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Urgent: DDS AD9854 Q-Output Not coming

Question asked by Sudhanshu on Jan 16, 2013
Latest reply on Feb 4, 2013 by sitti

I have a strange behaviour of DDS AD9854. Please refer to the Schematic as attached for AD9854. The Input clock to DDS is 25 MHz differential and is above 400mV P-p centered around 1.6V DC.

 

 

I am doing the programming via SPI as of now. The aim is to get 50 MHz output signal (0x2a, 0xaa, 0xaa, 0xaa, 0xaa, 0xaa) in quadrature for testing purpose. I have programmed only two registers-Control register and then FTW1 register, in order.

 

 

1. When the register description of my Control register is 0x14, 0x4c, 0x00, 0x40. I am able to get the DDS_IOUT & DDS_IOUT_ signal as measured on spectrum analayzer as 11.5 dBm & 8 dBm respectively. However there is no output from DDS_Qout & DDS_QOUT_ as QDAC PD bit is set.

 

 

2. When the register description of my control register is 0x10, 0x4c, 0x00, 0x40. I cant get any output from DDS_IOUT & DDS_IOUT_ as well as DDS_QOUT & DDS_QOUT_ as expected from them.

 

 

Meaning, whether I turn Q DAC Bit On/Off in COntrol register, IOUT2 & IOUT2_ is always off. Why so?

 

 

I think there is some problem in my control register data, but I'm unable to figure it out. Please help me on this as soon as possible.

 

 

Sudhanshu

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