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Amplitude control of AD9914 under No-Dwell high Ramp generation

Question asked by Sunzeyue on Nov 10, 2016
Latest reply on Nov 18, 2016 by JLKeip

Hi!

  I now use the DDS chip AD9914. The sweep frequency generated by No-Dwell high Ramp generation is 400MHz~960MHz, whose system clock is 2.4GHz, and the frequency step is 2.8MHz. Step intervals is 50ns.The frequency spectrum of the output signal is shown in the appendix, which shows that the flatness of spectrum is not very good. The difference between  beginning point and the end point is nearly 10dB. What are the reasons for this problem?

In addition, how to control the amplitude of the output signal under No-Dwell high Ramp generation? Please help me as soon as possible. Thanks very much!

The following is my register configuration.

CFR1=0x01010308

CFR2=0x008CA800

CFR3=0x00400C27

CFR4=0x01052120

Digital Ramp Lower Limit=0x2AAAAAAA(register address is 0x04,400MHz)

Digital Ramp Upper Limit=0x66666666(register address is 0x05,960MHz)

Rising Digital Ramp stope=0x004C756B(register address is 0x06,2.8MHz)

Falling Digital Ramp stope=0x004C756B(register address is 0x07,2.8MHz)

Digital Ramp Rate Register=0x00050005(register address is 0x08,50ns)

Profile 0=0x0E660000(register address is 0x0C,amplitude factor is 0.9)

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