ADS6145: ADS6145

Syed Asif Abdullah

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	0	0	1	1	0	0	1	1	0	0	1	1	0	1
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

over 8 years ago

0 Richard Prentice over 8 years ago

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 Syed Asif Abdullah over 8 years ago 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 Richard Prentice over 8 years ago 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.

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ADS6145: ADS6145