Design of new intelligent reversing radar main control chip

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Design of new intelligent reversing radar main control chip [Copy link]

[Abstract] According to the current status of domestic reversing radar systems, this paper designs a hardware implementation method with better stability and higher intelligence. It can effectively prevent sound wave diffraction, realize self-adaptation to the surrounding environment, and intelligently process the ultrasonic amplitude judgment reflected by objects of different sizes; it can also realize alarm output and display suitable for different applications.
[Keywords] Radar, intelligence, ultrasonic, alarm, application-specific integrated circuit

1 Introduction
As the popularity of automobiles increases year by year, consumers have more requirements for automobile configuration while using automobiles as a means of transportation, especially for comfort and safety. For many drivers, especially novices, reversing is undoubtedly a headache. Reversing radar can help drivers solve this problem, so more and more businesses have entered this market. From the current market situation, domestic reversing radar manufacturers all use single-chip microcomputers with peripheral op amps and phase-locked loop circuits to complete ultrasonic ranging and provide alarms. There is a lack of single-chip solutions. The use of single-chip microcomputer solutions requires manufacturers to have the ability to develop software and hardware, and there are unstable factors in using software control. If the entire system function can be realized with a dedicated chip, for reversing radar manufacturers, it can not only reduce development and production costs, but also greatly improve the reliability of the entire machine.
At present, Chengdu Guoteng Microelectronics Co., Ltd. has taken the lead in launching chip-level reversing radar solutions.
2: System Overview
2.1 System Block Diagram

Figure 1 Chip pin diagram

Figure 2 System internal structure diagram
2.2 Functional overview
The system provides 4 ultrasonic probe interfaces. After receiving the reflected signal, it determines the danger level of the obstacle distance according to the time difference between sending and receiving, and outputs the corresponding alarm signal. After the alarm signal is encoded, it is output in a two-wire differential mode. The content of the output signal includes: the danger level of the obstacle distance detected by each probe, the direction of the nearest obstacle, the distance value of the nearest obstacle and additional messages.
2.3 Interface protocol
The alarm signal adopts a two-wire differential serial output method to improve the transmission accuracy of the transmission signal in a long distance and strong interference environment. The specific format of two-wire differential transmission is: ALOUTP outputs the actual required signal, and ALOUTN outputs the level signal opposite to ALOUTP.
2.3.1 Reversing mode
The alarm signal is output in a data packet format. Each data packet includes 3 bytes. The format and content are as follows:
The first byte: The first byte has four high bits as the start flag, which is used to indicate whether the alarm data is in the reversing mode or the stealing mode. The reversing mode is "0101" and the stealing mode is "1010". The data format in the reversing mode is shown in Figure 3. The lower 2 bits of the first byte are used to output additional messages. The output data indicates whether probe 1 or 4 enters the environmental adaptation mode. S1 indicates whether probe 1 enters the environmental adaptation mode, "1" indicates entering the environmental adaptation mode, and "0" indicates normal reversing mode; S4 indicates whether probe 2 enters the environmental adaptation mode, "1" indicates entering the environmental adaptation mode, and "0" indicates normal reversing mode. The lower 4 bits SX1 and the lower 3 bits SX0 indicate the direction of the nearest obstacle. 00 indicates the direction of probe 1, 01 indicates the direction of probe 2, 10 indicates the direction of probe 3, and 11 indicates the direction of probe 4.

Figure 3 First byte data format
Second byte: As shown in Figure 4, SXA and SXB represent the danger level of the obstacle detected by sensor X. The danger level is divided into four levels: safe, warning, dangerous, and stop, represented by 00, 01, 10, and 11 respectively. For example, the second byte data is "10010000", which means that the first sensor detects a dangerous state, the second sensor detects a warning state, and the third and fourth sensors are in a safe state.

Figure 4 Second byte data format
Third byte: The third byte outputs the distance value of the nearest obstacle. The data format is shown in Figure 5. DA1DA0 represents the first bit of the nearest obstacle distance, encoded in BCD, with a maximum value of 3; DB0~DB3 represents the second bit of the nearest obstacle distance, encoded in BCD, with a maximum value of 9; DC0 represents the third bit of the data, 0 represents 0, and 1 represents 5.

