Let’s calculate the propagation delay/time delay using trace length and vice-versa. Mathematically, time delay is
tpd:1/v
. Where v is the speed of the signal in a PCB transmission line. In vacuum/air, it’s equal to 85ps/in.
What is the speed of signal approx?
In circuit boards made of FR-4 material, the signal velocity is typically about
six inches (15 cm) per nanosecond
. In circuit boards made of Polyimide material, the signal velocity is typically about 16.3 cm per nanosecond or 6.146 ps/mm.
What is a PCB transmission line?
A PCB transmission line is
a type of interconnection used for moving signals from the transmitters to the receivers on a circuit board
. It is composed of two conductors: a signal trace and a return path which is usually a ground plane.
What is crucial for high speed design?
Power supply –
power supply bypassing to minimize “noise”
is especially important for high speed circuitry. Incorporating common methods such as rails-to-ground or rail-to-rail can provide effective results.
What is a high speed circuit?
Whether it is a high-speed circuit depends only on their rise time. More people have quantified the definition of high speed, that is,
when the delay of the digital signal in the circuit on the transmission line is greater than 1/2 rise time
, it is called a high speed circuit.
Which geometry has faster clock and logic signal propagation?
Even if you adjust the trace widths on each layer so that the impedances are the same, the speed of propagation on the
microstrip layers
is always faster.
What is relative propagation delay in PCB?
Relative Propagation Delay:
Specifies the matching or relative delay requirements for a group of pin pairs
.
What is propagation delay in PCB?
Propagation Delay is
the length of time taken for a signal to reach its destination in printed circuit boards (PCBs)
. To keep a good high-speed signal quality from driver to receiver on a PCB is not an easy task for designers.
How fast do electrons travel in a wire?
The individual electron velocity in a metal wire is typically
millions of kilometers per hour
. In contrast, the drift velocity is typically only a few meters per hour while the signal velocity is a hundred million to a trillion kilometers per hour.
Is voltage speed of electrons?
No, voltage is not the speed of electrons through a wire
, but current (almost) is. You said, “Current is the amount of electrons passing through a wire,” but this is not quite correct. Current is the amount of electric charge (electrons) passing through a conductor per unit of time.
How far does an electron travel along the wire?
In the case of a 12 gauge copper wire carrying 10 amperes of current (typical of home wiring), the individual electrons only move about
0.02 cm per sec or 1.2 inches per minute
(in science this is called the drift velocity of the electrons.).
What is crosstalk in PCB?
Crosstalk on PCB
The term crosstalk refers to the
unwanted electromagnetic coupling that is created between the traces of a printed circuit board
. An excessive voltage or current affecting one trace can produce unwanted effects on another trace, without the two being in physical contact with each other.
Why is impedance matching required for high speed signals?
The function of a PCB trace is to transfer the signal power from the driver device to the receiving device. Power needs to be propagated throughout the length of the trace. But
maximum signal power can only be achieved
with matching impedances on the PCB. So, that is why there is a need for impedance matching.
What is considered a transmission line?
In electrical engineering, a transmission line is
a specialized cable or other structure designed to conduct electromagnetic waves in a contained manner
. The term applies when the conductors are long enough that the wave nature of the transmission must be taken into account.
What is 3W rule?
3W principle
When the line center spacing is not less than 3 times the line width, most of the electric fields can be kept from interfering with each other
. This is the 3W rule. The 3W principle means that when multiple high-speed signal lines are routed over a long distance, the spacing should follow the 3W principle.
What is 3W rule in PCB?
If you’ve ever wondered how far you need to keep your traces from each other to minimize coupling, then use the 3W rule. It states that
the separation between traces must be three times the width of a single trace when measured from center to center
.
What are design challenges for high speed PCB?
2、High-Speed PCB Design Challenges
These are
tolerances typically for things like controlled impedance traces, board Stackup, and capacitance, and also the overall length and width of marks
.
What is high frequency PCB?
High Frequency PCB is
a type of PCB which is widely used in applications involving special signal transmission between objects
. It is available in frequency range of 500MHz to 2GHz and is an ideal choice for mobile, microwave, radio frequency and high speed design applications.
How do you make a circuit faster?
What is considered high frequency in a circuit?
Usually when
F>100MHz
, it can be called a high frequency circuit. Therefore, in a digital circuit, whether it is a high-frequency circuit does not depend on the signal frequency, but mainly depends on the rising and falling edges.
Can propagation delay?
At lower data rates, the allowed bit time is longer, so the propagation delay (and thus the cable distance) can also be longer.
At the maximum standard CAN data rate of 1 Mbps, the allowed propagation delay is more limited
, though ISO 11898-2 specifies a bus length of 40 meters for operation at 1 Mbps.
What is strip line method?
Stripline is
a form of printed circuit transmission line where the signal trace is sandwiched between upper and lower ground planes
, as shown in three-dimensional form in Figure 3.14 (a) and in cross-section form in Figure 3.14 (b).
How does oscilloscope measure propagation delay?
You measure the delay in the test cable connecting the DUT1 output to the oscilloscope. You measure the total delay from the DATA1 and NDATA1 inputs to the DUT1 output and through the cable to the oscilloscope. The data from these measurements let you calculate the signal delay through the IC.
What is transmission line delay?
Data transmission line propagation delay is
the duration of time that the data signal takes to propagate from one point in the transmission line to another
. It is the reciprocal of propagation speed.
How do I know if my transmission is delayed?
Time taken to put the data packet on the transmission link is called as transmission delay. Mathematically, Transmission delay ∝
Length / Size of data packet
.
Transmission delay ∝ 1 / Bandwidth
.
What is the dielectric constant of FR4?
The dielectric constant of FR4 ranges from
3.8 to 4.8
, depending on the glass weave style, thickness, resin content, and copper foil roughness.
