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Old 10th December 2008, 05:37 PM   #1
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Default single-ended to differential?

Hi DIYs,

I have an IC with a differential analog input and I will be connecting a single-ended signal to this input.

My approach will be to ground the VIN- of the IC and connect the positive signal part of the single-ended input to VIN+ on the IC. And then connect the grounds.

Just want to hear if there is a better way....

Thanks,

Jesper
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Old 10th December 2008, 05:44 PM   #2
gmarsh is offline gmarsh  Canada
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What's the IC?
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Old 10th December 2008, 05:54 PM   #3
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PCM 4202 - A/D converter from Burr-Brown.


http://focus.ti.com/lit/ds/symlink/pcm4202-ep.pdf

Regards,

Jesper
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Old 10th December 2008, 06:18 PM   #4
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I don't think that's such a great idea; it would kind of defeat the purpose of using such a high end ADC. If you look in the datasheet it recommends using an OPA1632 as an input buffer. You can connect the negative input of the OPA1632 to ground for single ended input.
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Old 10th December 2008, 06:26 PM   #5
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Default @anonymous

uhuh, seems I'm opening up for more than just the quick advice I was looking for....

As far as I remember from the theory I learned some years ago not connecting it in differential mode will cost 3 or 6 dB SNR...

Are you thinking of something else when you say
Quote:
it would kind of defeat the purpose of using such a high end ADC
?

Best Jesper
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Old 11th December 2008, 02:28 AM   #6
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Reduced CMRR perhaps?
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Old 11th December 2008, 06:17 AM   #7
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An opamp would be the simplest choice. Check page 23 of the PCM4202 datasheet.
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Old 11th December 2008, 07:24 AM   #8
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Note that the analog inputs have an absolute max range of -0.3V to (Vcc+0.3V). So if you grounded one input, the other would only be able to swing 0.6 Vpp, assuming a symmetrical audio signal. Is that enough for your purposes?
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Old 11th December 2008, 12:50 PM   #9
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Quote:
Originally posted by Cauhtemoc
An opamp would be the simplest choice. Check page 23 of the PCM4202 datasheet.
Figure 14 on page 23 of the datasheet is a buffer for the common-mode reference voltage, not the inputs.

Quote:
Originally posted by mako1138
Note that the analog inputs have an absolute max range of -0.3V to (Vcc+0.3V). So if you grounded one input, the other would only be able to swing 0.6 Vpp, assuming a symmetrical audio signal. Is that enough for your purposes?
That would be -0.3V to 5.3V (assuming Vcc is 5V), not -0.3V to 0.3V.
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Old 11th December 2008, 07:24 PM   #10
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Quote:
Originally posted by theAnonymous1
Figure 14 on page 23 of the datasheet is a buffer for the common-mode reference voltage, not the inputs.
I was obviously refering to figure 13.
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