LMH0302 as single ended reciever.

I have an application using the LMH0302 as a single ended HD-SDI receiver. That datasheet claims that this is an acceptable configuration, but provides no other guidance.  Do you recommend that I used the input connection diagram of the LMH0344? Should I include a 75ohm termination network inside the DC blocking caps?

Thanks,

John

  • The LMH0302 input is high impedance, so it can be terminated in whatever impedance works best for your application.  The input to the LMH0302 can be single ended provided the unused input is properly terminated.

    If your input is 75 ohms single ended and AC coupled, then configure the LMH0302 input as follows:

    On the active input you should have a 75 ohm termination resistor to ground, followed by the AC-coupling capacitor, then followed by the LMH0302 input pin.

    You'll want to terminate the unused input to balance the active input.  The active input sees the 75 ohm input in parallel with the 75 ohm input termination for an equivalent impedance of 37.5 ohms.  Thus, on the unused input you should have a 37.4 ohm termination resistor to ground, followed by the AC-coupling capacitor, then followed by the LMH0302 input pin.

    As you noted, this is identical to the Typical Application diagram on the front page of the LMH0344 datasheet (minus the return loss network).

    As noted earlier, the LMH0302 input can be terminated in a different impedance if desired.  For example, if your input is 50 ohms single ended, then the LMH0302 input can be terminated with a 50 ohm termination resistor on the active input and a 25 ohm termination resistor on the unused input.

    Please be aware that the LMH0302 is a cable driver and not an equalizer like the LMH0344, so if your input has appreciable loss (>10m precision 75 ohm coaxial cable) you will want to consider using an equalizer prior to the LMH0302.