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POWER SUPPLIES AND GROUNDING

DAC OUTPUT FILTER CIRCUITS

–

2

3

1

OPA2134

+

A

R

2

R

1

S0053-02

PCM1609A

SLES145A – AUGUST 2005 – REVISED AUGUST 2006

APPLICATION INFORMATION (continued)

A typical application diagram is shown in Figure 31. The REG1117-3.3 from Texas Instruments is used to

generate the system clock input at SCKI, as well as generating the clock for the audio signal processor.

Series resistors (22-

Ω to 100-Ω) are recommended for SCKI, LRCK, BCK, DATA1, DATA2, DATA3, and

DATA4. The series resistor combines with the stray PCB and device input capacitance to form a low-pass filter

which removes high-frequency noise from the digital signal, thus reducing high-frequency emission.

The PCM1609A requires a 5-V analog supply and a 3.3-V digital supply. The 5-V supply is used to power the

DAC analog and output filter circuitry, whereas the 3.3-V supply is used to power the digital filter and serial

interface circuitry. For best performance, the 3.3-V supply should be derived from the 5-V supply using a linear

regulator (see Figure 31).

Two capacitors are required for supply bypassing (see Figure 30). These capacitors should be located as close

as possible to the PCM1609A package. The 10-

µF capacitors should be tantalum or aluminum electrolytic,

whereas the 0.1-

µF capacitors are ceramic (X7R type is recommended for surface-mount applications).

Delta-sigma DACs use noise-shaping techniques to improve in-band signal-to-noise ratio (SNR) performance at

noise must be low-pass filtered in order to provide optimal converter performance. This is accomplished by a

combination of on-chip and external low-pass filtering.

Figure 32 and Figure 33 show the recommended external low-pass active filter circuits for dual- and

single-supply applications. These circuits are second-order Butterworth filters using the multiple feedback (MFB)

circuit arrangement, which reduces sensitivity to passive component variations over frequency and temperature.

For more information regarding MFB active filter design, see the FilterPro™ MFB and Sallen-Key Low-Pass

Filter Design Program application report (SBFA001), available from the TI Web site (www.ti.com).

Because the overall system performance is defined by the quality of the DACs and their associated analog

output circuitry, high-quality audio operational amplifiers are recommended for the active filters. The OPA2134

and OPA2353 dual operational amplifiers from Texas Instruments are shown in Figure 32 and Figure 33, and

are recommended for use with the PCM1609A.

Figure 32. Dual-Supply Filter Circuit

32

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