Trying to understand the evolution of USB-C earphones ? - Page 1
Forum section: electronics / projects

author: autobot
author_rank: Regular Contributor
timestamp: May 28, 2017, 05:49:08 pm
content: USB-C is becoming more common in phones, replacing the audio-jack.Assuming that our goal is to create earphones with enough features(good sound quality, buttons, great active-noise-cancellation), but at the lowest price, and since we know that earphones tend to break often, a reasonable strategy would be to integrate as much electronics as possible in the phone, right ?So how far can we go with it(assuming support by chip companies) ?

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 28, 2017, 06:21:44 pm
content: The DAC chips are incredibly cheap in bulk nowadays, even though they're next to impossible to obtain by themselves at the hobbyist level. The 3.5mm jack is actually a bit of a pain to design around for portable equipment, requiring either a negative rail or bulky coupling capacitors. They could have invented a small form factor connector for differential drive headphones to solve that and boost the SNR, but that at best would be a stopgap before going to a digital interface.

author: tooki
author_rank: Super Contributor
timestamp: May 30, 2017, 12:22:23 pm
content: Huh? What do you mean that a 3.5mm "requires" a negative rail or bulky caps? There are plenty of class D headphone amps out there that use just a +5V or +3.3V rail and don't need many external components at all. Heck, even the venerable LM386 is single-supply.As for digital, as Apple has done in the iPhone 7, well... then you need the DAC in the plug, where the space constraints are arguably worse than in the phone. And yet it's easily done (teardowns of Apple's Lightning to 3.5mm adapter show a single IC and a bunch of tiny passives, so it must be a custom chip containing a Lightning interface, DAC, and ADC).

author: tszaboo
author_rank: Super Contributor
timestamp: May 30, 2017, 12:34:15 pm
content: There are several issues with the TRS (Jack is a pirate) and TRRS connectors. One of them, the terminals are shorted, when the plug is inserted. And there are different pinouts, so you need analog switches to switch between them. It is an evolution of a 1900 technology, not really designed for todays use. Maybe you want stereo microphone? Proper volume control? Well, you cannot.So it is OK to let it die.

author: tooki
author_rank: Super Contributor
timestamp: May 30, 2017, 03:07:44 pm
content: What do you mean that proper volume control is not possible??

author: m98
author_rank: Frequent Contributor
timestamp: May 30, 2017, 03:47:55 pm
content: Quote from: NANDBlog on May 30, 2017, 12:34:15 pmWho cares that the terminals get shorted? It's not like that's ever been an issue in their current application. The different TRRS pinouts of different phones are a pain, but that's just because device manufacturers couldn't agree on one uniform standard. But you don't need an analog switch, it's just that the additional controls and microphone of a headphone made for one standard don't work on a device made for another. The analog switch is only needed for devices like the iPod shuffle that use the audio jack as a charging and USB-port.When you wish some extra useless features, fine, you can still connect USB-C headphones to a device that still has an audio and USB-C connector. But the majority of customers still uses regular headphones, even ones without control buttons and microphones, that can just readily be plugged into an audio jack.