Questions tagged [impedance-matching]

Impedance matching is a process of making one impedance equal to another another.

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31
votes
8answers
11k views

Why is 50 Ω often chosen as the input impedance of antennas, whereas the free space impedance is 377 Ω?

In order to efficiently deliver power to a different part of a circuit without reflection, the impedances of all circuit elements need to be matched. Free space can be regarded as a further element, ...
26
votes
3answers
2k views

What happens at the end of a transmission line?

Let's say I wanted to make a widget containing a relay to switch between two antennas. There is a coax transmission line coming in from the transmitter, and two going out, each to a separate antenna. ...
19
votes
5answers
26k views

What can reduce overshoot and ringing on a simple square wave pulse generator?

I've built a simple RC and Schmitt-trigger-based square wave pulse generator. On the breadboard, it has some obvious unwanted qualities due to jumper length, the breadboard itself, etc. Schematic and ...
17
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6answers
2k views

Does Impedance Matching Imply any Practical RF Transmitter Must Waste >=50% of Energy?

According to the maximum power transfer theorem, when a fixed source impedance is given, the load impedance must be chosen to match to the source impedance to achieve maximum power transfer. On the ...
16
votes
2answers
6k views

Can I solder a RG316 coax directly to a PCB instead of using the intended SMA connectors?

I have a length of RG-316 single shield 50Ω coaxial cable carrying a 5.8 GHz signal that I need to connect to a PCB. While cheap relative to most coaxial connectors, SMA connectors are still quite ...
15
votes
4answers
7k views

What's the importance of source impedance termination?

Given a circuit like this: simulate this circuit – Schematic created using CircuitLab What's the importance of R1? One can guess that it's to make the output impedance of BUF1 equal to the ...
12
votes
6answers
3k views

Does non-matching impedance of amplifier and speaker distort the sound?

I'm about to buy a pair of headphones and an audio interface with built in amplifier. The specs say that the amp's impedance is "<30 Ohms". The headphone I'd like to buy is a Beyerdynamic DT 990, ...
11
votes
2answers
10k views

How do I lay out PCB traces for a given “differential impedance”

This is an attempt to craft a good general question and answer for a topic that's been asked before, but only in specific situations. Could you describe what I need to know, prior to laying out a PCB ...
11
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1answer
2k views

Balun/matching network question

I am having problem to verify what an app note (AN068) explains to calculate Balun values. I would appreciate if someone could tell me what/where am I doing wrong? The summary of the RF part: Blue ...
10
votes
3answers
9k views

Question about trace length matching patterns for high speed signals

A colleague and I had a discussion and a disagreement about the different ways high speed signals can be length-matched. We were going with an example of a DDR3 layout. All the signals in the ...
10
votes
2answers
8k views

Effects of impedance matching between 50 and 75 Ohm coaxial cables for 10 Mbit/s, Manchester-coded signals (20 MHz)

TL,DR: This is quite a bunch of text because I have included plenty of background info. However, there will finally be a good, and precise question: Should I use an impedance matching network when ...
9
votes
2answers
15k views

Terminating a 50 Ohm source into 1M Ohm oscilloscope input

Due to buying some equipment several months apart I am now faced with the task of connecting a high speed ,up to 1GHz, light detector that requires a 50\$\Omega\$ load impedance, but my oscilloscope ...
9
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2answers
2k views

Transmission Line: characteristic impedance matching

The textbook explains a situation in which when you have 2 unmatched transmission lines (different characteristic impedance), you can connect a new line in between such that the input impedance would ...
8
votes
2answers
1k views

At what cable length does matching the impedance at the ends of the cable become important?

I'm building a base for a PMT that outputs pulses of width <=1 µs. In Hamamatsu's PMT handbook it states on pg. 112 (emphasis mine): When using a photomultiplier tube which is not a fast ...
8
votes
3answers
1k views

Audio transformer: What to do with an unused winding?

For the purpose of impedance matching and floating a single-ended, ground-referenced signal, I am planning to use an audio transformer like this one. Here's the schematic from the data sheet: My ...
8
votes
2answers
15k views

Why Characteristic Impedance must be 50 ohms?

