| Figure
1 |
 |
| The turnover point (negative peak) of a
quartz crystal is a function of the type of cut.
An oven-controlled crystal oscillator uses a
crystal with a high turnover temperature, because
the first derivative of frequency with
temperature is zero at that point. |
| Figure 2 |
 |
| A complicated, multiresistor/multithermistor
network compensates for the nonlinear frequency
drift of a quartz crystal. The interactive
adjustment requires a computer to solve
simultaneous equations. |
| Figure 3 |
 |
| The phase noise in an oscillator consists of
flicker noise (a), 1/f noise (b), and the
broadband noise floor (c). |
| Figure 4 |
 |
| As in a TCXO, a varactor diode pulls the
crystal's frequency in a VCXO (a). A practical
pulling range is approximately ±200 ppm (b). Figure 3 |
| Figure 5 |
 |
| Heterodyning two oscillator signals allows
you to obtain a wider tuning range than that
available from one oscillator. |
| Figure 6 |
 |
| The all-pervasive µC finds use in
oscillators, too. Here, the µC and an EE-PROM
look-up table compensate for temperature drift to
yield perform-ance almost equal to that of an
OCXO. |
| Figure A |
 |
| A SAW delay line is the heart of a series of
wide-range VCOs from Andersen Laboratories. |
| Back |
