ADC32RF45: Load/Store Offset Corrector Coefficients

Ozer Ozaydin18

Prodigy 50 points

Part Number: ADC32RF45

Hi,

In order to suppress spurs at certain frequencies, we use the offset corrector like the following way:

1) Make sure no signal on inputs.

2) Enable offset corrector and wait for sometime to collect enough data for estimation

3) Freeze corrector

4) Now ADC can receive signal without spurs.

Instead of doing this procedure every time, we would like to make the calibration at factory and store the coefficients. In that case, we will be able to calibrate the ADC by only loading related coefficients without any extra calibration step (with no signal on input). Otherwise, while using the ADC in the field, at least for every startup, we need to apply a calibration procedure with no signal.

Is it possible to load/store offset coefficients?

Thanks,

Ozer

over 6 years ago

0 Jim Brinkhurst1 over 6 years ago

TI__Mastermind 44680 points

Hi Ozer
Sorry for the delay. One of our ADC experts is reviewing this question. You should get a response today or Monday.
Best regards,
Jim B

0 Vijayendra Varma Siddamsetty over 6 years ago in reply to Jim Brinkhurst1

TI__Genius 10865 points

Hi Ozer,

It should be possible to do factory calibration as you described. I'm checking with the design team for the procedure to read and write the offset corrector coefficients. I will verify it on an ADC32RF45EVM and update you.

Regards,
Vijay

0 Ozer Ozaydin18 over 6 years ago in reply to Vijayendra Varma Siddamsetty

Prodigy 50 points

Hi Vijay,

Thanks for the update. It's been a while and no answer, so we played around with the registers and reverse engineered some of the registers in page 0x61. We guess that registers at 0x08, 0x09, 0x10, 0x11, 0x0c and 0x0d may be related to DC offset settings. Of course without your procedure definition it's not easy to finalize, waiting for your update..

Thanks,

Özer

0 Vijayendra Varma Siddamsetty over 6 years ago in reply to Ozer Ozaydin18

TI__Genius 10865 points

Hi Ozer,

Please find the procedure below:

At factory:

1) Power up and run complete device configuration exactly as it will be used in the field.

2) Wait for a few seconds for temperature to settle. (It is important for the temperature to be same as it will in the field for better correction performance)

3) Turn off input signal to the device.

4) Wait for at least 0.4 ms for the corrector to estimate internal offset.

5) Freeze offset estimation using the writes shown in the table below:

SPI write/ Read	Address	Value	Comment
Write	0x4004	0x61	Page select
Write	0x4003	0x00	Page select
Write	0x4002	0x00	Page select
Write	0x4001	0x00	Page select
Write	0x6068	0xA2	Freeze corrector for channel A
Write	0x4003	0x01	Page select
Write	0x6068	0xA2	Freeze corrector for channel B

6) Read coefficients as shown in the table below:

SPI write/ Read	Address	Value	Comment
Write	0x4004	0x61	Page select for channel A
Write	0x4003	0x00	Page select for channel A
Write	0x4002	0x06	Page select for channel A
Write	0x4001	0x00	Page select for channel A
Read	0x6050	Save as c1	Coefficient read register 1
Read	0x6051	Save as c2	Coefficient read register 2
Read	0x6052	Save as c3	Coefficient read register 3
Read	0x6053	Save as c4	Coefficient read register 4
Read	0x6054	Save as c5	Coefficient read register 5
Read	0x6055	Save as c6	Coefficient read register 6
Read	0x6056	Save as c7	Coefficient read register 7
Read	0x6057	Save as c8	Coefficient read register 8
Read	0x6058	Save as c9	Coefficient read register 9
Read	0x6059	Save as c10	Coefficient read register 10
Read	0x605A	Save as c11	Coefficient read register 11
Read	0x605B	Save as c12	Coefficient read register 12
Read	0x605C	Save as c13	Coefficient read register 13
Read	0x605D	Save as c14	Coefficient read register 14
Read	0x605E	Save as c15	Coefficient read register 15
Read	0x605F	Save as c16	Coefficient read register 16
Write	0x4003	0x01	Page select for channel B
Read	0x6050 to 0x605F	Save as c17 to c32	Coefficient read registers for channel B

In the Field:

1) Power up and run complete device configuration.

