REV. B

AD9884A

–17–

Table VII. Recommended VCORNGE and CURRENT Settings for Standard Display Formats

Refresh

Horizontal

Standard

Resolution

Rate

Frequency

Pixel Rate

VCORNGE

CURRENT

VGA

640

× 480

60 Hz

31.5 kHz

25.175 MHz

00

000

72 Hz

37.7 kHz

31.500 MHz

00

000

75 Hz

37.5 kHz

31.500 MHz

00

000

85 Hz

43.3 kHz

36.000 MHz

00

001

SVGA

800

× 600

56 Hz

35.1 kHz

36.000 MHz

00

001

60 Hz

37.9 kHz

40.000 MHz

00

001

72 Hz

48.1 kHz

50.000 MHz

00

010

75 Hz

46.9 kHz

49.500 MHz

00

001

85 Hz

53.7 kHz

56.250 MHz

01

010

XGA

1024

× 768

60 Hz

48.4 kHz

65.000 MHz

01

010

70 Hz

56.5 kHz

75.000 MHz

01

011

75 Hz

60.0 kHz

78.750 MHz

01

011

80 Hz

64.0 kHz

85.500 MHz

10

011

85 Hz

68.3 kHz

94.500 MHz

10

011

SXGA

1280

× 1024

60 Hz

64.0 kHz

108.000 MHz

10

011

75 Hz

80.0 kHz

135.000 MHz

11

100

85 Hz

91.1 kHz

157.500 MHz*

01

100

UXGA

1600

× 1200

60 Hz

75.0 kHz

162.000 MHz*

01

100

65 Hz

81.3 kHz

175.500 MHz*

10

100

70 Hz

87.5 kHz

189.000 MHz*

10

101

75 Hz

93.8 kHz

202.500 MHz*

10

101

85 Hz

106.3 kHz

229.500 MHz*

10

110

VESA Monitor Timing Standards and Guidelines, September 17, 1998

*Graphics sampled at 1/2 incoming pixel rate using Alternate Pixel Sampling mode.

Figure 11 illustrates the AD9884A’s jitter as a percentage of the

total clock period over the range of operating frequencies.

Though the jitter is very low over most of the range (less than

5% of the pixel period), the jitter increases at clock rates below

40 MHz. At lower frequencies, the jitter can be reduced by

operating the AD9884A at twice the desired frequency, and

using only every other data sample produced. This can be easily

implemented by placing the part in Dual Channel mode (for

example, as in Figure 21), and reading the data from only one of

the output ports. The DATACK and

DATACK outputs will

run at the desired, lower, sample rate.

PIXEL CLOCK – MHz

0

0

100

20

40

60

80

120

140

160

5

15

10

JITTER p-p (%)

OVERSAMPLED RATE

JITTER p-p (%)

Figure 11. Pixel Clock Jitter vs. Frequency