| 摘要 |
PURPOSE: A device for observing a reference clock is provided to improve the stability of a system by sensing the error of operation of a reference clock generating portion circuit by the circumstance of the system and preventing the wrong operation of the system by the unstability of a system clock. CONSTITUTION: The device for observing the reference clock includes the first dispenser(10), a local oscillator(20), the second dispenser(30), a PLL portion(40), a voltage level comparator(50), a low band filter(100), a level comparator(110) and a single shot multivibrator(120). The first dispenser(10) dispenses the outer reference clock(2.048MHz) into 4KHz. The local oscillator(20) generates the inner reference clock. The second dispenser(30) dispenses the clock input from the local oscillator(20) into 4KHz. The PLL portion(40) inputs the clock signal of 4KHz, which the first dispenser(10) and the second dispenser(30) dispensed, and detects the difference of the phase between the two clocks and outputs it. The voltage level comparator(50) compares the signal of the PLL portion(40) with the reference voltage and outputs the voltage control signal to the local oscillator(20). The low filter(100) makes the signal input from the PLL portion(40) pass the low band frequency and outputs it to the voltage level comparator(50) or other devices. The level comparator(110) maintains the voltage as the regular level if the outer reference clock is stable but outputs the change of the level if the outer reference clock is not stable. The single shot multivibrator(120) outputs the reference clock alarm if the change of the level is input from the level comparator(110).
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