CONSTANT CURRENT DRIVEN OSCILLATING CIRCUIT

PROBLEM TO BE SOLVED: To maintain margin for oscillation in an oscillator with a simple configuration and at low current consumption. SOLUTION: When VXT>Vtn, the charge charged to a capacitor 22 is discharged, one of discharge currents is caused to flow to ground with a drain current Ibh caused to flow through a P-MSOFET, and the other discharge current is caused to flow to one polarity of a crystal vibrator 20 through a return resistor 34. The discharge current flowed to the one polarity of the crystal vibrator 20 is oscillated on the basis of an oscillation frequency of the crystal vibrator 20. The return resistor 34 returns the oscillated signal to the one polarity of the crystal vibrator 20 to continue oscillation. A back electric potential VD satisfies VD=VD2-(-VXT). When the value of the back electric potential VD becomes larger, since the depletion layer of the N-substrate of the P-MOSFET 26 becomes wider, the threshold voltage of the P-MOSFET 26 becomes small, and the amount of the drain current Ibh becomes small, wherein VXT is an electric potential of a node XT, Vtn is a threshold voltage of an N-MOSFET 28, and VD2 is the voltage of a power supply. COPYRIGHT: (C)2010,JPO&INPIT