LouijieC написал(а):
It was described in the data sheet that 4 LSB's is enough to create an output which approximately 60 dB below the full scale DAC code. In your case the value of 0x0501 would be 0x0F. For the phase offset value, a 180 degree phase shift would just equal to b100000000 wherein bit 9 is set to 1. I just want to emphasize that you still need to experiment to get the maximum attenuation of the spur by adjusting your phase offset greater/less than 180 degree offset.
Best Regards
Louijie
I did what you wrote to me, but had no effect.
quote a fragment of the code, initialization Spur Killer
---------------------------------------------------------------------------------------
#define Spur_A_Harmonic_Add 0x0500 // address AD9912
#define Spur_A_Magnitude_Add 0x0501
#define Spur_A_Phase1_Add 0x0503 // 1-8 bit
#define Spur_A_Phase2_Add 0x0504 // 9bit End
---------------------------------------------------------------------------------------
//***********I/O Register Map section
void IO_UPDETE(void)
{
Nop();
PORTBbits.RB2 = 1; // set IO_UPDETE
Nop();
PORTBbits.RB2 = 0; // reset IO_UPDETE
Nop();
}
-----------------------------------------------------------------------------------------------------
DDS_FREQ_WRITE(LookUpFTW[190]); // Value = Fout(Mhz) - 10
Nop();
SPI_24(WORD_DATA(Spur_A_Harmonic_Add, 0x02)); // Set SpurKillerharmonic
IO_UPDETE(); // M IO_UPDETE
SPI_24(WORD_DATA(0x0013, 0x80)); // Set bit 7 PD fund DDS
IO_UPDETE(); // M IO_UPDETE
SPI_24(WORD_DATA(Spur_A_Harmonic_Add, 0x82)); // Enable SpurKiller Set harmonic
IO_UPDETE(); // M IO_UPDETE
SPI_24(WORD_DATA(Spur_A_Magnitude_Add, 0x0F)); // SpurKiller
IO_UPDETE(); // M IO_UPDETE
SPI_24(WORD_DATA(0x0013, 0x00)); // Clear bit 7 PD fund DDS
IO_UPDETE(); // M IO_UPDETE
SPI_24(WORD_DATA(Spur_A_Phase1_Add, 0x00)); // Setting Phase inverting 180
IO_UPDETE(); // M IO_UPDETE
SPI_24(WORD_DATA(Spur_A_Phase2_Add, 0x01)); // Setting Phase sign minus-
IO_UPDETE(); // M IO_UPDETE
Look at the chart FFT, you can see that the 2 nd harmonic large, Spur Killer does not give effect. I think that is not correct initialization, or incorrect values I write to the registers.
