Circuit Operating Descriptions
7-37
7-8 MTS
1) Outline
The Multiplex signal that come from Tuner/demode block(TM block IF DEMOD) enters into the MTS IC11 pin
and sap or stereo signal can be detected. The components of the signal are roughly separated 4
areas(stereo,dbx,matrix and sap)
2) STEREO BLOCK
(a) L+R(Main)
After the audio multiplexing signal input from SIF (pin48) passes through VCA, the SAP sinal 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 frequency characteristics are flattened
(de-emphasized) and input to the matrix
(b) 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 side band 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 modulation
of the L-R signal.
3) SAP BLOCK
SAP is an FM signal using 5fh as a carrier as shown in the Fig(base band spectrum) 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 characteristic flattened using SAP
LPF,and the SAP signal is input to the dbx-TV block.
4) dbx-TV BLOCK
Either the L-R signal and SAP signal input 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 pass through an external capacitor and is applied to
VCA(Voltage Control Amp) 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 circuit 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.
5) MATRIX
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 mode control.
