Datasheet

PCM1753
PCM1754
PCM1755
SLES092C – OCTOBER 2003 – REVISED FEBRUARY 2009
www.ti.com
28
THEORY OF OPERATION
The delta-sigma section of the PCM1753/54/55 is based on an 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 32. 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.
The combined oversampling rate of the delta-sigma modulator and the interpolation filter is 64 f
S
.
The theoretical quantization noise performance of the 8-level delta-sigma modulator is shown in Figure 33 and
Figure 34. The enhanced multilevel delta-sigma architecture also has advantages for input clock jitter sensitivity
due to the multilevel quantizer, with the simulated jitter sensitivity shown in Figure 35.
KEY PERFORMANCE PARAMETERS AND MEASUREMENT
This section provides information on how to measure key dynamic performance parameters for the
PCM1753/54/55. In all cases, an Audio Precision System Two Cascade audio measurement system or
equivalent is used to perform the testing.
Total Harmonic Distortion + Noise
Total harmonic distortion + noise (THD+N) is a significant figure of merit for audio D/A converters because it
takes into account both harmonic distortion and all noise sources within a specified measurement bandwidth.
The average value of the distortion and noise is referred to as THD+N.
For the PCM1753/54/55, THD+N is measured with a full-scale, 1-kHz digital sine wave as the test stimulus at
the input of the DAC. The digital generator is set to 24-bit audio word length and a sampling frequency of
44.1 kHz or 96 kHz. The digital generator output is taken from the unbalanced S/PDIF connector of the
measurement system. The S/PDIF data is transmitted via a coaxial cable to the digital audio receiver on the
DEM-DAI1753 demonstration board. The receiver is then configured to output 24-bit data in either I
2
S or
left-justified data format. The DAC audio interface format is programmed to match the receiver output format.
The analog output is then taken from the DAC post filter and connected to the analog analyzer input of the
measurement system. The analog input is band limited using filters resident in the analyzer. The resulting
THD+N is measured by the analyzer and displayed by the measurement system.
+
+
−
Z
–1
+
++
+
+
+
8-Level Quantizer
−
Z
–1
IN
8 f
S
OUT
64 f
S
+
+
Z
–1
+
+
Z
–1
+
Figure 32. Eight-Level Delta-Sigma Modulator