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Frequency to Voltage Converter

Jan Bock
Intellectual 2575 points
Other Parts Discussed in Thread: VFC320

Hello,

my customer ask if we have frequency to voltage converters. They have a test &measurement application with an input of 4MHz to 11 MHz input frequency and they want to convert it to a pulse signal with 500Hz.

I couldn't find sth. in that high frequency range on our website. Do we have a Ref-Design or some suggestion which parts (OPAMPS, ADC etc.) he can use for those type of application.

Regards

Jan

  • 0
    TI__Guru* 93105 points

    Hi Jan,

    Frequency-to-Voltage (F-to-V) converters do just what their name indicates; convert in ac input into a corresponding dc output. None of our V-to-F converters are usable with an input frequency as high as 4 to 11 MHz. Our fastest, the VFC320, tops out at about 1 MHz and all others have a lower maximum usable frequency.

    I don't know of any specific applications notes that address this requirement. However, it would seem to me that the easiest way to convert a 4 to 10 MHz input signal to a lower frequency (~ 500 Hz) pulse stream would to be to do it digitally. For example, square up the 4 to 11 MHz input signal with a Schmitt trigger or fast comparator circuit, and then follow its squared up output with a series of digital decade dividers. Dividing 4 to 11 MHz by 10,000 (4 decades) would produce an output stream from 400 Hz to 1100 Hz. This doesn't require a complex design, could use common 74Hxx logic circuits and the output frequency would be in step with the input frequency.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    TI__Intellectual 2575 points

    Hi Thomas, 

    thank you very much. Sorry for confusion with the pulse signal. It was just an assumption from the request I got. The customer called me afterwards and clarified the requirement on the 500 Hz. They want to measure a frequency between 4MHZ and 11 MHz. Therefore they want to convert the frequency to a voltage level and then sample this voltage level with 500 Hz sample rate. The requirement is also to do conversion without a uC. 

    Regards 

    Jan

     

  • 0 in reply to Jan Bock
    TI__Guru* 93105 points

    Hi Jan,

    Okay, I now better understand what they are trying to accomplish with the circuit. A digital solution seems like the obvious way to go, but for whatever reason they need to go straight analog.

    Unfortunately, none of our V-to-F or F-to-V products are fast enough to handle a 4 to 11 MHz input frequency range. I looked for alternate analog solutions, but I am not coming up with anything usable. You might want to check with the High-Speed Amplifiers team on their e2e forum. The 4 to 10 MHz frequency range is well within the frequency range of their products which extends much higher than our in Precision Amps.

    Maybe they have encountered this kind of application requirement before, or have some other ideas about a high-speed analog solution.

    Regards, Thomas

    Precision Amplifiers Applications Engineering