REV. 0

–12–

AD722

Synchronous vs. Asynchronous Operation

The source of RGB video and synchronization used as an input

to the AD722 in some systems is derived from the same clock

signal as used for the AD722 subcarrier input (FIN). These

systems are said to be operating synchronously. In systems

where two different clock sources are used for these signals, the

operation is called asynchronous.

The AD722 supports both synchronous and asynchronous op-

eration, but some minor differences might be noticed between

them. These can be caused by some details of the internal

circuitry of the AD722.

There is an attempt to process all of the video and synchroniza-

tion signals totally asynchronous with respect to the subcarrier

signal. This was achieved everywhere except for the sampled de-

lay line used in the luminance channel to time align the lumi-

nance and chrominance. This delay line uses a signal at twice

the subcarrier frequency as its clock.

The phasing between the delay line clock and the luminance sig-

nal (with inserted composite sync) will be constant during syn-

chronous operation, while the phasing will demonstrate a

periodic variation during asynchronous operation. The jitter of

the asynchronous video output will be slightly greater due to

these periodic phase variations.

1

2

2

1

33

44

5

6

5

6

77

=+

NONINTERLACED

ODD FIELD

EVEN FIELD

a. Conversion of Noninterlace to Interlace

2

1

3

4

5

6

7

=+

NONINTERLACED

ODD FIELD

EVEN FIELD

1

2

3

4

5

6

7

b. Line Doubled Conversion Technique

2

1

3

4

5

6

7

=+

NONINTERLACED

ODD FIELD

EVEN FIELD

1

2

3

4

5

6

7

c. Line Averaging Technique

Figure 17.

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

16-Lead SOIC (R-16) (Wide Body)

PIN 1

0.2992 (7.60)

0.2914 (7.40)

0.4193 (10.65)

0.3937 (10.00)

1

16

9

8

0.0192 (0.49)

0.0138 (0.35)

0.0500 (1.27)

BSC

0.1043 (2.65)

0.0926 (2.35)

0.4133 (10.50)

0.3977 (10.00)

0.0118 (0.30)

0.0040 (0.10)

0.0125 (0.32)

0.0091 (0.23)

0.0500 (1.27)

0.0157 (0.40)

8

°

0

°

0.0291 (0.74)

0.0098 (0.25)

x 45

°