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SN74LVC112A: LVC112A frequency divider for RF applications

József Hermann
Expert 1010 points
Part Number: SN74LVC112A

Dear Forum Members,

I would like to use LVC112A FF's as frequency divider for FM radio VCO to measure and display station frequency in the 2..3V supply voltage range.

Two packages of the '112A could provide 1/16 division ratio by a ripple counter fashion (it has an advantage the next stages toggle freqency even lower yielding less overall power consumption).

The VCO signal level typ. 700mV peak-to-peak sinusoid. I would like to design the VCO buffer as simplest as possible which in fact a common collector

amplifier (Av=1). According to the '112A datasheet, the CLK input does not have Schmitt trigger action, therefore - theoritically - it can accept low levels when the input biased to VCC/2 using a simple resistor network between VCC-GND and the signal is AC coupled (internal input inverter hopefully could enough shape and recover the ideally square waveform to the other internal circuitry)

I would like to ask whether somebody has similar experiments with the LVC family when such low level and high frequency signals applied?

Previously I succesfully used the 74LV163A but on fixed 3V3 supply and ca. 1,5-2V peak-to-peak level.

Thanks in advance,

Joseph 

  • 0
    TI__Guru* 96862 points
    I would recommend feeding your sinusoidal signal into either a comparator (preferred) or a Schmitt-trigger to clean up the edges prior to the first flip flop, otherwise the input edges will be too slow and will cause excessive current draw.

    As long as you are operating below the max frequency of the device (120 MHz @ 1.8 V) then you should be fine using this. It sounds like an interesting project.