Patent ID: 7592877
Filing Date: 2009-09-22
Classification: H03K,H03L,H03M

Abstract:
1. A variable frequency oscillator, comprising: a power supply terminal for connection to an external power supply; a ring oscillator having delay circuits arranged in a plurality of stages, the delay circuits being cascade-connected in a ring, and each of the delay circuits being connected to the power supply terminal in common, the ring oscillator outputting an oscillation signal of a frequency based on a control current; and a current source for frequency control connected to each of the delay circuits in common to supply the control current to the ring oscillator, wherein the current source for frequency control includes a first current source and a second current source connected to the ring oscillator via a common terminal, wherein the first current source generates current for frequency control based on an input frequency control voltage, wherein the second current source generates current for compensation based on an environmental variation, wherein the current for frequency control and the current for compensation are added to provide the control current for the ring oscillator, wherein the second current source includes a reference voltage source circuit, a reference voltage conversion circuit, a first voltage select switch circuit, and a second voltage controlled current source circuit, and wherein the first voltage select switch circuit includes a plurality of MOS transistors which are controlled by a portion of an input logic signal to vary an effective gate size of the first voltage select switch circuit, the first voltage select switch circuit multiplying input voltages from the reference voltage source circuit and the reference voltage conversion circuit and outputting the multiplied input voltages to the second voltage controlled current source circuit.