Questions tagged [characteristic-impedance]

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30 views

Matching line driver output impedance over wideband

I'm designing a high impedance line tap for 10-10GBASE-T ethernet signaling. In the AFE I have a JFET LNA for high input Z which goes to a var. gain amplifier that is a fully differential ADC driver. ...
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1answer
38 views

How does wiring two LNAs in parallel affect charactaristic impedance?

It appears that wiring amplifiers in parallel improves the signal to noise ratio. I thought I would experiment with two SAV-541+ LNAs in parallel and see how they perform: How does wiring an LNA in ...
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1answer
50 views

Coax Cable Wave Impedance, Capacitive Load

I am studying the behaviour of cables over frequency, especially what a source sees, and have 2 Questions, as I did some simulations in LtSpice. As a model for the cable I used the "Lossy ...
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1answer
20 views

Load to Source impedance match for non-constant load impedance

i have a rf-system that is working in frequency range of 100 MHz and try to match the impedance of the load to the source system (50 Ohm). So, in general, i know that a network (P- or T-Network) has ...
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1answer
35 views

Impedance Matching of an Antenna

I am reading about antenna design and have a few questions which I could not get clarified. I read about "Stubs". I got to know that Stubs are used for impedance matching of an Antenna either by ...
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1answer
39 views

Stripline (with target impedance) between ground and power planes?

The common idea for a stripline is that the trace is sandwiched between two ground planes. My question: is it the same, for the purpose of characteristic impedance, to have a ground plane or a power (...
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1answer
118 views

Why is 50ohm sometimes used as a differential impedance?

I'm creating a design where I convert an RF single-ended signal to a differential signal with a 5400BL15B050E RF balun that is then fed to a ADL5802 RF mixer. The balun datasheet specifies the single ...
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1answer
71 views

The explanation about why do we define the formula of Characteristic impedance,propagation constant and Velocity propagation

There is a long transmission line 1.Characteristic impedance \$Z_C=\sqrt{\frac{z}{y}}=\sqrt{\frac{impedance}{admittance}}\$,and in the lossless line,\$Z_C=\sqrt{\frac{L}{C}}\$ 2.propagation ...
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5answers
2k views

Physics behind signal reflections and series termination

I have been looking for cause of signal reflections in transmission lines. Everywhere it is concluded that the reason is impedance mismatch. I can understand if the impedance changes in the path of ...
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0answers
40 views

Transmission Line Impedance 3 phase

I have the following question that I can't seem to figure out. The question ask to solve for the impedance of a 3ph transmission line. I've found the De (distance relative distance) and XL using the ...
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1answer
59 views

Confusion in understanding characteristic impedance and input impedance of an open circuited transmission line

The characteristic impedance Zo can be derived by considering LC sections throughout the line with open circuit at the end of the line, and this value is independent of length of the transmission line ...
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0answers
38 views

Impedance matching to minimize VSWR

I was trying to determine what the impact of impedance mismatching would be to an RF output and I came across this. About half way down the page, the author makes this claim. In general, if the ...
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2answers
91 views

Ringing problems on the output of inverter/comparator

I'm trying to drive some RF switches that need 0 to -5 V control logic with a 0 to 3.3 V signal. I found 2 topologies for this level shifting effect, one using a comparator and one using an inverter. ...
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3answers
241 views

How to estimate characteristic impedance for a random cable and tolerance of the termination resistor?

When we have a source with 50 Ohm output impedance we use a coaxial cable with a 50 Ohm characteristic impedance. And if we don’t know the output impedance then we use a 50 Ohm termination resistor at ...
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0answers
178 views

Twisted pair with shield and drain wire

Ive been posed with a problem regarding calculating the characteristic impedance of a shielded twisted pair with a drain wire. While I understand how to calculate this for a "normal" shielded twisted ...
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0answers
71 views

Characteristic impedance of a coplanar line in 4-layer PCB

I'm trying to do a simple task: designing a 50 ohm Z0 coplanar waveguide for a 4-layer PCB. The stack can be seen from this link. With that information I've used this online calculator to calculate ...
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3answers
184 views

