2000 California Micro Devices Corp. All rights reserved.
9/27/2000
1
PACAC97
CALIFORNIA MICRO DEVICES
215 Topaz Street, Milpitas, California 95035 Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com
PC Audio Resistor Network
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 compli-
ant Codec as well as gain setting resistors for head-
phone 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 gain-
setting resistors for the headphone and microphone
amplifiers. The PACAC97 provides exceptional inter-
channel 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
SCHEMATIC CONFIGURATION
C0441098
R23
33K
28
AMP_OUT1
IN1
AMP2
IN2
GND
LINE_IN_L
AC97LINE_R
LINE_IN_R
AC97LINE_L
GND
AC97CD_R
AC97CD_L
AC97CD_GND
AC97MIC
MIC IN
MIC+
MIC
CD_R
CD_GND
CD_L
MIC_AMP_OUT
AMP_OUT2
AMP1
27
R23
22K
R22
33K
25
26
24
23
22
21
20
19
18
17
16
15
R21
22K
R20
4.7K
R19
33K
R15
510K
R16
100K
R18
4.7K
R17
100K
R13
6.8K
R2
6.8K
R1
6.8K
1
2
3
4
5
6
8
9
10
14
12
11
R4
6.8K
R3
6.8K
R14
6.8 K
R11
3.4K
R12
3.4K
R9
6.8K
R10
6.8K
R7
6.8K
R8
6.8K
AC97AUX_R
AC97AUX_L
AUXIN_R
GND
7
13
R5
6.8K
R6
6.8K
AUXIN_L
2000 California Micro Devices Corp. All rights reserved.
9/27/2000
215 Topaz Street, Milpitas, California 95035 Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com
2
PACAC97
CALIFORNIA MICRO DEVICES
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 0
jumper connection, if so
desired. Bias voltage needs to be provided for con-
denser 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,
TYPICAL APPLICATIONS CIRCUIT
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. LINE-
IN, LINE-OUT and MIC jack signals are externally de-
coupled 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 20Hz20KHz audio band. Three examples
are provided to illustrate inter-channel and channel-
channel cross talk measurements that have been
performed on the PACAC97. Similar measurements were
performed for all audio functions deemed critical be-
cause of layout considerations.
LINE IN
LINE OUT
GND
GND
GND
MIC
GND
PACAC97
+
P1
R LINE IN
P28
P2
P27
P2
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
P15
+
MIC IN
+
R CD IN
+
CD GND IN
+
L CD IN
TO
CODEC
+
R AUX IN
+
L AUX IN
+
L LINE IN
ATAPI CD IN
TO
CODEC
FROM
CODEC
+
+
+
MIC BIAS
L LINE OUT
R LINE OUT
2000 California Micro Devices Corp. All rights reserved.
9/27/2000
3
PACAC97
CALIFORNIA MICRO DEVICES
215 Topaz Street, Milpitas, California 95035 Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com
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 10K
resistor while the IN1 pin is
Figure 2*.
terminated with a 1K
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.
510
100
10K
6.8K
6.8K
5,7,22
TP2
18 MIC_AMP_OUT
2Vms
AC97CD_R
6 AC97MIC
8
17
TP1
10K
GND
GND
GND
GND
GND
Figure 1*.
10K
33K
22K
33K
22K
26
25
24
23
5, 7, 22
27
28
1K
2Vms
2Vms
GND
GND
GND
GND
Figure 1 shows a cross talk measurement of the micro-
phone 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
10K
load resistor while pins 5,7,17 and 22 on the
device are grounded. Crosstalk measured over the audio
band of 20Hz20KHz is in excess of 90dB.
Channel-to-Channel Crosstalk: Microphone CD
Inter-channel Crosstalk: AMP2-AMP1 (LINE_OUT)
2000 California Micro Devices Corp. All rights reserved.
9/27/2000
215 Topaz Street, Milpitas, California 95035 Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com
4
PACAC97
CALIFORNIA MICRO DEVICES
Figure 3*.
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
are loaded by 10K
resistors and pins 5,7 and 22 on the
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.
6.8K
6.8K
6.8K
6.8K
10K
1 LINE_IN_L
2 LINE_IN_R
3
TP2
4
5, 7, 22
2Vms
GND
GND
GND
GND
10K
TP1
GND
Inter-channel Crosstalk: LINE_IN_L LINE_IN_R
N
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*Measurements made using Tektronix TDS684, 5GHz digitizing oscilloscope with passive probes.
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