancing
radar performance by managing the impact of these issues.

7 References
1. Texas Instruments, Programming Chirp Parameters in TI Radar Devices Application Report
2. Texas Instruments, IWRL6432AOP Single-Chip 57 to 64GHz Industrial Radar Sensor Antenna-On-Package(AOP) Data Sheet
3. Texas Instruments, AWRL6432AOP Single-Chip 57- to 64GHz Automotive Radar Sensor Antenna-OnPackage (AOP) Data Sheet
4. Texas Instruments, IWRL6432AOP Device Silicon Errata
5. Texas Instruments, AWRL6432AOP Device Silicon Errata
6. Texas Instruments, mmWave Sensing Estimator

8 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision * (May 2024) to Revision A (August 2024)
Page• Updated EINF and Average EINF Plots across frequencies, added recommendation about increased noise at60GHz, and added recommendation regarding using TDM MIMO mode instead of BPM MIMO mode inSection 2 ............................................................................................................................................................2• Added recommendation regarding relaxation of TX backoff restriction in Section 4 ......................................... 4

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