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CX-961
3) RF amplifier unit
The head amplifier LSI, TA2150FN, adds, amplifies and
equalizes photodetector output (A+C) and (B+D), then
outputs RF signal to the RFI pin. (This signal enables
checking eye patterns.) Low frequency element
contained in RFI voltage is formulated as follows:
RFI = (A + B + C + D) × 5.43.
RFI is used for RF Offset Control circuit. RFI signal
output from Pin 28 is AC-coupled externally, and then
re-input to Pin 27 and amplified by the RFAG amplifier
to obtain RFO signal.
As described later, TA2150FN has a built-in RFAGC
function that controls the RFAGC amplifier gain so that
RFO output stays within 1.2 ± 0.3V p.p. range.
This RFO signal is used for EFM and RFAGC control
circuit and for generating RFRP and RFCT signals for
track counting.
Besides, the frequency characteristics of an RF
equalizer are switched at double-speed reproduction.
(Switching using the HSSW terminal)
Further, with RWSW the gain at the RF amplifier stage
is raised by 13db, compared with that in normal
operation, when the gain lowers because of stains on
the lens or while playing a CDRW.
Fig.4:RF CIRCUIT
4
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