Hello to everybody.
I am experiencing a strange behavior on a demo prototype I am testing over 0..+40°Celsius temperature cycles.
The prototype uses 74HC4051 analog mux to scan some sensors. Although I know it is not correct, the CMOS are povered at 5V while the digital inputs are controlled by 3.3V logic MCU outputs.. when I built the board I had only 75HC4051 available and no HCT with same function.
What I am experiencing is that when the tempertature drops below 13-15°C all the analog signals scanned through the 74HC51 become very noisy, while other analog signal arriving to the ADC through a different path are not. Everything returns normal when the temperature is raised again abotve that values.
I am wondering if this can be problem related to the voltage drift of the low-to-high logic threshold of the CMOS mux. My theory is that, lowering the temperature, the V(LH) thresholds jumps around or above the 3.3V high level of control logic thus making the logic switching unstable.
Unfortunately I found very little on the net about the drift of the CMOS logic levels with temperature, and knowing if the problem is compatible with this theroy would help me understanding if the problem can be simply fixed by changing the muxes to 74HCT4051 or if further investigation is needed.
Thanks in advance!
I am experiencing a strange behavior on a demo prototype I am testing over 0..+40°Celsius temperature cycles.
The prototype uses 74HC4051 analog mux to scan some sensors. Although I know it is not correct, the CMOS are povered at 5V while the digital inputs are controlled by 3.3V logic MCU outputs.. when I built the board I had only 75HC4051 available and no HCT with same function.
What I am experiencing is that when the tempertature drops below 13-15°C all the analog signals scanned through the 74HC51 become very noisy, while other analog signal arriving to the ADC through a different path are not. Everything returns normal when the temperature is raised again abotve that values.
I am wondering if this can be problem related to the voltage drift of the low-to-high logic threshold of the CMOS mux. My theory is that, lowering the temperature, the V(LH) thresholds jumps around or above the 3.3V high level of control logic thus making the logic switching unstable.
Unfortunately I found very little on the net about the drift of the CMOS logic levels with temperature, and knowing if the problem is compatible with this theroy would help me understanding if the problem can be simply fixed by changing the muxes to 74HCT4051 or if further investigation is needed.
Thanks in advance!