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CXA2078Q

I²C Bus-Compatible Audio/Video Switch with Electronic Volume

Sony Semiconductor 

CXA2078Q

Description of operation

1. Explanation of Video Section

The video section comprises of 12 high impedance (120kΩ) inputs switched through to 8 video outputs. A

+6dB internal amplifier is connected to each output. The amplifier is required to compensate for the 6dB

attenuation which occurs at the external emitter follower stage used for driving video loads. The typical

external configuration is shown in Fig. 1-1.

A Y/C mixer can be used for mixing Luma and Chroma signals for use with an external RF modulator

connected to Vout8. The Y/C mixer is controllable via the I2C data bus. The circuit is shown in Fig. 1-2 with a

trap circuit used to give 3dB attenuation at 4.43MHz of the Luma signal.

SCART_in

75Ω

0.47µ

75Ω

Vin

Vbias

Switch

120kΩ

Video element

Video_VCC = 9V

AMP

Vbias

VCC = 12V

beta = 250

BC547B

Vout

SCART_out

Load

75Ω

1kΩ

75Ω

Fig. 1-1. Video circuit element: 6dB gain amplifier with external emitter follower

R/C

CVBS/Y

6dB

6dB

1kΩ

1kΩ

0dB

6.5kΩ

147Ω

0dB

6.5kΩ

Fig. 1-2. Y/C MIXER Circuit

– 21 –

Vout3

Vout4

Vout8

6dB

TRAP

1kΩ

47µF

25pF

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