1. The Q of your tank.
The reactance XL of your 100nH inductor at 100MHz is 63 ohms. The resistance of your DAC is about half the resistance of the MSB (lowest value) resistor (0.533 for a 4-bit DAC, to be more precise). Q=R*XL. To avoid killing the Q, you should probably keep the resistance at least 100*XL, or greater than about 6k. Nigel's advice is spot on, as usual.
I would hope that the impedance of the resonating tank would be much higher than just the XL of its inductor. Therefore DAC resistors should be in the hundreds of k ohms. :lol:
I would hope that the impedance of the resonating tank would be much higher than just the XL of its inductor. Therefore DAC resistors should be in the hundreds of k ohms. :lol:
This applies to series resonant circuits with a series R, or parallel resonant where the resistor is in series with the L or the C. It should be obvious that, for a parallel resonant tank with a parallel resistor, the Q is proportional to resistance, while in the case that you posted, it is inversely proportional to resistance.
Regarding √L/C, if you do the math for Fr=100MHz, L=100nH, you will find that this equals 63 ohms, which is identical to reactance of L and C individually. This is NOT the same as the impedance of the tank, which is, for ideal components, infinite at resonance.