Case Study Competition Be an engineer of the future! Innovating cars using the latest instrumentation!

Transcription

1 Case Study Competition 2013 Be an engineer of the future! Innovating cars using the latest instrumentation!

2 The scenario You are engineers working on a project team that is tasked with the development of a vehicle radar system for automatic detection of the distance to the car ahead during travel. Based on the requirements definition for a frequency-modulated continuous-wave (FMCW) radar system for distance detection, you will first consider the general system aspects related to a radar system. A monolithic microwave integrated circuit (MMIC) is used to handle signal processing and to provide the required transmit power to the individual antenna elements in the radar system. You need to prepare the MMIC s level diagram and topology taking into account the technologies available in your organization. The radar system must be connected as a module to the CAN bus of the vehicle's electrical system. This work will be carried out by a technical department under your commission. You will develop methods that allow you to test signal integrity on the bus system. Finally, it needs to be verified that the individual components in the radar system do not mutually interfere with one another, that the vehicle as a whole complies with the legal regulations on electromagnetic compatibility (EMC) and that the measured data from the radar system can be transmitted to an on-board processing unit and from there over a radio link to a traffic control center. Rohde & Schwarz Case Study Competition

3 Aspects of radar system design The radar system should have a range of 120 m and a center frequency of 77 GHz. Your customer also expects the radar to have a field of view of ±20. The overall system to be developed consists of a sensor module and an ABS control module, which communicate over the CAN bus. Exercise 1 (4 points) The radar system should be capable of reliably detecting a person who suddenly appears in front of a vehicle under any weather conditions and especially during rain. Use the radar equation to determine the transmit power required for the radar system. Based on your experience, you can initially assume that the antenna has an isotropic gain of 20 dbi. You can assume that the receiver has a sensitivity of 106 dbm. Note: Fluctuation losses upon reflection at the target and internal losses of the transmitter/receiver should be neglected. Rohde & Schwarz Case Study Competition

4 Aspects of radar system design Exercise 2 (2 points) You intend to use a solid-state amplifier to provide the transmit power. Your preferred solid-state technology unfortunately only produces 13 dbm transmit power due to its breakdown voltage. Your colleague proposes using a cost-intensive technology with a higher breakdown voltage and maximum power. Explain to your colleague why this is not good practice and why you would prefer to increase the antenna gain. How much antenna gain would be necessary to provide the required transmit power? Rohde & Schwarz Case Study Competition

5 Aspects of radar system design Exercise 3 (2 points) The senior manager proposes to you to reduce the frequency to 24 GHz in order to cut costs. Explain why this is not good practice and explain why you think that optimizing the antenna gain would be a better approach. How much antenna gain would be necessary in this case? Rohde & Schwarz Case Study Competition

6 Aspects of radar system design Exercise 4 (3 points) You choose a gain of 26 dbi for the antenna in order to compensate for losses in the transmit and receive paths. What is the effective area required for this antenna if no losses are assumed? If the antenna consists of an array of slot radiators, how many radiators are required? Exercise 5 (1 point) With the necessary gain, the antenna does not illuminate the complete field of view required for the radar system. What could you do to achieve full coverage? Rohde & Schwarz Case Study Competition

7 Aspects of amplifier topology Exercise 6 (2 points) The radar system s output amplifier is to be implemented as an integrated circuit. Amplifiers can be implemented in different classes. a) What class do you choose? b) What advantages are relevant to your choice and what disadvantages do you accept? Rohde & Schwarz Case Study Competition

8 Aspects of amplifier topology Exercise 7 (4 points) a) The amplifier should have an output power of 13 dbm. The technologies listed in the table below are available. Which technology do you choose? b) For what reason(s) are you choosing this technology? SiGe BiCMOS GaAs GaN CMOS Unit Costs per mm Transistor breakdown voltage V Maximum current density in transistor ma/µm Expected yield % Rohde & Schwarz Case Study Competition

