CALIFORNIA MICRO DEVICES
PACAC97
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
Applications
• Analog audio system for Pentium II Class personal
computers, used in conjunction with Audio Codec,
CS4297 or AD1819A.
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
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
AMP1–
AMP_OUT1
28
R23
33KΩ
27
R23
22KΩ
IN1
26
25
R22
33KΩ
AMP_OUT2
AMP2–
24
R21
22KΩ
IN2
23
GND
22
MIC IN
21
MIC+
20
MIC_AMP_OUT
MIC–
19
R17
100KΩ
18
CD_R
17
CD_GND
16
CD_L
15
R20
4.7KΩ
R19
33KΩ
R13
6.8KΩ
R15
510KΩ
R14
6.8 KΩ
R16
100KΩ
R11
3.4KΩ
R9
6.8KΩ
R18
4.7KΩ
R12
3.4KΩ
R10
6.8KΩ
R4
6.8KΩ
R2
6.8KΩ
R5
6.8KΩ
R7
6.8KΩ
R1
6.8KΩ
R3
6.8KΩ
R6
6.8KΩ
R8
6.8KΩ
1
2
3
4
5
6
AC97MIC
7
GND
8
9
10
11
12
13
AUXIN_L
14
AUXIN_R
LINE_IN_L
AC97LINE_R
GND
LINE_IN_R
AC97LINE_L
AC97AUX_R
AC97CD_GND
AC97CD_L
AC97AUX_L
AC97CD_R
© 2000 California Micro Devices Corp. All rights reserved.
9/27/2000
C0441098
215 Topaz Street, Milpitas, California 95035
Tel: (408) 263-3214
Fax: (408) 263-7846
www.calmicro.com
1
CALIFORNIA MICRO DEVICES
TYPICAL APPLICATIONS CIRCUIT
PACAC97
LINE OUT
LINE IN
PACAC97
GND
+
+
P1
P2
TO
CODEC
R LINE IN
L LINE IN
P3
P4
P5
P6
P7
P8
P9
+
+
+
+
+
+
AUX IN
P10
P11
P12
P13
P14
P28
P27
P26
P25
P24
P23
P22
P21
P20
P19
P18
P17
–
+
GND
–
+
R LINE OUT
FROM
CODEC
L LINE OUT
MIC
MIC IN
R CD IN
TO
CODEC
CD GND IN
L CD IN
R AUX IN
L AUX IN
–
+
P16
P15
GND
MIC BIAS
ATAPI CD IN
GND
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 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,
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 20Hz–20KHz 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.
©2000 California Micro Devices Corp. All rights reserved.
2
215 Topaz Street, Milpitas, California 95035
Tel: (408) 263-3214
Fax: (408) 263-7846
www.calmicro.com
9/27/2000
CALIFORNIA MICRO DEVICES
Channel-to-Channel Crosstalk: Microphone CD
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
PACAC97
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.
2Vms
18 MIC_AMP_OUT
510Ω
17
GND
6.8KΩ
GND
100Ω
6.8KΩ
6 AC97MIC
TP2
10KΩ
GND
5,7,22
GND
8 AC97CD_R
TP1
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
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.
10KΩ
GND
28
33KΩ
27
1KΩ
GND
26
22KΩ
2Vms
GND
25
33KΩ
24
22KΩ
2Vms
GND
23
5, 7, 22
Figure 2*.
© 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
3
CALIFORNIA MICRO DEVICES
Inter-channel Crosstalk: LINE_IN_L – LINE_IN_R
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 10KΩ resistors and pins 5,7 and 22 on the
6.8KΩ
6.8KΩ
PACAC97
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.
6.8KΩ
1 LINE_IN_L
2Vms
6.8KΩ
2 LINE_IN_R
3
TP2
10KΩ
4
TP1
10KΩ
GND
GND
5, 7, 22
GND
GND
GND
Figure 3*.
STANDARD PART ORDERING INFORMATION
Package-Narrow
Pins
Style
28
QSOP
Ordering Part Number
Tubes
Tape & Reel
PACAC97/ T
PACAC97/ R
Part Marking
PACAC97Q
*Measurements made using Tektronix TDS684, 5GHz digitizing oscilloscope with passive probes.
©2000 California Micro Devices Corp. All rights reserved.
4
215 Topaz Street, Milpitas, California 95035
Tel: (408) 263-3214
Fax: (408) 263-7846
www.calmicro.com
9/27/2000
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