Currently i am making the PCB (for analog front end) for the digitization of some sensors(electro-chemical and photo-ionizations).

To simply the things this sensors are giving output in Milli volt(photo-ionizations sensors) and uA current(electro-chemical sensors).

I have BOTH(independent) the circuit ready which are taking input and giving digital output. (one circuit is based on the trans-impedance amplifier while another is based on the operational amplifier) Now the thing is i want to make a single channel PCB which works for both the sensor(one at a time) at same input terminal. All the sensors have the 3 leads. Probably i required the programmable switch (decoder demultiplexer) so that MCU can switch the routing path of that 3 leads when user gives input to the MCU. (when sensor(uA output) is connected then he will press the switch-A and vice versa for the sensor(mv output) with switch-B).

Please let me know suggestion that it will work or not for that lower inputs (i mean very low current and voltage).Any suggestion of the IC will be great help.

Added below details lead terminal of sensor Info :- - 1:- GND - 2:- Current Output/Voltage Output - 3:- Not Used in most of cases.

Range of mills volt :- 1mv to 500mv Current output sensor are just floating photo sensors.

Speed for switching is not concern i can adjust with lower speed also. And isolation is also not required for ground of both sensor.(however isolation will not be in picture as at a time only any one sensor get connected)

Thanks, Bhautik

Added Photo to simplify things more. As from picture "solution should select the Path A or Path B" based on the input signal to it. enter image description here

  • \$\begingroup\$ It sounds like you want to switch the low level signals. Is your voltage range from 0 to Xmv, or +/-X mv? Is the current just a floating photo sensor? You say there are there 3 terminals? What is each of the terminals? Are any of them ground? Are you trying to isolate the grounds between the sensors? \$\endgroup\$
    – crj11
    Commented Mar 20, 2018 at 17:48
  • \$\begingroup\$ What accuracy must you achieve? And what speed? How fast to settle after switching, so the ADC can accurately perform quantization? \$\endgroup\$ Commented Mar 20, 2018 at 17:49
  • \$\begingroup\$ Hi crj11 and analogsystemrf , thanks for your comments i added some details in the summary of question after "Added below details" bold text line.i hope that clicks or please ask if more information needed. \$\endgroup\$
    – Bhautik R.
    Commented Mar 20, 2018 at 18:04

1 Answer 1


The simplest solution is a high isolation reed relay. A "Form C" or SPDT relay would allow you to select between two sources. You could perhaps use a low leakage analog switch like the ADG779, but because analog switches are not passive devices, you could have higher leakage and offset issues. However, analog switches are generally less expensive.

The relays have > 1000 GOhm isolation. Remember that at pA leakage levels, you need to worry about issues like surface contamination on the PCB potentially increasing the leakage.

  • \$\begingroup\$ Hi crj11, Thanks for your answer. But here ,Source will be one only(either with output as current or voltage). i required to select different path for both output as same amplifier circuit will not work for both sensor. to simplify things i added one image in the summary. \$\endgroup\$
    – Bhautik R.
    Commented Mar 21, 2018 at 4:39

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