I am working with DAC38J84 in NCO mode in the following way:
1. set a new frequency through SPI (registers 0x14 - 0x16)
2. using a one sysref pulse to update the NCO ( 0x1E = 2222 , 0x1F = 2220)
DAC_CLOCK = 1920MHz
SYSREF WIDTH = 500psec
DAC configuration is attached
0x00 0x0218
0x01 0x0003
0x02 0x2050
0x03 0xA300
0x04 0xF0F0
0x05 0xFF07
0x06 0xFFFF
0x07 0x3100
0x08 0x0000
0x09 0x0000
0x0A 0x0000
0x0B 0x0000
0x0C 0x0400
0x0D 0x0400
0x0E 0x0400
0x0F 0x0400
0x10 0x0000
0x11 0x0000
0x12 0x0000
0x13 0x0000
0x14 0x0000
0x15 0x0000
0x16 0x4200
0x17 0x0000
0x18 0xAAAA
0x19 0x52AA
0x1A 0x0020
0x1B 0x0000
0x1E 0x2222
0x1F 0x2220
0x20 0x2022
0x22 0x1B1B
0x23 0x01FF
0x24 0x0010
0x25 0x4000
0x26 0x0000
0x2D 0x0001
0x2E 0xFFFF
0x2F 0x0005
0x30 0x0000
0x31 0x1000
0x32 0x0000
0x33 0x0000
0x34 0x0000
0x3B 0x3800
0x3C 0x0228
0x3D 0x0088
0x3E 0x0108
0x3F 0x0000
0x46 0x1882
0x47 0x01C8
0x48 0x3143
0x49 0x0000
0x4A 0x001E
0x4B 0x0801
0x4C 0x0903
0x4D 0x0300
0x4E 0x0F0F
0x4F 0x1C61
0x50 0x0000
0x51 0x00DC
0x52 0x00FF
0x53 0x0000
0x54 0x00FC
0x55 0x00FF
0x56 0x0000
0x57 0x00FF
0x58 0x00FF
0x59 0x0000
0x5A 0x00FF
0x5B 0x00FF
0x5C 0x1133
0x5E 0x0000
0x5F 0x3210
0x60 0x5764
0x61 0x0211
0x64 0x0001
0x65 0x0001
0x66 0x0001
0x67 0x0001
0x68 0x7709
0x69 0x0000
0x6A 0x0000
0x6B 0xBD07
0x6C 0x0007
0x6D 0x0090
0x6E 0x0000
0x6F 0x0000
0x70 0x0000
0x71 0x0000
0x72 0x0000
0x73 0x0000
0x74 0x0000
0x75 0x0000
0x76 0x0000
0x77 0x0000
0x78 0x0000
0x79 0x0000
0x7A 0x0000
0x7B 0x0000
0x7C 0x0000
0x7D 0x0000
SYSREF PULSE:
For each sysref trigger a different result is obtained.
for example, when i set the dac output to 495MHz i got the following result:
good output - low spurs:
bad output - high spurs (sometimes even higher than my desirable signal):
when i use a SIF SYNC trigger instand of sysref , everything works fine.
Please advise what is wrong with my configuration?
Thanks,
Asaf
