CXA2134Q Datasheet, PDF (27/35 Pages) Sony Corporation – US Audio Multiplexing Decoder

CXA2134Q
(5) dbx-TV block
Either the L – R signal or SAP signal input respectively from ST IN (Pin 22) or SAP IN (Pin 25) is
selected by the mode control and input to the dbx-TV block.
The input signal then passes through the fixed de-emphasis circuit and is applied to the variable de-
emphasis circuit. The signal output from the variable de-emphasis circuit passes through an external
capacitor and is applied to VCA (voltage control amplifier). Finally, the VCA output is converted from a
current to a voltage using an operational amplifier and then input to the matrix.
The variable de-emphasis circuit transmittance and VCA gain are respectively controlled by Each of
effective value detection circuits. Each of the effective value detection circuits passes the input signal
through a predetermined filter for weighting before the effective value of the weighted signal is
detected to provide the control signal.
(6) Matrix, TVSW
The signals (L + R, L – R, SAP) input to “MATRIX” become the outputs for the ST-L, ST-R, MONO and
SAP signals according to the BUS data and whether there is ST / SAP discrimination.
“TVSW” switches the “MATRIX” output signal, external input signal (input to AUX1-L, R), external input
signal (input to AUX2-L, R) and external forced MONO.
(7) Sound processor block
The sound processor block contains "SURROUND" (quasi-surround function), “BASS/TREBLE” tone
control functions, and “VOLUME”.
• Surround
At "SURROUND", the L and R differential components are phase-shifted and these components are
added to the left and right channels.
When surround is OFF (SURR = 0)
Inputs are output as is.
{ Lout = Lin
Rout = Rin
When surround is ON (SURR = 1)
{ Lout = Lin – 1 – jωRC (Lin – Rin)
1 + jωRC
1 – jωRC
Rout = Rin +
(Lin – Rin)
1 + jωRC
{ R = 24kΩ (On-chip)
C = 0.022µF (Externally attached to Pin 40)
(Lin, Lout) and Rin, (Rout) indicate the left- and right- channel I/O of the surround circuit.
(8) Others
“MVCA” is a VCA which adjusts the input signal level to the standard level of this IC.
“Bias” supplies the reference voltage and reference current to the other blocks. The current flowing to
the resistor connecting IREF (Pin 15) with GND become the reference current.
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