cxa2074q Sony Electronics, cxa2074q Datasheet - Page 23

• Manufacturer Part Number: cxa2074q
• Description: Us Audio Multiplexing Decoder
• Manufacturer: Sony Electronics

(1) L + R (MAIN)
(2) L – R (SUB)
(3) SAP
(4) Mode discrimination
(5) dbx-TV block
(AUX1-R)
After the audio multiplexing signal input from COMPIN (Pin 17 (Pin 14)) 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 frequency
characteristics are flattened (de-emphasized) and input to the matrix.
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.
SAP is an FM signal using 5f
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. When there is no SAP signal, the Pin 26 output is
soft muted.
Stereo discrimination is performed by detecting the pilot signal amplitude. SAP discrimination is
performed by detecting the 5f
noise near 25kHz after FM detection of SAP signal.
Either the L – R signal or SAP signal input respectively from ST IN (Pin 24 (Pin 22)) or SAP IN (Pin 27
(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.
(AUX1-L)
35
36
(AUX2-L) (AUX2-R)
(Lch)
from MATRIX
38
TVSW
(Rch)
37
(LPOUT-L) (LPOUT-R)
40
39
H
Fig. 4. Sound processor block
H
carrier amplitude. NOISE discrimination is performed by detecting the
(LPIN-L)
as a carrier as shown in the Fig. 1. First, the SAP signal only is
42
PASSSW
(LPIN-R)
41
– 23 –
VOL-R
VOL-L
BASS
TREBLE
(LSOUT-L)
(LSOUT-R)
7
8 (3)
(2)
CXA2074Q/S