UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
275 of 362
1.
Features
•
Dual DAC with 16- to 24-bit input
•
Streaming Analog Out (SAO) module provides FIFO input buffering
•
Digital de-emphasis for standard sampling frequencies
•
Digital gain control and soft mute function
•
Interpolation filter and noise shaper for high S/N with low frequency operation
2.
Description
The dual channel bitstream DAC can be used for stereo audio and other one- or
two-channel D-to-A applications, particularly those involving regular, periodic conversion.
The basic architecture of the block consists of an input block that receives 24-bit inputs at
the Nyquist sample frequency of interest (fs), up-samples and interpolates to 128 fs using
16-bit coefficients and performs noise shaping, after which the digital results are
converted to analog voltages.
It includes several advanced features such as digital de-emphasis, digital gain control,
muting, and polarity control that are described in the following sections.
shows the block diagram of the Dual DAC module.
The interpolation from 1 fs to 128 fs is realized in four steps:
1. The first stage is a 99-tap halfband filter (HB) which increases the sample rate from 1
fs to 2 fs. This stage also includes digital de-emphasis.
2. The second stage is a 31-tap FIR filter which increases the data rate from 2 fs to 8 fs
and scales the signal. For this filter 2 sets of coefficients can be chosen realizing 2
different transfer characteristics.
UM10208
Chapter 22: Dual-channel 16-bit Digital-to-Analog Converter
(DDAC)
Rev. 02 — 1 June 2007
User manual
Fig 30. Dual DAC block diagram
AOUTL
AOUTR
DE-
EMPHASIS
HALF BAND
FILTER
VOLUME
CONTROL &
MUTE
1
FIR
FILTER
LINEAR
INTERPOLATOR
DAC
NOISE
SHAPER
1 fs
8 fs
2 fs
128 fs
1
-90.3 dB to 0 dB