9 Aspects of amplifier topology Exercise 8 (4 points) Estimate the amplifier's power loss. In your opinion, what are the reasons why it is not possible to attain the maximum theoretical efficiency? Exercise 9 (2 points) The radar system is intended for use in the automotive sector, and production costs play a major role. It is therefore necessary to calculate the chip price starting in the development phase. What costs are involved in chip development and production? Prepare a qualitative list of the individual cost items. Rohde & Schwarz Case Study Competition

10 Predicted lifetime (hours) Aspects of amplifier topology Exercise 10 (5 points) Since the chip will also contain circuit components other than the amplifier components, assume a total power loss of 500 mw. Estimate the lifetime of a chip in the automotive sector. Based on your estimate and using the diagram below, determine the maximum thermal resistance of the package. What criteria do you take into account when selecting the package? Junction temperature Rohde & Schwarz Case Study Competition

11 Troubleshooting the CAN bus The radar sensor in the car's bumper is connected to the car's control computer via a CAN bus. When the radar sensor is integrated into a prototype of a new car, the control computer cannot establish a connection to the sensor. Your task is to determine the cause. Exercise 11 (5 points) In order to become familiar with the CAN bus, prepare a brief overview of the key technical specifications (data rates, topology, functions). Exercise 12 (4 points) What do you think are the advantages and disadvantages of CAN bus systems in automobiles? Rohde & Schwarz Case Study Competition

12 Differential signals Exercise 13 (2 points) On the CAN bus used in the vehicle electrical system, data is transmitted using differential signals. Give a clear explanation of how differential signal transmission works. Exercise 14 (2 points) State the main advantage and the main disadvantage of transmitting data using differential signals. Rohde & Schwarz Case Study Competition

13 Measuring signal integrity I The following figure shows an equivalent circuit diagram for the CAN bus: CAN- nodes Knoten CAN- nodes Knoten CAN- nodes Knoten CAN_H CAN_H CAN_L verdrillte twisted Leitung pair CAN_L Using an oscilloscope, you would like to measure the quality of the signals on the CAN bus to which the radar sensor is connected. The CAN bus has a data rate of 1 Mbit/s in this case. Exercise 15 (1 point) There is a rule of thumb that says that for analyzing a digital data signal, the combined bandwidth of the oscilloscope and probe must extend up to at least the 7th harmonic of the data signal. What is the frequency of the 7th harmonic of the CAN bus signal used? Rohde & Schwarz Case Study Competition

14 Measuring signal integrity II To measure signals on both lines of the CAN bus, you would like to use the R&S RT-ZP10 passive probe. The following figures show what is printed on the probe: Exercise 16 (3 points) What does "CAT II" mean? Can you even use this passive probe to measure signals on the CAN bus? Exercise 17 (3 points) When used on the CAN bus, what is the probe's impedance at the 7th harmonic of the CAN bus signal? Do you think this passive probe is suitable here? Rohde & Schwarz Case Study Competition

15 Measuring signal integrity III You are using two probes to measure the two signals CAN_L and CAN_H on the CAN bus. The signals appear highly distorted. Your colleagues think the bus is not working because of this distortion. Exercise 18 (3 points) How can you demonstrate using a simple mathematical function on the oscilloscope that this is common-mode interference and is therefore not responsible for the malfunctioning of the bus (the signal obtained using trace mathematics is shown at the top of the above diagram)? Rohde & Schwarz Case Study Competition

16 What's wrong here? After removing the commonmode interference, distortion is no longer present in the bus signals, as revealed by the diagram. Yet, the CAN bus is still not working. Exercise 19 (3 points) Can you explain why the bus is still not working? Rohde & Schwarz Case Study Competition

17 Now it's working! Finally, the CAN bus is working (see diagram). Because of the problems encountered during startup, your project supervisor is concerned about the reliability of the CAN bus. Exercise 20 (3 points) Convince the project supervisor that the error detection mechanisms available on the CAN bus are adequate. Good technical arguments are required. Rohde & Schwarz Case Study Competition

