Production Data

WM9704Q

WOLFSON MICROELECTRONICS LTD

PD Rev 2.3 January 2001

11

DEVICE DESCRIPTION

INTRODUCTION

The WM9704Q Codec comprises two channels of ADC and four channels of DAC. This enables a

four channel surround sound solution to be implemented (Quad mode). A symmetric mixer is

provided which allows analogue signals such as CD inputs to be mixed into both front and rear

channel paths simultaneously.

Alternatively, the device can be configured in 6-channel I

GPIO pins to output rear channel and centre and LFE data in I

(WM8725) to build a full 6 channel surround sound solution.

The WM9704Q can also be configured as a standard AC’97 Revision 2.1 compliant device, including

line level outputs and with support for the variable rate audio sample rates (2 channel mode).

The WM9704Q comprises a stereo 18-bit Codec, (that is, 2 ADCs and 2 DACs) plus two additional

DACs. The WM9704Q also has a comprehensive analogue mixer with 4 sets of stereo inputs, plus

phone, 2 microphone, and PC-beep inputs. On-chip reference circuits generate the necessary bias

voltages for the device, and a bi-directional serial interface allows transfer of control data and DAC

and ADC words to and from the AC’97 controller. The WM9704Q supports 18-bit resolution within the

DAC and ADC functions, but the AC’97 serial interface specification allows any word length up to 20-

bits to be written to, or read from, the AC’97 Codec. These words are MSB justified, and any LSBs

not used will simply default to 0. Normally it is anticipated that 16-bit words will be used in most PC

type systems. Therefore, for the DAC, 16-bit words will be downloaded into the Codec from the

controller, along with padding of 0s to make the 16-bit word up to 20-bit length. In this case, the

WM9704Q will process the 16-bit word along with 0 padding bits in the 2 LSB locations (to make 18-

bit). At the ADC output, WM9704Q will provide an 18-bit word, again with 0s in the two LSB locations

(20-bit). The AC’97 controller will then ignore the 4 LSBs of the 20-bit word. When the WM9704Q is

interrogated, it responds indicating it is an 18-bit device.

The WM9704Q has the ADC and DAC functions implemented using oversampled, or sigma-delta

converters, and uses on-chip digital filters to convert these 1-bit signals to and from the 48ks/s 16/18-

bit PCM words that the AC’97 controller requires. The digital parts of the device are powered

separately from the analogue to optimise performance, and 3.3V digital and 5V analogue supplies

may be used on the same device to further optimise performance. Digital IOs are 5V tolerant when

the analogue supplies are 5V, so the WM9704Q may be connected to a controller running on 5V

supplies, but use 3.3V for the digital section of WM9704Q. WM9704Q is also capable of operating

with a 3.3V supply only (digital and analogue).

An internally generated midrail reference is provided at pin CAP2 which is used as the chip

reference. This pin should be heavily decoupled.

Additional features added to the Intel AC’97 specification, such as the EAPD (External Amplifier

Power Down) bit, internal connection of PC-beep to the outputs in the case where the device is reset,

are supported, along with optional features such as variable sample rate support.

OPERATIONAL MODES

The WM9704Q is pin programmable to operate in the following modes:

MODE1

PIN

MODE0

PIN

OPERATIONAL

MODE

RESULTING DEVICE BEHAVIOUR

0

0

2-channel

Rev 2.1 compliant codec (2-channel mode)

0

1

6-channel I

Rev 2.1 compliant codec (6-channel mode)

1

0

Quad mode

Quad DAC mode (with I

Table 1 Operating Modes