Hi,
this is more of a 'coult this work' than a real application question. I apologise for the long text with no pictures... if this sparks interest I will put in some more effort. So here goes an idea I had at work today:
As some may have encountered as well, sometimes you need isolated digital signals. If then are of high data rates, LVDS signals is often the way to go. There are high speed (say 200MHz ore more) digital Isolators, like the fancy new ADN4621 but they are expensive and draw quite a lot of current, about 60mA on primary and secondary side in this case. While these ICs are a nice solution I was thinkging: what if I would just be using a pulse transformer? They are cheap and basically do the same thing (but limited to maybe 500MHz). Main problem is: they are AC coupled, so good if the signal is symmetrical like a clock at a reasonably high frequency, bad for data. Ok, good point.
Now, a slow clock (or data) provides the typical rising/falling edge with an exponential decay. Looking at simulation data of this I wondered:
is there a (simple or at least cheap) way to recover the input signal?
This may be a stupid approach but just to get the Idea across:
As the secondary side is isolated, the negative line of the LVDS signal could be just set to a 'common mode voltae' say 1V. Now we monitor the positive line which will swing 300mV up and down the common mode voltage.
Since it is AC coupled by the transformer, we need to detect the rising and falling edges. This could be done with two comparators (or one window comparator) set at 1.1V and 0.9V and some kind of sample and hold circuit (not quite sure how but just as a concept, a flipflop maybe?). Of course this would have to be reasonably fast, if possible done by some FETs or BJTs as high-speed comparators probably are expensive or power hungry (I may be wrong here).
The output of this sample and hold could then be fed into an LVDS driver. This would of course not perform as well as the IC solution and also is not as small but it may be lower power and cheaper and more versatile.
Long story short my question is this: can an AC coupled (LVDS) signal be recovered using some kind of simple 'sample and hold' circuit or is this just too complex?
Since there are no ICs supporting this (Signal Isolation using small SMD pulse transformers) there may be a catch I do not see...