WM8738

Production Data

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PD Rev 4.3 November 2004

9

DEVICE DESCRIPTION

INTRODUCTION

The WM8738 is an ADC designed for audio recording. It’s features, performance and low power

consumption make it ideal for recordable CD or DVD players, karaoke, MP3 players and mini-disc

players.

The on-board stereo analogue to digital converter (ADC) is of a high quality using a multi-bit high-

order oversampling architecture delivering optimum performance with low power consumption. The

ADC includes a selectable digital high pass filter to remove unwanted DC components from the audio

signal. The device supports system clock inputs of 256, 384, 512fs or 768fs (fs is the sampling rate)

The output from the ADC is available on the digital audio interface in either I

data formats.

ADC

The WM8738 uses a multi-bit over sampled sigma-delta ADC. A single channel of the ADC is

illustrated in Figure 3.

LIN/RIN

ANALOG

INTEGRATOR

MULTI

BITS

TO ADC DIGITAL FILTERS

Figure 3 Multi-Bit Oversampling Sigma Delta ADC Schematic

The use of multi-bit feedback and high oversampling rates reduces the effects of jitter and high

frequency noise.

The ADC Full Scale input is 1.0V rms at AVDD = 5.0 volts. Any voltage greater than full scale will

possibly overload the ADC and cause distortion. Note that the full scale input tracks directly with

AVDD.

The ADC filters perform true 24 bit signal processing to convert the raw multi-bit oversampled data

from the ADC to the correct sampling frequency to be output on the digital audio interface.

ADC DIGITAL FILTER

The ADC digital filters contain a digital high pass filter, selectable via pin NOHP.

NOHP = 0

Digital high pass filter enabled

NOHP = 1

Digital high pass filter bypassed

The high-pass filter response detailed in Digital Filter Characteristics. The operation of the high pass

filter removes residual DC offsets that are present on the audio signal.