2) Load offset correction coefficients into the device as shown in the table below:

SPI write/ Read	Address	Value	Comment
Write	0x4004	0x61	Page select for channel A
Write	0x4003	0x00	Page select for channel A
Write	0x4002	0x05	Page select for channel A
Write	0x4001	0x00	Page select for channel A
Write	0x6000	c1	Coefficient write register 1
Write	0x6001	c2	Coefficient write register 2
Write	0x6002	c3	Coefficient write register 3
Write	0x6003	c4	Coefficient write register 4
Write	0x6004	c5	Coefficient write register 5
Write	0x6005	c6	Coefficient write register 6
Write	0x6006	c7	Coefficient write register 7
Write	0x6007	c8	Coefficient write register 8
Write	0x6008	c9	Coefficient write register 9
Write	0x6009	c10	Coefficient write register 10
Write	0x600A	c11	Coefficient write register 11
Write	0x600B	c12	Coefficient write register 12
Write	0x600C	c13	Coefficient write register 13
Write	0x600D	c14	Coefficient write register 14
Write	0x600E	c15	Coefficient write register 15
Write	0x600F	c16	Coefficient write register 16
Write	0x4003	0x01	Page select for channel B
Write	0x6000 to 0x600F	c17 to c32	Coefficient write registers for channel B

3) Enable loading external offset correction coefficients using the writes shown in the table below:

SPI write/ Read	Address	Value	Comment
Write	0x4004	0x61	Page select
Write	0x4003	0x00	Page select
Write	0x4002	0x00	Page select
Write	0x4001	0x00	Page select
Write	0x6069	0x01	Enable loading external offset coefficients for channel A
Write	0x4003	0x01	Page select
Write	0x6069	0x01	Enable loading external offset coefficients for channel B

Regards,

Vijay

0 Ozer Ozaydin18 over 6 years ago in reply to Vijayendra Varma Siddamsetty

Prodigy 50 points

Hi Vijay,

Thanks for the info, however it seem that after the ADC is initialized the saved coefficients doesn't work correctly. It is better, but not enough. Please check the averaging spectrum outputs (half of real spectrum) below for each step. ADC is in 14bit real mode, 1.5GSPS sampling rate, 2048 points fft average around 100ms.

1-Initial spectrum after ADC init, notch filter disabled.

2- corrector block enabled, not frozen

3- after corrector frozen

4- save and load coefficients as described. Without ADC re-init, it's OK. We're sure that coefficients are really loaded, we made tests with incorrect coefficients and saw the difference.

5- reinitialize ADC, corrector disabled initially.

6- enable corrector block

7- load previously saved coefficients. as you can see, it's better than without correction, but not acceptable.

We repeated this scenario many times but after ADC reinitialized (soft reset, without poweroff-on, without temperature/environment change) the coefficients seemed to be not working correctly. As mentioned above, if you just save and load coefficients without reinit ADC, it's working fine.

Thanks,

Ozer

0 Ozer Ozaydin18 over 6 years ago in reply to Ozer Ozaydin18

Prodigy 50 points

Hi,

Do you have any updates about the issue above? It's really not a good option to ask our customer handle calibration in field.. Thanks,

Ozer

0 Ozer Ozaydin18 over 6 years ago in reply to Vijayendra Varma Siddamsetty

Prodigy 50 points

Details above.

0 Vijayendra Varma Siddamsetty over 6 years ago in reply to Ozer Ozaydin18

TI__Genius 10865 points

Hi Ozer,

Sorry for the delay. Your results are as expected by design. I have verified that spurs at multiples at Fs/4 better than -60 dBFs when coefficients from a previous power-up are loaded.
Enabling and freezing offset calibration after power-up (in field) gives better performance. Note that this procedure can be done without input disconnected if input doesn't have power at multiples of Fs/8.

Regards,
Vijay

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ADC32RF45: Load/Store Offset Corrector Coefficients