Line impedance on PCB?

[ygor1]

A few beginner questions.

1. If we lead the signal from 50 ohm source to 50 ohm load is a good line to PCB design with 50ohm impedance as microstrip line. How will solve the line on PCB in the case where source is operation amplifier and load have impedance 1000 Ohm?

2.If we had two operational amplifiers with input impedance of 10M, how to choose between them line impedance and the line load for first amplifier?

 

[crutschow]

What is the highest frequency of the signal? You only need to match the line impedance on the PCB for high frequency signals.

 

[ygor1]

It is clear, let us assume that the frequency as 1MHz

 

[albbg]

You mean 1MHz sinewave ? take into account that for different waveforms you have to consider the frequency of the higher harmonic you have to send.

 

[ygor1]

Is a model example, suppose an ideal sine 1MHz amplitude +- 2,5V

 

[crutschow]

You generally don't have to worry about impedance matching until the signal line length reaches 1/4 wavelength or 75 meters for a 1MHz signal.

 

[ygor1]

You're right, I chose the example of inappropriately.
Say that the frequency will be 300MHz, 1/4 wavelength is 25cm and and is a measurement application, therefore it is necessary to take into account that the sinus has the largest voltage change during the first 10% of the sinusoid.

 

[crutschow]

For 300MHz, line impedance will be important. If the input is an op amp (that's a fast op amp) then you would add a resistor to ground in front of the input such that the parallel value of that with the op amp input impedance is equal to the characteristic impedance of your line. For a 1kΩ input the closest 1% resistor to add would be 52.3Ω