CD4066B: Signals seems to interfere between them

Efrain Avina

Part Number: CD4066B
Other Parts Discussed in Thread: CD74HC4316, TMUX6211

Tool/software:

Hello, I'm trying to use 2 CD4066BM chips in order to select one of 5 signals (DUT_FILT_CH1, DUT_FILT_CH2, ..., DUT_FILT_CH5) to be connected to "Read_ADC_CH_Filtered" so only 1 ADC Channel is needed.

DUT_FILT_CH1 is a sine wave with an offset near zero volts.

So, problem comes when the signal from (let's say) DUT_FILT_CH1 is connected to Read_ADC_CH_Filtered by putting CONTROL B to HIGH.
The signal at "Read_ADC_CH_Filtered" instantly receives an offset and becomes a sine wave mounted on top of ≈2.2V.

Thought it had something to do with pull-down, so I placed pull-downs on pins 4,8,11,3,9 and 10 but the problem still continued.

Any ideas on what may be causing this ?

Thanks!

9 months ago

0 Nir Gilgur 9 months ago

TI__Genius 11855 points

Hello Efrain,

Can you please provide scope shots of the DUT_FILT_CH1 and Read_ADC_CH_Filtered signals?

Thanks,

Nir

0 Efrain Avina 9 months ago in reply to Nir Gilgur

Prodigy 50 points

Hello, Nilgur.

This is the scope shot of pin #4 DUT_FILT_CH1:

and this is the scope of pin #3: Read_ADC_CH_Filtered:

Scope shots of all the pins:

Pin #1: SIG_OUT

Pin #2: IN5

Pin #5: CTRL_FILT_CH1

Pin #6: CTRL_FILT_CH2

Pin #7: -3V3

Pin #8: DUT_FILT_CH2

Pin #9: Read_ADC_CH_Filtered

Pin #10: Read_ADC_CH_Filtered

Pin #11: DUT_FILT_CH3

Pin #12: CTRL_FILT_CH3

Pin #13: CTRL_INCH5

Pin #14: 3V3

Thanks,
Efrain.

+1 Clemens Ladisch 9 months ago in reply to Efrain Avina

Guru 295560 points

The control inputs are references to VSS, so the control input voltage must be near −3.3 V to disable a channel. (The recommended operating conditions table says "0 V", but it is lying.)

0 Efrain Avina 9 months ago in reply to Clemens Ladisch

Prodigy 50 points

Thank you so much, Clemens. This solved my issue.

I had been struggling with this error for a long time.
Indeed, connecting a control input to -3.3V (Vss) disables the corresponding channel.

Now, the Read_ADC_CH_Filtered is the same as the one in DUT_FILT_CH1.

0 Efrain Avina 9 months ago in reply to Clemens Ladisch

Prodigy 50 points

Hello, Clemens!

Now, I've connected Vss to GND so I understood putting the control input voltage near GND disables a channel.
Unluckily, the offset has returned to the Read_ADC_CH_Filtered and I don't understand why.

What am I doing wrong?

0 Clemens Ladisch 9 months ago in reply to Efrain Avina

Guru 295560 points

I/O voltages must not be lower than VSS. Are they?

The CD74HC4316 or TMUX6211 have a separate GND pin for the control signals.

0 Efrain Avina 9 months ago in reply to Clemens Ladisch

Prodigy 50 points

No, they aren't. In order to test GND as Vss and logic low levels using GND, the DUT_FILT_CH1 signal is chopped using a voltage follower with an Opamp which V- supply is connected to GND.

Thanks for the IC recommendations.
As 5CHs are being read, is there any IC with 8SPST channels? Couldn't find any on TI's analog switching section but maybe I'm looking at the wrong section

0 Nir Gilgur 9 months ago in reply to Efrain Avina

TI__Genius 11855 points

Hello Efrain,

Please see link for our portfolio page filtered for 1:1 (SPST) 8-channel muxes.

Thanks,

Nir

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CD4066B: Signals seems to interfere between them