CXA1734S View Datasheet(PDF) - Sony Semiconductor

Part Name

Description

Manufacturer

CXA1734S

US Audio Multiplexing Decoder

Sony Semiconductor 

CXA2064M

(1) L + R (MAIN)

When the audio multiplexing signal is inputted to COMPIN (Pin 7), 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 frequency characteristics are 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.

(3) SAP

SAP is an FM signal using 5fH as a carrier as shown in the Fig. 2. 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 characteristics flattened using SAP LPF, and the SAP signal

is input to the dbx-TV block via the NRSW circuit.

(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 STIN (Pin 1) or SAPIN (Pin 27) 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

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 and whether there is ST / SAP discrimination.

(7) Others

“Bias” supplies the reference voltage and reference current to the other blocks. The current flowing to

the resistor connecting IREF (Pin 5) with GND become the reference current.

– 15 –

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