Hey everyone, I'm trying to get prepped from my EE Professional Engineering exam and there is a question that I cannot solve in the prep-guide. I'm hoping that someone might be able to help because it can be solved in MatLab (as noted in the book). Here is the problem description:
*You are an engineer working at a major automotive manufacturer that offers a back-up/obstacle-detection system using sensors installed in the rear bumper. The sensors emit an ultrasonic signal ranging from 40-50 KHz. When an object is present, some of the ultrasonic signal is reflected back and the system will alert to driver to the obstacle. In minimal signal required for this detection is -70dBuV. The amplitude of the returned signal is indicative of the object's size.
Alongside the system, there is an electronic module radiating noise at 75 KHz. The level of this noise can be as high as -60dBuV. In order for this back-up system to function properly, the noise must be 15 dB below the desired signal. Note that the impedance and load impedance is 50 Ohms.
Part A. Design an analog filter that will eliminate the impact of the noise on the system in a cost effective manner. Note any impacts that the filter may have on the back-up system.
Part B. Implement an Infinite Impulse Response (IIR) digital filter based on the analog filter in Part A. [Utilize MatLab]
Part C. Implement a Finite Impulse Response (FIR) digital filter that will eliminate the impact of the noise on the system. [Utilize MatLab] *
I really appreciate any help that you all would have to offer! This is the one problem that I haven't been able to solve in the manual!
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Dont know about question A, but B and C I would do in fdatool in Matlab:
While I said I wouldn't answer ...
The question is incomplete requiring assumptions about the phase response and the passband ripple acceptable in the filter. Because of this lack of information you need to choose either a Butterworth or a Chebyshev Type II filter as you analog filters (as they have no passband ripple). Presumably any echo detector is going to be sensitive to phase delays, but there really is nothing you can do in the absence of the required information. This is the type of unspecified job that you should turn down as a professional enigneer.
For the FIR filter, the phase repsonse isn't a problem, but passband ripple is a major problem. In addition a lack of specification on the device implmenting the filter makes evaluating the cost of different filter lengths impossible. Similarly, the frequency at which the signal is sampled isn't specified. In order to prevent aliasing you would need to sample at 150 kHz, but there is no reason to prevent aliasing of a signal you are going to filter out. Creative manipulation of the sampling rate may allow for considerably shorter filters.