cxa2054s Sony Electronics, cxa2054s Datasheet - Page 22

• Manufacturer Part Number: cxa2054s
• 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-L)
(AUX1-R)
40
39
After the audio multiplexing signal input from COMPIN (Pin 19) 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 5 f
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 28 output is soft muted.
Stereo discrimination is performed by detecting the pilot signal amplitude. SAP discrimination is performed
by detecting the 5 f
kHz after FM detection of SAP signal.
Either the SAP signal or L-R signal input respectively from ST IN (Pin 26) or SAP IN (Pin 29) 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.
from MATRIX
(Lch) (Rch)
SW1
(TVOUT-L) (TVOUT-R)
44
43
(AUX2-L) (AUX2-R)
41
H
SW2
carrier amplitude. NOISE discrimination is performed by detecting the noise near 25
40
VOLLIM
H
as a carrier as shown in the Fig. 1. First, the SAP signal only is extracted
Fig. 4. Sound processor block
PREVOL
—22—
SURROUND
BASS
TREBLE
(SURRIN)
VOL-R
VOL-L
SW3
4
(LSOUT-R)
(LSOUT-L)
7
6
VOL-S
(SURROUT)
CXA2054S
5