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frequency sweep with ADF4158

Question asked by electrosoni on Apr 5, 2013
Latest reply on Apr 9, 2013 by electrosoni

Hello,

I am evaluating ADF4158 and I am working with its evaluation board. I need to generate a frequency sweep with vco input signal

having a triangle shape (or as close as possible to that shape). With frequency sweeps below  21 us, the shape I get is a sine wave.

I tried to change ramp clock, ramp steps and charge pump current but I could not get that triangle input shape (see figure with the

vco input in yellow and the desired input in red). If I increase the time per ramp to 27 - 35 us, it starts to get better and with 63 us, vco

input is close to a triangle shape. Is there any way to get the desired vco input shape for frequency sweep close or below 21 us? Is that

feasible for this part? (see figure with configuration used for this test)

 

In the ADF4158 PLL software, there is a field call "Up/Down ramp DEV offset". According to datasheet, it could have values between 0 and 15 (4 bits), but in the program I only can change values between 0 and 9. Is that an error?

 

Thanks in advance for your help,

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