18 EMC aspects Exercise 21 (1 point) Before the radar module can go into production, an electromagnetic compatibility (EMC) test is mandatory. What two basic directions of impact must be taken into account when testing a vehicle for electromagnetic compatibility with its environment? Exercise 22 (4 points) Electromagnetic susceptibility (EMS) testing in line with ISO requires measurements in the frequency range between 80 MHz and 18 GHz at an electric field strength of up to 100 V/m. What electrical properties are required for the room in which the testing is performed? What type of antenna would be suitable for broadband EMS measurements in the frequency range between 80 MHz and 200 MHz? Sketch the radiation pattern for this type of antenna in the E and H planes. Rohde & Schwarz Case Study Competition

19 EMC aspects Exercise 23 (4 points) The antenna you chose for electromagnetic susceptibility testing has a gain of 22 dbi. How much power do you need to supply to its feedpoint, assuming a lossless antenna, in order to obtain an effective field strength of 100 V/m at a distance of 2 m in the main direction of radiation? Exercise 24 (7 points) The collision warning radar system operates in frequency-modulated continuouswave (FMCW) mode. The carrier frequency is modulated between 76 GHz and 77 GHz with a sawtooth signal with a period of 100 μs. The radar module must be very compact to keep costs under control. Unfortunately, your mechanical designer did not pay attention to spatially separating the analog and digital signal lines while creating the layout. The IF signal, which is carried by a microstrip line with a 50 characteristic impedance, runs for some length in parallel to the LVTTL line, which connects the microcontroller to the CAN bus driver. The two coupled lines can be characterized as a linear four-port network as shown in the sketch on the next page. Rohde & Schwarz Case Study Competition

20 EMC aspects C Z out : Z in : 100 k Bidir Drv A/D CAN Port Z 0i k 4 50 Z out : 50 Z in : f t DB( S(1,1) ) DB( S(1,2) ) DB( S(1,3) ) DB( S(1,4) ) Frequency (GHz) DB( S(3,1) ) DB( S(3,2) ) DB( S(3,3) ) DB( S(3,4) ) Frequency (GHz) DB( S(4,1) ) DB( S(4,2) ) DB( S(4,3) ) DB( S(4,4) ) DB( S(2,1) ) DB( S(2,2) ) DB( S(2,3) ) DB( S(2,4) ) Frequency (GHz) Frequency (GHz) Rohde & Schwarz Case Study Competition

21 EMC aspects Exercise 24 (continued) Assume that a radar target at a distance of 100 m produces an IF power of 5 dbm. Can the coupling of the two lines in this situation lead to bit errors on the CAN bus? Note: The CRC error correction provided by the CAN bus protocol should not be taken into account here. Rohde & Schwarz Case Study Competition

22 EMC aspects Exercise 25 (3 points) The distance to the car in front as measured by the radar provides, in conjunction with the vehicle's speed as determined by the tachometer, a measure of the current traffic density. This information can be transferred to an on-board processing unit and then sent via a radio link to a traffic control center, which generates traffic congestion warnings or navigation suggestions. A radio link of this sort could be established, for example, in line with the IEEE p standard, which is a further development of the IEEE 802 WLAN standard specifically for vehicles (Car-2-X). The frequency bands allocated for IEEE p communications worldwide are around 5.9 GHz. The radio link is established either between a stationary transceiver (road side unit, RSU) and a mobile transceiver (on-board unit, OBU) or between two OBUs. Name two physical effects that would make radiocommunications with an OBU more difficult compared to communications with an RSU. Which of these effects do you consider to be the more serious (state your reasons)? Rohde & Schwarz Case Study Competition

23 Now get going and good luck! We hope you enjoy solving these exercises and wish you the best of luck with them! Rohde & Schwarz Case Study Competition