A/D and D/A Converters for Audio
Very high quality audio data converters are available from AKM, Analog Devices, Burr-Brown (Texas Instruments), and Crystal (Cirrus Logic). Each seems to periodically leapfrog the other.
At the time of this writing, the leading stereo (2-channel) A/D parts were the AKM AK5394 and Crystal’s CS5396. Leading stereo D/As include Crystal’s CS43122, AKM’s AK4395, Analog Devices’ AD1853, and TI/Burr-Brown’s PCM1738.
Due to the success of home cinema and surround-sound, and now with the introduction of DVD-Audio, the availability of high quality multichannel (at least 6-channel) D/As is increasing.
Particularly interesting are Analog Devices’ AD1833 and AKM’s AK4355 offering six-channel volume control, wide dynamic range (>/=106 dB typ) and low THD+N (
A new 8-channel part just released from TI/Burr-Brown is the PCM1608, with 24-bit conversion, dynamic range of 105 dB typ (98 dB min) and max THD+N equal 0.008% (44.1 kHz sample rate; no frequency stated).
Codecs (coder-decoders) create a separate family of specialized converters interesting to information appliance designers (Note: as used here the term “codec” refers only to that class of ICs that contain A/D and D/A converters; it does not mean the many devices used for data compression coding and decoding).
Usually containing at least two A/Ds and four D/As, what started out with telephone-audio quality has developed into something quite different.
High audio quality single-chip codecs include Analog Devices’ AD1836 Multi-Channel 96 kHz Codec, a high-performance, single-chip codec providing three stereo D/As and two stereo A/Ds (24-bit multibit delta-sigma) converters, 6-channel volume control, with 105 dB (typ) dynamic range and THD+N of only 0.003% (typ; no conditions given).
And Texas Instruments’ TLV320AIC27 audio-band codec features a stereo A/D and four D/A converter (18-bit delta-sigma) channels with an audio mixer for four stereo inputs, a phone, two microphones, and a PC-beep input.
Performance claimed is signal-to-noise of 95 dB (typ) and THD+N equal 0.002% (typ; no conditions given). And it is designed to interface directly with TI’s TMS320 DSP family discussed below.
Wolfson Microelectronics Ltd. (Edinburgh, Scotland) offers a family of ICs that add digital audio capabilities to digital camcorders, digital still cameras, DVD players and other Internet appliances, including MP3 players, cell phones with MP3, and PDAs.
These chips claim CD-quality audio not previously available in portable appliances.
For example the WM8731, a stereo codec (including a mic input with bias voltage) with integrated headphone amplifier, level control and programmable sample rates (8 kHz to 96 kHz), boasts signal-to-noise ratios of 97 dB for it’s A/D and 100 dB S/N for its D/A (24-bit multibit delta-sigma) converters, with a final headphone output THD level less than 0.1%, all for less than $5.00 in only 1,000-piece quantities. And it is fully compliant with the Secure Data Management Interface (SDMI).
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