TSH345(2007) 데이터 시트보기 (PDF) - STMicroelectronics

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TSH345
(Rev.:2007)

Triple video buffer with selectable filter for HD and SD video applications

STMicroelectronics 

Using the TSH345 to drive Y-C, CVBS, Y-U-V, Y-Pb-Pr and R-G-B video components

TSH345

Figure 4. Flexibility of the TSH345 for SD and HD signals

HD/PV/SD

Y,G

DAC

150Ω

Pb,B

150Ω

DAC

150Ω

Pr,R

150Ω

DAC

150Ω

150Ω

Y,G

DAC

Pb,B,C

DAC

Pr,R,CVBS

DAC

+5V

75Ω

75Ω

TSH345

TSSOP14

75Ω

SO14

Mux

Filter select

Standby

Cable

75Ω

Cable

75Ω

Cable

75Ω

TV

HD/PV/SD

Y,G

DAC

150Ω

Pb,B,C

DAC

150Ω

Pr,R,CVBS

DAC

150Ω

+5V

75Ω

NC

75Ω

NC

TSH345

TSSOP14 75Ω

NC

SO14

Mux (NC)

Filter select

Standby

Cable

75Ω

Cable

75Ω

Cable

75Ω

TV

The TSH345 is used to drive either high definition video signals up to 30 MHz, or progessive

and interlaced standard definition video signals on 75-ohm video lines. It can drive a large

panel of signals like Y-C and CVBS, Y-U-V, Y-Pb-Pr and R-G-B where the bottom of the signal

(the synchronization tip in the case of Y and CVBS signals) is close to zero volts. An internal

input DC value is added to the video signal in order to shift the bottom from GND.

The shift is not based on the average of the signal, but is an analog summation of a DC

component to the video signal. Therefore, no input capacitors are required, which provides a

real advantage in terms of cost and board space.

Under these conditions, it is possible to drive the signal in single supply without any

saturation of the driver against the lower rail.

Because half of the signal is lost through output impedance matching, in order to properly

drive the video line, the shifted signal is multiplied by a gain of 2 or +6 dB.

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