EVALUATION BOARD - Wolfson Microelectronics Co., Ltd.

WM9707 AMR WITH SPDIF OUTPUT

Audio M odem Riser (AM R) Car d Refer e nce Desi gn

Product Preview, August 2000, Rev 1.0

WOLFSON MICROELECTRONICS LTD

Lutton Court, Bernard Terrace, Edinburgh, EH8 9NX, UK

Tel: +44 (0) 131 667 9386

Fax: +44 (0) 131 667 5176

Email: sales@wolfson.co.uk

http://www.wolfson.co.uk

Product Preview data s heets contai n

specifications for product s in the formative

phase of development. These products may

be changed or discontinued without not i ce.

2000 Wolfson Microelectronics Ltd.

DESCRIPTION

The WM9707 AMR is an audio only daughter card

implementation of the Intel Audio Modem Riser (AMR) Rev

1.01 specificationi. This card can also be used in systems

supporting the ACR 1.0 specific at i on vi.

The design supports the connectivity requirements of a

typical sound card. Inputs include Phone, AUX, Video, CD

(Mitsumi and Sony types) and Mic1/2. Outputs include Line

Out, Mono, Headphones and di gi t al SPDIF .

The Audio Codec us ed in the design is the W M9707 Rev 2.1

Stereo Audi o Codecii. The WM9707 is f ully com pl iant with t he

Intel 2.1iii AC’97 Codec specification and supports

primary/ secondary ID selec tion as well as variable audio and

modem sample rates with the additional function of a digital

SPDIF output.

FEATURES

• Reference des i gn for WM9707 Revision 2.1 Audio Codec

with SPDIF output

• AMR audio only add-in c ard conform i ng t o I ntel AMR card

specifications

• May be used in sys t ems s upporting the ACR (A dvanced

Communicat i ons Riser) 1.0 specification

• Analogue connections f or Li ne In, Line Out, MIC-I n and

Headphone

• Design ki t available inc l udi ng schem atics (P ADS) layout

and Gerber files and bill of materials

• Meets Microsoft’s PC’97, P C’ 98 and P C’ 99iv requirements

and advanced audio performance requirements

BLOCK DIAGRAM

VIDEO

AUX

IN CD IN

HEADPHONE AMP

SPDIF

OUT HEADPHONE

OUT LINE

IN MIC

PHONE

WM9707

MIC 2

MONO

OUT

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WOLFSON MICROELECTRONICS LTD PP Rev 1.0 August 2000

INTRODUCTION

The W M9707 AMR is an audio only daughter c ard implem entation of the Int el Audio Modem Riser

(AMR) Rev 1.01 specification. This card will support both primary codec down and primary codec

up configurat i ons. A bloc k diagram of the card is shown in Figure 1.

TO I/O

BRACKET

AUDIO

MINI-

JACKS

WM9707

AC’97

REV 2.1

CODEC

HEADPHONE

AMP

AUDIO/MODEM RISER

+12V MAIN

+5.0V MAIN

+3.3V MAIN

RESETB

BIT_CLK

SYNC

SDATA_IN0

SDATA_OUT

AC-LINK

POWER

PRIMARY_DN#

PCBEEP

MOTHERBOARD

Figure 1 Block Diagram of WM9707 AMR

The card is designed to fully utilise the performance of the WM9707 Stereo Audio Codec and

achieves signal-to-noise ratios of better than 95dB on replay and 92dB for the record path. The

board perform ance is comparable to a t ypical PCI s oundcard.

WM9707 AC’97 AUDIO CODEC

The W M9707 is fully c ompliant with Rev 2. 1 of the AC’97 spec ificati on. The W M9707 compris es a

stereo 18-bit Codec, plus a comprehens i ve analogue mixer with 4 sets of stereo input s, plus phone,

2 microphone, and PC-beep inputs. Additionally, a bi-directional serial interface allows transfer of

control data and DAC and ADC words to and from the AC’97 controller.

WM9707 supports operation as either a master or a slave codec. Configuration of the device as

either a master or as a slave, is selected by tying the CID pin (pin 45 on the package).

Fundamental ly, a device identi fied as a m aster (CID = 0) produces BITCLK as an output, whereas

a slave (CID = 1) must be provi ded with B ITCLK as an input .

The WM9707 incorporates a 5-pin digital serial interface that links it to the motherboard based

AC’97 controller via the A MR bus. A C-link is a bi-direc ti onal, f ixed rate, s erial P CM digit al st ream . I t

handles multiple input and output audio streams, as well as control register access employing a

time division multi pl exed (TDM) scheme.

