| 摘要 |
<p>Traditional radio transceivers, such as those used in the base stations of cellular mobile systems require delicate manual tuning. Regardless of the accuracy of the initial tuning, an uncompensated oscillator provides little compensation for temperature drift and component ageing. The invention provides a way of stabilising the frequency of a phase locked loop, provided that a stable reference voltage (VREF) is available. During recalibration, control unit (7) applies, via switch (SW1), reference voltage (VREF) to the input of a voltage controled oscillator (6). An adjustable control element (5) of the oscillator is adjusted until the frequency of the oscillator (6) is within a predetermined deviation from its nominal value. Correct tuning can be detected either by detecting a period without any up (U) or down (D) pulses originating from phase detector (2), or by detecting that the output voltage of integrator (4) equals the reference voltage (VREF).</p> |
