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Logic interface best practices

Other Parts Discussed in Thread: SN74CB3T3253

I have a frequency counter project that uses a 4 bit counter made up of a 74LVC109 followed by a 74LVC74 running at around 200 MHz followed by a micro-controller for the core counter.  

There are 3 front ends for this core counter that I want to select between: 1) A prescaler IC 2) an RF FET 3) a logic input that uses a 74LVC04

I'm looking at the SN74CB3T3253 to select between these 3 input devices; even though I only need 1 direction, I like the low propagation delay better than say a 74LVC139A - I will set the PCB up to have traces as short as possible but I'm looking for guidance on chip-chip interconnect best practices at around 200-300 MHz.  Should I include a series resistor to suppress ringing?  Do I need to attenuate the signals to avoid ground bounce? Maybe there is a document on logic interface best practices that I haven't found yet that would answer these questions?

Any help is appreciated. Thanks.

  • Hi Ted ,

    you can consider CB3Q3253 switches for higher bandwidth of operation and have 5V rail to rail switching at 3.3V Vcc due to the presence of charge pumps. The CB3T switches are lower operating frequency and BW.

    series resistors are good to suppress ringing and having proper bypass caps at the Vcc close to the device which will filter out the noise on the power rails which could couple to the output . some of the devices also have output damping resistors to avoid the ringing on the lines .

    Avoid floating inputs ,which might cause unexpected operation behavior. You can refer to deigning with logic which can be helpful .

  • Thanks Shreyas, I'll switch (no pun intended) to the CB3Q device.