Figure 5 Data format of the third byte
2.3.2 Anti-pickpocketing mode
In anti-pickpocketing mode, the output data packet also includes 3 bytes, but only the first byte is valid data, and the last two bytes are invalid and fixed to '0x00'. The data format of the first byte of the data packet is shown in Figure 6. The upper four bits are the start flag, which is used to indicate whether this alarm data is in the reversing mode or the anti-pickpocketing mode. The reversing mode is "0101" and the pickpocketing mode is "1010". The lower four bits indicate the direction. If the SX bit is 1, it means that the X probe detects a close-range obstacle, and if the SX bit is 0, it means that no close-range obstacle is detected.

Figure 6 Anti-car-pickpocketing mode alarm data format
3 Intelligent principle
3.1 Anti-sound wave diffraction processing
Due to the characteristics of sound wave transmission, the sound wave may return to the probe directly without being reflected by the actual object, causing the processor to think that it is the actual transmitted and received signal, which directly leads to false alarm. However, the interference intensity of sound wave diffraction is difficult to reach the ultrasonic intensity of the actual object's effective reflection, so it can be judged by identification. Once the hardware determines that the received ultrasonic signal is a signal returned by sound wave diffraction, it automatically ignores the result, and the chip continues to wait for whether there is an effective reflection wave within a fixed time △T. If there is, it will be processed, otherwise it will be transferred to the next probe drive.
3.2 Intelligent identification processing
Small objects on the ground, such as bricks, stones, and fruits, will cause ultrasonic reflections and be detected by the probe. These objects do not affect the vehicle's reversing operation, so it is actually a false alarm phenomenon. Therefore, the hardware must handle this situation to improve the accuracy of the alarm.
Intelligent identification processing can be judged by the different amplitudes of ultrasonic waves reflected by objects of different sizes. Therefore, once it is determined how big an object is that will not affect the reversing operation, the amplitude of the ultrasonic wave generated by the object at different distances and the converted level can be clearly measured. The processor can process in the analog or digital part according to the experimental test results and ignore the corresponding received signal according to the requirements. As with the anti-sound wave diffraction processing, after the hardware ignores the invalid reflected wave, it will continue to wait for whether there is a valid reflected wave within a fixed time △T. If there is, it will be processed, otherwise it will be transferred to the next probe drive.
3.3 Environmental Adaptation Processing
When a vehicle reverses into an alley or a parking space with other vehicles parked on both sides, there will be false alarms caused by environmental influences. Because in this case, in most of the reversing processes, the closest detection distance and direction are on both sides of the vehicle body (ultrasonic wave reflection of the wall or vehicles on both sides), but the driver can grasp the distance between the two sides through the mirrors on both sides, and the driver is concerned about the obstacles behind the vehicle body. Therefore, the processor should be able to identify and adapt in this environment.
The solution is to record and count the distances emitted by objects on both sides of the vehicle body. When it is found that the distances detected by probe 1 and probe 4, or one of them, are relatively constant or have a small range of variation within 6 alarm cycles, it is considered to be in the above environment. Therefore, after sending the corresponding message, the processor will no longer output the detection information of the corresponding probe, and only respond to the detection information of probe 2 and probe 3. However, if the detection distance variation range of probe 1 and probe 4 exceeds the set value (±△L meters), it will immediately return to the normal detection state machine mode, and switch to the environmental adaptation mode after the distance on both sides or one side becomes constant again. At the same time, the environmental adaptation mode also has a limit setting value (0.5 meters), that is, when the constant distance is less than 0.5 meters, the processor will return to the normal detection mode and output an alarm message for the detection information of the probe.
3.4 Anti-ground fixed sound wave reflection processing
Since the height and slope of the chassis and rear bumper of various vehicles are different, and the types of probes used by various reversing radar manufacturers are different, such as the single-angle probe with a wide emission range, it is very likely that there will be a fixed reflection after the ultrasonic wave is emitted to the ground. The processor must adapt and identify it as a fixed distance interference.
The processing method is: after each startup, if it is detected that the obstacle distance values received by the four probes within 6 alarm cycles are consistent and constant (the error is allowed to be within ±△L meters), then this distance will be regarded as ground reflection interference, and no response will be made in the future, but wait for other valid ultrasonic transmission signals within the set cycle time.
4 Hardware Implementation4.1
Code Implementation
//+FHDR==================================================================
// Copyright 2005,UESTC,All rights reserved.
// File Name : alarm_deal.v
// Author :Yangbing
// Release History
// Version Date Author Description
// 1.0 20/05/2005 initial version
//-FHDR===================================================================================
`timescale 1ns/10ps
module alarm_deal (clk,resetn,mode,dm,pulse_out,pulse_back,ch_sel,mux_enable,
alarm_out,alarm_outn);
//==================================================================
// input ports declaration
//========================================================================================================================================================================================
……………………………………………………………………………………………………………………………………………………………………
..
//=======================end module ====================================
endmodule
//=================== alarm_deal verilog file end ===============================
4.2 Circuit Structure
This system adopts 0.5u mix signal technology. With the support of the working platform of Chengdu Guoteng Microelectronics Co., Ltd., the comprehensive verification and layout design work have been successfully completed. The comprehensive circuit structure is shown in Figure 7:

