CS4329 Datasheet, PDF (13/36 Pages) Cirrus Logic – 20-Bit, Stereo D/A Converter for Digital Audio

CS4329
Figure 13 displays the CS4329 output noise spec-
trum. The noise beyond the audio band can be fur-
ther reduced with additional analog filtering. The
applications note "Design Notes for a 2-Pole Filter
with Differential Input " discusses the second-order
Butterworth filter and differential to signal-ended
converter which was implemented on the CS4329
evaluation board, CDB4329. The CS4329 filter is a
linear phase design and does not include phase or
amplitude compensation for an external filter.
Therefore, the DAC system phase and amplitude
response will be dependent on the external analog
circuitry.
CS4329
AOUT+
AOUT-
(2.2 + 1.4)V
2.2V
(2.2 - 1.4)V
(2.2 + 1.4)V
2.2V
(2.2 - 1.4)V
Full Scale Input level= (AIN+) - (AIN-)= 5.66 Vpp
Figure 12. Full Scale Input Voltage
0
-20
-40
-60
-80
-100
-120
-140
-160
0 .25 .50 .75 1.00 1.25 1.50 1.75 2.00 2.25 2.50
Frequency (x Fs)
Figure 13. CS4329 Output Noise Spectrum
Grounding and Power Supply Decoupling
As with any high resolution converter, the CS4329
requires careful attention to power supply and
grounding arrangements to optimize performance.
Figure 1 shows the recommended power arrange-
ments with VA connected to a clean +5volt supply.
VD should be derived from VA through a 10 Ω re-
sistor. VD should not be used to power additional
digital circuitry. All mode pins which require VD
should be connected to pin 6 of the CS4329. All
mode pins which require DGND should be con-
nected to pin 5 of the CS4329. Pins 4 and 5, AGND
and DGND, should be connected together at the
CS4329. DGND for the CS4329 should not be con-
fused with the ground for the digital section of the
system. The CS4329 should be positioned over the
analog ground plane near the digital/analog ground
plane split. The analog and digital ground planes
must be connected elsewhere in the system. The
CS4329 evaluation board, CDB4329, demonstrates
this layout technique. This technique minimizes
digital noise and insures proper power supply
matching and sequencing. Decoupling capacitors
should be located as near to the CS4329 as possi-
ble.
Performance Plots
The following collection of CS4329 measurement
plots were taken from the CDB4329 evaluation
board using the Audio Precision Dual Domain Sys-
tem Two.
Figure 14 shows the frequency response at a
48 kHz sample rate. The response is flat to 20 kHz
+/-0.1 dB as specified.
Figure 15 shows THD+N versus signal amplitude
for a 1 kHz 20-bit dithered input signal. Notice that
the there is no increase in distortion as the signal
level decreases. This indicates very good low-level
linearity, one of the key benefits of delta-sigma
digital to analog conversion.
Figure 16 shows a 16 k FFT of a 1 kHz full-scale
input signal. The signal has been filtered by a notch
filter within the System Two to remove the funda-
mental component of the signal. This minimizes
the distortion created in the analyzer analog-to-dig-
ital converter. This technique is discussed by Audio
DS153F1
13