I have a question about the amplitude of DDS chirp waveform.
In my application I am using AD9910 DRG mode to generate chirp waveform with frequency from 100MHz to 390MHz, but the signal amplitude has obvious variation. The amplitude variation and some information @described below:
1. The amplitude increasing with frequency increasing, and the inverse Sinc filter can not change the trend whether it enable or not.
2. Peak to peak value: Vpp≈500mV(f≈100MHz), Vpp≈610mV(f≈390MHz);
3. I have attached a test waveform.
1. Generally the amplitude decreasing with frequency increasing(without using inverse SINC), is my test waveform correct? If not corrent, what reason maybe cause the problem？
2. I expect the variation of amplitude as little as possible with frequency varied(constant is better), is it possible? If possible, what measure can be took?