| 摘要 |
An oscillation circuit is provided to constitute a ring oscillation circuit with four operational amplifiers to simplify structure of the circuit, stabilize an oscillation operation, and reduce a manufacturing cost. An oscillation circuit includes a ring oscillation circuit(202), a phase-locked loop(204), a reference signal source(206), a low pass filter(208), and an oscillation frequency control circuit(210). The ring oscillation circuit includes a plurality of differential operational amplifiers(20-1~20-4) which are capable of being variably controlled depending on output current of the oscillation frequency control circuit. The phase-locked loop generates an oscillation frequency control voltage(Vtune) depending on a phase difference between an oscillation signal(Vosc) outputted from the ring oscillation circuit and a reference signal outputted from the reference signal source. The oscillation frequency control circuit receives the smoothed oscillation frequency control voltage and changes a ratio of values of two output current(Ia,Ib) according to a difference between the oscillation frequency control voltage and the predetermined reference voltage. |
