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Compiler: lmx2571 Frequency switching rate

zhongheng lv
Prodigy 20 points

Other Parts Discussed in Thread: LMX2571

Tool/software: TI C/C++ Compiler

Hi：

       I use TrCtl to control F1F2 two frequency outputs。 But the two frequency signal switching  rate up to 40KHZ can not continue to improve. And the signal frequency of the two frequencies is not correct。I know that the output baud rate is related to the loop bandwidth, but what is the relationship? How can I change the switching rate of the output signal? Thank you!

  • 0
    TI__Guru** 121130 points
    Hi There,

    I would say 40kHz is already too fast. As you can see in the datasheet Section 8.2.1, the switching time between F1 and F2 is >40µs. that means, the max. switching rate should be around 20kHz.
    What is the purpose of have high speed switching between two frequencies?
    If 2FSK is desired, LMX2571 can support FSK operation, no need to toggle F1 and F2.
  • 0 in reply to Noel Fung
    Prodigy 20 points

    Hello there
        I'm very happy to have received your response.  With 2FSK modulation, high-speed switching frequencies allow faster transmission of signals. You said the use of 2FSK modulation do not need to switch F1F2, how to achieve? Manual said there are four ways, which can quickly and quickly achieve the 2FSK signal transmission rate I need (1MHZ or so)。I have tried spi fast mode and pin mode, but unfortunately there is no success, can you give some suggestions?

    Thank you

  • 0 in reply to zhongheng lv
    TI__Guru** 121130 points
    Hi There,
    FSK rate of 1MHz is not an issue. Care should be paid on the frequency deviation, i.e. the frequency difference between f1 and f2.
    Use Equation 4 or 5 in the datasheet, calculate the FSK step. The max. positive step is (2^16)/2 - 1. If your calculated FSK step is within the limit, then you should be able to use one of the FSK operation modes to do 2FSK.