| 摘要 |
Simplified measurement equipment (100) is described in which any two frequency sources can be accurately and quantitatively compared to each other. With this simplified measurement equipment, calibration can be performed on an oscillator (102,103) using an external reference signal (119), while the oscillator is being used in an active system. By simplifying the measurement equipment, the equipment can be built into a time base unit allowing recalibration to be performed at relatively short time intervals. A frequency difference detector (100) based on ring counters (108,109) and an existing controller (101) in a telecommunication switching system compare an accurate external reference (119) against an oscillator (102,103) of the time base unit for calibration in the field. Within the telecommunication switching system, a highly accurate external reference signal (119) is normally available from an interconnected telecommunication network. The use of ring counters (108,109) in the frequency difference detector (100) allows for simple measurement equipment which adds little to the cost of the time base unit. Further, since measurement equipment is all digital, no tuning of the equipment is necessary as is required of measurement equipment having analog components. <IMAGE>
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