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Class 5

Impedance Matching (CH9) The nine impedance matching topologies offered. Distortion of frequency response. PCFILT Editor (CH 21) J / K inverters The Norton Transform The Kuroda Transform Quiz Editor Menu Options Main MIS1 MIS2 MIS3 SCALE NORT The Stubber (Ch 23). Class 5.

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Class 5

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  1. Impedance Matching (CH9) • The nine impedance matching topologies offered. • Distortion of frequency response. • PCFILT Editor (CH 21) • J / K inverters • The Norton Transform • The Kuroda Transform • Quiz • Editor Menu Options • Main • MIS1 • MIS2 • MIS3 • SCALE • NORT • The Stubber (Ch 23) Class 5

  2. When you design a band pass filter for a natural Zo of 50 ohms, you may get element values that are inconvenient, or impossible. The matcher allows you to design the filter at some more convenient impedance level, then connect matching networks at the filter’s input and output, to match it to 50 ohms, or whatever impedance level you desire. These impedance matching sections basically match the filter to your desiered Zo at the center frequency. Since the matching sections don’t have infinite bandwidth, they do distort the filter’s frequency response a little, especially if it’s a broad band design. This distortion is most noticable in the filter’s return loss response. Suppose you had a 111 ohm Zo filter who’s output section was a parallel tank, as shown below. Suppose you wanted to match it to 50 ohms using the “L section” matching circuit also shown. Rather than put two capacitors in parallel, you would probably add up there values, and put a single capacitor in with that value. The matcher does something similar, so it usually changes the value of one of the components in the end resonator. The process will be elaborated in the section ahead on J/K inverters. The Matcher Impedance matching circuit Filter output section …

  3. Parallel output matching options These are the impedance matching options for a circuit with a parallel output resonator. Consider option A. This is simply the “L” matching circuit from the previous page. Note that the output resonator is shown, along with the series matching capacitor. On the previous page, we would have combined the two parallel inductors, and put only a single inductor in the circuit. Here, instead of changing the inductor value, PCFILT has changed the value of the resonator capacitor, which has a similar effect. The value of the resonator component which is being changed is shown, as well as the value of the added matching capacitor. A Node type filter with this type of matching circuit is saved as CLASS5A.DZN.

  4. Parallel(Node) output matching options cont. Option B works like option A, except that an inductor is used. Option C and D accomplish the same thing, with a slightly different circuit topology. Note that the component values are considerably different in options C and D, which may be more convenient. Option E is a two-stage impedance transformer. This will have better bandwidth. Finally, option T is a transformer coupled output, with the required turns ratio given.

  5. Series (Mesh) Matching Options A Mesh filter has a series resonator at its output, so different matching options are provided for it. Here, a mesh filter called CLASS5B.DZN, which has a natural impedance of 25 ohms is being matched to a 50 ohm input impedance. Note that Mesh filter impedances can only be transformed up, and Node filter impedances can only be transformed down with the impedance matching options provided. In the relatively rare event that you need to transform the filter’s impedance the other way, you can use Norton Transforms in the manual circuit editor, to be described later in this lesson.

  6. Starting the Matcher Matcher Status When you click the “maTcher” option on the main menu, the matcher status will cycle between “X”, and “?”. When the matcher status is X, the matcher is turned off. When the matcher status is ?, the matcher will give you the options discussed above, to transform your filter’s I/O impedance to the desired Zo. After you use the matcher, the matcher status will change to the letter code of the matching network you chose. So, if you chose network “A” to match the Source end, and option “F” to match the Termination end of the filter, the matcher status will indicate “Termination: A, Source: F.” When you click “Calculate”, either from the Parameters dialog, or from the main menu, the matcher will run. If the matcher status is “?”, it will give you the options discussed before. If the matcher status is e.g. “Termination: A, Source: F”, the matcher will just automatically apply those same matching networks to your filter as before.

