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# Tag Info

## Hot answers tagged impedance-matching

Accepted

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

You can simply forget about impedance matching for home Audio. Impedance matching is needed only where the wavelength of the signal comes close to the length of the cable transporting that signal. ...
• 79.8k
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### How do I lay out PCB traces for a given "differential impedance"

I'll try to answer this briefly, but a great resource for this type of question is Eric Bogatin's Signal and Power Integrity -- Simpified. You've listed and described several very high speed ...
• 6,226
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### Why is 50 Ω often chosen as the input impedance of antennas, whereas the free space impedance is 377 Ω?

The input impedance of certain devices/circuits (transformers) does not neccessarily need to match their output impedance. Consider a 50Ω (or whatever impedance) antenna as transformer that ...
• 16k
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### Does Impedance Matching Imply any Practical RF Transmitter Must Waste >=50% of Energy?

If your power source is a zero ohm output voltage source, followed by a 50 ohm resistor, then yes, what you think is correct. However, practical RF amplifiers (at least ones designed to be efficient)...
• 155k
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### Trace impedance ohm meaning

Ohms has dimensions volts/amps. When applied to a resistor, it's the ratio of applied voltage to current through the resistor. When applied to the behaviour of transmission lines, it's the ratio of ...
• 155k

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

All the answers name some valid points, but they fail to really answer the question which I want to repeat for clarity: ...
• 313
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### Why is length matching performed with the clock trace length as the target length?

Data is sent in respect to the clock signal. Data has to be stable before the clock edge (setup time) and it has to be stable after the clock edge (hold time). If the clock wiring is too long compared ...
• 119k
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### Why is the signal amplitude low on the oscilloscope even though the impedance is matched?

Do not confuse power transfer with voltage transfer. If the source is indeed 50 ohms, and your scope is set to 50 ohms, it becomes a voltage divider and what you see is half the voltage that you will ...
• 46.2k

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

Very few do. If your chip's datasheet does not say it has 50-ohm termination, then it almost certainly does not. Traditional CMOS and TTL logic does not provide matching termination, though a few ...
• 125k
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### Can I solder a RG316 coax directly to a PCB instead of using the intended SMA connectors?

Soldering directly to the pads of the SMA connector instead of using SMA connectors should work fine electrically. The obvious problem is that the cable is no longer removable. If you're fine with ...
• 310k

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

No, the 50-Ohms is not a convention for PCB tracks to carry signals. The 50 Ohms is a standard for coaxial cables and corresponding interconnects - dozens and dozens various SMA/SMB, BNC, type-N, etc. ...
• 38.6k

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

RF amplifiers do NOT in general have an output impedance remotely close to 50R..... They are however designed to drive a 50R load! Much like audio amplifiers the source impedance is generally far ...
• 17k
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### Output impedance of STM32H743 MCU?

Output impedance of (typically CMOS) output driver for any MCU can be calculated/estimated from VOH and VOL electrical characteristics from datasheets. The meaning of this table is that if a 8 mA ...
• 38.6k

### Coax cable - capacitive load

how does my signal source see the whole cable? The characteristic impedance ($Z_0$) of any transmission line be it coax or twisted pair (screened or unscreened) is determined by: - Z_0 = \sqrt{\...
• 426k

### Using a miniature BNC connector on a PCB to measure high-frequency content with an oscilloscope

You might consider adding an attenuator probe to your PCB consisting of a single series resistor. The 50-ohm coax cable to your oscilloscope can be any length - the oscilloscope input at the far end ...
• 22.2k
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### Impedance matching for high speed pulse generators

The characteristic impedance of any cable at high frequencies is determined by the inductance per unit length and the capacitance per unit length. It should not to be regarded as a conventional lossy ...
• 426k

### How is transmission line impedance selected?

Some impedances are more suited to higher power transmission and some are more suited to producing lower losses: - Diagram taken from Techplayon but is available from other sources. The one below is ...
• 426k

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

designed to operate at audio frequency or to match impedance? Both. The specification of a transformer covers both its frequency range, and its turns ratio. It gets more difficult to design a ...
• 155k

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

You can certainly forget about "impedance matching" for any reasonable quality amplifier, because the impedances are intentionally not matched! The output impedance of a good quality audio amp should ...
• 1,100

### How to measure the impedance of PCB trace

Unless you want to do your own S-Parameter de-embedding mathematics, you must fit a 50$\Omega$ connector to at least one end of the trace. You can either fit a connector to the other end, or a good ...
• 155k

### Transmission Line: characteristic impedance matching

Impedance matching is tricky, but the role of a quarter wave transmission line is to map from one impedance to another. The actual impedance of the line will not match either the input or the output ...
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### Audio transformer: What to do with an unused winding?

Option 3 is best It does not matter whether you connect the primaries together or not, you are still stuck with the primary voltage appearing on pins 3 and 4 as a result of transformer action, and ...
• 155k
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### At what cable length does matching the impedance at the ends of the cable become important?

The rule of thumb I use is that anything exceeding 1/20 of the wavelength is to be considered a transmission line. And bad terminated transmission lines have reflections that distort the signal. To ...
• 3,081
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### How and why is impedence matching done for a CAN bus?

The "terminators" of a CAN bus serve two purposes: They terminate the transmission line. The type of CAN you are referring to is intended to be implemented as a twisted pair. 120 Ω is roughly ...
• 310k
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### Class F Amplifier Harmonic Termination

From the article you've linked (p.70): [...] the efficiency of the power amplifier can be limited by the transistor output capacitance [...] $C_{ds}$, [...] if this capacitance is not ...
• 5,741

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

50 ohms is a convention. It's much more convenient if a room full of equipment all uses the same impedance. Why is it the convention? Because coax is popular, and because 50 ohms is a good value for ...
• 56.6k
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### Why should a receiving antenna be impedance matched to 50 ohm instead of a lower impedance?

However, what if you are only using your antenna to receive? An antenna (e.g. monopole) has a complex impedance characteristic versus frequency: - Picture from my answer here. So, if you are tuned ...
• 426k