AD8134

Rev. A | Page 17 of 20

–OUT R

+OUT R

–OUT G

+OUT G

–OUT B

+OUT B

+IN R

–IN R

SYNC LEVEL

+IN G

–IN G

+IN B

–IN B

R

1.5k

Ω

1.5k

Ω

AD8134

750

Ω

750

Ω

G

1.5k

Ω

1.5k

Ω

750

Ω

750

Ω

1.5k

Ω

1.5k

Ω

750

Ω

750

Ω

OPD

×2

2

2

2

Figure 34. AD8134 Sync-On-Common-Mode Encoding Scheme

0

0.5

1.0

1.5

2.0

4.0

3.5

4.5

2.5

3.0

5.0

0.98

0.99

1.00

1.01

1.03

1.04

1.05

1.02

1.06

1.07

TIME (

μs)

2.0

2.1

2.2

2.3

2.4

2.9

2.8

3.0

2.5

2.6

2.7

3.1

R

G

B

Figure 35. AD8134 Sync-On-Common-Mode Signals in Single 5 V Application

The transmitted common-mode sync signal magnitudes are

scaled by applying a dc voltage to the SYNC LEVEL input,

referenced to the negative supply. The difference between the

voltage applied to the SYNC LEVEL input and the negative

supply sets the peak deviation of the encoded sync signals about

the midsupply common-mode voltage. For example, with the

encoded sync pulses about the nominal midsupply common-

mode voltage is typically ±500 mV. The equations in Figure 34

color’s midsupply common-mode signal. In these equations, the

for low), and the constant K is equal to the peak deviation of the

encoded sync signals.

Figure 35 shows how the sync signals appear on each common-

mode voltage in a single 5 V supply application when the

voltage applied to the SYNC LEVEL input is 500 mV. A typical

setting for the SYNC LEVEL voltage is 500 mV above the

negative supply.

LEVEL-SHIFTING SYNC PULSES ON ±5 V SUPPLIES

The vertical and horizontal sync pulses received from a

computer video port are generally referenced to ground. When

using ±5 V supplies, these pulses must be level-shifted before

inputs because these inputs are referenced to the negative

supply. The circuit shown in Figure 36 provides the proper sync

pulse level-shifting for a negative supply voltage of −5 V. The

vertical and horizontal sync pulses each require a level-shift

circuit.

6.04k

Ω

2.21k

Ω

LEVEL-SHIFTED

SYNC PULSE

TO AD8134

GROUND-REFERENCED

SYNC PULSE

1k

Ω

2N3906

Figure 36. Level-Shifting Sync Pulses on ±5 V Supplies