- #1
likephysics
- 636
- 2
I am at a loss on how to apply transmission line theory when a probe is connected to a high speed bus or for a matched RF line.
For example, a signal going from a PCI clock to a bufffer which has a very short trace(so no termination is required). Now, if I connect a logic analyzer probe to this trace, how do I analyze this circuit.
The probe is in parallel with the buffer. Can I ignore the buffer (since the buffer input impedance is high) and just think of the circuit as a clock source connected to the logic analyzer?
This will reduce to a clock source with some internal impedance(maybe 10-20 ohms) connected to 20K probe tip and terminated by 1M resistor. So, the clock source will see an open circuit? Wouldn't there be any reflections because of the mismatch. (Fig 1)
In case of a 50 ohm matched source, tx line and load. How do I analyze, when a probe is connected at the source or load? (fig 2)
For example, a signal going from a PCI clock to a bufffer which has a very short trace(so no termination is required). Now, if I connect a logic analyzer probe to this trace, how do I analyze this circuit.
The probe is in parallel with the buffer. Can I ignore the buffer (since the buffer input impedance is high) and just think of the circuit as a clock source connected to the logic analyzer?
This will reduce to a clock source with some internal impedance(maybe 10-20 ohms) connected to 20K probe tip and terminated by 1M resistor. So, the clock source will see an open circuit? Wouldn't there be any reflections because of the mismatch. (Fig 1)
In case of a 50 ohm matched source, tx line and load. How do I analyze, when a probe is connected at the source or load? (fig 2)