I know that this is a 4:1 MUX, but what does the little line across the w1 w2 selection line mean?
You know, the little black line that has a "2" next to it.
Has it something to do with "array" or something?
Best Answer
This notation means a bus line with the width noted by the number written next to it. In your case it is 2-bit wide bus. It is used to make the drawing less convoluted by reducing lines drawn.
This looks like a spark gap.
(You could also look up gas discharge tube (GDT), which is similar to spark gap.)
The likely purpose of this component in your circuit is to protect the rest of the circuit from lightning strike and/or ESD. Spark gaps are often the first line of defense against high voltage.
Advantages of spark gaps: Once the arc is established, a spark gap acts as a crowbar, and it can dissipate a lot of energy. Because of that, spark gaps are used for protection against high voltage high energy threats (lightning, defibrillator). The parasitic capacitance of a spark gap is low, so it doesn't affect the signal. A spark gap can be formed as a PCB feature for free; it doesn't require an additional component in a BOM.
Weaknesses of spark gaps: They fire at a high voltage, hundreds of volts, and the firing voltage is not well reproducible or predictable. To address this weakness, there's usually another overvoltage protection device (such as TVS) in parallel with a spark gap. This additional device clamps at a lower voltage.
Not really. You either need enable pins on the MUXes, or you need a 2 to 1 MUX on the output. Seems like the problem statement explicitly mentions enable lines, so that's probably the solution they're looking for. If you are targeting a particular architecture (e.g. FPGA) then one of these may make more sense. For instance, you can't do tristates within an FPGA, so you would need to use a 2 to 1 mux. On an ASIC, you might be able to use a tristate, but you could pay for it in timing performance. With discrete TTL logic, tristate is probably the simplest implementation if the muxes have output enables.
Best Answer
This notation means a bus line with the width noted by the number written next to it. In your case it is 2-bit wide bus. It is used to make the drawing less convoluted by reducing lines drawn.