  7. Sheet 100 to 50 ohm impedance transformer (L section) Filter with 100 ohm output Z To illustrate the way the impedance matcher works, consider parallel output matching option A. It’s like having a filter with 100 ohms output impedance, and using an L section to transform the impedance down to 50 ohms. For a more precise understanding, study the Norton Transform. When these two circuits are connected together, we will have two inductors in parallel, which is equivalent to a single inductor, who’s inductance equals that of the parallel combination. That gives us the topology of matching circuit A. Notice that the L section works perfectly at only one frequency. That means that the impedance match will only be perfect at the filter’s center frequency. The matching circuits slightly degrade the VSWR of broad band filters. This is rarely a problem, but if you’re designing to a VSWR spec, you may need to overspecify the VSWR (therefore, amplitude ripple) of the filter, to allow for a little degradation by the matching circuit. Also notice that, because of the matching circuit’s limited bandwidth, the matcher will only work for band pass filters.

  8. Quiz

  9. The Editor • The PCFILT manual circuit editor allows you to perform all manner of truly whiz-bang circuit manipulations quickly and easily. The interface isn’t as intuitive as you might wish, but once you learn the ropes, you can really do a lot of useful things easily. • The editor allows you to perform many functions including: • Change component values. (to make some of them conform to standard value parts.) • Insert and delete components. • Transform elliptic notch sections to “coupled triplets.” • Add J and K inverters, which switch your resonators from series to parallel and vice versa. • Perform PI-Tee transforms, when you have three parts of the same type. (L, C, or R) • Force all the inductors, or resonator caps, to the same value. • Move parts around. • Replace lumped components with equivalent transmission line stubs. (Kuroda transform, etc.) • Scale impedances • Scale frequencies • Transform impedances stage by stage inside the filter (Norton Transform) • We won’t review every function in detail, but we’ll learn what all of the functions do, so you know what’s available. Each of the editor menus has a help function. For Randy Rhea’s tutorial on the Norton, and PI – Tee transforms, see http://eesof.viewmark.com/pdf/eagleware/apps/2024_Transforms.pdf

  10. These are the basic functions in the Mis1 menu. Editor Mis1 This is one example of the coupled triplet functions in the Mis1 menu. These are an optional topology for elliptic function filters.

  11. Note that the Pi-T transform only works on a network of three components of the same kind. The resulting Pi section will have exactly the same S parameters as the original T section. Editor Mis2

  12. Kuroda transforms are used to replace a lumped element with a transmission line structure. The Kuroda transform is exact only at one frequency. If you try to build a whole bandpass filter out of stubs, its stopband response won’t look much like the lumped element version. On the other hand, the technique works pretty well for Notch filters. See http://www.alkeng.com/btext.html Editor Mis3

  13. Editor Mis3

  14. Editor Mis3 If you have e.g. a pair of capacitors in parallel or series, you can use the combine function to make them into a single capacitor. The “Dipole Transform“ function changes the topology of a network which has one finite impedance pole, and one finite zero.

  15. Editor Scale An example of a network, and its dual.

  16. The Norton Transform C1 - C1 C2 Z1 (low Z) Z2 (High Z) Z1 (High Z) Z2 (Low Z) C1 - C1 C2 The Norton transform is an impedance transforming circuit. It works with either inductors or, as shown, capacitors. One of the circuit elements must have a negative value. Since ATC doesn’t have any negative capacitors on the shelf, you have to use the Norton transform with an adjoining circuit which can absorb the negative value. Notice that in the “parallel” network, the negative value is at the high impedance side of the transformer, while in the “series” network, the negative value is on the low impedance side. For a tutorial on the Norton, and PI – Tee transforms, see http://eesof.viewmark.com/pdf/eagleware/apps/2024_Transforms.pdf

  17. The Norton Transform C2 Z1 C1 - C1 C(in) Consider the Norton transform network above. Let’s use it as the input matching network for the filter shown to its right. Suppose C1 = 25pF, and C(in) = 100pF. When we put them in parallel, the combined capacitance will be 75pF. Now we have a realizable network. This is exactly how the Matcher’s option C works. Z1 C2 C1 {C(in) - C1}

  18. Editor Norton

  19. Editor Norton

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