TRF3765 - PLL with Integrated VCO - how to generate a wideband frequency sweep?

 Hi all,

I'm wondering is it possible to generate a wideband frequency sweep (wideband stepped frequency signal) with in a bandwidth of 2 GHz - 4 GHz with this device?

I want to generate a frequency sweep from 2 GHz - 4GHz for a short range FMCW radar application.

I need about 1 MHz - 2 MHz resolution and 1000 - 2000 frequency points.

As I can understand from the datasheet, the loop filter requires different component values for different frequencies. If that is the case can I use this device to generate the frequency sweep from 2GHz - 4GHz?

Could you please help me to figure out this problem?

Thanks,

Randy

  • It is easy to sweep the LO frequency using a wideband sythesizer such as the TRF3765. In this case, the multiplier ratio (NINT) will change but the pfd frequency will not. The loop filter only needs to change when the fpd frequency changes.

    The loop filter used for integer mode characterization was designed for pfd frequency of 1.6MHz, which corresponds to your stepsize requirements. Therefore, the performance graphs in the datasheet may be used to demonstrate the performance that can be achieved on the user's platform. It is also possible to use fractional mode.

    Stepsize and frequency range are critical parameters that you have identified. To determine further application details, you also need to understand what reference frequency constraints may apply in the system. That is, if the reference frequency has been pre-determined according to a system frequency. If the reference frequency is an integer multiple of 1.6MHz, then you may use the loop filter in datasheet table 17 without modifications. Otherwise, you may need to select a different pfd frequency and use the loop filter design tool--on the product page--to modify filter components. The tool is very easy to use.

    The TRF3765 is qualified for industrial temperature range: -40C to +85C.

    I would like to understand more details about this particular application. Please contact me through direct email at hsprf_apps@list.ti.com so that I may discuss it with you.

    Pete

  • In reply to Pete Hanish:

    Hi Pete,

    Thanks for your reply for my post in the forum and it was very helpful.. I tried to contact you through hsprf_apps@list.ti.com email address, but the mails get bounce back.

    If I go more specific about my requirement, I'm designing a low cost short range FMCW radar sensor for vehicle speed detection inside a car park.

    I've few more questions and they are mentioned below.
    It would be great if you could answer those as I'm new to RF design.

    You have asked about the constraints of reference frequency of the design.
    I can choose any reference frequency for the design. There are no constraints about the reference frequency.

    What I want is to generate a frequency sweep with 2 GHz - 4 GHz bandwidth with frequency steps of 1000 - 2000.

    1.If I hook up a microcontroller with this chip using a serial interface, then by configuring the proper registers, can I obtain the entire frequency sweep?

    The time could be allowed for the whole frequency band is around 1 second.
    As I can understand from the datasheet it is possible to achieve this time with the above requirements.
    2. Could you please tell me that is it possible to achieve this time with the frequency sweep generation?

    I would like to ask one more question about the PCB design for this synthesizer.
    3. If I use FR4, 1.6 mm thick board (0.2 loss tangent), will it be ok for the whole frequency band (2 GHz bandwidth over 2 GHz - 4 GHz ) or should I go for expensive PCBs with lower loss tangent values?

    I would be very grateful to you if you could clarify my doubts in using the device TRF3765.

    Thanks a lot again for your time.

    Cheers,
    Randy

  • In reply to Pete Hanish:

    Hello, I have a similar requirement, I need to sweep from 2.4 to 4.2 with a resolution of 1kHz to 20kHz, I was thinking on using it on fractional mode, but unsure how to implement it specially fpm restriction