topic NHS3152 Accuracy and Precision Problem in NFC

NHS3152 Accuracy and Precision Problem

d_schoenfisch — Wed, 23 Sep 2020 06:24:49 GMT

Hello there,

I would like to sample a voltage with the NHS3152 over a time of about 300 ms (about 30 samples).

This works quite well so far. However, I noticed that the precision and accuracy of the measurements is quite below these given in the data sheet (Noise of 11 LSB at 1V).

So I connected the ADC to a power source of exactly 0.5 V and sampled it. The voltage is relatively "clean" when I measure it with another device (NI MyDaq - picture with yellow line), but the values I read out with the NHS3152 are not (picture with the blue line; Noise of > 100 LSB).

(BTW: To avoid problems with the power supply I already used the development board with a battery.)

Hence my consideration or question if I do something wrong with the configuration of the ADC.

Thanks in advance

BR David

Here are the important poarts of my code:

void InitADC (void){
Chip_IOCON_SetPinConfig(NSS_IOCON, IOCON_ANA0_5, IOCON_FUNC_1)
Chip_ADCDAC_Init(NSS_ADCDAC0);
Chip_ADCDAC_SetMuxADC(NSS_ADCDAC0, ADCDAC_IO_ANA0_5);
Chip_ADCDAC_SetInputRangeADC(NSS_ADCDAC0, ADCDAC_INPUTRANGE_NARROW);
Chip_ADCDAC_SetModeADC(NSS_ADCDAC0, ADCDAC_SINGLE_SHOT);
}
void DoMeasurement(){
InitADC();
MeasurementNo++;
Chip_GPIO_SetPinOutHigh(NSS_GPIO, 0, 7); // Power Sensor on
for(int i = 0; i < CURVE_SAMPLES; i++) {
Chip_ADCDAC_StartADC(NSS_ADCDAC0);
while (!(Chip_ADCDAC_ReadStatus(NSS_ADCDAC0) & ADCDAC_STATUS_ADC_DONE)) {
; /* Wait until measurement complete.*/
}
MeasrementValues[i] = (int16_t) Chip_ADCDAC_GetValueADC(NSS_ADCDAC0);
Chip_Clock_System_BusyWait_us((uint32_t) (SAMPLING_INTERVAL));
}
Chip_GPIO_SetPinOutLow(NSS_GPIO, 0, 7); // Power Sensor off
DeinitADC();
}

Re: NHS3152 Accuracy and Precision Problem

mario_castaneda — Mon, 28 Sep 2020 17:54:24 GMT

Hi David,

I hope you are doing great.

All these buses are grounded by default.

During the operation of analog blocks (ADCDAC, I2D, C2D), analog bus(es) must be ungrounded.

This is ensured by usage of Chip_IOCON_SetPinConfig or by the respective analog block driver in its Chip_*_SetMux* function.

Please look at the Chip_IOCON_UngroundAnabus.

Regards,

Mario

Re: NHS3152 Accuracy and Precision Problem

driesmoors — Tue, 29 Sep 2020 08:41:55 GMT

Hi,

When measuring, did you disconnect the SWD cable? The debug communication will inject additional noise.

BR,
Dries.

Re: NHS3152 Accuracy and Precision Problem

d_schoenfisch — Tue, 29 Sep 2020 12:25:47 GMT

Dear Dries,

Thanks for your answer.

I have now removed the programmer as well as the the programmer cable.

Furhter I have added an additional " UngroundAnabus" in the code (although this is already done in the SetPinConfig and SetMux) and a " GroundAnabus" in the DeInit function. As suggested in the other post.

Furthermore I tried another input (AN1).

The measurement at 0.5V now looks like this:

A bit different than before but still not as it should be according to the data sheet.

What I noticed here is that the "noise" is always a little bit higher at the beginning of each measurement and then it becomes a little bit lower (at about 150ms).

BR David