Continue to Site

# Analog Multiplexer

Status
Not open for further replies.

#### Mojtaba67

##### Newbie
Hello everyone,
I am a very beginner.
Currently, I am using an 8-channel relay with a power consumption of (5 volts) × (70 mA) = 350 mW.
It is intended to find an analog mux with power consumption as low as possible.
Could you please introduce me to an analog multiplexer with 8 channels?
The sampling rate of the analog signal is 10 MHz.
Thank you so much for your attention and participation.
Mojtaba

Hi,

in electronnics we mainly work with voltage and amperes.
We don´t know what´s your supply voltage (I can only gess that´s the same 5V as for the relays), what´s your signal voltage range (with respect to supply_GND). Where does the signal come from, where does it go to?

I guess the sampling rate has nothing to do with the MUX. Please clarify.

Also. Please draw a sketch where we can see all the signals and power supplies around the MUX.

Klaus

As you can see quite a few choices, as stated by Klaus you need to provide better
description of what you are trying to do :

Do you need a 10 Msps A/D with a 8 channel front end ?

Regards, Dana.

Hi @danadakk and @KlausST

I have a Wave Generator ( Analog discovery 2) that generates a wave sine.

The peak-to-peak amplitude of this signal is 2 volts. (from minus one to one).

Because of some reasons (for instance the buffer size of the device and the speed of my laptop), I have set the sampling rate of this device to 1.2 MHz. In the other words, this device can generate 1.2 million samples in one second (so 1.2 million samples per second).

the time duration of this signal is 1 second.

My plan is to apply this signal to Circuit 1, please see the figure.

After one hour (as a big interval time to emphasize the switching speed is not important for this project ), I want to apply this signal to Circuit 2. Then 3, 4, 5, 6 7, and 8.

In the past, I was using an 8-channel relay for this purpose. but its power consumption was 5 volts * 70 mA = 350 mW.

Some people told me that if I use an analog Mux, the power consumption is much lower than this 8-channel relay.

I wanted to randomly select a Mux from an online shop, But I found an online page emphasizing that I should select a Mux having the correct bandwidth. please find this page here :

That's why I asked you that I am looking for a mux supporting a 10 MHz sampling rate ( 8 *1.2 MHZ = 10 MHz, is my safety factor to be sure that, the mux will work correctly).

Thank you very much in advance!

The sampling rate is irrelevant in your case. (First you say it’s 10 MHz, then you say it’s 1.2 MHz.) What is the frequency of the sine wave? THAT’S the important parameter. Are you saying you are SWITCHING the max at 1.2 MHz? (I doubt it). Why 8 x 1.2? That isn’t making sense.

Hi,

again: the sampling frequency has nothing to do with the MUX. The signal at the MUX will be the same for a 1kHz sample rate and a 10MHz sample rate. And the sampling frequency never is at he MUX.
--> Tell us the signal frequency instead.
In case the sampling frequency ever hits the MUX, please tell us.

****
The signal voltage is : -1V ... +1V.

With a relay the signal voltage is independent of the coil voltage.
This is diferent to an analog MUX. Here the signal voltage usually is related to GND and the power supply is related to GND. There is no galvanic isolation as with a relay.
Thus usually at a MUX the supply voltage needs to be wider than the signal voltage range.
If the signal goes down to -1V then the supply voltage needs to go lower than this 1V.

****

Sadly your drawing does not contain any information about the power supply as requested.
I guess it´s annyoing for you if I ask the same questions again, thus I avoid it. At least it´s time consuming for both of us.

Klaus

The power supply of the mux would be Raspberry Pi 4.

If you let me know which pins of Raspberry (3.3 or 5 volts) are good as the power supply of the Mux I would be thankful.

The power supply of the mux would be Raspberry Pi 4.

If you let me know which pins of Raspberry (3.3 or 5 volts) are good as the power supply of the Mux I would be thankful.
Wow, you're just not listening. Klaus just told you what you need for power supplies, and that you need a negative supply.

If you want to sample each channel at 1.2 Mhz, then yes the mux rate
will have to be 8 x 1.2 Mhz. Dont forget there are issues like mux settling
time to contend with. As pointed out earlier you have, I presume, Nyquist
considerations to be met, and that the 1.2 Mhz satisfies that signal ?

This might help with basic understanding of switches.

Regards, Dana.

Last edited:

Status
Not open for further replies.