Original question:
Hi
please see the new reply on this post.
I have ordered my PCB to a Chinese PCB manufacture, once in one of PCB modifications for the PCB manufacture, the ground plane was removed a little under LSB line of the DAC
as you see in the following picture the input capacitance is 5pF but how much the input resistance of the input is?
Best Regards
Actually I have a problem:
I have ordered my PCB to a Chinese PCB manufacture, once in one of PCB modifications for the PCB manufacture, the ground plane was removed a little under LSB line of the DAC as follow
the second layer under the bus (the distance between the TOP layer and L2 is only 4 mils):
the line is 1300 mils, width is 7mils, thickness is 1OZ, as usual we have a 22 OHM series resistor at the input of the line. the frequency is 200MHz (I haven't used 275MHz) and the logic level is 3.3V.
*can I replace the resistor with a 50 or 75 OM resistor to reduce ringing or overshoot?
*or can I scratch a part of the line and solder a 0402 resistor on the part like the below:
*or can I scratch a part of the line and solder a 50 OHM 0402 resistor at pretty close to the DB0 pin?
*or can I cover under the border and near the line with a copper tape?
that's why I wanted to know the input circuit of the DAC.
Thanks
I have modeled the problem as follow:
but I'm not sure about the input circuit of the DAC. please help me to find a solution :|
I have measured the line characteristic with a 10KHz SMD tester.
all the 50 OHM lines has 6pF capacitance to the DAC thermal pad but this pin doesn't have any capacitance but the line has 2.5pF capacitance to the beside ground layer.
from the below link I have calculated the inductance:
https://chemandy.com/calculators/flat-wire-inductor-calculator.htm
how much the resistance of the switch at the input of the pin is? it's very important. bcoz it can reduce any ringing and overshoot very effectively.
I'm very disappointed.
Thanks
