topic Re: ADC output distortion in LPC54608J512BD208 in LPC Microcontrollers

ADC output distortion in LPC54608J512BD208

prasannanaik — Mon, 25 Nov 2019 13:12:08 GMT

Hi,

I have used LPC54608J512BD208 microcontroller in protection relay. The external input voltage is stepped down,superimposed on a 1.65V DC signal and fed to the ADC input of microcontroller. I am using 6 ADC channels namely ADC0_0, ADC0_4, ADC0_5, ADC0_6, ADC0_7 & ADC0_8. The controller is driven by an external crystal of 16 MHz stepped up through PLL to 100 MHz. The following are the connections to adc pins:

I am getting no fluctuations when passing only DC signal at the ADC.

ADC gives distorted output when AC signal is superimposed on DC signal and applied to ADC.

I have observed the waveforms at ADC input pin without any distortion on a DSO.

I have attached my project, ADC samples and controller schematic for reference. Please help in resolving this issue.

Thanks & best regards,

Prasanna

Re: ADC output distortion in LPC54608J512BD208

jeremyzhou — Tue, 26 Nov 2019 06:59:00 GMT

Hi Prasanna Naik,

Thank you for your interest in NXP Semiconductor products and for the opportunity to serve you.
In your ADC_Test_Reslut.xls, it presents the signal which is superimposed on a 1.65V DC signal, these two lines are not only different but also both of them are a bit distorted.
So I'd like to suggest that you increase the sampling frequency and sample point to rebuild the signal. In further, I had done similar testing before, it may give you an insight into this phenomenon.

Have a great day,
TIC

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Re: ADC output distortion in LPC54608J512BD208

prasannanaik — Tue, 17 Dec 2019 03:22:09 GMT

Hi jeremy,

i have resolved the ADC distortion issue but i am facing a different issue now. i am applying constant 1.65 V DC at input of ADC but i am getting varying output depending on my clock configuration. I have attached the test results for your reference.

When i keep my core at 100 MHz then ADC gives very low output(1980 instead of 2048) whereas when i keep the core clock below or equal to 80 MHz ADC gives better results. Please check the attached results. I couldn't find any explaination for this. please help.

Thank and best regards,

Prasanna

Re: ADC output distortion in LPC54608J512BD208

jeremyzhou — Tue, 17 Dec 2019 07:12:49 GMT

Hi Prasanna Naik,

Thanks for your reply.
Whether you can tell me which clock mode you selected.

Have a great day,
TIC

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Re: ADC output distortion in LPC54608J512BD208

prasannanaik — Tue, 17 Dec 2019 07:54:57 GMT

Hi Jeremy,

I have tried both async and sync adc clocks with 100 MHz core clock but still no effect.

I have attached the test results of the various experiments that i tried with clock in "adc_clock_test_results.xlsx"

Thanks and best regards,

Prasanna

Re: ADC output distortion in LPC54608J512BD208

jeremyzhou — Thu, 19 Dec 2019 09:11:48 GMT

Hi Prasanna Naik,

Thanks for your reply.
It seems a bit weird actually, so I was wondering if you can share your demo project, then I can replicate the phenomenon on the OM13092 board and it can help me to figure it out.
Looking forward to your reply.

Have a great day,
TIC

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Re: ADC output distortion in LPC54608J512BD208

prasannanaik — Fri, 20 Dec 2019 06:17:38 GMT

Hi jeremy,

I have already attached the project in this query.

Please refer the following link.

ADC output distortion in LPC54608J512BD208

gauravmore‌

Thanks & best regards,

Prasanna

Re: ADC output distortion in LPC54608J512BD208

prasannanaik — Mon, 23 Dec 2019 06:11:45 GMT

Hi jeremyzhou‌,

Any update on this query?

We are stuck because of this in our development.

Please help.

gauravmore‌

Thanks and best regards,

Prasanna

Re: ADC output distortion in LPC54608J512BD208

jeremyzhou — Mon, 23 Dec 2019 08:39:05 GMT

Hi Prasanna Naik,

Thanks for your reply.
I've used the ADC channel4 pin to convert a 2.07V DC signal and the testing result is presented below.

Board: OM13092, demo project: lpcxpresso54608_lpc_adc_basic (From the SDK library)

1) async clock 80 MHz:
Clock tree:

ADC conversion result:

2) async_clock_100MHz:
Clock tree:

ADC conversion result:

3) sync_clock_80MHz
Clock tree:

ADC conversion result:

4) sync_clock_100MHz
Clock tree:

ADC conversion result

5) sync_clock_50MHz

Clock tree:

ADC conversion result

Conclusion: These results are almost the same actually.

Have a great day,
TIC

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Re: ADC output distortion in LPC54608J512BD208

prasannanaik — Tue, 24 Dec 2019 03:19:44 GMT

Hi Jeremy,

I have tested this on two boards and results are still the same as i explained in earlier query.

What could be going wrong any idea?

