| 摘要 |
PURPOSE:To obtain a prescaler having less fluctuation of the minimum input sensitivity against the fluctuation in power supply voltage and operating by a single power supply by dividing the power supply voltage to form a DC offset voltage. CONSTITUTION:An input signal 2 is formed into an AC component only by a capacitor 3 and inputted to an input terminal 4 of the prescaler. The input terminal 4 is biased by a DC voltage dividing the power supply voltage by resistors 13, 14. A 1/2 frequency-division circuit 1 is constituted by an enhancement type T and the input impedance of the prescaler can be regarded as being infinite at this DC voltage. Thus, the DC voltage is decided by the power supply voltage and the resistors, and follows up the fluctuation in the power supply voltage VDD. The input signal is offset by this DC voltage. Although the minimum input sensitivity of the 1/2 frequency division circuit 1 is almost proportional to the power supply voltage, since the input signal is offset by the DC voltage following the power supply voltage, the fluctuation in the minimum input sensitivity against the power supply fluctuation is less. |
