Hi, everyone, I have developed a PCB board with eight AD9910s. However, I have some problems which will be listed below. Would you please give me some help? Thanks in advance.
- The temperature of the AD9910 can reach up to 60°C when the frequency of the output signal is 98.6MHz. Have you ever encounter similar phenomenon?
- The crucial problem which bothers me a lot is that the amplitude of the output signal varies when AD9910 heated up. The frequency of the output signal is same as 98.6MHz.
As to the second problem, I have searched the DDS>Q&A section and the related links will be given at last. From the links, I learned about two things. The first one is that the temperature drift of the resistor which connected to "DAC_RSET" pin should be as low as possible. The second one is that the power supply for AVDD and DVDD should be stable. Based on those information, I have made some improvements of my design. First, I have used a very low temperature drift resistor( Temperature coefficient is 0.2 ppm/°C ) for "DAC_RSET" pin. Second, I have used six LDOs to respectively power the DVDD_3.3V, AVDD_3.3V, DVDD_1.8, AVDD_1.8V(pin 6), AVDD_1.8V(pin 3), AVDD_1.8V(pin 89, 92). The output pins 80, 81 of AD9910 are connected to ADT1-1WT's pin 4 and pin 6 as the below figure shows. And I measured the power of the signal on pin 3 of the ADT1-1WT with a frequency spectrograph. The measured power varies from -2.54dBm to -3.17dBm from 08:22am to 11:40am. However, we would ideally like an amplitude(power) drift of less than 1%. Now, I have purchased a low temperature drift(1 ppm/°C) voltage reference for DVDD_3.3V. I will post the new results when the new measured data is available.
Lastly, I am wondering whether the amplitude(power) drift of AD9910 can meet the 1% requirement. Please forgive me for the poor English.