| 摘要 |
PURPOSE: A voltage controlled oscillator for digital tuner is provided to improve the characteristic of a phase noise by changing the register value of a PLL(Phase Locked Loop) IC(Integrated Circuit). CONSTITUTION: A PLL IC(110) changes a pump current value by changing an internal register value according to a control signal of a CPU(Central Processing Unit)(120) and outputs the changed pump current value to a low pass filter(2). The PLL IC(110) is composed of 5 bytes. The register values are the first to the fourth bit of each byte. The CPU(120) controls all operations of a system. The CPU(120) outputs a control signal to the PLL IC(110) according to a phase difference outputted to the PLL IC(110). The intensity of voltage outputted from the low pass filter(2) is changed since a time constant is changed according to a current size of the PLL IC(110).
|
