# Does the input of a CD4016 need to be baised?

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.)

• Wait why would VSS be +9V? You would be reverse biasing the chip, potentially damaging it. Commented Aug 7 at 21:01

The datasheet makes if fairly clear that the input can't go more than 0.5 V above VCC or 0.5 V below VSS. 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.

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:

simulate this circuit – Schematic created using CircuitLab

For a lower oscillation frequency:

simulate this circuit

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

• Thank you. I've also read an idea of putting a diode between Vdd and OV and using the junction of the diode with the 4016 as the ground reference. Sounds like either one would work. Commented Aug 8 at 1:16

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.

• The only reason I was considering 4016s is because I found a bag of 5 of them for \$1 at the thrift store. Commented Aug 8 at 1:15
• @Duston Aside from a lot of resistance, especially at low supply voltages, 4016s also lack the built-in control voltage translation that 4051/52/53 have, which can complicate things. Commented Aug 8 at 1:18