Datasheet

PCM1741
20
SBAS175
FIGURE 18. Test Setup for Dynamic Range and SNR Measurements.
S/PDIF
Receiver
Evaluation Board
PCM1741
(1)
DEM-DAI1741
2nd-Order
Low-Pass
Filter
Notch FilterBand Limit
HPF = 22Hz
LPF = 22kHz
f
C
= 1kHz
f
–3dB
= 54kHz
0% Full-Scale,
Dither Off (SNR)
–60dBFS,
1kHz Sine Wave
(Dynamic Range)
S/PDIF
Output
Option = A-Weighting
(2)
A-Weight
Filter
(1)
rms Mode
Analyzer
and
Display
Digital
Generator
NOTES: (1) Infinite Zero Detect Mute disabled.
(2) Results without A-Weighting will be approxi-
mately 3dB worse.
data is transmitted via a coaxial cable to the digital audio
receiver on the DEM-DAI1741 demo 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 ana-
log 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 resi-
dent in the analyzer. The resulting THD+N is measured by
the analyzer and displayed by the measurement system.
DYNAMIC RANGE
Dynamic range is specified as A-Weighted, THD+N mea-
sured with a –60dBFS, 1kHz digital sine wave stimulus at
the input of the DAC. This measurement is designed to give
a good indicator of how the DAC will perform given a low-
level input signal.
The measurement setup for the dynamic range measurement
is shown in Figure 18, and is similar to the THD+N test
setup discussed previously. The differences include the band
limit filter selection, the additional A-Weighting filter, and
the –60dBFS input level.
IDLE CHANNEL SIGNAL-TO-NOISE RATIO
The SNR test provides a measure of the noise floor of the
DAC. The input to the DAC is all “0”s data, and the DAC’s
Infinite Zero Detect Mute function must be disabled (default
condition at power up for the PCM1741). This ensures that
the delta-sigma modulator output is connected to the output
amplifier circuit so that idle tones (if present) can be ob-
served and effect the SNR measurement. The dither function
of the digital generator must also be disabled to ensure an all
“0”s data stream at the input of the DAC. The measurement
setup for SNR is identical to that used for dynamic range,
with the exception of the input signal level (see the notes
provided in Figure 18).