About audio DAC for headphone application

[jnuhope]

Hi all,

I am wondering how do people design the output stage for headphone application which has resistive load as low as 8Ω. In order to achieve 24 bits application, the output stage has to have large gain at all swings.

Even using 3 stages cascaded opamp architeture is hard to achieve the gain requirement because the last stage can easily give you -25dB for a reasonable device size (gm × 8 )

Is there any structure that industry often use? Can anyone point me any reference paper or have experience on this and would like to share here?

Thanks in advance!

 

[re007972]

**broken link removed**

 

[jnuhope]

For Class D opamp, the output has to have some kind of filter (L, C, and R), which would consume system cost. A solution would be driving the 8 Ohm directly. Then one can not use Class D.