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ADS5295: using 14x serialization.

sungsik kang1
Prodigy 160 points
Part Number: ADS5295

Hi. 

I posted a question before, but it hasn't been completely solved, so post a new question.

Now i'm using ADS5285.

Table 20 on page 75 of the manual shows that ads5295 supports 14x serialization and has to be used with digital processing function (such as averaging and decimation filter).

However, there is only a timing diagram for 10x and 12x serialization in the manual and no timing diagram for 14x serialization.

My question is

1. ADS5295 has 12bit resolution. If i use 14x serialization, how can 12bit data be 14bit?  Are two zero padding bits added? Or is it changed to 14bits by digital filter?

2. If it is correct to change by digital filter, please tell me more about which filter to use. (averaging filter? decimation filter? both?)

   I would appreciate it if you could let me know the register that needs to be modified for using digital filter.

Thanks you.

  • 0
    TI__Mastermind 49956 points

    Hello Sungsik,

    I wanted to let you know that the device expert is out of the office due to the holidays, he will be back in the office next week.

  • 0 in reply to Praveen Aroul
    TI__Genius 12025 points

    Hello Sungsik,

    Thanks for using ADS5295 device.

    We will reply your question to you soon.

    Thank you!

    Best regards,

    Chen

  • 0 in reply to Chen Kung
    TI__Genius 12025 points

    Hello Sungsik,

    Yes, since this is 12bit default mode, if you use capture 14-bit data with 2 lower bits '0's are added.

    because when doing averaging, the number of bits of each sample can be increased

    in order to keep more information. Also when doing decimation filter, it needs more bits than

    the 12bit (original bits) mode to keep more information.

    Both averaging and decimation filter are different methods

    and need increasing number of bits for accuracy.

    (Of course, you can still select output signal has the same as 12bit output only.)

    Thank you,

    Best regards,

    Chen

  • 0 in reply to Chen Kung
    Prodigy 160 points

    Thanks Chen.

    Now I understand I need more bits if I use the averaging filter or  decimation filter.

    So, you mean  1) if i set Bit[11:8] of register 46h to 0100 (for 14x serialization) and disable filter (such as averaging, decimation) , the output contain 2 lower bits '0'.    

    and                  2)  if i set Bit[11:8] of register 46h to 0100 (for 14x serialization) and enable filter , all of 14bits contain information of sample. 

    is this right?

    All I want is to do 14x serialization on eight channels. It doesn't matter if the zero padding bit is added.

  • 0 in reply to sungsik kang1
    TI__Genius 12025 points

    Hi Sungsik,

    Yes, please enable register 46, D15=enable,

    choose 14x mode from D11-D8 (for your need).

    Later if you start to use decimation filter,

    you probably need to choose DATA_RATE[1:0] on Register 38.

    Thank you!

    Best regards,

    Chen

  • 0 in reply to Chen Kung
    Prodigy 160 points

    Hi. chen . Thanks for reply.

    I have a few more questions about ADS5295.

    I posted a new question. Can you check it?

    https://e2e.ti.com/support/data-converters/f/73/t/873049

  • 0 in reply to sungsik kang1
    TI__Genius 12025 points

    Hi Sungsik,

    For your concerns, first please look at the ADS5295 datasheet page 64

    Figure 61. Digital Processing Block Diagram.

    Because this is a 12-bit ADC device (as you can see from page 14), after you have been using

     for examples, the averaging filter or  decimation filter, you can increase the data to be 14bit  or 16bit resolution

    inside the Digital Processing Block.

    And then after the Digital Processing Block, you can deliver this parallel data into serial data by through Serialization Block (Please see this from page 64, Figure 61)

    which can give you 12x, 14x, or 16x mode options. (this will be your option to select).

    Please look at Figure 61 on page 64 again, you can see Test Pattern (including sync pattern, ramp pattern)

    is not related to averaging and/or decimation filter circuits. Therefore, when you change from 12x

    into 14x or 16x, then you will only receive two or four more '0' bits from the Serialization block.

    Thank you!

    Best regards,

    Chen