Figure 7 Circuit structure

Figure 8 Layout structure

4.3 Layout design
This layout design adopts 0.5u mix signal process, and the layout structure is shown in Figure 8.
5 Application system design

Figure 9 Typical application
The core of this typical application system (Figure 9) is composed of the data processing part with the reversing radar main control chip GM3101 independently developed by Chengdu Guoteng Microelectronics Co., Ltd. as the core and the data display part with the single-chip microcomputer as the core. After testing, it
fully meets the requirements of high-end products on the market, and even has improvements in display distance, display sensitivity, system working stability, etc. Compared with other reversing radar systems on the market, it has the following advantages:
(1) Anti-interference and reliability
Traditional reversing radars use single-chip microcomputers based on RAM and ROM structures, so they cannot be compared with pure hardware ASIC chips in terms of electromagnetic interference resistance and stability. The GM series reversing radar dedicated chip works reliably and stably without freezing.
(2) Simple design and easy production
Traditional reversing radars are complex in design, with many components and a greater possibility of failure. They also require programming, production and debugging are troublesome, the performance of separate components varies greatly, and the overall indicators are not easy to unify. The GM series reversing radar product design and application are very simple. It only needs an external probe and a small amount of resistors and capacitors to work, which reduces the development workload and significantly reduces the area and size of the host, which can be 1/3 the size of traditional reversing radars.
(3) Automotive-grade working indicators
GM series reversing radar products are designed with full automotive-grade working environment indicators, which are far higher than civilian-grade single-chip microcomputers and fully meet and adapt to the working conditions in the car.
(4) Reliability of data communication
GM3101 and its matching display part adopt differential communication, which has extremely strong anti-interference and reliability, which cannot be achieved by single-chip microcomputers.
(5) Preventing interference from sound wave diffraction
Traditional reversing radars are difficult to handle the interference of sound wave diffraction on detection due to the processing power of single-chip microcomputers. GM series reversing radar products can completely filter out the interference of sound wave diffraction, making detection more reliable and accurate.
(6) Intelligent recognition function
Since any object will reflect sound waves, the reversing radar can detect the distance of the object. In actual reversing applications, many small objects, such as fruits and softballs, will be considered obstacles by the reversing radar and alarm, but these small objects do not affect the normal reversing of the vehicle. Therefore, the GM3101 chip can intelligently identify the material properties and size of the object, and then perform alarm processing, avoiding the above-mentioned unnecessary alarms.
(7) Preventing interference from fixed ground reflections
The height of the rear bumper and the inclination of the vertical surface of the rear of various vehicles are inconsistent. Sometimes the installation angle of the probe is too low, and the sound waves are reflected on the uneven ground, causing the reversing radar to mistake it for an effective obstacle and alarm. The GM3101 chip can automatically adapt to the reflection interference caused by the ground and avoid false alarms.
(8) Environmental intelligent adaptation
When a vehicle enters an alley or a parking space with vehicles parked on both sides and reverses, since the distance between the two sides of the vehicle is smaller than the distance behind the vehicle for a long time, ordinary reversing radars can only respond to the detection at the closest distance, making it impossible for the driver to understand the real situation behind the vehicle. GM3101 can intelligently judge the situation in the parking area, allowing the reversing radar to focus on the situation behind the vehicle that the driver is more concerned about, and will not ignore the detection on both sides.
6 Summary
Through the detailed analysis and design of the Chengdu Guoteng Microelectronics reversing radar system, the interference of sound wave diffraction, environmental adaptation, intelligent recognition and processing, and alarm output selection corresponding to different application situations have been successfully realized. This system can effectively prevent unstable factors in software control, which not only reduces the development and production costs of reversing radar production, but also greatly improves the reliability of the whole machine. Currently, the chip GM3101 has been put on the market.

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