Tool/software:
I am trying to generate an automatic ramp signal between 10.2 and 10.25 GHz over 5 microseconds with the LMX2595EVM. However, when I configure the ramp parameters for this waveform, I am not able to generate the desired ramp signal. However, if I change the ramp time from 5 us to 20 us, I am able to generate the desired signal. What is the maximum ramp slew rate for the LMX2595? It looks like 50 MHz over 5 us (10 MHz/us) exceeds this limit, while 50 MHz over 20 us (2.5 MHz/us) works.
Would it be possible to achieve a 50 MHz over 5 us (10MHz/us) ramp with the LMX2595 if I increase the bandwidth of the loop filter?
Hello,
Our expert for this device is out of office today. I've assigned this thread to them, please expect a response tomorrow.
Regards,
Connor
Hi Jack,
What is your reference clock and fpd frequency? What is your loop bandwidth?
Hello,
The team is out for the holidays. Please expect a response by Jan 2 at the earliest.
Thanks,
Kadeem
Hi Jack,
Looks to me that this could be a loop bandwidth/response issue.
I am not able to make successful ramp up and down when the ramp duration are both 5µs.
However, if I set ramp up time = 10µs while keeping the ramp down time to 5µs, I can make it ramp robustly.
From the plot, we can see that even though ramp up time is 10µs, the trace is not a straight line. Compared with the ramp down trace, it is more or less a straight line and the duration is only 5µs. This behavior tells us that the synthesizer's response time is not fast enough to ramp up in 5µs.
I believe, if we increase the loop bandwidth, we may be able to reduce ramp up response time. You may also need to use C0G/NP0 or film capacitor in the loop filter in order to get a faster charging/discharging time.
Jack,
We also have this article app note discussing the slew rate limitations with loop bandwidth