lesson38

lesson38 - Lesson 38 Filters III (Variant of Section 12-4)...

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Lesson 38 – Filters III (Variant of Section 12-4) (Variant of CLO 12-2) This is the last of two lessons on filter analysis and design. The first focused on first-order LP and HP. The second focuses on BP and BR. In discussing BP and BR filters start by using ideal models – students seem to grasp easily the concept when presented that way. Again re-introduce our block diagram and point out that in an ideal system |H(j ϖ )| , the filter’s gain, can be only either “1” or “0”. If the signal falls in the pass band it comes out the output unscathed ( |H(j )| = 1). If, however it falls in the stop band it does not exit at all ( | H(j )| = 0). If we look at the ideal filters, we see that the LPF will pass all signals up to LP and the HPF will pass signals greater than HP . Since the two filters are connected in cascade, only those signals that are between HP and LP will pass through both filters. Hence, we have a BPF with a Bandwidth, B, of HP LP . Once they appreciate how an ideal filter works draw in “real” filter curves so they can see what performance to expect. Next, show how they can design a BRF. There are two differences between BPF and BRF. The first is that in a BRF the two filters are connected in parallel rather in cascade – and therefore requiring a summer. The other difference is that the LP filter’s cutoff LP is the desired low frequency cutoff of the filter. In a BPF the LP is the cutoff of the HP filter. Similarly, that the HP filter’s cutoff HP is the desired high frequency cutoff of the filter. In a BPF the HP is the cutoff of the LP filter. Devote a good amount of time to actually designing a BPF. Since there will be a HPF and LPF designed, this exercise will review the earlier lesson as well as this one. Once a student understands how to design a BPF designing a BRF is not difficult. In their BPF design efforts the students will need to find the transfer function for their particular design. Then they can partition the solution into two or three stages. They can design it as Filter 1
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This note was uploaded on 10/12/2010 for the course MAE 140 taught by Professor Mauriciodeoliveria during the Spring '08 term at UCSD.

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lesson38 - Lesson 38 Filters III (Variant of Section 12-4)...

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