AN49 [INTERSIL]
Digital Audio Amplifier Gain Control using Logarithmic; 使用对数数字音频放大器增益控制
| 型号： | AN49 |
| 厂家： | 
Intersil |
| 描述： | Digital Audio Amplifier Gain Control using Logarithmic |
| 文件： | 总2页 (文件大小：156K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Digital Audio Amplifier Gain Control using Logarithmic
Intersil Digitally Controlled Potentiontiometers (XDCPs)
®
Application Note
April 21, 2005
AN49.0
Author: Applications Staff
Often the power amplifier stage of a communications device
is located some distance from the control panel. The typical
solution is to mount the volume control on the front panel
and run a pair of shielded cables back to the power amplifier
stage. A better solution is to use the Intersil X9314
logarithmic taper digitally controlled potentiometer. This
completely eliminates the need for shielded cables since the
digital pot can be located on the printed circuit board near
the low level input stages of the power amplifier. The
up/down volume switches can be located yards away as
these are merely low speed TTL signals.
The frequency of the oscillation (and consequently the
speed at which the volume can be controlled) is determined
by C1 and R1. The values shown will advance the X9314
through all 32 wiper taps in about 5 seconds. R1 can be
changed from 5KW to 1MW to suit your preference. When
the pushbutton switches are released, R2 and C2 delay the
release of the X9314 chip select in order to ensure that the
last increment pulse is written.
The X9314W needs little else to apply it to most audio
circuits, but C9 has been included here to remove any DC
component that may be present on the input signal. Also,
lowpass filter R7 and C8 removes residual high frequency
noise from the digital pots’ internal charge pumps.
Circuit Description
Figure 1 shows the X9314 with the low voltage LM386 power
amplifier. This circuit will produce 250mW of audio power
with only a 5V DC source. Figure 2 is a similar circuit that
uses the higher power LM380 and is capable of delivering
over 1W of audio if a 12V DC source is available. Either
circuit will provide plenty of sound for intercom,
The LM380 and LM386 power amplifiers have fixed gains of
34dB and 26dB respectively. The gain of the LM386 can be
increased to 46dB (X200) by connecting a 10µF capacitor
from pins 1 to 8. The positive pole of the capacitor should be
connected to pin 1. The output snubber network (R6 and C5)
is required for stability and should be located close to the
output pin of the power amplifier. These amplifiers have fairly
high gain and wide bandwidths, so be careful with PCB trace
lengths. All connections to these amplifiers should be as
short and direct as possible.
communications, or monitoring applications. The 1W circuit
would be preferred when higher ambient noise is present,
such as in an automobile.
A 74HC132 quad Schmitt nand gate (U2) plus a few
discretes are all that are required to interface to U1, the
X9314W 10kΩ XDCP. When either pushbutton switch, S1 or
S2, is depressed, U2A output will be HIGH. This immediately
brings U2B output LOW which enables the XDCP. After a
short delay determined by R3 and C3, the astable
multivibrator (U2C) will begin generating increment pulses.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1
1-888-INTERSIL or 1-888-352-6832 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2005. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
Application Note 49
J1
JACK
C9
AUDIO INPUT
1µF
U1
C7
LM386
C4
.1µF
V
4
CC
250µF
2
3
-
5
4 OHM
R7
7
2
1
3
5
6
U/D
CS
INC
VH
VW
VL
+
SPEAKER
7.5K
U2B
6
R6
2.7
4
6
R4
10K
R5
10K
5
CR1
R2
C6
.1µF
C8
470pF
1N4148
27K
74HC132
X9134
C5
.1µF
S1
C2
DECREASE
1000pF
U2A
1
2
3
C10
10µF
74HC132
S2
INCREASE
V
CC
R3
27K
CR2
1N4148
U2D
10
9
8
74HC132
C3
1000pF
C1
1µF
R1
220K
FIGURE 1. Low Voltage Audio Amplifier
+V
BAT
J1
JACK
C9
C10
AUDIO INPUT
10µF
1µF
U1
C7
U3
C4
250µF
.1µF
V
7
CC
LM386
2
3
-
6
4-16 OHM
R7
7.5K
7
2
1
3
5
6
U/D
CS
INC
VH
VW
VL
+
SPEAKER
5
U2B
4
R6
2.7
4
6
R4
10K
R5
10K
5
CR1
1N4148
R2
27K
C6
.1µF
74HC132
X9134
C6
.1µF
S1
C2
1000pF
DECREASE
U2A
1
2
3
74HC132
S2
INCREASE
V
+V
BAT
CC
R3
27K
CR2
1N4148
VR1
U2D
10
9
LM78L05AC2
8
1
8
OUT
IN
U2
2
1
74HC132
9V-16V DC
GND
C3
1000pF
C1
1µF
R1
220K
C11
.1µF
FIGURE 2. 1 Watt Audio Amplifier
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to
verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
AN49.0
2
April 21, 2005
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