[SI-LIST] Re: Running analog video on micro-coax
- From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
- To: <nagaraju.nerella@xxxxxxxxxxxx>, <joel@xxxxxxxxxx>, "SI-List" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 2 Jun 2006 10:05:26 -0700
If you are putting a buffer amplifier between the 75 Ohm line there is no
need for the 25 Ohm resistor. Schematically:
75 Ohm Driver-----75 Ohm trace-----25 Ohm resistor--------50 Ohm coax---50
Ohm load
75 Ohm Driver-----75 Ohm trace-----matching network-------50 Ohm coax---50
Ohm load
75 Ohm Drvier-----75 Ohm trace-----50 Ohm Driver----------50 Ohm coax---50
Ohm load
If the output impedance of the driver does not match the load it is driving
you may want to back (series) terminate the drivers to match the load. For
example, if the output impedance of the 50 Ohm driver is 35 Ohms you would
add a 15 Ohm resistor between the driver and the 50 Ohm coax.
50 Ohm Driver (Zout = 35 Ohm)---15 Ohm resistor---------50 Ohm coax
Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Nagaraju Nerella
Sent: Thursday, June 01, 2006 9:13 PM
To: tom@xxxxxxxxxxxxx; joel@xxxxxxxxxx; SI-List
Subject: [SI-LIST] Re: Running analog video on micro-coax
Here I have one doubt if suppose the impedance viewed to input side
after the 25-ohm resistor will be 100ohms how it will match with 50 ohms
impedance.
75ohms analog signal--------> Buffer amplifier----->25 ohms
resistor--->50 ohms cable.
If my question is not sounds good, please forgive me.
I feel instead of that impedance transformer network is better based on
the analog signal operation frequency.
Thanks & Regards,
Nagaraju
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Tom Dagostino
Sent: Friday, June 02, 2006 4:56 AM
To: joel@xxxxxxxxxx; SI-List
Subject: [SI-LIST] Re: Running analog video on micro-coax
Joel
You could try a simple impedance matching network. The simplest would
be a
25 Ohm resister in series between your 75 Ohm driver and the 50 Ohm
cable.
You also might look at what Mini Circuits or other vendors have that
will
meet your requirements in surface mount networks.
Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Joel Brown
Sent: Thursday, June 01, 2006 2:13 PM
To: SI-List
Subject: [SI-LIST] Running analog video on micro-coax
We have an application which requires running 75 ohm analog video over
coax for a distance of 75 Inches.
Conventional VGA cables are much to large and bulky because we need to
run the cable through hinges and cable retractors.
I have seen some micro-coax products from several companies which use
very small diameter cable.
However all of the micro coax products are 50 ohm and seem to be
targeted for digital signals such as LVDS.
One approach I am considering is to use a buffer amplifier to receive
the 75 ohm signal and then redrive it on the 50 Ohm cable.
The only drawback is possible signal distortion from the buffer
amplifier. The signal bandwidth is 100 MHz.
Any thoughts or ideas would be appreciated.
Thanks - Joel
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