PCM1741ESLASH2K datasheet(20/24 Pages) TI2

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PCM1741

SBAS175

FIGURE 18. Test Setup for Dynamic Range and SNR Measurements.

S/PDIF

Receiver

Evaluation Board

PCM1741(1)

DEM-DAI1741

2nd-Order

Low-Pass

Filter

Notch Filter

Band Limit

HPF = 22Hz

LPF = 22kHz

C = 1kHz

–3dB = 54kHz

0% Full-Scale,

Dither Off (SNR)

–60dBFS,

1kHz Sine Wave

(Dynamic Range)

S/PDIF

Output

Option = A-Weighting(2)

A-Weight

Filter(1)

rms Mode

Analyzer

and

Display

Digital

Generator

NOTES: (1) Infinite Zero Detect Mute disabled.

(2) Results without A-Weighting will be approxi-

mately 3dB worse.

data is transmitted via a coaxial cable to the digital audio

receiver on the DEM-DAI1741 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 ana-

log output is then taken from the DAC post filter and

connected to the analog analyzer input of the measurement

system. The analog input is band limited using filters resi-

dent 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 DAC. This measurement is designed 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 18, and is similar to the THD+N test

setup discussed previously. The differences include the band

limit 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

DAC. The input to the DAC is all “0”s data, and the DAC’s

Infinite Zero Detect Mute function must be disabled (default

condition at power up for the PCM1741). This ensures that

the delta-sigma modulator output is connected to the output

amplifier circuit so that idle tones (if present) can be ob-

served 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 DAC. 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 18).

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