THEORY OF OPERATION
KEY PERFORMANCE PARAM-
ETERS AND MEASUREMENT
This section provides information on how to measure key
dynamic performance parameters for the PCM1600 and
PCM1601. In all cases, an Audio Precision System Two
Cascade or equivalent audio measurement system is utilized
to perform the testing.
The delta-sigma section of PCM1600 is based on a 8-level
amplitude quantizer and a 4th-order noise shaper. This
section converts the oversampled input data to 8-level delta-
sigma format.
A block diagram of the 8-level delta-sigma modulator is
shown in Figure 19. This 8-level delta-sigma modulator has
the advantage of stability and clock jitter sensitivity over the
typical one-bit (2 level) delta-sigma modulator.
TOTAL HARMONIC DISTORTION + NOISE
The combined oversampling rate of the delta-sigma modu-
lator and the internal 8x interpolation filter is 64fS for all
system clock combinations (256/384/512/768fS).
Total Harmonic Distortion + Noise (THD+N) is a significant
figure of merit for audio D/A converters, since it takes into
account both harmonic distortion and all noise sources
within a specified measurement bandwidth. The true rms
value of the distortion and noise is referred to as THD+N.
The theoretical quantization noise performance of the
8-level delta-sigma modulator is shown in Figure 20. The
enhanced multi-level delta-sigma architecture also has ad-
vantages for input clock jitter sensitivity due to the multi-
level quantizer, with the simulated jitter sensitivity shown in
Figure 21.
For the PCM1600 and PCM1601 D/A converters, THD+N is
measured with a full scale, 1kHz digital sine wave as the test
stimulus at the input of the DAC. The digital generator is set
–
+
+
Z–1
Z–1
Z–1
Z–1
8fS
+
+
+
+
8-Level Quantizer
64fS
FIGURE 19. Eight-Level Delta-Sigma Modulator.
CLOCK JITTER
125
0
–20
120
115
110
105
100
95
–40
–60
–80
–100
–120
–140
–160
–180
90
85
80
0
100
200
300
400
500
600
0
1
2
3
4
5
6
7
8
Jitter (ps)
Frequency (fS)
FIGURE 20. Quantization Noise Spectrum.
FIGURE 21. Jitter Sensitivity.
®
27
PCM1600, PCM1601
BB [ BURR-BROWN CORPORATION ]
