Analog Multiplexer.. does it exist?

hello, i need somthing like an analog data selector, where i can select 1 of many analog lines to monitor.

i was starting to try to make a design using a bunch of op-amps... then i said maybe there is a dedicated chip for that..

i googled and found the HCC4529B.. but don't seem to me like it is for analog applications...

Is it doable with op-amps? is there a way to get High-impedence outputs with an opamp? (this way i could isolate all of them, but the one i need from the output...)


sory there is no schematic yet.. but i need a basic idea.

thx everybody!

Yeah, they do. They're used quite often in ADCs.

**broken link removed**

If I tried to make one discretely, I'd be using a bunch of transistors and logic gates instead of Op-amps. One MOSFET per channel, and a multiplexer (or a bunch of logic gates connected to make a multiplexer) so that I can enable only one channel at a time (via the transistor gate).

dknguyen said:

Yeah, they do. They're used quite often in ADCs.

**broken link removed**

If I tried to make on discretely, I'd be using a bunch of transistors and logic gates instead of Op-amps.

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aha.. i thought about this too.. okay.. i really want to do it discretly, as a personal chalenge! (as long as it can be done, sure!)

So i think the most STUPID but simple solution would be to use relays! because there wont be any voltage drop across them... lol am not serious here! sure i want to do it solid state!

So,

If i use transistors.. in which configuration should i use them? common emmiter right? (with a huge resistence between emitter and GND, i guess)

thx in advance!

You need to use FETs since they act like resistors, rather than BJTs which act like diodes. I'm pretty sure of this- but remember I am totally biased towards FETs rather than BJTs.

How did you plan on selecting the channel? YOu could pull off a parallel interface discretely or with a multiplexer driving all the transistors...if it is serial you need a separate PIC driving the channel transistors and accepting the serial commands so you might as well buy an IC.

When you said you wanted high impedence output with op-amps...why would you want that? You want the output impedence (of anything) to be low. When you want high impedence is for an input so the current that has to be driven into the load is very small to achieve a certain voltage.

There is a complete range of CMOS switch IC's designed for this exact purpose - no need to build anything yourself!.

Take a look at the 74HC4051, HC4052 series. Or the 74HC4851 and HC4852 which are the same as the 4051/4052 but with built-in injection current protection.

And if you need more-complex switching schemes (like two sources on at one time), you can drive 4016s or 4066s with a demultiplexer. As mentioned, there are several analog multiplexers available in CMOS.

Dean

I like the 4016. it's simply what i needed. thanks a lot guys.

However, the 4066 with its identical function has better specifications!

Dean