| 摘要 |
An economical, compact frequency hopping spread spectrum wireless data telemetry transceiver is adapted to establish and maintain communication links at 2.4 GHZ. The wireless transceiver includes RF and computer control components in a compact package approximately the size of a deck of cards and is adapted to be built into original equipment manufacturer (OEM) products to support a wide range of wireless data telemetry applications. The transceiver includes an inexpensive VCO which is controlled by novel method including steps to characterize and adjust the frequency output of the crystal. As ambient temperature around a quartz crystal varies, the resonant frequency of the crystal varies, in different ways, depending on the method used to cut the crystal from a quartz blank. Employing a quartz crystal in an oscillator circuit to generate a reference frequency subjects the oscillator to the same frequency variations over temperature as the quartz crystal. In accordance with the present invention, a temperature sensor constantly outputs a signal proportional to the temperature of the crystal in the oscillator. A micro-controller initiates a conversion via the analog to digital converter (ADC) and the micro-controller then uses the ADC output signal to look up an adjustment number in a pre-programmed lookup table; the adjustment number is input to the digital to analog converter, which then performs a conversion to output a DC voltage to the VCO, adjusting the frequency of the oscillator to the desired reference frequency, thus effectively providing an open loop VCO control system.
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