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Questions tagged [characteristic-impedance]

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1answer
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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
50 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
70 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
183 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
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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
120 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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1answer
246 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
54 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
62 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
243 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
153 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
61 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
430 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
315 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 ...
3
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3answers
951 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 ...
3
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2answers
605 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
527 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
4k 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
879 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
401 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
6k 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
334 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
99 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....
3
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2answers
600 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
455 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
2k 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 ...
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8answers
3k views

What is the physical meaning of the characteristic impedance of a transmission line? [duplicate]

If it was per unit length, I'd understand, but apparently it is a constant of the whole line. Consider if I change the length of the transmission line, the impedance of the whole thing should ...
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0answers
214 views

Calculate input impedance of transmission line without knowing L or C

I have the following problem: A TV antenna lead-in wire 10 cm long has a characteristic impedance of 250 ohms and is open-circuited at its end. If the line operates at 400 MHz, determine its input ...
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1answer
391 views

Reflections on a differential transmission line

I understand why reflections occur when there is an impedance mismatch on a single-wire transmission line. However, when we introduce a differential line, I am having trouble picturing what would ...
3
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1answer
311 views

How much is the propagation velocity affected by the characteristic impedance?

Someone posted the (very educational!) video Similiarities of Wave Behavior from 1959 in another answer, and after watching the part about impedance mismatches, it strikes me that the propagation ...
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3answers
746 views

Characteristic impedance of a D-subminiature connector

I would like to know what the characteristic impedance of two adjacent pins of a D-subminiature connector is, or how I can go about calculating it. For example, see below 50-pin D-sub, if I were to ...
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1answer
378 views

IBIS Model Characteristic Impedance

I have tried to understand how to match my 50 ohm pcb trace, which is carrying a high-speed data signal, with a digital chip's input pin. The problem is that I don't understand why the calculations ...
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2answers
1k views

BNC cable's characteristic impedance and voltage drop

As far as I understand, the characteristic impedance matters when a signal is oscillating since the BNC coaxial cable can be modeled as having inductors and capacitors as in the figure: I have couple ...
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3answers
764 views

Height of the substrate in online PCB impedance calculators

Is the height of the substrate just the non conductive portion between copper layers ? Using this calculator as an example In a 4L board, if the top and bottom traces are of the same thickness and ...
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2answers
2k views

What is the 'characteristic frequency' of a certain impedance?

I'm not familiar with that term. Could somebody explain it to me? Is it the frequency at which the phase of the AC current running through the impedance goes to zero? Edit: Here is the context in ...
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2answers
368 views

Role of “HDMI Baluns”?

I understand that an HDMI cable contains essentially 4 shielded twisted pairs, along with additional control lines. Each of the twisted pairs is specified, to my understanding, to be a balanced ...
3
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3answers
889 views

How does a passive 1x Scope probe work?

I understand about input impedance and capacitance... My question relates to the cable: What is the characteristic impedance of the cable connecting the probe to the scope? It must be terminated in a ...
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1answer
660 views

How to minimize characteristic impedance mismatches caused by vias?

This question springs from an answer here. When using stripline configurations for rf signalling, the conductors are routed on an inner layer of the pcb, sandwiched between two ground planes. I ...
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2answers
612 views

Which of these Stripline Impedance Calculations is correct?

Different sources are giving me drastically different characteristic impedance values, and am hoping someone will verify them for me. Generally, with microstrip, I start with an online calculator to ...
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3answers
3k views

Can differential USB traces be routed relative to Power (not Ground) planes?

I would like to route my USB 2.0 (12MHz) signal on the bottom layer of a 4-layer PCB. However, the edge-coupled microstrips would then be referenced to the power plane, not the ground plane. The ...
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2answers
334 views

Characteristic impedance of a transmission line

characteristic impedance of a transmission line depends on frequency of transmission as can be seen by its expression. What will be the characteristic impedance of TL if my signal has two frequency ...
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1answer
122 views

Routing trace characterstic impedance determination based on interface

I have seen specifying routing impedance of interfaces from manufacturers like for USB Differential impedance of 90 ohms DDR2 Single ended impedance 50-60 Ohms, Differential impedance - 100-120 Ohms. ...
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3answers
362 views

Output impedance refers to open circuit o/p impedance or short circuit o/p impedance?

When we specify output impedance of a two port network, does it imply open circuit output impedance or short circuit output impedance? Wikipedia: output impedance ; Wikipedia: two-port network g22 (...
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3answers
236 views

Controlled Impedance Microstrip Frequency

Are you supposed to calculate the characteristic impedance for the frequency you are using or at 1GHz? I see pretty much everything calculated at 1GHz in all examples and papers. For example - for ...
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1answer
2k views

Calculating differential PCB traces - Edge-Coupled Microstrip

I finally have the microstrip characteristic impedance thing figured out. But now, of course, I need to learn about differential signalling on PCB traces. I've spent some time researching. Here is ...
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2answers
8k 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 ...
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2answers
2k views

What types of signals should be considered to have a 50 Ω trace impedance?

Generally speaking, what time of signals should be designed to have a 50 Ω trace impedance ? Some datasheets I've read have specifically mentioned 50 Ω but others have not. Is it good practice to ...
3
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1answer
597 views

RF Circuit (what does capacitor do?)

I'm trying to work out why a 0.7pF capacitor was chosen. The circuit operates at 12GHz. At 12GHz, the capacitor has an impedance of about \$18\Omega\$. Also at 12GHz, ...
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1answer
177 views

RF Ground (Reflections?)

I'm trying to understand how someone can ground an RF signal (especially relating to microstrip lines). I think I'm missing something... Since the impedance of ground is supposed to be \$0\Omega\$, ...