CXA2126 Sony Corporation, CXA2126 Datasheet - Page 22

• Manufacturer Part Number: CXA2126
• Description: Audio/Video Switch with Electronic Volume for 2 Scart
• Manufacturer: Sony Corporation

2. Explanation of Audio System
Inputs and Outputs
The audio system consists of 3 stereo inputs, 2 stereo outputs and separate mono and phono outputs. The
stereo outputs can be connected to any one of the 3 stereo inputs. All audio inputs have a –6dB attenuator
except RIN1 and LIN1. Thus, the net gain of the audio system is 0dB, as the internal switch is followed by an
audio amplifier having +6dB of gain. The stereo input RIN1/LIN1 does not have an input attenuator and
therefore the net gain from input to output is +6dB. The output impedance of each audio amplifier is near zero,
and can be capacitively coupled directly to the external scart circuit. The output circuitry is typically a 10µF
capacitor, and an optional 560Ω series compliance resistor. Depending on the length and type of cable used in
the scart cable connector, the load seen at the scart terminal will consist of a parallel capacitor, (100pF to
400pF) and mandatory 10kΩ resistor connected to ground. The customer may chose to place an alternative
audio filter at the AV switch output.
TV Audio Output
The TV audio section is composed of an audio switch followed by two variable gain stages, corresponding to
the coarse and fine electronic volume control. The coarse volume control gives a 0 to –56dB range in 8dB
steps. Similarly the fine control gives a 0 to –7dB range in 1dB steps. The volume control section is followed by
a switchable 0/+6dB amplifier which allows compensation for low level signals from a DAC. Finally, a mono
switch allows the mixed R + L signal to be switched to the R and L output channels. (Fig. 2-1)
TV Mute
The I
after a audio zero cross detection to reduce click noise, or immediately depending on the I
can be seen from the I
software to action an immediate mute, make any suitable changes to the audio source or electronic volume
control and after a minimum period of 6
ample time to allow any transient ac voltages to settle during an audio source change.
Audio
Source
1 F
2
C mute function acts only on the TV, phono and mono audio circuit. Audio mute can be implemented
RIN1
RIN2
RIN3
LIN1
LIN2
LIN3
12
22
14
24
3
5
–6dB
–6dB
–6dB
–6dB
2
C write format that the same mute bit occurs in DATA 1 and DATA 7. This allows the
Mute
Fig. 2-1. TV Audio Output
90µs (540µs) un-mute the output buffer. Such a period provides
Volume 0, –63dB + mute
TV Audio Output
8dB
8dB
– 22 –
ZCD
1dB
1dB
Switchable Amp
0/6dB
0/6dB
Mono Switch
2
2
2
2
35
40
42
37
2
C setting of ZCD. It
PHONO_R
RTV
LTV
PHONO_L
560
Optional
Low Pass Filter
10 F
C
CXA2126Q
Scart Pin