| 摘要 |
A variable frequency oscillator comprises a first phase-locked loop (204; 206 or 207; 209) including a first voltage controlled oscillator (209), a second phase-locked loop (214, 215, 218) including a second voltage controlled oscillator (218) having the same constants as the first voltage controlled oscillator, and an oscillator (202) for generating a stable pulse train. The arrangement is such that, in operation, the first phase-locked loop is synchronised with a sequence of input data (at 219), the second phase-locked loop is synchronised with the pulse train from the oscillator (202) and the first voltage controlled oscillator (209) is stabilized with the control voltage (added at 208) which is applied to the second voltage controlled oscillator (218). The arrangement is used to derive window pulses for reading data reproduced from a floppy disk. <IMAGE> |
