– 60 –
MTS CIRCUIT
(1) L+R (MAIN)
After the audio multiplexing signal input from COMPIN (Pin 13) passes
through MVCA, the SAP signal and telemetry signal are suppressed by
STEREO LPF. Next, the pilot signals are canceled. Finally, the L–R signal
and SAP signal are removed by MAIN LPF, and the frequency response is
flattened (de-emphasized) and input to the matrix.
(2) L–R (SUB)
The L–R signal follows the same course as L+R before the pilot signal is
canceled. L–R has no carrier signal, as it is a suppressed-carrier double-
sideband amplitude modulated signal (DSB-AM modulated). For this
reason, the pilot signal is used to regenerate the carrier signal (quasi-sine
wave) to be used for the demodulation of the L–R signal. In the last stage,
the residual high frequency components are removed by SUB LPF and the
L–R signal is input to the dbx-TV block via the NRSW circuit after passing
through SUBVCA.
(3) SAP
SAP is an FM signal using 5fH as a carrier as shown in the Fig. 1. First,
the SAP signal only is extracted using SAP BPF. Then, this is subjected
to FM detection. Finally residual high frequency components are removed
and frequency response flattened using SAP LPF, and the SAP signal is
input to the dbx-TV block via the NRSW circuit. When there is no SAP
signal, the Pin 24 output is soft muted.
(4) Mode discrimination
Stereo discrimination is performed by detecting the pilot signal amplitude.
SAP discrimination is performed by detecting the 5fH carrier amplitude.
NOISE discrimination is performed by detecting the noise near 25kHz after
FM detection of SAP signal.
(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 AUS2-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)
Input are output as is.
When surround is ON (SURR=1)
(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 becomes the reference current.
Lout=Lin
Rout=Rin
{
Lout=Lin–
Rout=Rin+
{
1– j
ω
RC
1+ j
ω
RC
(Lin–Rin)
1– j
ω
RC
1+ j
ω
RC
(Lin–Rin)
R=24k
Ω
(On-chip)
C=0.022µF (Externally attached to Pin 40)
{