The DACs and ADCs on this device support all the recommended sample rates specified in the

Intel Rev 2.1 specification for both audio and modem rates. Default rate is 48ks/s. If alternative

rates are selected, the AC’97 interface continues to run at 48k words per second, but data is

transferred across the link in bursts such that the net sample rate selected is achieved. It is up to

the AC’97 Rev 2.1 c ompliant c ontroller to ens ure that data is s upplied to the AC l ink, and rec eived

from the AC link, at the appropriat e rate.

An additional feature that the WM9707 supports that is not a requirement of the Rev2.1

specification from Intel is a digital SPDIF output (pin 48 on the package). The fixed rate, 48kHz

sam ple rate SP DIF output, may be enabl ed through writing to the S PDIF enable bit in register 5Ch

or pulling pin 44 high.

AUDIO MODEM RISER SPECIFICATION

The Audio Modem Riser Specification, originally defined by Intel Corporation, is an open industry

standard s pecification that def i nes a motherboard ri ser board and interface.

The specification supports various configurations for audio and modem partitioning within the PC.

The riser module can include audio only, modem only, or audio and modem functions depending

on the need of the m anufac turing OEM. The bac kbone of the A MR interface i s an A C’97 com pliant

link, power signals and digital IO for defining for example, the status of the codec on the riser

module.

WM9707 AMR Product Preview

WOLFSON MICROELECTRONICS LTD PP Rev 1.0 August 2000

The AMR specif ication has been superseded by the Advanc ed Communi cations Ris er (ACR). This

card is fully compliant with this specification and can be used without modification in systems

designed to the ACR 1.0 specification.

DESIGN IMPLEMENTATION

The WM9707 AMR reference design is implemented using a hierarchical design methodology.

This allows t he design to be spl i t i nto logical parts that are easy to explain and follow.

FUNCTIONAL DIAGRAM

The Functional Diagram on S heet 1 of the schem atic depict s the interconnect ivity of the other five

sheets . The flow of data can easi l y be s een from thi s.

Sheet 1 Functional Diagram

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WOLFSON MICROELECTRONICS LTD PP Rev 1.0 August 2000

AMR_BUS

Signal fl ow in and out of the AMR bus is shown on Sheet 2.

The ground references defined in the AMR specification have been partitioned on the reference

design to provi de a s eparate “clean” analogue ground (A GND) from that used f or the digit al signals

(GND).

The PRIMARY_DN# f unctionalit y defined in the AMR spec ificati on is us ed to gate switch U4 when

the board is plugged into systems which have a primary codec on the motherboard. This puts the

AC97_SDATA_IN0 output int o a high impedance st ate and prevents c ontention on t he AC’97 link.

The codec on the AMR reference design can then act as a slave, outputting data on

AC97_SDATA_IN1, AC97_SDATA_IN2 or AC97_SDATA_IN3, by populating either R54, R56 or

R55 with a 49R9 resistor*. If there is a PRIMARY_DN# codec on the motherboard, the

PRIMARY_DN# will be active (low) and will therefore put the AMR codec into slave mode. To

configure the AMR codec as a m aster codec in this situation, pins 1 and 2 on switch U4 must be

shorted together. In addition, R39 must be depopulated t o avoid forcing the AMR codec into slave

mode.

*Note: In order to operate the W M9703 as a slave device, R35 needs to be populated with 0R and

X1, C33 and C34 need to be unpopulated. A MSTRCLK then needs to be s upplied f rom t he m ast er

device through t he AMR connect or. In sl ave mode, it m ust als o be noted that BITCLK becom es an

input to t he WM9703.

Sheet 2 AMR BUS

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WOLFSON MICROELECTRONICS LTD PP Rev 1.0 August 2000

WM9707

Connection t o the WM9707 codec is shown on Sheet 3.

The CID pin (pin 45) is configured via resistor R39 and R40. W ith the connections as shown (i.e.

R40 = unpopulated and R39 = 1K), the W M9707 will be configured as a m aster device unless the

board is plugged into a system with a primary codec on the motherboard. In which case the

PRIMARY_DN# will be active and force CID low putting the device into slave mode. A further

option for configuring the CID pin is avail abl e by popul ating the R40 si te with a 0ohm resistor. Ref er

to the WM9707 datas heet for further details.

A 6-pin header (J13) is provided for external connect ion of the W M9707 EAPD pin, SPDIF enable,

SPDIF output and BI TCLK signal. These can be us ed as desc ribed in the W M9707 dat asheet. The

SPDIF output can be hardware enabled by inserting a jumper l ink in header J11.

Sheet 3 WM9707 Codec

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WOLFSON MICROELECTRONICS LTD PP Rev 1.0 August 2000

AUDIO_IN

All the external audi o i nput signals t o t he board are shown on Sheet 4.

