[time-nuts] Transmission line question
Hello, If I have a pin with two 50 ohm lines leading in opposite directions from its land (let's say they are arbitrarily long so as to truly look like 50 ohm lines), what is the effective impedance that the pin sees? Thanks, Donald ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Transmission line question
Just for the record I meant pin as in the metal contact of a device, not a PIN diode. So I need the impedance the pin see's (that of the transmission line(s)) to be the same as the output impedance of the pin. Here's an extrapolation on the original question. If this is a high speed digital signal, with frequency elements ranging from say 133 MHz to 1GHz, then what I am really worried about, given the trace lengths (maybe 2 cm each way) is the high frequency components getting reflected or not sent down the line properly. If my source impedance from the the device is 50 ohms, the lines are each 100 ohms, and the terminations at each end are 100 ohms (probably AC terminated, but let's just say 100 ohms for simplicity), am I setting myself up for the best possible signal integrity? Here's a primitive diagram of the setup 100 ohm line 100 ohm line 100 ohm term. to gnd _100 ohm termination to gnd | | | 50 ohm source | Donald ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Transmission line question
Oh dear it looks like the diagram got horribly screwed up. Well I hope you get what I'm trying to communicate anyways. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Transmission Line Question
Well actually there's another level here which is that some of the lines are bidirectional data lines - each device at the end of the lines will occasionally drive these. However one of the devices (lets call it device A) can request a wait from the center device via a separate line so it should be possible to mediate issues for that device by just telling the center device to wait until the signals are stable. However, the other device (lets call it device B), with no wait request line, is probably not going to be as happy. But I think that (assuming that the data pins of the center device are high impedance while device B is driving the line and device B has a 50 ohm source impedance), then device B is going to see a 100 ohm transmission line in parallel with a 100 ohm termination, which should be fine, and at the other end of the transmission line (device A) a 100 ohm termination, which is also fine. Assuming the center device is high impedance, then there shouldn't be any weird reflections. Don Hi Don excuse me I was thinking RF :-)) That should be OK Though it depends what you are trying to do bus termination is usually slightly different to RF. At least you should not get nasty reflections from the ends like that. There may come a problem if you send a pulse from a 100 termination into the network. There will be a little diggle and reflection as it sees the 50 ohm pin as a small mis-match. But if driving out only from the middle I see no problem. (but then I might just be wrong :-)) ) Alan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
