single-ended to differential?

gentlevoice · 10th December 2008, 06:37 PM

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

gmarsh · 10th December 2008, 06:44 PM

What's the IC?

gentlevoice · 10th December 2008, 06:54 PM

PCM 4202 - A/D converter from Burr-Brown.

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

Regards,

Jesper

theAnonymous1 · 10th December 2008, 07:18 PM

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.

gentlevoice · 10th December 2008, 07:26 PM

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

theAnonymous1 · 11th December 2008, 03:28 AM

Reduced CMRR perhaps?

Cauhtemoc · 11th December 2008, 07:17 AM

An opamp would be the simplest choice. Check page 23 of the PCM4202 datasheet.

mako1138 · 11th December 2008, 08:24 AM

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?

theAnonymous1 · 11th December 2008, 01:50 PM

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.

Cauhtemoc · 11th December 2008, 08:24 PM

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.

10th December 2008, 06:37 PM	#1
gentlevoice diyAudio Member Join Date: Oct 2007	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

10th December 2008, 07:18 PM	#4
theAnonymous1 diyAudio Member Join Date: Feb 2004 Location: Anonymityville	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. __________________ "Men willingly believe what they wish" - Julius Caesar

11th December 2008, 03:28 AM	#6
theAnonymous1 diyAudio Member Join Date: Feb 2004 Location: Anonymityville	Reduced CMRR perhaps? __________________ "Men willingly believe what they wish" - Julius Caesar

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10th December 2008, 06:44 PM	#2
gmarsh diyAudio Member Join Date: Apr 2004 Location: Halifax, NS, Canada	What's the IC?

10th December 2008, 06:54 PM	#3
gentlevoice diyAudio Member Join Date: Oct 2007	PCM 4202 - A/D converter from Burr-Brown. http://focus.ti.com/lit/ds/symlink/pcm4202-ep.pdf Regards, Jesper

11th December 2008, 07:17 AM	#7
Cauhtemoc diyAudio Member Join Date: Jun 2007	An opamp would be the simplest choice. Check page 23 of the PCM4202 datasheet.

11th December 2008, 08:24 AM	#8
mako1138 diyAudio Member Join Date: Nov 2007	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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