Looking for a 27MHz VCO

Other Parts Discussed in Thread: SN74S124, CLOCK-TREE-ARCHITECT, LMK61E2, LMX2571, LMX2572, LMK04133

Hi 

While searching for a VCO with output frequency as 27MHz, I found the part number SN74S124. But the datasheet doesn't have any formula to determine the exact external capacitance value for 27 MHz. If possible, could you share the formula for the same. I viewed the graph mentioned in the datasheet but if formula is available it would be better.

Also, this is an old product. If possible, could you suggest any new Voltage Controlled Oscillators (VCOs) with output frequency 27 MHz and Voh and Vol within 2V?

Thanks & Regards

Shuresh Vishag C

  • Hello Shuresh,

    We do have a lot of newer products with VCOs, however they packaged with PLLs and operate at much higher frequencies.  The outputs could be divided

    The outputs could be divided down to 27 MHz however.  The other complexity if you want only a VCO, they generally speaking need to lock closed loop with the PLL.  Could these parts be of any use to you?

    I'll see if I can find out any info about a formula.

    73,
    Timothy

  • Hi Timothy

    Thanks for responding;

    Could you please suggest any PLL parts to get 27 MHz as output frequency consider it as an VCO?

    Thanks & Regards

    Shuresh Vishag C

  • Hello Shuresh,

    You might take a look at our tool, clock-tree-architect, to further explore options.

    If you just need 27 MHz, then an oscillator like our LMK61E2 may work.

    If you need to access the tuning voltage, you'll need to ensure the device doesn't fully integrated loop filter.

    You might consider the LMX2571 or LMX2572.  With the LMX2571 you'd have to power down the charge pump after locking, then you can open loop control the VCO.  With the LMX2572 you could break the loop loop externally.

    Another option would be to use one of our clocking devices like the LMK04133 (I used the clock-tree-architect and sorted by price).  This device give you all sorts of options as it includes two PLLs.  At a minimum you would need to use the second PLL with a reference to lock the VCO.  Then you could modulate frequency closed-loop by applying a signal to the CPout pin, or program the device to power down the charge pump and directly set the frequency with the voltage open loop at the CPout pin.  This part also provide CMOS outputs.

    73,
    Timothy