Hi everybody,

I want to know if anyone knows what is the maximum value that I can put on my linear sweep in terms of frecuency/time. I imagine that there has to be a maximum of how much frecuency you can sweep in terms of the time that the board spends on generate that new frecuency and I need that value to compare.

I use the AD9959 with external control over the P0, P1, P2, P3 pins and then I send the output of the AD9959 on a PLL. The PLL can keep changing the frecuency of a linear sweep at most 100Mhz/10microsec. , I want to know if the AD9959 has one value of this kind on the linear sweep mode.

Sorry for my english.

Thanks.

Javier.

You control a sweep via two parameters: sweep step rate and sweep step size. Well, technically, it is four parameters because you specify the step rate and step size for the positive and negative slopes of a sweep independently. So, for a give sweep slope, you can use large steps with a low step rate or small steps with a high step rate. Of course, the recommendation is to use the smallest possible step size as it yields the most linear sweep.

Note the minimum time between steps is 4/fs, where fs is the system clock frequency. Hence, for a 500MHz system clock, the minimum step time is 8ns. The minimum step size is 1 LSB of the 32-bit rising (or falling) delta word, which equates to fs/(2^32). For fs=500MHz, the minimum step size is approximately 0.116Hz.

Because your PLL has a tracking limit of 10MHz/us, you will need to choose a step size and step rate combination that yields a sweep slope no steeper than 10MHz/us.