To prevent damage to the WM9707 and to allow for the ful l 2Vrms input si gnal defi ned in the P C’99

specif ication, all the audio input signals of the reference des ign (apart from MIC) have been pot ted

down by a simple resistor divider. This provides approximately 7dB of attenuation to the input

signal.

The microphone input circuits to the reference design provide support for 3-pin electret (bias on

ring), 2-pin electret (tip and ring shorted together) and 2-pin dynamic microphones. The bias

circui ts for the microphone inputs provide the required drive characteris tics stipulated in the P C’99

System Design Guide, Chapter 17, "A udi o Components". The WM9707 can be program med to gi ve

a +20dB gain on the microphone input path if required – refer t o the datasheet.

Sheet 4 Audio In

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WOLFSON MICROELECTRONICS LTD PP Rev 1.0 August 2000

AUDIO_OUT

The audio outputs from the reference design are shown on Sheet 5.

The Mono and Line Out signals are passed to the output connectors via passive high-pass filters.

This enables the signals to meet the bandwidth suggested in the PC’97 Hardware Design Guide

FAQv and AC couple the outputs. These outputs are capable of driving a 10Kohm load.

The Line Level outputs are buffered through a MAX4167 op-amp which is capable of driving

impedances as low as 32ohms i.e. headphones.

The SPDIF output is buff ered through an SN75LBC179 line driver and t hen transform er coupled to

a phono socket. This arrangement provides the correct impedance matching and drive capability

detailed in the IEC60958 specification. It also gives the board electrical isolation from cable born

interference via the SC982-04 audio transformer.

Sheet 5 Audio Out

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WOLFSON MICROELECTRONICS LTD PP Rev 1.0 August 2000

POWER

The power supply circui try for the reference design is shown on Sheet 6.

The analogue +5V supply to the codec i s provi ded from t he regulated down +12V AMR Bus s upply.

An MC78L05ACD regulator with suitable bypassing is used for this purpose. If the +12V system

supply proves to be excessively noi sy, LINK L2 c an be repl aced with a suitabl e i nductor.

The digital supply is taken directly from the AMR Bus +5VD and +3.3VD power signals. This is

jumper selectabl e on t he board.

Note: For SPDIF output operation on this AMR, the DVDD supply for the board must be +5VD.

The WM9707 does support SPDI F output with DVDD at +3. 3V but due to the SN75LBC179D li ne-

driver having a fixed operating voltage of +5V the SPDI F out put will not work below this level.

In order to allow for possibl e EMC com pliance tes ting is sues with t he board, the connec tions to the

PC bracket have been left as unpopulated sites (L1 and L3). These can easily be linked out or

populated with suitable components at test ti me.

Sheet 6 Power

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WOLFSON MICROELECTRONICS LTD PP Rev 1.0 August 2000

GROUNDING AND LAYOUT CONSIDERATIONS

The pin-out of t he WM9707 allows the s im ple part it ioning of the analogue and di gital ground planes

on the board. Returning ground currents can then flow in their respective ground planes, and the

cross talk bet ween them is m inim ised. A connec tion between the two ground planes is made with a

1.27m m track close t o the codec t o maintain the proper reference potential for each ground pl ane.

In order to allow for possibl e EMC com pliance tes ting is sues with t he board, the connec tions to the

PC bracket have been left as unpopulated sites (L1 and L3). These can easily be linked out or

populated with suitable components at test ti me.

All the front panel 3.5mm jack connections have 220pF capacitors connected to ground to guard

against hi gh frequency noise which might c ause the board to f ai l E MC t ests.

Figure 2 Top Layer Silkscreen

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WOLFSON MICROELECTRONICS LTD PP Rev 1.0 August 2000

Figure 3 Top Layer Figure 4 Bottom Layer

REFERENCES

i Intel A udi o Modem Riser Specific ation, Rev 1.01. S eptember 10, 1998

http://developer.intel.com/pc.supp/platform.ac97/index.htm

vi Adva nced Communications R iser (ACR) sp ec if ication h ttp://www.acrsi g.co m

ii Wolfson Microelectronics, WM9707 AC’97 Rev 2. 1 Audio Codec with SP DI F Output Datasheet,

http://www.wolfson.co.uk/9707fr.htm

iii Intel A udi o Codec AC’97 Component Specific ation, Rev 2.1 http://developer.intel.com/pc. supp/platform/ac97

iv Intel and Microsoft, PC’99 System Des ign Guide http//www.mi cr os oft.com/hwder/desguide/

v The PC’97 Hardware Design Guide FAQ h ttp://www.m icro so ft.com/hwtest/faqs/aud.htm