Questions about AD converter

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david753
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Questions about AD converter

Post by david753 » Wed Jan 19, 2005 1:30 am

I got new problems in AD9057.<p>1. I use OSC to measure the bias voltage of AD9057.
I got 2.5~2.48 in two boards, and got 2.525 ~ 2.523 in another two boards.
Meanwhile, the sensitivity of 2.5~2.48 is -30dbm that is better than
2.525~2.523 that is -18dbm sensitivity.
Is it reasonable?
What kind reasons affect the bias voltage?<p>2. I calculate the mapping relationship between the bias voltage and sensitivity, I got an interesting phenomenon.
When the input signal Vp-p is 4mVp-p(4.98~5.02), the sensitivity is -44dbm, But, When the input signal is 12mVp-p(4.94~5.06), the sensitivity is -34dbm.
Please refer to
http://user52.starbeta.org/others/ad9057.xls
There is a big gap between the digital output is 7F and 7E.
May I have another type that amplification curve is exponential shape?
Does it useful in improving sensitivity?

cato
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Re: Questions about AD converter

Post by cato » Wed Jan 19, 2005 1:59 am

Your input voltages are way outside the input range of the part. The AD9057 has a maximum input range of 1V p-p when AC coupled and -0.5 to 0.5 when DC coupled. See Figs. 2 and 3 in the data sheet.<p>http://www.analog.com/UploadedFiles/Dat ... 9057_d.pdf

david753
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Re: Questions about AD converter

Post by david753 » Wed Jan 19, 2005 2:13 pm

You misunderstand what I mean.
The bias voltage is 2.5 V.
The input voltage is from 3.0~2.0, so the dynamic range is +0.5(3.0-2.5) ~ -0.5(2.0-2.5)<p> <blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by cato:
Your input voltages are way outside the input range of the part. The AD9057 has a maximum input range of 1V p-p when AC coupled and -0.5 to 0.5 when DC coupled. See Figs. 2 and 3 in the data sheet.<p>http://www.analog.com/UploadedFiles/Dat ... 9057_d.pdf<hr></blockquote>

cato
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Re: Questions about AD converter

Post by cato » Wed Jan 19, 2005 3:14 pm

Are you saying that you are using ac coupling as shown in Fig. 2 of the data sheet?

david753
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Re: Questions about AD converter

Post by david753 » Thu Jan 20, 2005 12:57 am

yes, you got.<p> <blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by cato:
Are you saying that you are using ac coupling as shown in Fig. 2 of the data sheet?<hr></blockquote>

cato
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Re: Questions about AD converter

Post by cato » Thu Jan 20, 2005 1:20 pm

Well then, I'm afraid I'm out of ideas as to what might be causing the problem you are seeing.

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