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LMX2582: LMX2582 Configuration for 2.4GHz-2.5GHz 100kHz-Step Continuous Frequency Sweep

user6150974
Prodigy 130 points

Part Number: LMX2582
Other Parts Discussed in Thread: LMX2491

Dear TI Technical Support Team,

I am currently developing a signal source based on the LMX2582 wideband frequency synthesizer, targeting an output frequency range of 2.4 GHz to 2.5 GHz. The design requires a continuous frequency sweep with a fixed 100 kHz step size. A critical requirement is that the RF output must remain uninterrupted throughout the entire frequency sweeping and switching process, with the instantaneous output frequency deviation strictly limited to a small margin relative to the current or next target frequency.

According to the LMX2582 datasheet, the VCO3 core has a native tuning range of 4481 MHz to 5092 MHz. Its subsequent divide-by-2 output path can fully cover the entire 2.4 GHz to 2.5 GHz target band.

I would greatly appreciate it if you could confirm whether the LMX2582 can fully satisfy these performance requirements. If feasible, could you also provide a step-by-step, register-level configuration procedure to implement this function properly?

Thank you for your assistance.

  • 0
    TI__Guru** 121240 points

    Hi There,

    All wideband synthesizers such as LMX2582 consist of multiple VCOs. As such, a VCO calibration is required in order to pick the right VCO and VCO sub-band. Usually, each VCO can support calibration-free range of approx. 10% of the VCO coverage. 

    Your requirement is 100MHz at output --> 200MHz at VCO. We don't have any synthesizers can support this calibration-free range.

    You may consider discrete PLL + VCO solution. LMX2491 can meet your requirement, it has a ramp function so you don't need to program the PLL continuously in order to sweep the frequency.

  • 0 in reply to Noel Fung
    Prodigy 130 points

    thanks for reply.

    What happens if the VCO output frequency exceeds the calibration‑free range? Will it automatically perform a calibration? During this process, can the output signal remain or be mute? Over what frequency range does it vary? I do not need the loop to remain locked at all times during the frequency sweep (or to lock from one frequency to another very quickly); I only need the output to be maintained, and before locking to the next frequency, the output frequency should not drift too far away. Is this achievable?

  • 0 in reply to user6150974
    TI__Guru** 121240 points

    Hi There,

    Can you accept a staircase ramp, such as 

    What is your target sweep time?

  • 0 in reply to Noel Fung
    Prodigy 130 points

    That is acceptable. In the figure you provided, the highest output frequency does not exceed 4.860 GHz, and the lowest frequency on the vertical axis only goes down to 4.730 GHz. During the sweep, does the frequency ever go below this value?

    Additionally, if I need to use auto-calibration or even fast calibration to improve the locking speed, while also needing to specify VCO3, how should I configure the device? What is the proper configuration flow?