AD9914/AD9915 Super Nyquist Zones

I am successfully using an AD9915 with a 2.5 Ghz clock to generate a 2.856 GHz signal. The first thing to do is to put a high pass filter directly on the output. Otherwise the low frequency component will overload the amplifiers that follow. I then use a low noise amplifier to make sure I get a good signal to noise ratio. Then I amplify the signal to 20 mW or so. I place a bandpass filter in front of the last amplifier stage. For a bandpass filter I use L-Com WiFi filters. They are tuned to 2.4 GHz or so, but I have had no problem tuning them to 2.856 GHz or even 3.0 GHz. I use the 4-pole filters because I don't want a lot of phaseshift with frequency for my application. They have an 8 pole version as well. This approach is much cheaper than custom filters. I adjust only the tuning screws and not the coupling adjustments. It's easy to disassemble one to see what is what, assuming you have an idea of how BandPass filters work. I always buy the ones for the two highest bands, but I think they are all the same, just tuned differently.

My problem is synchronizing two 9915s. I have succeeded in keeping the phase offset constant during operation, including profile register changes, amplitude, phase, and frequency changes, but I can't zero the phase accumulator registers reliably.

Jim

I am successfully using an AD9915 with a 2.5 Ghz clock to generate a 2.856 GHz signal. The first thing to do is to put a high pass filter directly on the output. Otherwise the low frequency component will overload the amplifiers that follow. I then use a low noise amplifier to make sure I get a good signal to noise ratio. Then I amplify the signal to 20 mW or so. I place a bandpass filter in front of the last amplifier stage. For a bandpass filter I use L-Com WiFi filters. They are tuned to 2.4 GHz or so, but I have had no problem tuning them to 2.856 GHz or even 3.0 GHz. I use the 4-pole filters because I don't want a lot of phaseshift with frequency for my application. They have an 8 pole version as well. This approach is much cheaper than custom filters. I adjust only the tuning screws and not the coupling adjustments. It's easy to disassemble one to see what is what, assuming you have an idea of how BandPass filters work. I always buy the ones for the two highest bands, but I think they are all the same, just tuned differently.

My problem is synchronizing two 9915s. I have succeeded in keeping the phase offset constant during operation, including profile register changes, amplitude, phase, and frequency changes, but I can't zero the phase accumulator registers reliably.

Jim