If I want to use an analog de/multiplexer as a digital demultiplexer, do I have to use pull-up / pull-down resistors?
For example when driving a CMOS IC like the 4015 with the CMOS analog 4051, do I have to use pull-down resistors?
Electronic – Using an analog demultiplexer as a digital demultiplexer
cmosdigital-logicintegrated-circuit
Related Solutions
Typically you'd use a comparator for this. Or you could make a transistor version with a long-tailed pair.
A Schmitt-trigger would be a nice solution for a 0 to 5V input:
(Source)
But you pointed to an op-amp circuit...
Here's the idea. An opamp as a comparator with logic output.
It's worth reading through ADI's application note on that (source for the picture).
Their Conclusion is accurate in my opinion and worth bearing in mind:
"In conclusion, although op amps are not designed to be used as comparators, there are, nevertheless, many applications where the use of an op amp as a comparator is a proper engineering decision. It is important to make an educated decision to ensure that the op amp chosen performs as expected"
Simplest and probably cheapest solution is to use 1/3 of a 74HCT4053, or use a 74HC4053 with a 4.7K pullup resistor on the 74LS output. Connect VEE to GND for this application.
A0 to V2
A1 to V1
AN is the output
S0 is the control input
/E should be grounded (to enable)
Unused inputs S1, S2 should be tied to GND or Vcc, the others can be left floating.
Related Topic
- Electronic – Analog to Digital convertor using capacitor
- Electrical – Digital counter with analog output
- Electronic – Categorizing ICs as digital or analog
- Electronic – PCB analog and digital split impossible with multiplexers
- Electronic – Analog CMOS layout finger size
- Electronic – Why don’t pull-up/pulldown resistors prevent microcontroller I/O pins from changing state
Best Answer
Only if an input could be left floating. For example, if you select between several outputs to a single input, all analog inputs are tied to something (or you believe they can never be selected) and the mux is always enabled then you don't need a resistor.
Chances are that if you are using it as a digital de-multiplexer this condition won't be true and you need one resistor per mux output.
Also keep in mind that the switch-off will be relatively sluggish compared to push-pull drive, depending on the resistor value.