Does the input of a CD4016 need to be baised?

Question

I have a 4016 analog switch with an AC input (in this case, millivolt level.) If I put +9v on Vss and 0v on Vdd, do I have to put a DC bias on the input of the 4016 to make sure the signal doesn't go below zero? None of the data sheets, write-ups or circuits I've found mention the topic. (I realize the high resistance of the 4016 may make it unsuitable for this application.)

Answer 1

The datasheet makes if fairly clear that the input can't go more than 0.5 V above V_CC or 0.5 V below V_SS. Bear in mind that those are Absolute Maximum Ratings and not where you want to be operating.

For millivolt signals you can probably work without a bias but the input protection diodes may distort your signal.

Answer 2

None of the data sheets, write-ups or circuits I've found mention the topic.

All CMOS inputs are protected by diodes to supply rails. Going even a little bit below negative rail will bias the protection diode into weak conduction. This is not desirable. And things are worse if there are any heavy currents on GND that may locally shift GND above the average of the analog signal.

do I have to put a DC bias on the input of the 4016

Just supply that 4016 with a negative supply. The supply current is so minuscule that there are many cheap ways of getting that supply. For example:

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For a lower oscillation frequency:

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Either approach takes one chip: any of CD4069, CD40106, CD4049, or CD4572, and a few discrete parts.

Answer 3

There will be no problem for relatively low voltages like -100mV with 0V/9V supplies, assuming your source resistance is reasonable. In fact the switch series resistance is near minimum at that voltage.

As you get more negative there will be increasing amounts of “leakage” current to the negative supply, in particular at high temperatures.

If you want a conservative estimate of the current, simulate it with a 1N4148 diode to Vss at the maximum operating temperature.

You can use the 4066 for lower resistance at a similar cost.