Characteristic Impedance of a port

I thought that the characteristic impedance was a parameter defined only for transmission lines. But now I have this question: is it defined also for a port? And, eventually, what does it represent ...
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3answers
186 views

LC Filter Design with coaxial input and output

I was trying to design a Chebychev high pass filter of 400MHz corner bandwidth, 0.2db ripple and 5 poles. I am confused with the proposed design in this filter design calculator. This calculator asks ...
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3answers
558 views

Velocity Factor in Transmission Line

For a lossless line, you have \$Z_0=\sqrt{\frac{L}{C}}\$ and \$VF=\frac{1}{c\sqrt{LC}}\$. For a line with R, L, G and C parameters, we have \$Z_0=\sqrt{\frac{R+j\omega L}{G+j\omega C}}\$. But how ...
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1answer
78 views

Why this evaluation board use different track impedance than the right one? Ethernet PHY, routing

Im doing a design with a implementation of 1Gb ethernet switch, for that I bought a evaluation board to do it well. The problem is that in the layout of the ev board I can check that the track ...
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2answers
83 views

What does line impedance stabilization mean?

What exactly does line impedance stabilization mean? What parameters of line impedance are stabilized and how? How does line impedance / source impedance vary with frequency?
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3answers
81 views

What exactly is Characteristic impedence in transmission lines? [duplicate]

Please help me to understand what does a characteristic impedance mean. I am unable to get the exact idea of what does it actually mean and its physical significance.
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3answers
248 views

USB cable characteristic impedance

Does differential impedance between D+ and D- not only depends on separation between and wire gauge of D+ and D-, dielectric constant of the insulation, but also the GND wire and shielding? I want to ...
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1answer
195 views

analog signal generator output in Volts vs dBm

I am connecting a mixer to a microwave source and need to be careful of how much power I am giving to the LO and RF of the mixer. If I just stay in the unit of dBm, it would be ok but I became ...
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3answers
125 views

Equivalent Characteristic Impedance for Different Trace Widths

Suppose I have a PCB trace that needs to be impedance matched, but the trace width changes as it travels from its source to its destination. Something like this: The 5mil trace would have a certain ...
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1answer
146 views

RF layout bend over Component

We lay out the RF trace for below model. GSM 900MHz RF trace maintain at 50Ω impedance. As I know, the RF trace needs to be as short as possible for better signal. Do we need to bend RF trace ...
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1answer
841 views

Routing large RF trace to small SMD pad

I am designing an RF board in Altium where due to the dielectric selected and its thickness, the trace width for a 50 ohm characteristic impedance is thicker than some of the SMD component pads. What ...
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0answers
145 views

Some calculations on Transmission Lines

I have to do some (simple) calculations for a transmission line. I was given a power supply of \$11V\$/\$22\Omega\$, \$Z_0 = 50\Omega\$, \$v = 2.2 \times 10^8 m/s\$, a load capacitance of \$1.124nF\$ ...
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1answer
440 views

Impedence Matching of Antenna and Coaxial Cable

There is a scenario based question which is confusing for me Antenna had four rods each 15cm arranged as a plus sign. its brass shielding was cut and it had two 75 ohm coaxial cables in it. one 10 cm ...
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2answers
558 views

What is the definition of characteristic impedance of a lattice network?

We were being taught about Lattice networks in class, today, and our professor mentioned that the characteristic impedance of a symmetrical lattice network like is given by: $$Z_0=\sqrt{Z_aZ_b}$$ I'...
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1answer
109 views

Difference in the characteristic impedance of a low frequency signal

In one of my PCB design, for a RS 485 signal termination resistor of 120 ohm is there. But the differential characteristics impedance of the signal is taken as 100 ohm instead of 120 and the signal ...
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1answer
170 views

Calculating Characteristic Impedance of Jumper Wire

I'm conducting a test of the LTC490 driver/receiver (http://www.analog.com/media/en/technical-documentation/data-sheets/490fb.pdf), using a small incremental encoder. I'll make the connections using ...
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2answers
915 views