Thanks and best regards,

Prasanna

Re: ADC output distortion in LPC54608J512BD208

jeremyzhou — Tue, 24 Dec 2019 05:58:41 GMT

Hi Prasanna Naik,

Thanks for your reply.
It seems a bit weird, and I have no idea about the phenomenon now.
In my opinion, maybe you can do these tests on the OM13092 as I did, as I hadn't encountered the phenomenon you explained.

Have a great day,
TIC

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Re: ADC output distortion in LPC54608J512BD208

prasannanaik — Thu, 26 Dec 2019 14:28:46 GMT

Hi jeremy,

My development board is not working from past two weeks. It is getting hot when i plug it so i am not able to use that as reference.

I have attached my schematic. Please review it and let me know if anything is wrong.

Thanks & best regards,

Prasanna

Re: ADC output distortion in LPC54608J512BD208

jeremyzhou — Fri, 27 Dec 2019 02:19:21 GMT

Hi Prasanna Naik,
Thanks for your reply.
After having a review of the schematic, I've not found something wrong with it, and I hope I can dig deeper later.

Have a great day,
TIC

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Re: ADC output distortion in LPC54608J512BD208

prasannanaik — Tue, 07 Jan 2020 06:17:49 GMT

Hi Jeremy,

Any update on the issue?

Thanks & best regards,

Prasanna

Re: ADC output distortion in LPC54608J512BD208

jeremyzhou — Wed, 08 Jan 2020 06:45:54 GMT

HiPrasanna Naik,

Until now, I've not encountered a similar phenomenon as you mentioned when running the code on OM13092 for testing.

Have a great day,
TIC

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Re: ADC output distortion in LPC54608J512BD208

prasannanaik — Mon, 20 Jan 2020 17:20:09 GMT

Hi Jeremy,

On bypassing adc calibration, the adc seems to be working fine. Usually we provide adc calibration at power up so that offset will be calibrated but this observation seems strange.

Thanks and best regards,

Prasanna

Re: ADC output distortion in LPC54608J512BD208

prasannanaik — Mon, 27 Jan 2020 04:00:41 GMT

Hi Jeremy,

Any update on the query?

Thanks & best regards,

Prasanna

Re: ADC output distortion in LPC54608J512BD208

prasannanaik — Wed, 08 Jul 2020 09:20:17 GMT

Dear jeremyzhou‌,

I have performed some experiments on the OM13092 development board to check the problem observed on LPC546 microcontroller. We have found fluctuations in the development board as well.

Details of connection/board configuration:

1) Channels used ADC0_4 (J12/2),ADC0_5 (J12/4) & ADC0_6 (J12/6)

2) Evaluation board: OM13092

3) Power: Debug port J8 of OM13092

4) Core clock: 100 MHz (External 12MHz crystal frequency stepped up through PLL)

5) ADC clock: 1 MHz (Synchronous)

6) ADC sample time number = 7

I have attached picture of the set up used in Experiment 1.

Experiment 1: GND from P3 of OM13092 connected to ADC0_4, ADC0_5 & ADC0_6

ADC channel	ADC output
ADC channel	Min	Max
ADC0_4	0	10
ADC0_5	0	6
ADC0_6	0	5

Fluctuations of 10 count with GND input

Experiment 2: 1.65V DC generated through a Voltage divider circuit of 10K each fed to channel ADC0_4

3.3V(J10/12) of OM13092 and GND (J10/18) is used to dirve the voltage divider network.

ADC Channel	ADC Output
ADC Channel	Min	Max
ADC0_5	2041	2053

Fluctuation of 12 count with a fixed DC input.

I have also attached the code for your reference.

Please help in resolving the issue.

Two issues have been identified so far in LPC546 controller :

1) PE Micro debugger causes fluctuations in ADC output in custom board:

I have used uart to verify the issue of PE Micro debugger.

Card 1:

Input Voltage(V)	ADC Channel	With PE Micro		Without PE MIcro
Input Voltage(V)	ADC Channel	Min	Max	Min	Max
1.65 V (DC)	ADC0_0	2014	2075	2047	2051
	ADC0_4	2020	2064	2045	2054
	ADC0_5	2032	2058	2046	2051
	ADC0_6	2016	2060	2048	2056
	ADC0_7	2021	2056	2046	2052
	ADC0_8	2018	2051	2041	2048

Card 2:

Input Voltage(V)	ADC Channel	With PE Micro		Without PE MIcro
Input Voltage(V)	ADC Channel	Min	Max	Min	Max
1.65 V (DC)	ADC0_0	2010	2066	2046	2052
	ADC0_4	2035	2061	2047	2054
	ADC0_5	2031	2062	2045	2051
	ADC0_6	2025	2059	2050	2056
	ADC0_7	2019	2056	2046	2052
	ADC0_8	2037	2049	2041	2048

2) Fluctuations in ADC output even on LPC546 board as explained earlier.

Kindly help in addressing these issues.

Thanks & best regards,

Prasanna

Re: ADC output distortion in LPC54608J512BD208

prasannanaik — Mon, 03 Aug 2020 06:03:32 GMT

Hi @Jeremy,

Any update on the above query?

Thanks & best regards,

Prasanna