Transmission Line Design Handbook Pdf Free Download [TOP]

Over the last ten to twenty years, advances in IC fabrication technology have led to huge increases in both the operating frequencies and edge rates of switching signals in digital circuits. This has really pushed digital circuit design into the frequency domains that were previously considered RF and/or microwave. As a result, it has become important to consider the transmission line parameters of the connecting traces used for digital signals in circuit boards as much as they have always been considered for RF connections.

A transmission line is a two or more port network connecting a generator circuit at the driving end to a load at the receiving end. Transmission lines most commonly consist of two conductors (although sometimes more). A three phase power transmission line for example uses three or more conductors. Examples of commonly used transmission lines are a simple two-wire line, a co-axial cable, or a circuit board trace and return path as in the case of microstrip and stripline.

Transmission Line Design Handbook Pdf Free Download

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At DC and low frequencies, where wavelength is much longer than the circuit path, a transmission line was often thought of in terms of resistance only and early transmission line modeling was based on resistive loss with voltage drop as the only real concern. Analysis could be done using traditional static circuit theory and lumped elements. An equivalent electrical circuit used for DC analysis of low speed transmission lines could be created with resistive elements only, as follows:

At higher frequencies however, the wavelength is now much shorter than the typical circuit size, the parasitic inductive and capacitive elements of the transmission line start to have an effect and the behavior of the transmission line is considerably different. Analysis requires high frequency transmission line theory with distributed elements.

An equivalent electrical circuit for a high speed transmission line can be drawn with only passive components in a ladder network. The complete transmission line is made of cascaded sections of the same equivalent circuit. For exact analysis we would need an infinite number of infinitely small segments of length x. The transmission line can then be represented as follows:

If we assume the transmission line is physically constant and the dielectric is uniform over the entire length, then usable results can be modeled by defining the characteristics of the transmission line per unit length.

There is a wealth of information regarding the analysis of transmission line characteristics and the effect these characteristics have on high frequency signals. It is important that layout designers understand that the traces they create in their designs are not simply copper connections to transfer a signal from one point to another, albeit that is what they actually do. These connections are actually transmission lines, and need to be designed carefully if they are not to cause the design to function poorly or even not at all.

The higher the operating frequencies, and more importantly, the faster the edge rates of the signals, the more important it is to understand that transmission line design needs to be considered. Higher signal speeds and edge rates means that what used to be considered a short trace is now actually a long trace in terms of the wavelength of the signal.

Detailed transmission line analysis is an extremely complex topic, and is well beyond the scope of this guideline. In the next sections some common types of planar transmission lines used in circuit board design are shown and the formulae for calculating the characteristic impedance and propagation delay. This is by no means a complete reference on any of these transmission line structures. One of the most complete references available, and highly recommend to both layout designers and electrical engineers, is:

Use the microstripLine object to create a microstrip transmission line. A microstrip line is a transmission line that is a basic building block for most RF planar microwave devices. You can use this transmission line to connect two PCB components or to create components such as filters, couplers, and feeding elements of various types of antennas.

This PCB object supports behavioral modeling. For more information, see Behavioral Models. To analyze the behavioral model for a microstrip transmission line, set the Behavioral property in the sparameters function to true or 1

I was recently needing to design an antenna feed line for a particular transceiver chip we are using. This chip called for the feed to be on the top layer, copper keepouts on the inner layers, and a bottom-layer ground. By definition this resulted in a GCPW structure.

A transmission line loudspeaker is a loudspeaker enclosure design which uses the topology of an acoustic transmission line within the cabinet, compared to the simpler enclosures used by sealed (closed) or ported (bass reflex) designs. Instead of reverberating in a fairly simple damped enclosure, sound from the back of the bass speaker is directed into a long (generally folded) damped pathway within the speaker enclosure, which allows far greater control and use of speaker energy and the resulting sound.

