I am working on making a frequency synthesizer getting ~900 MHz out of a VCO, using ADF4106 PLL.

Now, for programming the PLL, I am intending to use AVR ATmega8A microcontroller.

Everything is good, but the problem that I have stumbled upon is, the datasheet of Atmega8A says, minimum logic input high voltage is 0.6Vcc.

I intend to use 3.3 V Vcc. So, if I am right, the microcontroller needs minimum 1.98 V for appropriate detection of a high input, which seems pretty high for logic input.

Now the ADF4106 datasheet says, minimum output high voltage is 1.4 V. Which is ~0.6 V lower than the minimum needed.

I want to get a lock detect from the MUXOUT and read serial data. Now if the ADF4106 gets a lock detect or as part of serial data it gets the MUXOUT pin high, that is, raised to 1.4 V, what if my microcontroller cannot detect it as it is less than 1.98 V?

Is it that the minimum output high voltage that the ADF4106 mentions just the worst case, while generally it would actually be above 2 V? Or the ATmega8A should detect high input well at 1.4 V, it is just some worst case likewise? Or is it something I should actually worry about?

If it should actually be a concern, what should be the easiest way to overcome the problem? Or am I missing something or mistaking anywhere?

Datasheets of ADF4016 and ATmega8A:



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1 Answer 1


Use the CMOS output rather than open-drain with a pull-up to 1.8V, and a 3.3V DVdd power supply and you will have compatible logic levels.

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  • \$\begingroup\$ Man, this datasheet link I gave here is revision F, while what I was studying on my phone is revision 0. What should I suppose, was this a mistake in the datasheet, or has the device design been renewed? I imported the ADF4106 chips a few months ago from China. How do I know which datasheet my device follows? What should I expect? \$\endgroup\$
    – shafik
    Mar 18, 2022 at 23:55
  • \$\begingroup\$ And it seems unlikely anyway, that the CMOS minimum output high voltage would be so low, 1.4 V is really low for logic devices. \$\endgroup\$
    – shafik
    Mar 18, 2022 at 23:57
  • \$\begingroup\$ You can see the revision 0 output voltage, I have added an image in the main post. \$\endgroup\$
    – shafik
    Mar 19, 2022 at 0:18
  • 1
    \$\begingroup\$ Yeah, that's an error in your datasheet. The chip should be fine. \$\endgroup\$ Mar 19, 2022 at 1:50

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