Datasheet PACAC97Q Datasheet (California Micro Devices)

CALIFORNIA MICRO DEVICES

PC Audio Resistor Network

PACAC97

Features

• Signal conditioning and gain setting resistors for
all standard audio functions

• Low noise thin film resistors ±1% match

• Better than 1% matching between channels

• Gain modification by changing resistors
externally

• Better than –90dB inter-channel and channel-to-

channel crosstalk

• Single 28-pin QSOP package

• Saves board space and reduces assembly cost

Product Description

High quality audio systems have become standard for
most personal computers. Furthermore, the audio
functions have been migrating to the motherboard,
putting pressure on available board space. The
PACAC97 provides the components necessary for signal
conditioning of analog audio inputs for an AC97 compli­ant Codec as well as gain setting resistors for head­phone and microphone amplifiers. Since analog signal
levels can be as high as 2Vrms, the PACAC97 provides
6dB of attenuation (to 1Vrms) for LINE-IN, AUX, and CD
inputs. The CD line level inputs of the PACAC97 have an
additional ground signal, CD_GND, that supports the
pseudo differential amplifier present in AC97 Codecs.
This feature facilitates attenuation of common mode
ground noise typically present at the output of CD ROM

Applications

• Analog audio system for Pentium II Class personal
computers, used in conjunction with Audio Codec,
CS4297 or AD1819A.

drives. Connecting the CD pins as indicated in the
application circuit provides attenuation of common mode
noise from the CD inputs, thereby producing a higher
quality CD signal. Finally, the device provides gain­setting resistors for the headphone and microphone
amplifiers. The PACAC97 provides exceptional inter­channel and channel-to-channel crosstalk attenuation
necessary for high quality audio.

The PACAC97 provides performance, high reliability, and
low cost through manufacturing efficiency, utilizing high
volume and low cost IC manufacturing and processes.
The process yields low noise and highly stable resistors
demanded in audio applications. In addition, the 28-pin
QSOP package is an industry standard that is easy to
handle in manufacturing and provides package reliability

AMP_OUT1 IN1 AMP2– IN2 GND

28

27

R23

R23

33KΩ

22KΩ

R4

6.8KΩ

R2

6.8KΩ

R3

R1

6.8KΩ

6.8KΩ

123456 89 10 141211

LINE_IN_L AC97LINE_R

LINE_IN_R AC97LINE_L

© 2000 California Micro Devices Corp. All rights reserved.

9/27/2000

215 Topaz Street, Milpitas, California 95035 Tel: [phone] Fax: [phone] www.calmicro.com

SCHEMATIC CONFIGURATION

R19
33KΩ

AC97CD_L

MIC_AMP_OUTAMP_OUT2AMP1–

R17

100KΩ

R18

4.7KΩ

AC97AUX_R

R13

6.8KΩ

R15
510KΩ

R16
100KΩ

R14

6.8 KΩ

AC97AUX_L AUXIN_R

AUXIN_L

R11

3.4KΩ

R12

3.4KΩ

R5

6.8KΩ

R6

6.8KΩ

MIC IN MIC+ MIC– CD_R CD_GND CD_L

2526 24 23 22 21 20 19 18 17 16 15

R22

R21

33KΩ

GND

22KΩ

AC97MIC

GND

R20

4.7KΩ

7 13

AC97CD_GND

AC97CD_R

R9

6.8KΩ

R10

6.8KΩ

R7

6.8KΩ

R8

6.8KΩ

C0441098

1

CALIFORNIA MICRO DEVICES

TYPICAL APPLICATIONS CIRCUIT

PACAC97

LINE OUT

TO

CODEC

TO

CODEC

R LINE IN

L LINE IN

MIC IN

R CD IN

CD GND IN

L CD IN

R AUX IN

L AUX IN

LINE IN

+

+

+

+

+

+

+

–

PACAC97

GND

+

+

P1

P2 P27P2 P27

P3 P26

P4 P25

P5 P24

P6 P23

P7 P22

P8 P21

P9 P20

P10 P19

P11 P18

P12 P17

P13 P16

P14

AUX IN

GND

P28

P15

ATAPI CD IN

+

–

+–

GND

R LINE OUT

L LINE OUT

MIC BIAS

GND

FROM
CODEC

MIC

R1, R2 and R3, R4 provide 6dB pads for the LINE-IN
stereo signals in order to scale a 2Vrms input to a
1Vrms Codec input. Similarly, R5, R6, R7, R8 and R9,
R10, R13, R14 provide the necessary attenuation for
the AUX and CD signals going to the Codec. With an
external Operational Amplifier, resistors R17 and R18
provide nominally 27dB of gain for the microphone
signal (non-inverting amp). R15, R16 divide down the
microphone output signal, thereby protecting the Codec
from any transient voltages coming from the microphone
amplifier. This is particularly important if this amplifier
runs of

+12V supplies. The R15/R16 divider can be
bypassed with an external 0Ω jumper connection, if so
desired. Bias voltage needs to be provided for con­denser type microphones. Resistors R21, R22, R23 and
R24 are the gain setting resistors for the headphone
amplifier. The gain is set at 3.5dB with the output
amplifiers in an inverting configuration. The output gain
can be changed with the addition of external resistors,

©2000 California Micro Devices Corp. All rights reserved.

