Datasheet

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BYPASS AND DECOUPLING CAPACITOR REQUIREMENTS
I/V SECTION
POST LOW-PASS FILTER DESIGN
PCM1738
SBAS174C – FEBRUARY 2002 – REVISED FEBRUARY 2007
Various sized decoupling capacitors can be used, with no special tolerances being required. All capacitors
should be located as close as physically possible to the power supply and reference pins of the PCM1738 to
reduce noise pickup from surrounding circuitry. Aluminum electrolytic capacitors that are designed for hi-fi audio
applications are recommended for larger values, while metal-film or monolithic ceramic capacitors are
recommended for smaller values.
Using the circuit shown in Figure 40 for I/V conversion achieves data-sheet performance. To obtain 0.0005%
THD+N, 117-dB signal-to-noise ratio audio performance, THD+N and input noise performance, an operational
amplifier IC must be considered. Input noise of the operational amplifier directly affects the output noise level of
the application.
All components of the I/V section should be located physically close to the PCM1738 current outputs. All
connections should be made as short as possible to eliminate pickup of radiated noise.
The out-of-band noise level and sampling spectrum level are much lower than typical delta-sigma type DACs,
due to the combination of a high-performance digital filer and the advanced segment DAC architecture. The use
of a second- or third-order filter is recommended for the post low-pass filter (see Figure 40 for a second-order
filter) following the I/V conversion stage. The cutoff frequency of the post LPF is dependent upon the application,
given the variety of sampling rates supported by the CD-DA (f
S
= 44.1 kHz), DVD-M (f
S
= 96 kHz), DVD-A (f
S
=
192 kHz), and SACD (f
S
= 44.1 kHz) systems.
42
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