Back in the late 80s I remember when Digital audio DACs were just industrial DACs that did not pass the DC specification tests. One bit DACs were usually fairly noisy, but Cirrus Logic designers took care of that problem (See their solution a little further down in this blog).
Just to show you some of the older designs, back in 1985, Ira Miller wrote a paper1 regarding A custom six-bit DAC, a three-channel multiplexer, a four-channel amplifier, and a comparator for Personal Computers as the interface to a cassette recorder and the audio sound channel. It also interfaced joysticks to the PC.
The schematic of the IC in Reference 1 (Image courtesy of Reference 1)
Well we have certainly come a long way from that effort 30 years ago (When Cirrus Logic began) to the tiny, low-power, Hi-Fi DACs that fit into headphones in the mobile audio market.
Better content is driving the need for better hardware. We have progressed from the CD to MP3 and now to:
Similar to MP3, Free Lossless Audio Codec (FLAC) is virtually lossless in that it compresses the audio with no loss of fidelity, just as Zip works on files, but with far more advanced compression that is audio-specific.
Spotify has millions of songs and ready-made playlists.
Hi-Res Audio is a SONY site for music lovers as well as audiophiles. SONY has also launched their Audiophile Walkman.
Tidal is another site with high-end audio. Sprint has invested $200M in Tidal.
Now, the 2 billion smartphone users, need to have a way to get downloadable and streaming Pro Audio to their Smartphones.
I spoke to Carl Alberty, VP of Audio Marketing, on the Cirrus Logic team recently and the Cirrus team is well aware of where the portable Hi-Fi audio is headed. They know that Direct Stream Digital (DSD) and Digital eXtreme Definition (DXD) are fostering the development of high-end portable audio amplifiers. See this video and the video on Hi-Fi challenges.
Cirrus Logic’s CS43130 is their most recent MasterHIFI DAC and Amplifier for this effort.
Here is where the Cirrus Logic designers improved the 1-bit DAC, they crafted 512 single-cell DACs into this architecture which reduces jitter degradation of good audio sound. The IC also filters out unwanted noise through each of the 512 DACs in sequence. In the earliest days of the compact disc, DACs did not employ oversampling, and thus most of the image energy removal was done with a high order analog circuit.
With up to -108 dB of THD+N and 130 dB of Dynamic Range distortion cannot be heard and audio from the lowest levels to the loudest will not have reduced quality of sound.
The IC’s amplifier is able to drive large, over-the-ear high-impedance headphones, with no problem—while helping to extend the phone’s battery. These large headphones are becoming very popular and users are becoming aware of audible benefits of having large headphone drivers. What makes these types of headphones complicated is that they have higher impedances up to 600 Ohms, as compared to 16 or 32 Ohms for in-ear headphones. This means they require a higher voltage to be driven correctly, without distortion.
In a typical mobile headphone, the amplifier output delivers up to 1Vrms, which is fine for smaller impedances, but a 1Vrms driven into large impedance headphones means the volume can be too low for comfortable listening levels or the fine detail getting lost when listening to low level audio such as in classical music.
The CS43130 can drive up to 1.7Vrms at 600 Ohms, which delivers the correct output levels for the larger over the ear headphones and maintain the level of detail that gives the listener a better audio experience.
The impedance of the headphones is automatically detected upon plug in, the correct voltage level is then automatically set to ensure safe and correct levels for the headphones being used.
I really like the design architecture and the technical detail to which Cirrus Logic designers paid attention in this IC.
1 A Custom Data Conversion Subsystem for Personal Computers, IRA MILLER, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. SC-20, NO. 2, APRIL 1985