How can I design the headphone audio DAC

Hi Duy,

This sounds like a fun project!

Consider the block diagram as something like this:

1.  The USB source can be a lot of things.  Some DSPs and microcontrollers have I2S interfaces, but those will need firmware to be developed for it.  This is can be a big undertaking.  There are some solutions that are found in common USB DAC+HP driver solutions from XMOS and CMedia.  This can also give you an SPI or I2C master to configure the DAC if it has some advanced features (like an integrated volume control).  

Though if you are looking to keep this a simple project, then check out the PCM2706C, which is a USB interface with DAC output.  Though you could just this output, generally an external DAC device will give you better performance.  But what makes the PCM2706C special is that it also has an I2S output that samples at 44.1kHz.  So that is a pretty simple way to convert USB to I2S.  

2.  There are DACs that have some advanced digital features, like integrated DSP, volume control, and clock configurations (PCM5122/42).  These devices would need some kinds of MCU to configure them.  But for the same analog performance, you can use the PCM5102A which is hardware controlled. 

3. Power is something to consider as well.  Some USB devices are bus-powered, but the DAC and Headphone driver will need their own power.  Most headphone drivers are class AB amplifiers, which means they need a bipolar supply.  This can present a problem as negative supplies require some kind of switched-mode power supply.  This adds complexity to the designs.  

The benefit of a device like the PCM5102A is that it is "DirectPath", meaning that the device generates its own negative supply.  This means that it only needs 3.3V to operate.

I am not an expert in the power side of things, so I suggest posting a question to the power forum about a good battery charging reference design.

4. The headphone driver is important as well, as it would also require a bipolar supply.  Fortunately, TI offers a wide line of DirectPath amplifiers as well.  Consider the TPA6133A2 for example.

So if you asked me what the simplest solution would look like, it would say PCM2706+PCM5102A+TPA61xxx+Power management.

Hope this helps!

Paul

1. I am not sure about strict audio DSPs. I have seen some implementations using the C6000 DSP from TI.  There are some other IC companies that make audio DSPs as well.  Note that the PCM5122/42 has an integrated DSP.  You can implement some fairly complex process flows on that DSP.  If you are looking to do some simple stuff, like biquad filters, DRCs, bass-boost, etc. you could consider that.  You would just need a microcontroller to program the DAC at startup as it does not have non-volatile memory.

2. ADCs can be used for microphone inputs or some advanced stuff like noise cancellation. But I doubt you require an ADC in this solution.  Most codecs have both because they are used in personal electronics (cell phones) that usually feature both speakers and microphones.

Thanks,

Paul