| 摘要 |
According to a frequency comparing circuit of the present invention, there is provided a negative switched capacitor circuit (10) having negative equivalent resistance, the value of which is determined according to the reference frequency and the frequency to be compared, and a positive switched capacitor circuit (20) having positive equivalent resistance, the value of which is determined according to the reference frequency. A constant DC voltage (V) is supplied in parallel to one terminal of the two switched capacitor circuits. The respective terminals of the switched capacitor circuits are commonly connected in order to produce the composite current of both output currents of the two switched capacitor circuits. The composite current is integrated by an integrator (30). Further, there is provided a Schmitt-type oscillating circuit (83). The oscillating frequency signal from the Schmitt-type oscillating circuit is supplied to the negative switched capacitor circuit. The higher level threshold voltage (VH) of the Schmitt-type oscillating circuit is determined according to the composite current of both output currents of the two switched capacitor circuits, thereby adjusting the frequency of the oscillating signal of the Schmitt-type oscillating circuit. The oscillating signal is supplied to the positive switched capacitor circuit. The lower level threshold voltage (VL) of the Schmitt-type oscillating circuit is determined according to the composite current of both output currents of the two switched capacitor circuits. Therefore, the frequency of the oscillating signal of the Schmitt-type oscillating circuit is adjusted. |
