Datasheet

AD9776/AD9778/AD9779
Rev. A | Page 37 of 56
Table 18. VCO Frequency Range vs. PLL Band Select Value
Typical PLL Lock Ranges
VCO Frequency Range in MHz
Typ at 25°C Typ over Temp
PLL Band Select
f
LOW
f
HIGH
f
LOW
f
HIGH
111111 (63) Auto mode Auto mode
111110 (62) 2056 2170 2105 2138
111101 (61) 2002 2113 2048 2081
111100 (60) 1982 2093 2029 2061
111011 (59) 1964 2075 2010 2043
111010 58) 1947 2057 1992 2026
111001 (57) 1927 2037 1971 2006
111000 (56) 1907 2016 1951 1986
110111 (55) 1894 2003 1936 1972
110110 (54) 1872 1981 1913 1952
110101 (53) 1852 1960 1892 1931
110100 (52) 1841 1948 1881 1920
110011 (51) 1816 1923 1855 1895
110010 (50) 1796 1903 1835 1874
110001 (49) 1789 1895 1828 1867
110000 (48) 1764 1871 1803 1844
101111 (47) 1746 1853 1784 1826
101110 (46) 1738 1842 1776 1815
101101 (45) 1714 1820 1752 1794
101100 (44) 1700 1804 1737 1779
101011 (43) 1689 1790 1726 1764
101010 (42) 1657 1757 1695 1734
101001 (41) 1641 1738 1679 1714
101000 (40) 1610 1707 1649 1684
100111 (39) 1597 1689 1635 1666
100110 (38) 1568 1661 1607 1639
100101 (37) 1553 1641 1592 1617
100100 (36) 1525 1613 1562 1592
100011 (35) 1511 1595 1548 1572
100010 (34) 1484 1570 1519 1549
100001 (33) 1470 1552 1506 1528
100000 (32) 1441 1525 1474 1504
011111 (31) 1429 1509 1463 1487
011110 (30) 1403 1485 1433 1464
011101 (29) 1390 1469 1422 1447
011100 (28) 1362 1443 1391 1423
011011 (27) 1352 1429 1380 1407
011010 (26) 1325 1405 1352 1385
011001 (25) 1314 1390 1340 1369
011000 (24) 1290 1368 1315 1350
010111 (23) 1276 1351 1302 1332
010110 (22) 1253 1331 1277 1313
010101 (21) 1239 1313 1264 1295
010100 (20) 1183 1255 1205 1240
010011 (19) 1204 1275 1227 1259
010010 (18) 1151 1221 1172 1207
010001 (17) 1171 1240 1193 1224
010000 (16) 1148 1218 1170 1204
001111 (15) 1137 1204 1159 1189
Typical PLL Lock Ranges
VCO Frequency Range in MHz
Typ at 25°C Typ over Temp
PLL Band Select
f
LOW
f
HIGH
f
LOW
f
HIGH
001110 (14) 1116 1184 1137 1170
001101 (13) 1106 1171 1127 1157
001100 (12) 1086 1152 1106 1138
001011 (11) 1075 1138 1095 1124
001010 (10) 1055 1119 1075 1106
001001 (9) 1045 1107 1065 1093
001000 (8) 1027 1090 1047 1076
000111 (7) 1016 1076 1034 1062
000110 (6) 998 1059 1016 1046
000101 (5) 987 1046 1005 1032
000100 (4) 960 1017 977 1004
000011 (3) 933 989 949 976
000010 (2) 908 962 923 950
000001 (1) 883 936 898 925
000000 (0) 859 911 873 899
VCO Frequency Ranges
Because the PLL band covers greater than a 2× frequency range,
there can be two options for the PLL band select: one at the low
end of the range and one at the high end of the range. Under
these conditions, the VCO phase noise is optimal when the user
selects the band select value corresponding to the high end of the
frequency range.
Figure 75 shows how the VCO bandwidth and
the optimal VCO frequency varies with the band select value.
VCO Frequency Ranges over Temperature
The specifications given over temperature in Table 1 8 are for a
single part in a single lot. Part-to-part, and lot-to-lot, these
specifications can exhibit a mean shift of several register
settings. Systems should be designed to take this potential shift
into account to maintain optimal PLL performance.
PLL Loop Filter Bandwidth
The loop filter bandwidth of the PLL is programmed via SPI
Register 0x0A, Bits<4:0>. Changing these values switches
capacitors on the internal loop filter. No external loop filter
components are required. This loop filter has a pole at 0 (P1),
and then a zero (Z1) pole (P2) combination. Z1 and P2 occur
within a decade of each other. The location of the zero pole is
determined by Bits<4:0>. For a setting of 00000, the zero pole
occurs near 10 MHz. By setting Bits<4:0> to 11111, the Z1/P2
combination can be lowered to approximately 1 MHz. The
relationship between Bits<4:0> and the position of the zero pole
between 1 MHz and 10 MHz is linear. The internal components
are not low tolerance, however, and can drift by as much as ±30%.
For optimal performance, the bandwidth adjustment
(Register 0x0A, Bits<4:0>) should be set to 11111 for all
operating modes with PLL enabled. The PLL bias settings