I would like to try and use the LT6900 oscillator as a LO for the SA612 mixer. Does the LT6900 require any buffering or can it be used directly to the LO input on the SA612?
My apologies for the delayed reply. Our web system did not forward this to me as it should. The LTC6900 has a standard CMOS output much like any typical 74HC00 logic type. It is definitely not intended to drive a 50 ohm load or anything like that. The output levels are specified as sourcing and sinking 1mA and 4mA. The equivalent output series resistance of the MOSFETs (Rds(on)) are shown in the Typical Performance Characteristics plot on page 4 and is similar to standard logic parts. If this looks like a match for your load, then you would not need a buffer.
One word of caution about using this part in what seems like an RF type of application. This part is intended for logic and switching power supply applications and in addition to an accuracy of about 2 percent, is also has a substantial amount of jitter. Using this part as an LO in a radio application is usually not a good idea unless the system can tolerate a lot of LO jitter.