CXA2521Q

The CXA2521Q is an IC for RF signal processing of compact discs.Mirror circuit performs peak and bottom hold after RFT signal has been amplified.The peak hold is executed for Pin 22 with the time constant which follows the traverse signal of 30kHz for OFF (connection to GND) and maximum 80kHz (adjustable with DC voltage of Pin 23) for ON (connection to Vcc). The bottom hold is executed with the time constant which follows the rotation cycle envelope fluctuation.

Features of the CXA2521Q are:(1)supports quadruple speed (RF signal fc 8MHz); (2)peak hold circuit time constant of mirror circuit can be adjusted (switching function provided) accurate mirror detection is possible from traverse signal of high/low speed search; (3)fluctuations  of  characteristics  are  very  small,which are caused by variations of resistance value and deviations of temperature characteristics for IC internal/external resistors, because the input and feedback resistors of the tracking error amplifier are externally attached; (4)APC (automatic power control) function.

The absolute maximum ratings of the CXA2521Q can be summarized as:(1)supply voltage:7V;(2)storage temperature:-65 to +150;(3)allowable power dissipation:800mW.The mirror signal is output by comparing to the signal K (2/3 level of the J peak value which is peak-held with a large time constant) where the difference of hold signals H and I is obtained. The mirror output is low for tracks on the disc and high for the area between tracks (the mirror areas).In addition, a high signal is output when a defect is detected. The mirror hold time constant must be sufficiently large in comparison with the traverse signal.The focus OK circuit creates the timing window okaying the focus servo form the focus search state.The low frequency component of RF CXA2521Q can be get by obtaining the difference of the  Pins 24 and 25 RF signals, whose low frequency components are removed,at the focus OK amplifier.