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Dynamic Range

S/PDIF

Receiver

Evaluation Board

PCM1748(1)

DEM−DAI1748

2nd−Order

Low−Pass

Filter

Notch Filter

Band Limit

HPF = 22Hz

LPF = 22kHz

f

C = 1kHz

f

− 3dB = 54kHz or 108kHz

0% Full−Scale,

Dither Off (SNR)

− 60dBFS,

1kHz Sine Wave

(Dynamic Range)

S/PDIF

Output

A−Weight

Filter(2)

rms Mode

Analyzer

and

Display

Digital

Generator

Idle-Channel Signal-to-Noise Ratio

PCM1748

SBAS165B – MAY 2001 – REVISED APRIL 2005

KEY PERFORMANCE PARAMETERS AND MEASUREMENT (continued)

Dynamic range is specified as A-weighted, THD+N measured with a –60-dBFS, 1-kHz digital sine-wave stimulus

at the input of the DAC. This measurement is designed to give a good indicator of how the DAC performs given a

low-level input signal.

The measurement setup for the dynamic range measurement is shown in Figure 36 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 –60-dBFS input level.

(1)

Infinite-zero-detect mute disabled

(2)

Results without A-weighting are approximately 3 dB worse.

Figure 36. Test Setup Dynamic Range and SNR Measurements

The SNR test provides a measure of the noise floor of the DAC. The input to the DAC is all-0s data, and the

DAC infinite-zero-detect mute function must be disabled (default condition at power up for the PCM1748). This

ensures that the delta-sigma modulator output is connected to the output amplifier circuit so that idle tones (if

present) can be observed and affect the SNR measurement. The dither function of the digital generator must

also be disabled to ensure an all-0s 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 36).

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