Where does this number come from? For single ended it must be 50 ohm and for differential pairs 100 ohm. Why? For PCB with controlled-impedance these are that common numbers. Outside of the PCB you ...
8
votes
3answers
2k views

RS485 termination: AC + failsafe + parallel + bidirectional

Knowing that I need to refine my RS485 circuitry, I've been reading. I have a series of specific questions and I hope that you'll indulge me as I describe how I attempted to follow through an ...
8
votes
2answers
10k views

Impedance of an Edge-Coupled Coplanar Waveguide With Ground

How can I compute the differential impedance of an Edge-Coupled Coplanar Waveguide With Ground? I couldn't find any free calculator online, so I wrote a small program which computes the the ...
8
votes
1answer
3k views

Antenna matching network. What? Why? How?

I'm designing a small board featuring a transmitter in the 900 MHz band. Since RF is definitely not my strongest subject, I'm basically trying to follow all the datasheet recomendations regarding ...
8
votes
1answer
410 views

Antenna matching network topology

In tuning an antenna, there are multiple possible topologies that will take it to the middle of the smith chart. Some differences that I can see between them are: Component ESR (losses). Effect of ...
8
votes
2answers
2k views

A poor man's alternative to a network analyzer for antenna matching

I'm doing a small board with a 915 MHz transceiver. A small helical antenna is used, which is located on board with a very short path (10 mm) from the IC, including balun and a matching network. There ...
7
votes
4answers
2k views

Are I/O buffers of ICs design to have 50ohm impedance?

Is it true that 50ohm characteristic impedance is a convention followed for signal carrying PCB tracks? Also, are the IC I/O buffers also designed to have a close to 50ohm impedance to match this?
7
votes
4answers
1k views

What is an audio output transformer? Is it the same thing as an impedance matching transformer?

What is meant by an audio output transformer, does it mean that it is designed to operate at audio frequency or to match impedance?
7
votes
2answers
4k views

How to measure the impedance of PCB trace

I am working on some front end electronics design working at 200MHz to 1 GHz for my MS project. I have designed the circuit and PCB. Trace width were calculated by simulations. After I given this to ...
7
votes
2answers
2k views

Why do we not care about matching the input impedance of non-RF amplifiers?

Talking about BJT topologies: A common base amplifier is always given as an example of an amplifier with very similar characteristics to the CE amplifier but with the low input impedance. simulate ...
7
votes
2answers
5k views

Best method for impedence matching?

Impedance matching is one of the major application of common collector configuration. Is Common Collector configuration the best method for impedance matching? why?
7
votes
1answer
1k views

Wideband matching network design

I have read about matching networks, authors usually will describe a target impedance to be presented, to say, the output of an amplifier, and then they design the matching network. To widen the ...
7
votes
1answer
2k views

Wideband Impedance Matching

I have designed a common-emitter RF amplifier, with input and output impedance matched for my load and source impedance. I have used Smith Chart for the matching. The matching is good for the ...
6
votes
1answer
991 views

Why is the signal amplitude low on the oscilloscope even though the impedance is matched?

I have a photodetector with differential outputs that are each 50-ohm terminated. When I connect one output to the oscilloscope to look at the signal, I see a higher signal amplitude with higher ...
6
votes
2answers
2k views

Matching RF traces

The datasheet for this part states the input and output are internally matched to 50 ohms. However what exactly does this mean? For example the output, would I still need a 50 ohm microstrip to ...
6
votes
1answer
716 views

“Antenna matching networks for dummies”?

I'm working on a project where I'm building a custom NFC antenna that will be connected to a PN532 NFC controller. The antenna has already been designed (for 13.56 MHz) and built, the PN532 is also ...
6
votes
2answers
2k views

Why is the bunny-ears TV antenna normally connected to 300 ohm twin lead?

The bunny-ears antenna is similar to a dipole, which has an impedance of ~75 ohm. Why are the elements of such antennas connected directly to 300 ohm ladder line? Wouldn't that cause mismatch losses (...
6
votes
2answers
3k views

When is impedance matching necessary? Isn't it much less efficient on all other aspects?

I understand that discontinuities of the physical properties of conductors create reflections much like dioptres reflect a bit of light, but : in which cases does impedance matching become ...
6
votes
3answers
513 views

How is transmission line impedance selected?

