Hi, I am newbie in things electrical so don't give me too hard time.

I know how DACs work in concept, but i don't get how single ended DAC with +V power supply and 0V ground can have -V output. I see datasheets stating e.g. DAC left or right channel outputs 2 pins one V+ and the other V-.

Is it biased in the middle? (output from e.g.: 0 to 2 Volts is considered as minus and output from 2 - 4 Volts represents the positive side of audio wave)

Or is it biased only up to I/V converter which somehow splits positive wave part to +V electrical and the lower part to -V?

I think i am missing something deeper, can anyone help me please?

 

Got a particular spec sheet in mind?

 

http://www.datasheetcatalog.com/datasheets_pdf/T/D/A/1/TDA1547.shtml

This is just an example of numerous datasheets i have seen with V+ and V- outputs per single channel.

Check out pins 14, 15 right channel and pins 18,19 for left. I know that this DAC has internal I/V conversion. So outs are V.

http://www.ti.com/lit/ds/symlink/pcm1798.pdf
legs 17,18 and 25,26.

 

http://www.analog.com/static/imported-files/data_sheets/AD1955.pdf
this one states it's differential outputs, legs 11,12 and 17,18.

 

PCM1798 and AD1995 are both differential CURRENT output, not voltage output.

 

PCM1798 and AD1995 are both differential CURRENT output, not voltage output.

Ok, than how DAC makes + and - output from +V supply and and ground? I mean what happens inside?

 

Both outputs of the AD1995 have a current output referenced to the plus supply. + and - refers to the phase of the output. The + output increases with increasing digital input and the - output decreases with an increasing digital input. The outputs are biased at about 1/2 full-scale (see ANALOG OUTPUTS in the ANALOG PERFORMANCE table). The differential outputs are designed to drive a differential amplifier (see Figures 7 through 12).

 

16 bit DAC has 65536 values which typically are represented from 0 to 4 volts at analog output(or something like that). 0 to 2 volts represent 32768 of negative part of the waveform and 2 to 4 volts represent the positive part of the waveform. The first 0 - 2 volts are electrically positive, how do you make them into electrically negative output?

Differential outputs would use phase splitter like this, here is an animation:

http://www.falstad.com/circuit/e-phasesplit.html

But there you have an input of 40Hz which goes from + to -V. Lets say this input would go from DAC outs. So how in the hell DAC can output negative voltage using +V supply and GND only? and how does it split 0 to 2 V as negative electrical output and 2 to 4 as positive?

P.S. I find circuit sim app much better than spice for learning.

http://www.falstad.com/circuit/

 

16 bit DAC has 65536 values which typically are represented from 0 to 4 volts at analog output(or something like that). 0 to 2 volts represent 32768 of negative part of the waveform and 2 to 4 volts represent the positive part of the waveform. The first 0 - 2 volts are electrically positive, how do you make them into electrically negative output?

Differential outputs would use phase splitter like this, here is an animation:

http://www.falstad.com/circuit/e-phasesplit.html

But there you have an input of 40Hz which goes from + to -V. Lets say this input would go from DAC outs. So how in the hell DAC can output negative voltage using +V supply and GND only? and how does it split 0 to 2 V as negative electrical output and 2 to 4 as positive?

P.S. I find circuit sim app much better than spice for learning.

http://www.falstad.com/circuit/

You seem to be hung up on this negative thing. The plus and minus indicators for the outputs don't mean the output is a negative voltage, it's referring to the fact that they have opposite phase (even though both are positive voltages).

Your sim app example shows that very thing. The two outputs from the transistor have opposite phase, but they are both positive voltages.

If you really want a negative output voltage then you will need to use an op amp level shifter that is powered by plus and minus supply voltages.

Sim app may be fine for simple simulations but Spice is much better for simulating complex circuits.

 

You seem to be hung up on this negative thing. The plus and minus indicators for the outputs don't mean the output is a negative voltage, it's referring to the fact that they have opposite phase (even though both are positive voltages).

Your sim app example shows that very thing. The two outputs from the transistor have opposite phase, but they are both positive voltages.

If you really want a negative output voltage then you will need to use an op amp level shifter that is powered by plus and minus supply voltages.

Sim app may be fine for simple simulations but Spice is much better for simulating complex circuits.

The outputs of phase splitter are both positive but opposite phase, thats fine. But the input isn't. The input is changing from + to -. I believe a phase splitter input would receive a varying + to - Voltage signal from DAC , the point is i don't know how the DAC can do varying output of + to - Voltage with +V supply and GND only. Am i missing something else?

 

The outputs of phase splitter are both positive but opposite phase, thats fine. But the input isn't. The input is changing from + to -. I believe a phase splitter input would receive a varying + to - Voltage signal from DAC , the point is i don't know how the DAC can do varying output of + to - Voltage with +V supply and GND only. Am i missing something else?

The DAC doesn't do a varying + to - voltage, either internally or externally. The input you are talking about doesn't exist.

The DAC differential output is generated by its own particular internal differential stages which are nothing like the phase splitter circuit you posted. Here's some general info on DAC differential outputs.

 

The DAC differential output is generated by its own particular internal differential stages.

Would you have any more specific example of DAC differential output generated by its own particular internal differential stages.

BTW how would single ended DAC output look like before any I/V conversion, before any post conversion filtering internally (low pass filters etc.)?

 

Would have any more specific example of DAC differential output generated by its own particular internal differential stages.

BTW how would single ended DAC output look like before any I/V conversion, before any post conversion filtering internally (low pass filters etc.)?

Here's another link that discusses the output interface.

Finding the actual internal circuit design for a specific DAC is difficult since that is usually considered proprietary information by the manufacturer.

A current output DAC generates an output current whose magnitude is determined by the digital input word value. If you have this current go through a small resistor to ground (the maximum allowed resistor value is given in data sheet) then you will convert that varying current into a varying voltage.