PCM1606

SLES014B − OCTOBER 2001 − REVISED AUGUST 2002

21

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APPLICATION INFORMATION

D/A output filter circuits

Delta-sigma D/A converters utilize noise shaping techniques to improve in-band signal-to-noise ratio (SNR)

The out-of-band 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 30 and Figure 31 show the recommended external low-pass active filter circuits for dual- and

single-supply applications. These circuits are 2nd-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 your local Texas Instruments sales

office.

Because the overall system performance is defined by the quality of the D/A converters and their associated

analog output circuitry, high-quality audio op amps are recommended for the active filters. Texas Instruments’

OPA2134 and OPA2353 dual op amps are shown in Figure 30 and Figure 31, and are recommended for use

with the PCM1606.

2

3

1

OPA2134

−

+

VOUT

R4

C2

C1

R3

R2

R1

VIN

A

R

2

R

1

Figure 30. Dual-Supply Filter Circuit

2

3

1

OPA2134

−

+

VOUT

R4

C2

C1

R3

R2

R1

VIN

A

R

2

R

1

OPA337

−

+

PCM1606

VCOM

C2

10

µF

+

To Additional

Low-Pass Filter

Circuits

Figure 31. Single-Supply Filter Circuit