Issue link: https://resources.mouser.com/i/1437732
31 littelfuse.com The radar subsystem provides the input for forward and side pedestrian detection and collision avoidance (Figure 3). The circuit generally has two DC power supplies, a low-noise supply powering the analog radar transmitter and receiver circuit blocks, a conventional supply for the logic and communication circuits. Like the camera subsystem power supply, radar subsystem power supplies need over-current protection, transient surge protection, reverse polarity, and ESD protection. One set of protection components can handle over- current and reverse polarity for both supplies. Again, design engineers can employ either a conventional surface-mount fuse or a PPTC resettable fuse. In series with the input line to both supplies, a low-forward- voltage Schottky diode will protect against reverse polarity for both power supplies and the radar subsystem circuit blocks. Design engineers should provide each supply with surge protection at the input. TVS diodes are the recommended surge protection component. They can absorb large amounts of transient power, such as 600W for 1msec. These diodes can also absorb up to 100A of transient current. Designers select a TVS diode based on its transient power rating (400W/600W for low-power transients and 1.5kW/7kW for high-power transients). The waveform generator and the analog front end are part of the radar transmitter and radar receiver. They are separate from the transmitter and receiver blocks because protection components on the transmitter output and receiver input blocks would alter their transmission and reception impedance. The protection components safeguard as much of the circuits as possible. A bipolar diode array is the recommended component for ESD protection. A component similar to the diode array protecting the image sensor in the camera subsystem will provide the necessary ESD protection. The high-sensitivity analog front end requires ESD protection that will not interfere with the circuit's low-level signal integrity. Designers should consider a bipolar polymer ESD suppressor. The ESD suppressor has a capacitance below 0.1pF and draws under 1nA of leakage current for a minimal impact on the circuit's gain and bandwidth. As with the camera subsystem, the radar subsystem sends its information to the vehicle central processing subsystem. Bipolar diode arrays provide ESD protection for both the high and low sides of CAN I/O lines. The Ethernet transceiver can use either diode arrays or polymer ESD suppressors to minimize signal distortion and not impact the Ethernet transmission rate. The radar system is crucial for the safe, proper operation of an autonomous vehicle. It is, like the camera system, the set of eyes that monitor the road. Protection of its circuit blocks from the external environment is essential. Figure 3: Radar subsystem power supplies need over-current protection, transient surge protection, reverse polarity, and ESD protection. (Source: Littelfuse)