help to create a simple activity indicator for a LVDS signal

[korsi]

LVDS activity indicator

Hi

Can anybody help me with ideas to create a simple activity indicator for a LVDS signal, where the activity is between 100 MHz and 500 MHz?

I am thinking of a LED that is lit (or unlit) when there is activity on the LVDS pairs.

I have a solution with a capacitor, a resitor, one diode and one led.

R1 lvdsp n1 10
C1 n1 n2 1p
D1 vdd n2 (small diode)
LED n2 gnd

With this solution, I can adjust the vdd level so that the led is faintly glowing. When I apply a LVDS clock source on lvdsp, the LED will get brighter. This works great for frequencies up 100 MHz. Over 100 MHz D1 is acting as a capacitor, and the LED will not light up.

 

[tonthatvan]

Re: LVDS activity indicator

By using one output of LVDS diff pair to make an activity indicator, the loading at the diff signal is not longer balance.
Do you see the output at high frequency without the indicator?
Do you use this output for LED only? or it's connected to a receiver?

 

[korsi]

LVDS activity indicator

The LVDS pair is terminated in 100 ohms. And I'm of course making a balanced load for the diff pair.

There is no receiver, it is only for verifying that the LVDS transmitter is working. It is for testing the driver over time. So that it is easy to see if the LVDS activety stops.