Application information

TSH122

10/16

3.2

Implementation considerations

3.2.1

Input

The DC level shifter optimizes the position of the video signal with no clamping on the output

rails.

3.2.2

Filter

A reconstruction filter is used to attenuate the DAC’s sampling frequency because it

generates a parasitic signal in the video spectrum (typically at 27 MHz in the case of

standard video). This function is fulfilled while keeping a low group delay and a good gain

flatness along the video band.

Figure 25.

Internal schematic

3.2.3

Output

In an AC-coupling configuration, the SAG correction allows use of two small low-cost

capacitors in place of one large capacitor (see Figure 26). The AC-coupling output reduces

the power consumption by removing the DC component included in the signal.

Nevertheless, the output can be directly connected to the line without any capacitor. In this

case, the OUT and SAG pins are connected together and the equivalent gain of the buffer

remains at 6 dB (see Figure 27).

+

-

2.25 V to 5 V

LPF

1

6

2

4

5 Power-down

2R

R

2R

DC shifter

+

SAG

3

2R

+Vcc

GND

Output

Input

+

-

2.25 V to 5 V

LPF

1

6

2

4

5 Power-down

2R

R

2R

DC shifter

+

SAG

3

2R

+Vcc

GND

Output

Input