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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-tochannel 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 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 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
SCHEMATIC CONFIGURATION
AMP1- AMP_OUT1 28 R23 33K 27 R23 22K IN1 26 25 R22 33K AMP_OUT2 AMP2- 24 R21 22K IN2 23 GND 22 MIC IN 21 MIC+ 20 MIC_AMP_OUT MIC- 19 R17 100K 18 CD_R 17 CD_GND 16 CD_L 15
R20 4.7K
R19 33K
R13 6.8K R15 510K R14 6.8 K R16 100K
R11 3.4K
R9 6.8K
R18 4.7K
R12 3.4K
R10 6.8K
R4 6.8K R2 6.8K R5 6.8K R7 6.8K
R1 6.8K
R3 6.8K R6 6.8K R8 6.8K
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
(c) 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 0 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,
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.
(c)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 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
PACAC97
10K 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 510
17 GND 6.8K
GND 100 6.8K
6 AC97MIC TP2 10K GND
5,7,22 GND
8 AC97CD_R TP1 10K 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 10K resistor while the IN1 pin is 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.
10K GND 28 33K 27
1K GND 26 22K
2Vms GND 25 33K 24 22K
2Vms GND 23 5, 7, 22
Figure 2*.
(c) 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 10K resistors and pins 5,7 and 22 on the
6.8K 6.8K
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.
6.8K 1 LINE_IN_L 2Vms
6.8K 2 LINE_IN_R 3 TP2 10K 4 TP1 10K 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.
(c)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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