| 摘要 |
PURPOSE: A ring oscillator is provided to generate a clock signal of a stable period regardless of a wafer processing variation by supplying a control voltage to a bias voltage generating circuit constantly. CONSTITUTION: A ring oscillator comprises a NOR gate(21), two inverters(I11,I12), and first and second voltage adjusting circuits(22,23). The NOR gate(21) receives first to third control signals(S11-S13), and the inverter(I11) receives an output of the NOR gate(21) to generate a first control voltage(V1). The inverter(I12) is connected to an output of the inverter(I11), and generates a second control voltage(V2). The first voltage adjusting circuit(22) generates a third control voltage(V3) according to the second control voltage(V2), and consists of a reference voltage generating part(24) and a control part. The reference voltage generating part(24) generates a reference voltage according to the second control voltage(V2), and the control part controls an output of the reference voltage generating part(24). The control part consists of an NMOS transistor(N11), whose gate is connected to receive the second control voltage(V2). The second voltage adjusting circuit(23) receives the third control voltage(V3) from the first voltage adjusting circuit(22) and the first control voltage(V1), and generates a fourth control voltage(V4).
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