For professional digital audio recording and processing, Texas Instruments' PCM4220 and PCM4222 24-bit, 216-kHz delta-sigma analog-to-digital converters (ADCs) provide up to 124dB signal-to-noise ratio (SNR). While sampling at 48 kHz, these two-channel ADCs
consume 305 mW, permitting designs
that power computer audio interfaces
entirely through a USB or Firewire bus.
The 6-bit output from the delta-sigma
modulators in the PCM4220 is routed to
a digital decimation filter, whose output
provides linear pulse-code modulation
(PCM) data. This data then is available at
the audio serial port interface. In the
PCM4222, the modulator output bypasses the decimation filter so designers can implement the digital filter in an FPGA
for end-product differentiation.
To provide more power-supply rejection than ADCs that use the power-supply rails as the modulator reference,
these chips employ a bandgap reference
circuit. The audio serial port supports
common audio data formats at sampling
rates from 8 to 216 kHz. The 24-bit PCM
data can be reduced to 20-, 18-, or 16bit word lengths, if needed.
The PCM4220's multistage finite
impulse response (FIR) digital decimation filter provides two filter-response
options: "classic" and "low group delay."
The classic response will be familiar to
most audio engineers. The low-group-delay filter response provides lower latency. Specifically, the group delay for
the classic filter is 39 output sample
periods, while the low-group-delay filter
provides a 21-output sample period
group delay.
Digital high-pass filtering can be
turned on or off independently. Also,
individual overflow outputs indicate the
overflow status for each channel, allowing designers to optimize for studio or
live sound.
The PCM4222 and PCM4220 come in
48-pin thin quad flat-pack (TQFP) packages. The PCM4222 costs $14.95 and
the PCM4220 costs $9.95, both in
quantities of 1000 units.
Texas Instruments
www.ti.com