Normally, the off-resistance of a multiplexer should be several tens of megohms when measured with a tester in order to prevent unintended conduction with other switches.
However, in the case of my measurement this time, a value of 16 kΩ of off-resistance was detected. The voltage applied to each channel in that case was as follows.
The multiplexer DG408-E3 is powered by a signal power supply. 0V (Low) was input to No. 1 (A0), 5V to No. 2 (EN), 0V to No. 3 (V-), 5V to No. 13, 0V to No. 14 (GND), 0V (Low) to No. 15 (A1), 0V (Low) to No. 16 (A2), 0V (Low) to A0, A1 and A2. and the combination was changed from No.1 to No.8 electrodes.
The positive and negative values of the tester when measuring the off-resistance are as follows.
The minus was measured at No. 8 (D), at the location of the switch where the plus was not conducting.
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If anyone knows how to improve it, I would like to know.Thank you.
Hi pso2playazinomoto,
You have not stated what sort of testing device you are using to measure the impedance. That matters quite a lot, as one cannot use a typical ohmmeter to measure impedance of an analog switch because it’s not a simple resistor - it consists of multiple internal FETs with several tiny leakage currents associated with them.
To more accurately measure off-state impedance, it requires special test equipment and typically involves applying a known voltage on an input pin (S1, S2, … S8) and measuring the tiny current (typically less than 1nA) on the output pin (D). From this, using Ohm’s Law, you can try to estimate off-state impedance.
However, even when doing this, it may not be very accurate, as there are other leakage currents independent of the input-to-output leakage when the device is powered on. Leakage can come directly from V+ to the output D and from SX to V- or GND.
The point is, measuring off-state resistance of an analog switch cannot be done without special test equipment and special measurement procedures.
Thanks for answering my question.
I used two types of testers from this URL.
https://www.monotaro.com/p/6844/2823/?t.q=�f�W�^���J�[�h�e�X�^�[
What is the special testing equipment? I would like to know.
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Hi pso2playazinomoto,
I do not know what equipment might be capable of accurately measuring the “Off Resistance” of an analog multiplexor.
There is a reason that datasheets for analog multiplexers don’t publish the “Off Resistance” specification. The reasons are twofold: First, because it is extremely difficult to test, and second, it is not relevant to most, if not all applications. It is generally not relevant because it is always a very high value, and the dominant specification, when off, is the leakage current rather than the off resistance.
The current that one sees on the output side when the analog switch is off is almost entirely due to leakage from the power supply passing from the V+ pin to the output pin rather from current passing from input to output.
From a user standpoint, the leakage current is the relevant spec because that can cause measurement errors on the output side or give you a non-zero reading even though no signal is passing from input to output. Note also that at higher frequencies, capacitance and charge injection can further affect the signal.
I found this video which helps to describe these leakage currents and why they are relevant.
Below are a few screen shots from that video:
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Thank you for your valuable input. I will review the video once and review the specs and give it a try.
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