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74HC4046 square wave input for NFC transmitter circuit

Discussion in 'General Electronics Discussion' started by suki, Jul 11, 2010.

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  1. suki

    suki

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    Jul 11, 2010
    I am currently working on 74HC4046 vco for designing Near-Field Comm. transmitter circuit. I am not really good in looking at the datasheet as I am a student. I am searching for the information about what is the input square wave for 74HC4046 vco. Anybody that know please help me in finding it because I need to work out the input by using voltage adder circuit before I feed the input to the vco, therefore, i need to confirm with the square wave input of 74HC4046. thanks!
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
  3. suki

    suki

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    Jul 11, 2010
    hello,

    Thanks for the useful page Davenn.

    However, i really couldnt find out the correct input square wave until now for 74HC4046. do u have any idea about it?

    for example, i found that vco of POS25 needs the input square wave of 3.7v - 4.2v to ensure transmission at 13.5 MHz. at first i plan to use pos25 in my circuit, however, POS25 isn't available in PSPICE. therefore, i try using different component which is 74HC4046. but I stuck at the input, i don't know what's the it needs for the square wave.
     
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    NO, the POS25 like all VCO's that im aware of use a plain DC voltage to tune them
    in its case varying the tuning voltage from 1V to 11V will change the output freq from 15MHz
    to 25MHz
    going by the datasheet the POS25 wont go down to 13.5MHz
    (It may a big MAYBE get there but it wouldnt be garanteed)

    the 3.7 - 4.2 Volts you mentioned is going to produce ~ 18MHz output
    At 1 Volt its going to be 15MHz

    time to look for another VCO that will cover the freq you want

    maybe you dont realise that the 4046 already has an inbuilt VCO have another look at the datasheet link I gave you earlier

    cheers
    Dave
     
  5. suki

    suki

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    Jul 11, 2010
    Hello,

    How did you count this at the first time? i need to count it as well for using vco that built in 74HC4046 as the replacement. can u pls teach me how did u count it?
     
  6. davenn

    davenn Moderator

    13,877
    1,964
    Sep 5, 2009
    read my comments in the previous post :)

    the POS25 has a tuning range of 15 - 25MHz to tune across that range it requires a tuning voltage of 1V to 11V

    so a tuning voltage of 3.7 - 4.2V is going to be roughly around 18MHz

    1V = 15MHz
    11V = 25MHz

    Dave
     
  7. suki

    suki

    11
    0
    Jul 11, 2010
    ooo...got it...thanks! but referring to the link that u gave me last time, the tuning range is determined by setting the R1 and R2 values to get the required output value.
    hmm...but still need to work out with the required input because, after i have tune the vco at the range of 13.5MHz, I need to feed the vco with the output from a Non-Inverting Summing Voltage as shown in the diagram below.
     

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