MCIMX233CJM4B Datasheet, PDF (1183/1612 Pages) Freescale Semiconductor, Inc – i.MX23 Applications Processor Reference Manual

Chapter 28
AUDIOIN/ADC
This chapter describes the AUDIOIN/ADC module implemented on the i.MX23, including DMA, sam-
ple rate conversion, and internal operation. Programmable registers are described in Section 28.4, “Pro-
grammable Registers.”
28.1 Overview
The i.MX23 features an audio record path that consists of a sigma-delta analog-to-digital converter
(ADC), followed by the AUDIOIN digital multi-stage Finite Impulse Response (FIR) filter.
The microphone or line input is oversampled by the ADC, and the 1-bit digital stream is input to a cas-
caded-integrator comb filter, where the signal is parallelized, sent through a high-pass filter to remove
DC offset, and the sample rate is converted to the AUDIOIN’s internal rate. Next, the signal is filtered
using a three-stage FIR filter. The resultant parallel PCM samples are then transferred to a buffer in mem-
ory using the APBX bridge DMA, where it can be read by system software.
The analog audio source can be selected from one of three possible inputs:
• Mono microphone input, with settings for 0dB, 20dB, 30dB and 40dB gain.
• Stereo line inputs, with 0dB to 22.5dB gain, in 1.5dB steps.
• Looped back from the stereo headphone amplifier
The AUDIOIN module implements the following functions:
• Serial to parallel bit-stream integrator/averager
• Sample rate converting (SRC) cascaded-integrator comb (CIC) filter
• High-pass filter (HPF)
• Three-stage downsampling FIR filter: 7-tap (8:4), 11-tap (4:2), 33-tap (2:1) supporting conversion
from quarter, half, full, double, and quad sample rates that are multiples of the standard 32 kHz,
44.1 kHz, and 48 kHz rates
• 16- or 32-bit PCM sample widths
• APBX bridge DMA interface
• Independent control of each channel’s volume (including mute)
• DAC-to-ADC internal loopback for product development
• Control bit fields used for analog ADC settings
Freescale Semiconductor
i.MX23 Applications Processor Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
28-1