TSH343

Using the TSH343 to Drive Y-Pb-Pr Video Components

Rev. 2

11/14

DACs.

The TSH343 is used to drive high definition video signals up to 30MHz on 75-ohm video

lines. It is dedicated to driving YPbPr signals where the synchronization tip—close to zero

volts—is included in Y signal, as seen in (1). An internal input DC value of 600mV is added

to the video signal in order to shift the bottom from 0V to 600mV as seen in (2).

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.

Assuming that we lose half of the signal by output impedance-matching in order to properly

drive the video line, the shifted signal is multiplied by a gain of 2 or +6dB (3).

4.1

Delay between channels

Figure 29. Measurement of the delay between each channel

Delay between each video component is an important aspect in high definition video

systems. To drive porperly the three video components without any relative delay, the dice of

the TSH343 is layouted out with a very symetrical geometry. The effect is direct on the

synchronization of each channel, as shown in

Figure 30. No delay appears between each

channel when the same Vin signal is applied on the three inputs. Note that the delay from

the inputs the outputs equals 4ns.

75

Ω

75

Ω Cable

75

Ω

75

Ω

75

Ω Cable

75

Ω

75

Ω

600mV

75

Ω Cable

75

Ω

+6dB

+

+

+6dB

+

+

+6dB

+

+

600mV

600mV

5V

Vin

V1

V2

V3

75

Ω