WM8739 / WM8739L

Advanced Information

AI Rev 2.2 September 2001

11

DEVICE DESCRIPTION

INTRODUCTION

The WM8739 is a low power analogue to digital converter (ADC) designed for audio recording. Its

features, performance and low power consumption make it ideal for recordable CD players, MP3

players and portable mini-disc players.

The device includes programmable level line inputs, a crystal oscillator, configurable digital audio

interface and a choice of 2 or 3 wire MPU control interface. It is fully compatible and an ideal partner

for a range of industry standard microprocessors, controllers and DSPs.

The WM8739 has low noise line inputs with programmable +12dB to –34.5dB logarithmic volume

adjustments and mute.

The ADC is of a high quality using a multi-bit high-order oversampling architecture delivering

optimum performance with low power consumption. The output from the ADC is available on the

digital audio interface. The ADC includes a digital high pass filter to remove unwanted dc

components from the audio signal.

The design of the WM8739 has given much attention to power consumption without compromising

performance. It includes the ability to power off parts of the circuitry under software control, including

a standby and power off mode.

The device caters for a number of different sampling rates including industry standard 8kHz, 32kHz,

44.1kHz, 48kHz, 88.2kHz and 96kHz.

There are two unique schemes featured within the programmable sample rates of the WM8739:

Normal industry standard 256/384 fs sampling mode may be used. A special USB sampling mode is

also included, whereby all audio sampling rates can be generated from a 12.00MHZ USB clock. The

WM8739’s unique sample rate converter thus allows the user to generate the required sampling rate

clocks from the 12MHz USB clock. The digital filters used for recording are optimised for each

sampling rate used.

The digitised output is available in a number of audio data formats I

which frame sync plus 2 data packed words are transmitted), MSB-First, left justified and MSB-First,

right justified. The digital audio interface can operate in both master or slave modes.

The WM8739 can generate the system master clock using an on-chip crystal oscillator, or

alternatively it can accept an external master clock from the audio system. All features are software

controlled using either a 2 or 3-wire MPU interface.

LINE INPUTS

The WM8739 provides Left and Right channel line inputs (RLINEIN and LLINEIN). The inputs are

high impedance and low capacitance, thus ideally suited to receiving line level signals from external

Hi-Fi and other audio equipment.

Both line inputs include independent programmable volume level adjustments and mutes. The

scheme is illustrated in Figure 8. Passive RF and active Anti-Alias filters are also incorporated within

the line inputs. These prevent high frequencies aliasing into the audio band or otherwise degrading

performance.