Inside a transmission line (TL) loudspeaker is a (usually folded) pathway into which the sound is directed. The pathway is often covered with varying types and depths of absorbent material, and it may vary in size or taper, and may be open or closed at its far end. Used correctly, such a design ensures that undesired resonances and energies, which would otherwise cause undesirable auditory effects, are instead selectively absorbed or reduced ("damped") due to the effects of the duct, or alternatively only emerge from the open end in phase with the sound radiated from the front of the driver, enhancing the output level ("sensitivity") at low frequencies. The transmission line acts as an acoustic waveguide, and the padding both reduces reflection and resonance, and also slows the speed of sound within the cabinet to allow for better tuning.

Transmission line loudspeakers designs are more complex to implement, making mass production difficult, but their advantages have led to commercial success for a number of manufacturers such as IMF, TDL, and PMC. As a rule, transmission line speakers tend to have exceptionally high fidelity low frequency response far below that of a typical speaker or subwoofer, reaching into the infrasonic range (British company TDL's studio monitor range from the 1990s quoted their frequency responses as starting from as low as 17 Hz depending upon model with a sensitivity of 87 dB for 1 W @ 1 meter), without the need for a separate enclosure or driver.[1][2] Acoustically, TL speakers roll off more slowly (less steeply) at low frequencies, and they are thought to provide better driver control than standard vented-box cabinet designs,[3] are less sensitive to positioning, and tend to create a very spacious soundstage. Modern TL speakers were described in a 2000 review as "match[ing] reflex cabinet designs in every respect, but with an extra octave of bass, lower LF distortion and a frequency balance which is more independent of listening level".[4]

Although more complex to design and tune, and not as easy to analyze and calculate as other designs, the transmission line design is valued by several smaller manufacturers, as it avoids many of the major disadvantages of other loudspeaker designs. In particular, the basic parameters and equations describing sealed and reflex designs are fairly well understood, the range of options involved in a transmission line design mean that the general design can be somewhat calculated but final transmission line tuning requires considerable attention and is less easy to automate.

I have an intuitive abhorrence of resonance enhancement to give a loudspeaker more "kick" or apparent bass as they can sound "single-noted". Yes you can pick out the bass rhythm but what about the melody. What a transmission line gives in my experience is a much smoother and more realistic bass quality.

A transmission line is used in loudspeaker design to reduce time, phase, and resonance related distortions, and in many designs to gain exceptional bass extension to the lower end of human hearing, and in some cases the near-infrasonic (below 20 Hz). TDL's 1980s reference speaker range (now discontinued) contained models with frequency ranges of 20 Hz upwards, down to 17 Hz upwards, without needing a separate subwoofer.[2] Irving M. Fried, an advocate of TL design, stated that:

Essentially, the goal of the transmission line is to minimize acoustical or mechanical impedance at frequencies corresponding to the fundamental free-air resonance of the bass driver. This simultaneously reduces stored energy in the driver's motion, reduces distortion, and critically damps the driver by maximizing acoustic output (maximal acoustical loading or coupling) at the terminus. This also minimizes the negative effects of acoustic energy that would otherwise (as with a sealed enclosure) be reflected back to the driver in a sealed cavity.[9]

Transmission line loudspeakers employ this tube-like resonant cavity, with the length set between 1/6 and 1/2 the wavelength of the fundamental resonant frequency of the loudspeaker driver being used. The cross-sectional area of the tube is typically comparable to the cross-sectional area of the driver's radiating surface area. This cross section is typically tapered down to approximately 1/4 of the starting area at the terminus or open end of the line. While not all lines use a taper, the standard classical transmission line employs a taper from 1/3 to 1/4 area (ratio of terminus area to starting area directly behind driver). This taper serves to dampen the buildup of standing waves within the line, which can create sharp nulls in response at the terminus output at even multiples of the driver's Fs.

In a transmission line speaker, the transmission line itself can be open ("vented") or closed at the far end. Closed designs typically have negligible acoustic output from the enclosure except from the driver, while open ended designs exploit the low-pass filter effect of the line, and the resultant low bass energy emerges to reinforce the output from the driver at low frequencies. Well designed transmission line enclosures have smooth impedance curves, possibly from a lack of frequency-specific resonances, but can also have low efficiency if poorly designed. e24fc04721