Impedance Matching for Helical Antenna

I'm building a helical antenna at 1.7 GHz from scratch. Theory says that its characteristic impedance is 140 Ohm. The RF transmission line is 50 Ohm so there has to be an impedance transformer in ...
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3answers
682 views

Influence of I/O impedance in Butterworth passive filter design

I'm using a simple online simulator tool to build a passive Butterworth filter. An affirmation made in this page confused me: Enter the filter characteristic impedance. In all cases, unless you ...
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2answers
192 views

Preferable pattern for differential length matching

When the positive and negative tracks of a differential signal are not equal in length, we add some bumpy patterns in the shorter track to make them equal. On the other hand, we usually have a rule ...
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1answer
888 views

cable spec: differential characteristic impedance

I am hunting around for a cable with twisted-shielded pair conductors with the correct differential characteristic impedance for RS-485 (120 ohm) Most of the cable spec sheets for cables with twisted ...
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1answer
523 views

Finding cable impedance, to determine RS485 line termination

We have some Belden 6341PC cable which will be used with some RS-485 communications equipment, which of I'm learning will need line terminators. I'm told the resistor values needed should match the ...
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3answers
2k views

50 Ohm Single Ended Signal Impedances on PCBs

I have a basic understanding of transmission line theory and how 50ohm traces are designed on a PCB. I was wondering what the origin of this 50ohm impedance is. Are single ended digital signals on ICs ...
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2answers
1k views

Why is the characteristic impedance usually purely resistive?

I know the characteristic impedance to be the square root of the ratio of the impedance (Z) and the conductance (G) of the line, both complex numbers. Hence, the characteristic impedance must be also ...
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2answers
749 views

Routing USB, DVI and Ethernet signals on a large PCB vs using long cables

Properly routing USB, DVI and Ethernet signals over long distances (30 to 40 cm) on a PCB seems to be relatively challenging (skew, characteristic impedance, cross-talk, etc.). Yet using the standard ...
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2answers
7k views

Do USB Data Wires (D+/D-) have 90 ohm differential impedance and single ended 45 ohm impedance to ground and if so how is this made?

I understand that USB data transmission is done over various speeds where transmission line effects could come into play(max 480Mbps which means a max frequency that is much higher considering the ...
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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?
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2answers
2k views

Length of Transmission Line & Characteristic Impedance

Just a simple Question for clarification: Does the physical length of transmission line affect its impedance? We all understand that the height of dielectric (space between line and ground) affects ...
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4answers
556 views

Importance of Common-Emitter Input & Output h-parameters

Speaking for NPN Bipolar transistor: In many practical examples parallel resistance of base-emitter junction (aka hie) and finite collector-emitter parallel resistance resistance (aka hoe) are ...
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3answers
10k views

What is the difference between characteristic impedance and input impedance in transmission lines?

What is the difference between characteristic impedance and input impedance in transmission lines? When are these quantities are equal?
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1answer
756 views

Calculating characteristic impedance of a matching line

Attached is a question asking for the characteristic impedance of a matching line. A matching line of 0.25\$\lambda\$ has at its beginning an impedance equal to: $$Z_{in}=\sqrt{Z_{c}Z_{L}}$$ if I am ...
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1answer
161 views

Characteristic impedance of RF PCB when narrowing the trace width to fit pad

I am working on a PCB design that should be matched at a characteristic impedance of 50 Ohms. The circuit down converts a 2.4 GHz signal to a signal in the 2 Mhz- 100 Mhz range using a VCO and a mixer....
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2answers
1k views

Impedance matching network and power transfer to the load

The picture below is a circuit consisted of an RF generator, an impedance matching box, and RF plasma reactor. The RF generator with an output source impedance RS (= 50 ohm) is connected to an input ...
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1answer
859 views

Characteristic impedance vs. Resistance

Why is there voltage drop across resistors? Characteristic impedance is the ratio between voltage and current in a transmission line, but resistors also have impedance that translates to voltage drop....
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2answers
3k views

How is transfer impedance of a cable different from its characterstic impedance

i have been given a task to measure the impedance of a coaxial cable. i was doing some literature study and i came across two terms : transfer impedance and characterstic impedance. i am not able to ...