LOW-PASS FILTER AND DIFFERENTIAL-TO-SINGLE-ENDED CONVERTER FOR DAC OUTPUTS

10 F

m

47W

R

1

R

3

R

2

C

2

AnalogOutput

(2V

)

RMS

VOUTx+

(4V )

PP

10 F

m

R

1

R

3

VOUTx-

(4V )

PP

C

2

R

2

C

1

47W

R

1

R

3

R

2

C

2

AnalogOutput

(2V

)

RMS

VOUTx+

(4V )

PP

R

1

R

3

VOUTx-

(4V )

PP

C

2

R

2

C

1

PCM1789

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

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

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

Figure 38 and Figure 39 show the recommended external differential-to-single-ended converter with low-pass

active filter circuits for ac-coupled and dc-coupled applications. These circuits are second-order Butterworth

filters using a multiple feedback (MFB) circuit arrangement that reduces sensitivity to passive component

variations over frequency and temperature. For more information regarding MFB active filter designs, please

refer to Applications Bulletin SBAA055, Dynamic Performance Testing of Digital Audio D/A Converters, available

from the TI web site (www.ti.com) or your local Texas Instruments' sales office.

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

circuitry, high-quality audio op amps are recommended for the active filters. Texas Instruments’ OPA2134,

OPA2353, and NE5532A dual op amps are shown in Figure 38 and Figure 39, and are recommended for use

with the PCM1789.

Figure 38. AC-Coupled, Post-LPF and Differential to Single-Ended Buffer

Figure 39. DC-Coupled, Post-LPF and Differential to Single-Ended Buffer

Copyright © 2008, Texas Instruments Incorporated

Submit Documentation Feedback

33

Product Folder Link(s): PCM1789