No moving parts Solid-state "no moving parts" inductor-capacitor
(LC) circuits have been used to create oscillators since the
invention of the transistor. In fact, National Semiconductor
Corp. (Santa Clara, Calif.), Linear Technology (Milpitas,
Calif.) and others already have CMOS oscillator chips on the
market, but only for low-accuracy applications that do not
require a rock-solid quartz crystal reference. Unfortunately,
the CMOS inductors and capacitors used in these circuits are
non-precision, resulting in inaccuracies of more than 10,000
parts per million or more. What's more, the circuits are not
particularly stable, varying their output frequency in response
to changes in temperature, supply voltage and driving current.
The traditional solution has been to sync integrated oscillators
to a mechanical reference, like a quartz crystal using a PLL
circuit. However, with the invention of the cell phone, radio-
frequency circuitry has demanded that CMOS chips improve the
native accuracy of inductors and capac