TM4C1294NCPDT analog inputs noisy

Hello Mike,

A very wide discussion topic (and I sincerely hope some of our experts to pitch in).

1. Having an OP-AMP with a Low Pass Filter should take care of the noise as well as match the impedance of the signal being sensed to the ADC
2. Layout and Placement of the sense inputs is critical, so a description of the requirement would be very critical.

I'm doing software for an existing circuit that I can't change. What is the optimal software configuration for low noise?

Need to know

• bandwidth of the signal
• magnitude of the signal
• definition of low noise
• hardware input filter
• noise characteristics (amplitude, frequency etc...)

Good to know

• how well impedance matched the signal is to the input

Robert

measuring power supply voltages and temperatures
low speed sampling
temperature comes from opamp amplified thermistor
I'm seeing AD values with 20 or more counts of noise, adcs I've used in the past had 1-3 counts

mike peterson1 said:

measuring power supply voltages and temperatures

Temperature will be low bandwidth, voltage not necessarily so. What are the input signal magnitudes? What are the H/W filters?

mike peterson1 said:

low speed sampling

Define "low speed"

Also have you locked yourself into a sample rate yet (hopefully not)?

mike peterson1 said:

temperature comes from opamp amplified thermistor

That's a start but the post op-amp filter is important, especially the freewheel/storage capacitor. As are any number of other H/W considerations.

mike peterson1 said:

I'm seeing AD values with 20 or more counts of noise, adcs I've used in the past had 1-3 counts

We may be able to improve on that but have you read the A/D specifications?

Also what is your reference and how is it connected?

Robert

External reference

How about this question instead..What adc configuration registers affect noise performance?

I'm using the internal 16Mhz clock PIOSC

Robert Adsett said:

mike peterson1

I'm seeing AD values with 20 or more counts of noise, adcs I've used in the past had 1-3 counts

We may be able to improve on that but have you read the A/D specifications?

Also what is your reference and how is it connected?

One other thing I forgot to ask, how many degrees C does that 20 counts represent?

Robert

mike peterson1 said:

External reference

I gathered that, but how is it connected? Is there a buffer? What sort of de-spiking/buffer capacitance?

mike peterson1 said:

How about this question instead..What adc configuration registers affect noise performance?

What is possible depends on your HW setup. I am asking those questions for a reason. Since your HW is not malleable there is a limit to what is possible.

Also have you read the specification for the on-board A/D?

Robert

Hello Mike

Not to forget that the A/D readings also depend on the pre-processing circuit that has been used on the TM4C device v/s the other "UNKNOWN" device.

mike peterson1 said:

I'm seeing AD values with 20 or more counts of noise, adcs I've used in the past had 1-3 counts

1-3 counts from a (similar) 12 bit ADC - highly doubtful!