audio/videoZONE Products for the week of September 9, 2002
Wolfson Microelectronics Says . . .
WM9710: Wolfson's Audio Codecs Optimized For Smartphones
Wolfson Microelectronics, Ltd., a technical leader in developing audio ICs
for multimedia and communications applications, has developed a line of
audio codecs that can playback and record audio at the same time, but at
different sampling rates. The WM9710, a high-performance stereo audio codec,
conforms to the AC'97 Rev2.2 specification and thus eliminates the need
for an additional PLL, which consumes power, or a sample rate conversion
algorithm, which slows down the CPU. The end result of this approach is
longer battery life and reduced CPU overheads (i.e. user programs run faster
because CPU is not burdened with sample rate conversion.
"The newest generation of portable applications, like the PDA's, smartphones and tablet PCs based on the WinCE operating system, are more demanding. They require simultaneous audio playback and record at different sample rates, which the I2S standard can't handle, " said David Milne, Wolfson's managing director. "Wolfson was the first company to introduce an AC'97-compliant product specifically for this market. That product, the WM9705, with its resistive touchscreen interface has been well received."
The WM9710 performs full-duplex 18-bit codec functions and supports variable
sample rates from 8kHz to 48kHz with high signal-to-noise ratio. Analog
mixers are included to mix external (additional audio) signals into the
playback or record path. Mono inputs and outputs are provided to connect
to an external voice codec. The on-chip headphone driver can distinguish
between a stereo headphone and a mono headset and route the signals accordingly.
This high-quality audio stereo codec allows designers to easily integrate
phone functions with other audio functions such as MP3 playback and voice
recording.
analogZone Says . . .
I believe that Wolfson is the first company to have a deliverable rev2.2-compliant codec. It follows the pattern of previous AC'97 products but adds the on-chip sample rate conversion (for rates from 8 kHz to 48 kHz) and the ADC and DAC rates are fully independent.
Wolfson has never offered the leading-edge numbers that some manufacturers boast of but the performances for the applications involved are absolutely OK. A-weighted SNRs for the DACs to line out are a typical 92 dB and that for the ADC is a typical 87 dB. The PSRRs are a typical 50 dB from 20 Hz to 20 kHz (all with 48 kHz sampling and with both analog and digital rails at 3.3 V.)
In addition to the AC'97 rev2.2 features (which include the variable rate and 3-D stereo "enhancement" to make your brain believe you have further physical separation) the WM9710 offers headphone drive levels on the mono output, an additional routing switch after the mixer, auto-detect of headphone use and a reset power-down override. Circuit integration of the part requires a single crystal and about 28 capacitors.
The WM9710 is in production in a QFN-48 and a TQFP-48, both priced at
$4.21 in 1000-piece lots.