2

215 Topaz Street, Milpitas, California 95035 Tel: [phone] Fax: [phone] www.calmicro.com

allowing for maximum design flexibility. The resistors are
referenced as Amp1 and Amp2 rather then Left and
Right to provide added flexibility for board layout. LINE­IN, LINE-OUT and MIC jack signals are externally de­coupled in order to minimize EMI.

Crosstalk Test Circuit

Cross talk is a critical parameter for high quality audio.
Specifically, stereo cross talk (Left to Right) and channel
to channel cross talk must be minimized. For this reason
much attention has been paid to the circuit layout of the
PACAC97 in order to provide the necessary damping for
signals in the 20Hz–20KHz audio band. Three examples
are provided to illustrate inter-channel and channel­channel cross talk measurements that have been
performed on the PACAC97. Similar measurements were
performed for all audio functions deemed critical be­cause of layout considerations.

9/27/2000

CALIFORNIA MICRO DEVICES

Channel-to-Channel Crosstalk: Microphone CD

PACAC97

Figure 1 shows a cross talk measurement of the micro­phone to the Right Codec CD signal. The microphone
amplifier output pin (pin 18) is driven with a 2Vrms
signal. The Right CD Codec signal is terminated by a

2Vms

GND

18 MIC_AMP_OUT

510Ω

100Ω

6 AC97MIC 8

TP2

10KΩ

GND

Figure 1*.

Inter-channel Crosstalk: AMP2-AMP1 (LINE_OUT)

Figure 2 shows a crosstalk measurement of Left to Right
channel for the gain setting resistors of the headphone
amplifier (referred to as AMP1 and AMP2). The IN2
(output from Codec) and the AMP_OUT2 pin (pins 23
and 25) are driven by a 2Vrms source. The AMP_OUT1
is terminated by a 10KΩ resistor while the IN1 pin is

10KΩ load resistor while pins 5,7,17 and 22 on the
device are grounded. Crosstalk measured over the audio
band of 20Hz–20KHz is in excess of –90dB.

17

6.8KΩ

6.8KΩ

5,7,22

GND

GND

GND

AC97CD_R

TP1

10KΩ

terminated with a 1KΩ resistor which represents the
output impedance of the LINE_OUT output of the Codec.
Pins 5, 7, 22 and 24, on the device are grounded.
Crosstalk measured over the audio band of
20Hz to 20KHz is in excess of –90dB.

© 2000 California Micro Devices Corp. All rights reserved.

9/27/2000

215 Topaz Street, Milpitas, California 95035 Tel: [phone] Fax: [phone] www.calmicro.com

10KΩ

GND GND

28

33KΩ 22KΩ 33KΩ 22KΩ

1KΩ

26 25 24 23 5, 7, 2227

Figure 2*.

2Vms 2Vms

GND

GND

3

CALIFORNIA MICRO DEVICES

Inter-channel Crosstalk: LINE_IN_L – LINE_IN_R

PACAC97

Figure 3 shows a cross talk measurement for Left to
Right channel for LINE_IN signals. The LINE_IN_L input
is driven by a 2Vrms source. Both AC97 LINE signals

device are grounded. Crosstalk from
AC97LINE_IN_L to AC97LINE_IN_R, measured over the
audio band of 20Hz to 20KHz, is in excess of –90 dB.

are loaded by 10KΩ resistors and pins 5,7 and 22 on the

6.8KΩ

6.8KΩ

1 LINE_IN_L 2 LINE_IN_R 3

2Vms

6.8KΩ

6.8KΩ

GND

10KΩ

GND

TP2

4

10KΩ

GND

5, 7, 22

TP1

GNDGND

Figure 3*.

egakcaPworraN-rebmuNtraPgniredrO

sniPelytSsebuTleeR&epaTgnikraMtraP

82POSQT/79CACAPR/79CACAPQ79CACAP

*Measurements made using Tektronix TDS684, 5GHz digitizing oscilloscope with passive probes.

NOITAMROFNIGNIREDROTRAPDRADNATS

©2000 California Micro Devices Corp. All rights reserved.

4

215 Topaz Street, Milpitas, California 95035 Tel: [phone] Fax: [phone] www.calmicro.com

9/27/2000