Unmatched Controlled impedence signal
What happens to a controlled impedence signal (e.g 50 ohms) running through a PCB, that is not matched correctly. What will be the effect on your board and the entire design.
Solution:Jump to solution
The "signal" is AC current flowing from the sender through the transmission line into the receiver.
Each of the listed components has its characteristic impedance. The sender has its output impedance. The transmission line can be seen as a general impedance. The receiver has its input impedance.
In the correctly designed channel, the transmission line impedance is matched to the sender's output impedance, and, naturally, the receiver must have its input impedance of the same value as the sender's output impedance....
12 Replies
@Petr Dvořák @pallavaggarwal @Joseph Ogbonna
Solution
The "signal" is AC current flowing from the sender through the transmission line into the receiver.
Each of the listed components has its characteristic impedance. The sender has its output impedance. The transmission line can be seen as a general impedance. The receiver has its input impedance.
In the correctly designed channel, the transmission line impedance is matched to the sender's output impedance, and, naturally, the receiver must have its input impedance of the same value as the sender's output impedance.
A signal loss happens when either of those two transition points is not matched to the following element. As with signal loss, you can imagine transmission loss and reflection loss. Both losses represent attenuation of the signal along with the signal distortion.
Shortly: A signal loss happens.
Basically there will be reflection on the system which will generate noise that will distort and degrade the actual signal. It's always necessary to match your signals with the right impedence value. It makes sure that the data in the sender is not compromised before it gets to the receiver.
Thanks for the insight
@Chimmuanya Okere Please tell me what are you working on. Please give me your project details. Your questions differ significantly. What is the purpose of those questions?
Am trying to match my trace for a cellular with an SMA connector, and they said in the datasheet it should be 50 ohms impedence. Am just trying to confirm the effect of not using a 50 ohms trace for that particular part. Using SIM7080G from SIMCOM
Why are you considering not using a 50-ohm impedance track?
I didn't consider not using it, just wanted to know the effect of not using it
How about using a matching circuit if 50 ohms than a trace, how will that work
I don't understand your question. Please, can you elaborate on that?
If you use a matching circuit of 50 ohms e.g you have a resistor capacitor network that has an impedence of 50 ohms, is it still necessary to have a trace of 50 ohms impedence
The physical length of the 0402 resistor is 1.0 mm. Is the distance between the SIM7080G and the SMA connector 1.0 mm? If so, you don't need any track.
Is the problem in the calculation of the 50-ohm trace? If so, use https://jlcpcb.com/pcb-impedance-calculator because it cannot be easier.
Controlled Impedance Calculator - JLCPCB
JLCPCB‘s Free Impedance Calculator for impedance controlled PCBs, helps you calculate the track width value and recommended PCB stack-ups from target impedance.
