Patellar tendonitis is also known as "Jumper's Knee".
The main culprit for bodybuilders getting it is allowing your quads to greatly overpower your hamstrings.
Provided you arent going to be in a contest, take 1-2 weeks off of quad exercises period. If you feel you must, just do VERY light exercises. Work on strengthening your hamstrings with deads, leg curls, all the other stuff you've been neglecting.
Go to Wal-mart and buy a set of Jumper's Knee straps. They strap on your legs just under the knee. Usually you'll see basketball players and track athletes wearing them, but its no big deal. The ones I bought were little black straps, they help keep the knee in place when you jump/move.