The tag has no wiki summary.

learn more… | top users | synonyms

3
votes
1answer
90 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, ...
0
votes
1answer
34 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\$, ...
3
votes
3answers
73 views

Consensus on microstrip trace impedance calculations?

I'm designing a PCB that has a 2.4GHz signal that I'm routing to an SMA jack. I'm trying to figure out the geometry of the necessary microstrip trace. This is the first rf PCB I've worked on. The ...
-2
votes
2answers
65 views

Stripline impedace ..?

i have a doubt in stripline impedance calculation. general strip line calculations are taking strip line as having 2 planes on top and bottom . in our case stackup is such that, on bottom side plane ...
12
votes
2answers
250 views

Terminating shielded/screened twisted pair correctly

Theoretically, I can't see a problem if the twisted pair has an end of cable termination that is: - A single resistor (R) that matches the characteristic impedance of the cable placed across the two ...
3
votes
2answers
702 views

How can I guarantee 50 ohm impedance on PCB trace?

I have a question. Imagine that I need to have a 50 ohms impedance in a PCB trace. For simple cases it's just applying the formula found all over the internet or use one of the online calculators ...
7
votes
2answers
138 views

A transmission line with continuously varying impedance, how would reflection occur in this case?

Alright folks here it is, another transmission line question that has been bothering me. I understand the case where there is an abrupt change in impedance along a transmission line that leads to ...
1
vote
1answer
176 views

Derivation of Characteristic Impedance?

I start from the telegrapher's equation: \$-\frac{dV(z)}{dz}=(R'+j\omega L')I(z)\$, where \$V(z)\$ and \$I(z)\$ are the phasors of voltage and current respectively, in the transmission line model. ...
2
votes
1answer
391 views

Reflecting impedance in a transformer

Please can anyone tell me what exactly is meant by reflecting of impedance in a transformer? I do not know much about transformers, but I want to know about its uses and phenomena behind it. I will ...
2
votes
0answers
153 views

Problem related to the compliance voltage

I have a question that I am using a stimulator to generate biphasic current source for stimulation. At the output of the stimulator, a 1K resistor is in series with 0.1uF capacitor. The I use two ...
2
votes
2answers
151 views

terminated cable capacitance

As much as I know, the input impedance of a coaxial cable with a characteristic impedance of 50 \$\Omega\$ which is terminated with a 50 \$\Omega\$ load resistor, should be 50 \$\Omega\$ as well. This ...
-5
votes
1answer
96 views

Formula for finding the magnitude of the impedance of a ratio z = (x+jw)/(a+jb) [closed]

How do I calculate the magnitude of the impedance of the following ratio, \$z\$? $$z=\frac{x+jw}{a+jb}$$
22
votes
4answers
3k views

How can PCB trace have 50 ohm impedance regardless of length and signal frequency?

Hmm, this seems to be just another question on line impedances. I understand that when we say "transmission line" effects we talk about things like cross talk, reflections and ringing (I guess that ...
5
votes
2answers
1k views

Why Characteristic Impedance must be “50” ohms?

Where does this number came 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 ...
10
votes
1answer
617 views

GPS Design Review (RF Input)

I've designed a PCB in Eagle to host a GPS Receiver module and a GPS patch antenna. The RF input to the module is specified as a 50Ω unbalanced (coaxial) RF input. I used this calculator to calculate ...
18
votes
3answers
427 views

Transmission line reflection. I would like a non-mathematical explanation

I am a licensed radio amateur, and find bewildering the many different explanations, which range from folksy urban myth to Maxwell-Heaviside Equations, of what happens at the termination of a ...
4
votes
2answers
589 views

Impedance Matching for Short-Low Frequency Traces

Is it necessary to have impedance matching for short PCB traces if the frequency is lower than say 100MHz ? I've read somewhere that for a trace to be considered a transmission line it should have a ...
1
vote
3answers
531 views

Why is impedance represented as a complex number?

Let me know one thing. Why is impedance represented by a complex number when considering loss? Usually it is said that imaginary part is because of loss. Is it True? If it is true then does that ...
6
votes
3answers
489 views

Controlled impedance in presence of vias and through-hole components (PTHs)

We have some controlled impedance traces on layer 4 of a board. Layer 3 is a GND plane. Layer 5 is a 3.3V plane. Both planes are unbroken (they occupy the entire layer), with the exception of vias and ...
2
votes
2answers
1k views

When does controlled impedance on a PCB matter?

Suppose I have a PCB that contains a microprocessor, or an FPGA (a "controller"). This "controller" drives a single-ended signal to an LVDS driver IC and a single-ended signal to a connector that goes ...