1
\$\begingroup\$

I am designing an anemometer for university project. I intend to use analog switches to switch between ultrasonic sensors. I use this circuit as my first stage - it adds offset to the signal and has high-pass filter. The input signal is centered around 0V I want to know if this could be a problem for the switch I am going to be using the signal not that large (tens of millivolts).enter image description here

I have also read about charge injection and I learned that it is inversely proportional to the load capacitance I am not really sure if it's going to be a problem or not in this case.

This is the datasheet of the switch I plan to use : http://www.ti.com/lit/ds/symlink/ts3a5018.pdf

\$\endgroup\$

1 Answer 1

1
\$\begingroup\$

I would recommend that you use two separate op-amp gain stages and then put the switch at the outputs of these two stages. This way the switch can be used with the +5 and GND supply connections and the signal is centered in the supply range of the switch. This would typically be the optimum way to operate the analogue switch.

There are also some advantages of simplifying the circuit path that your lowest level signals pass through to keep circuit connections short and give a better chance of eliminating noise pickup in sensitive the amplifier front end.

\$\endgroup\$
6
  • \$\begingroup\$ Michael has got a point. Perhaps, it also begs a question: why is there a need to switch between the transducers? Overall, what will the setup look like? \$\endgroup\$ Nov 27, 2016 at 2:07
  • \$\begingroup\$ There are going to be 4 transducer in the circuit. I transmit one of them and receive from another transducer I have to send and receive from every transducer and I have only two receive paths. You think signal being centered around 0 is going to be a problem for the switches? İn the datasheet it says the signal can be 0.5 v less than gnd. Do you think its going to be a problem? \$\endgroup\$
    – palpurul
    Nov 27, 2016 at 3:20
  • \$\begingroup\$ Sorrya I was wrong in thr datasheet it says the signal can only be 0 volt. Is there anything you can suggest me to simplify the circuit? If I connect the switches to the output of opamps I should have 4 opamps. \$\endgroup\$
    – palpurul
    Nov 27, 2016 at 3:23
  • \$\begingroup\$ @palpurul - I said all what I meant to in the answer; Amplify your signals before the switching circuit and utilize switches with signal in the middle of the switch's voltage range. BTW they do make opamps that come four to a package if that makes a difference for you. \$\endgroup\$ Nov 27, 2016 at 7:18
  • \$\begingroup\$ Thanks for the help. I just have one more question. I've found that switch that has "negative signalling capability" basically it can pass any signal that is below 5.5v from ground. Do you think I can use this switch in the configuration that I want? \$\endgroup\$
    – palpurul
    Nov 27, 2016 at 11:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.