Quoting Dave Tweed : > David Van Horn wrote: >> Now I'm told that to find the "best" values, I should take these values = and >> calculate Sqrt (LC) and use that value for the inductor and capacitor. >> >> When I pull the Sqrt of (L*C) the result is in time. 159nS in this case. >> I start to feel like we're doing something sketchy here, but I plug in 1= 59uH >> and 159pF and I get another resonant pair at 1MHz with ZL or Zc =3D 1k. >> >> Running a couple of different examples, it seems I always end up with 1k >> Impedances. >> >> Is this wierd trick legit? > > No. > > The "wierd trick" is simply based on the fact that you chose an L value t= hat > is 1,000,000 times larger than the C value. The square root of that ratio= is > 1000. > > If you had instead *followed instructions* and used 159 nH and 159 nF, yo= u > would have gotten impedances of 1 ohm for both. > > And if you keep going, 159 pH and 159 uF gives you 0.001 ohms. > > There is no "best" set of values, except as determined by other constrain= ts > such as manufacturability. > > -- Dave Tweed One such constraint is the parasitics in the parts. The Q will be affected by the non-ideal nature of the components, usually t= he inductor is dominant there. For a series RLC circuit Q =3D (1/R)*sqrt(L/C). The higher the series resistance of the inductor the lower the Q. And there= is the self-resonant frequency of the inductor. I'm not clear where that rule of thumb comes from- it does seem "reasonable= " in real world situations but it may not be optimum in any mathematical sens= e. Or maybe I'm missing something there. --sp --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .