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ADS6145: ADS6145

Syed Asif Abdullah
Prodigy 50 points
Part Number: ADS6145

Hello guys,

I am using ADS6145 to convert a measured analog signal of  50 MHz to Digital 14 bits, I am using CMOS mode and 2s complement format,

FOR simplicity , I sent a DC input of 0.8 differential,

According to the datasheet its max. Diff. input is 2V. I calculated the transfer function , I presumed that my digital input will be the binary code of the Decimal value , 3277, calculating the 2's complement ,

I should get following output,

Input

Voltage

D13

D12

D11

D10

D09

D08

D07

D06

D05

D04

D03

D02

D01

D00

800 mv

0

0

1

1

0

0

1

1

0

0

1

1

0

1

3277

2’S complement

1

1

0

0

1

1

0

0

1

1

0

0

1

1

Measured Bits

1

1

0

0

1

1

0

0

1

-

-

-

-

-

As,, demonastrated in the fig. I am not geting any specific output from the LSBs, (D04-D00), rather noise at a rate of clock freq, which is difficult to distinguish whether high or low. I think , Owing to this problem , I am not getting proper output in Digital to analog converter in the receiver side.

I will be really thankful if anyone can  give me the insights regarding this problem.

Kind regards,

asif

  • 0
    TI__Mastermind 29220 points

    Hi,

    If the analog input voltage is a fixed DC value, then there will generally be a few lsb's of noise in the digital output code.  This is commonly called idle-channel noise.  For a 14 bit device, it would be common to see two or maybe three of the lsb's be toggling.   Seeing 5 of the lsb's toggle is a bit excessive, but it might also be influenced by the purity of the sample clock.  If there is jitter on the sample clock then that would increase the amount of noise seen in the output sample. 

    By the way, the only difference between the offset binary format and the 2's complement format is that the msb is inverted between the two formats.  If you have offset binary format and invert the msb, then you get 2's complement.  If you invert the msb again you get back to offset binary. 

    Regards,

    Richard P.

  • 0 in reply to Richard Prentice
    Prodigy 50 points
    Thanks for your blessing reply, I need some more guidelines from you,
    would you mind recommand some DAC's model which would be best compatible with ADS 6145,
    I have tried with AD9707 from analog devices, it did not give me convicing output.

    Regards,
    Asif
  • 0 in reply to Syed Asif Abdullah
    TI__Mastermind 29220 points

    Hi,

    We have many different DACs in our product portfolio.  We would need to have some idea of what it is you wish to see in a DAC before we could make a recommendation.  Such as sample rate, resolution, number of channels, digital features that could be useful, and how you wish to use the device.    And putting the request in a fresh posting with an appropriate subject would help make sure that our DAC people don't skip over reading the posting because it has a different part number mentioned in the subject.

    Regards,

    Richard P.