I understand (roughly) why transmission line impedance has to be matched to the source and the load. What I don't understand is how different technologies have chosen to use different impedance. (...
6
votes
1answer
2k views

Impedance matching with only capacitors?

I need to do impedance matching for 33 + j32 ohm source and 16.5 + j0 ohm load. The copper traces adds 99 ohm impedance and 20 degree electrical length. According to smith Chart below, I need to use ...
6
votes
1answer
2k views

Transmission lines and power transfer

I'm trying to understand power transfer in transmission lines. Consider a voltage source with complex voltage \$V_t\$ and internal impedance \$Z_t\$. Suppose we connect it to a transmission line with ...
6
votes
1answer
757 views

How Significant is VGA Impedance Matching?

I've seen a multitude of different resistor DAC solutions for a VGA signal, however they almost always have an impedance of >200 ohms per color, e.g. when I've been lead to believe that we want to ...
6
votes
1answer
459 views

Help with Matching circuit

I'm using a SAW filter which has balanced input and output. In the datasheet there is shown a matching application for 50ohms balanced output. But plotting the S22 parameters into a Smith Chart and ...
6
votes
2answers
761 views

Transmission Line Impedance Matching Basics

From what I understand, matching a load to a transmission line means that no signal is reflected from the load, which means that at the two sides of the connection point between the load and the ...
6
votes
3answers
2k views

Cable Splitter Loss and Impedance Matching

From my memory, cable splitters (such as for splitting a cable tv coax cable into two televisions) provide impedance matching to prevent signal reflections, etc. If one 50 Ohm line is split into two ...
5
votes
2answers
702 views

What is impedance 'masking' and how it is related to impedance 'matching'?

While reading ECSS-E-ST-20C Standard, I have encountered with a concept named 'impedance mask'. However, I could not find any detailed definition or explanation related to it. In the corresponding ...
5
votes
3answers
1k views

With parallel termination of a transmission line, why does the receiver see the full voltage?

With parallel termination of a transmission line, the line characteristic impedance \$Z0\$ is matched with the pull-down resistance \$Rt\$. But, in that case, shouldn't the receiver see half of the ...
5
votes
2answers
3k views

Causes of ringing in a PCB

Im trying to understand the source of ringing at the termination point of a PCB traces before i delve into actually designing a PCB. For example, by 'termination point', I mean a clock signal ...
5
votes
4answers
615 views

Why should a receiving antenna be impedance matched to 50 ohm instead of a lower impedance?

I'm in the process of getting to grips with RF design and am having some trouble understanding why we should always match antennas to \$50\Omega\$. I understand from the maximum power transfer ...
5
votes
2answers
3k views

Will a 75ohm cable work with (not break) a 50ohm gsm shield?

I need to have a long (100') stretch of cable from my antenna to a GSM box (remote control for heating via GPRS or SMS), and I need to minimize signal loss. In another (totally different) question ...
5
votes
2answers
2k views

Antenna Matching Network

I am trying to match a gsm antena, doing it on a pcb, first time in practice. I understand the whole process to adapt it, I've done it in simulators. However, I don't understand the need for a pi ...
5
votes
3answers
309 views

how to reproduce a matching network of a vendor

I'm trying to create a board using the BGT24MTR chip from infinion. I noticed that they said that there is a Tx/Txx impedance. To compensate for this impedance they created a matching network. Since ...
5
votes
4answers
1k views

Why is input impedance matching done for amplifiers?

I am trying to design a single transistor RF power amplifier. For a single transistor amplifier, the voltage at the base/gate of the transistor determines the current through the transistor and ...
5
votes
1answer
226 views

Quality factor in antenna matching / question about SX1261 LoRa transceiver

I have a question about how the quality factor is determined for RF antenna matching, especially for PI network matching. The reason for the question is the Reference Design for antenna matching for ...
5
votes
2answers
628 views

How to calculate the impedance of a rectifier?

I am working on RF energy harvesting. Now I am trying to calculate the impedance of the rectifier, in order to do the impedance matching. An antenna (50 ohm) receives RF signal (915 MHz) and finally ...

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