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LMX2595EVM: FMCW became half FM pulse wave

Part Number: LMX2595EVM
Other Parts Discussed in Thread: LMX2492

As I send the parameter to the register, I take it that the 2595 would create a FMCW ,range from 12GHZ to 12.2GHZ,cycle 300us. When I use an oscilloscope to measure the wave, the blue line in Figure 2 shows that within the half cycle of frequency rise, within 50us, the period changes from 46.3*2ps to 41.3*2ps, which is equivalent to 10.8GHZ rising to 12.1GHZ, but the waveform drops sharply from 12.1GHZ to 10.8GHZ in the half cycle of frequency fall. As I expected the wave should be a Triangular wave, it actually became a sawtooth wave. Can anyone tell me the reasons and how to change the settings? Thanks !!!!

  • 您好,

    已经收到了您的案例,调查需要些时间,感谢您的耐心等待。

  • Hi there,

    couples of issue in their configuration.

    1. CAL_CLK_DIV setting is not correct.

    2. MASH_ORDER is not correct. Integer mode ignores the fraction.

    3. Linear ramp is limited to around 100MHz ramp range at VCO frequency. If you are looking for linear ramp, the possible ramp range is around 100MHz at VCO frequency. In this case, you can get linear ramp if the stop frequency is 12100MHz. 

    You have setup calibration at every 25MHz frequency change, there will be 7 VCO calibrations in both ramp up and ramp down period.

    If your application requires linear ramp range greater than 100MHz, you need to use LMX2492 + discrete VCO.