PCM1737ESLASH2K.B datasheet(27/32 Pages) TI2

27 / 32 page

PCM1737

FIGURE 20. Test Setup for THD+N Measurement.

FIGURE 21. Test Set-Up for Dynamic Range and SNR Measurements.

DAC. The digital generator is set to 24-bit audio word

length and a sampling frequency of 44.1kHz, 96kHz, or

192kHz. The digital generator output is taken from the

unbalanced S/PDIF connector of the measurement system.

The S/PDIF data is transmitted via a coaxial cable to the

digital audio receiver on the DEM-DAI1737 demo board.

The receiver is then configured to output 24-bit data in

either I2S or left-justified data format. The DAC audio

interface format is programmed to match the receiver output

format. The analog output is then taken from the DAC post

filter and connected to the analog analyzer input of the

measurment system. The analog input is band limited using

filters resident in the analyzer. The resulting THD+N is

measured by the analyzer and displayed by the measurement

system.

DYNAMIC RANGE

Dynamic range is specified as A-Weighted, THD+N mea-

sured with a –60dBFS, 1kHz digital sine wave stimulus at

the input of the D/A converter. This measurement is de-

signed to give a good indicator of how the DAC will

perform given a low-level input signal.

The measurement setup for the dynamic range measurement

is shown in Figure 21, and is similar to the THD+N test

setup discussed previously. The differences include the

bandlimit filter selection, the additional A-Weighting filter,

and the –60dBFS input level.

IDLE CHANNEL SIGNAL-TO-NOISE RATIO

The SNR test provides a measure of the noise floor of the

D/A converter. The input to the D/A is all 0’s data, and the

D/A converter’s Infinite Zero Detect Mute function must

be disabled (default condition at power up for the PCM1737).

This ensures that the delta-sigma modulator output is con-

nected to the output amplifier circuit so that idle tones (if

present) can be observed and effect the SNR measurement.

The dither function of the digital generator must also be

disabled to ensure an all ‘0’s data stream at the input of the

D/A converter.

The measurement setup for SNR is identical to that used for

dynamic range, with the exception of the input signal level.

(see the notes provided in Figure 21).

S/PDIF

Receiver

Evaluation Board

PCM1737(1)

DEM-DAI1737

2nd-Order

Low-Pass

Filter

Notch Filter

Band Limit

HPF = 22Hz

LPF = 22kHz

C = 1kHz

–3dB = 54kHz or 108kHz

0% Full Scale,

Dither Off (SNR) or

–60dBFS,

1kHz Sine Wave

(Dynamic Range)

S/PDIF

Output

A-Weight

Filter(2)

RMS Mode

Analyzer

and

Display

Digital

Generator

NOTES: (1) Infinite Zero Detect Mute disabled.

(2) Results without A-Weighting will be

approximately 3dB worse.

S/PDIF

Receiver

Evaluation Board

–3dB = 54kHz or 108kHz

PCM1737

DEM-DAI1737

2nd-Order

Low-Pass

Filter

Notch Filter

Band Limit

HPF = 22Hz

LPF = 30kHz

C = 1kHz

RMS Mode

0dBFS,

1kHz Sine Wave

S/PDIF

Output

Analyzer

and

Display

20kHz

Apogee

Filter

Digital

Generator

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