PCM4108CPAPT datasheet(34/39 Pages) TI

34 / 39 page

PCM4108

SBAS354 − JUNE 2005

www.ti.com

APPLICATIONS INFORMATION

This section provides practical information for system and

hardware engineers that are designing in the PCM4108.

BASIC CIRCUIT CONFIGURATIONS

Figure 19 shows a typical circuit configuration for the

PCM4108 operated in Standalone and Software modes.

Power

supply

bypass

and

reference

decoupling

capacitors should be placed as close to the corresponding

PCM4108 pins as possible. Separate power supplies are

utilized for the analog and digital sections, with +5V

required for the PCM4108 analog supplies and +3.3V

required for the digital supply.

The +5V analog supply may be derived from a higher

valued, positive analog power supply using a linear

voltage regulator, such as the REG103 available from

Texas Instruments. The +3.3V digital supply can be

derived from a primary +5V digital supply using a linear

voltage regulator, such as the REG1117, also from TI. The

PCM4108EVM evaluation module provides an example of

how the common ground with separate supply approach

can be successfully implemented. The PCM4108EVM

User’s Guide includes schematics and PCB layout plots

for reference. The evaluation module is available through

Texas Instruments’ distributors and sales representatives,

or may be ordered online through the TI eStore, which can

accessed

through

the

home

page

http://www.ti.com.

The master clock generator supplies the system clock for

the PCM4108, as well as the audio data source, such as

a digital signal processor. The LRCK and BCK audio

clocks should be derived from the system clock, in order

to ensure synchronous operation.

ANALOG OUTPUT FILTER CIRCUITS

An external output filter is recommended for each

differential output pair. The external output filter further

reduces the out-of-band noise energy produced by the

delta-sigma modulator, while providing band limiting

suitable for audio reproduction. A 2nd-order Butterworth

low-pass filter circuit with a −3dB corner frequency from

50kHz to 180kHz is recommended.

The configuration of the output filter circuit depends on

whether a single-ended or differential output is required.

Single-ended outputs are commonly used in consumer

playback systems, while differential or balanced outputs

are used in many professional audio applications, such as

recording or broadcast studios and live sound systems.

Figure 20 illustrates an active filter circuit that uses a single

op amp to provide both 2nd-order low-pass filtering and

differential to single-ended signal conversion. This circuit

is used on the PCM4108EVM evaluation module and

meets the published typical Electrical Characteristics for

dynamic

performance. The single-ended output is

convenient for connecting to both headphone and power

amplifiers when used for listening tests.

The quality of the op amp used is this circuit is important,

as many devices will degrade the dynamic range and/or

total

harmonic

distortion

plus

noise

(THD+N)

specifications for the PCM4108. An NE5534A is shown in

Figure 20 and provides both low noise and distortion.

Bipolar input op amps with equivalent specifications

should produce similar measurement results. Devices that

exhibit higher equivalent input noise voltage, such as the

Texas Instruments OPA134 or OPA604 families, will

produce

lower

dynamic

range

measurements

(approximately 1dB to 2dB lower than the typical

PCM4108 specification), while having little or no impact on

the THD+N specification when measuring a full-scale

output level.

Figure 21 illustrates a fully-differential output filter circuit

suitable for use with the PCM4108. The OPA1632 from

Texas Instruments provides the fully differential signal path

in this circuit. The OPA1632 features very low noise and

distortion,

making

suitable

for

high-end

audio

applications.

Texas

Instruments provides a free software tool,

FilterPro

t, used to assist in the design of active filter

circuits. The software supports design of multiple

feedback (MFB), Sallen-Key, and fully differential filter

circuits. FilterPro is available from the TI web site.

Additionally, TI document number SBAF001A, also

available from the TI web site, provides pertinent

application information regarding the proper usage of the

FilterPro program.

PCM4108CPAPT Datasheet(PDF) 34 Page - Texas Instruments

PCM4108CPAPT Datasheet(HTML) 34 Page - Texas Instruments

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