AD9888
PV
D
C
P
0.0039 F
C
Z
0.039 F
R
Z
3.3k
3. The 3-Bit Charge Pump Current Register. This register allows
the current that drives the low-pass loop filter to be varied.
The possible current values are listed in Table III.
Table II. VCO Frequency Ranges
FILT
Figure 6. PLL Loop Filter Detail
PV1
0
0
1
1
PV0
0
1
0
1
Pixel Clock Range
(MHz)
10–45
45–90
90–150
150+
K
VCO
Gain
(MHz/V)
22.5
45
90
180
Four programmable registers are provided to optimize the per-
formance of the PLL. These registers are:
1. The 12-Bit Divisor Registers. The input Hsync frequencies
range from 15 kHz to 110 kHz. The PLL multiplies the
frequency of the Hsync signal, producing pixel clock fre-
quencies in the range of 10 MHz to 205 MHz. The Divisor
Register controls the exact multiplication factor. This regis-
ter may be set to any value between 221 and 4095. (The
divide ratio that is actually used is the programmed divide
ratio plus one.)
2. The 2-Bit VCO Range Register. To lower the sensitivity of
the output frequency to noise on the control signal, the VCO
operating frequency range is divided into four overlapping
regions. The VCO Range register sets this operating range.
Because there are only four possible regions, only the two
least significant bits of the VCO Range register are used. The
frequency ranges for the lowest and highest regions are shown
in Table II.
Table III. Charge Pump Current/Control Bits
Ip2
0
0
0
0
1
1
1
1
Ip1
0
0
1
1
0
0
1
1
Ip0
0
1
0
1
0
1
0
1
Current ( A)
50
100
150
250
350
500
750
1500
Table IV. Recommended VCO Range and Charge Pump Current Settings for Standard Display Formats
Standard
VGA
Resolution
640
×
480
Refresh
Rate (Hz)
60
72
75
85
56
60
72
75
85
60
70
75
80
85
60
75
85
60
65
70
75
85
60
75
Horizontal
Frequency (kHz)
31.5
37.7
37.5
43.3
35.1
37.9
48.1
46.9
53.7
48.4
56.5
60.0
64.0
68.3
64.0
80.0
91.1
75.0
81.3
87.5
93.8
106.3
Pixel Rate (MHz)
25.175
31.500
31.500
36.000
36.000
40.000
50.000
49.500
56.250
65.000
75.000
78.750
85.500
94.500
108.000
135.000
157.500
162.000
175.500
189.000
202.500
229.500
*
260.000
*
315.000
*
VCORNGE
00
00
00
00
00
00
01
01
01
01
01
01
01
10
10
10
11
11
11
11
11
10
11
11
Current
010
100
100
100
100
101
011
011
011
100
100
101
101
011
011
100
100
100
100
101
101
110
100
100
SVGA
800
×
600
XGA
1024
×
768
SXGA
1280
×
1024
UXGA
1600
×
1200
QXGA
2048
×
1536
2048
×
1536
*Graphics
sampled at 1/2 the incoming pixel rate using Alternate Pixel Sampling mode.
REV. A
–11–
AD [ ANALOG DEVICES ]
