CXD3018Q/R
§4. Description of Other Functions
§4-1. Channel Clock Regeneration by the Digital PLL Circuit
• The channel clock is necessary for demodulating the EFM signal regenerated by the optical system.
Assuming T as the channel clock cycle, the EFM signal is modulated in an integer multiple of T from 3T to
11T. In order to read the information in the EFM signal, this integer value must be read correctly. As a result,
T, that is the channel clock, is necessary.
In an actual player, the PLL is necessary to regenerate the channel clock because the fluctuation in the
spindle rotation alters the width of the EFM signal pulses.
The block diagram of this PLL is shown in Fig. 4-1.
The CXD3018Q/R has a built-in three-stage PLL.
• The first-stage PLL is for the wide-band PLL. When the internal VCO2 is used, an external LPF is necessary;
when not using the internal VCO2, external LPF and VCO are required.
The output of this first-stage PLL is used as a reference for all clocks within the LSI.
• The second-stage PLL generates the high-frequency clock needed by the third-stage digital PLL.
• The third-stage PLL is a digital PLL that regenerates the actual channel clock.
• A new digital PLL has been provided for CLV-W mode to follow the rotational velocity of the disc in addition
to the conventional secondary loop.
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ETC [ ETC ]
