Abstract: A microprocessor circuit is provided that allows the internal microprocessor clock speed to vary depending upon a register that can be programmed by software. In addition, the drive strength of the internal clock generator may similarly be varied by software programming. The programmer or user of the microprocessor may change the internal clock speed such that the microprocessor operates at a first frequency or at a second frequency depending upon the performance requirements. A lower frequency of operation may be selected for low power consumption and low EMI, while a higher frequency of operation may be selected for computational intensive and high performance applications.

Abstract: An oscillator circuit including a current-controlled phase shift circuit and a feedback circuit including a quartz resonator is capable of varying the oscillation frequency in accordance with control current signals. A phase shift circuit included in the current-controlled phase shift circuit includes a first low-pass filter including a resistor and a capacitor, a first buffer amplifier, a second low-pass filter including a resistor and a capacitor, and a second buffer amplifier. The phase shift circuit has a significant gain at any frequency for oscillation. Especially an oscillation circuit implemented by an integrated circuit satisfies the suitable condition in which relative value of resistances and capacitances do not vary.