AD5292 Analog Devices, AD5292 Datasheet - Page 25

• Manufacturer Part Number: AD5292
• Description: (AD5291 / AD5292) Digital Potentiometer
• Manufacturer: Analog Devices

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AUDIO VOLUME CONTROL
The excellent THD performance and high voltage capability
make the AD5291/AD5292 ideal for a digital volume control as
an audio attenuator or gain amplifier. A typical problem in
these systems is that a large step change in the volume level at
any arbitrary time can lead to an abrupt discontinuity of the
audio signal causing an audible zipper noise. To prevent this, a
zero-crossing window detector can be inserted to the SYNC
line to delay the device update until the audio signal crosses the
window. Because the input signal can operate on top of any dc
level rather than absolute 0 V level, zero-crossing in this case
means the signal is ac-coupled, and the dc offset level is the
signal zero reference point.
V
IN
1µF
C1
R
90kΩ
R
10kΩ
4
5
U6
AD8541
5V
V+
V–
100kΩ
Figure 53. Audio Volume Control with Zipper Noise Reduction
1
2
200Ω
R
R
1
2
CHANNEL 1
FREQ = 20.25kHz
1.03V p-p
R
100kΩ
5V
3
ADCMP371
ADCMP371
GND
GND
V
V
+5V
+5V
CC
CC
Figure 54. Zipper Noise Detector
U2
U3
Rev. 0 | Page 25 of 28
SYNC
4
5
U4B
7408
6
1
2
The configuration to reduce zipper noise is shown in Figure 53,
and the results of using this configuration are shown in Figure 54.
The input is ac-coupled by C1 and attenuated down before feeding
into the window comparator formed by U2, U3, and U4B. U6 is
used to establish the signal zero reference. The upper limit of
the comparator is set above its offset and, therefore, the output
pulses high whenever the input falls between 2.502 V and 2.497 V
(or 0.005 V window) in this example. This output is AND’ e d
with the SYNC signal such that the AD5293 updates whenever
the signal crosses the window. To avoid a constant update of the
device, the SYNC signal should be programmed as two pulses,
rather than as one.
In Figure 54, the lower trace shows that the volume level changes
from a quarter-scale to full-scale when a signal change occurs
near the zero-crossing window.
U4A
7408
SCLK
+15V
0.1µF
0.1µF
DIN
–15V
C3
C2
U1
V
V
SYNC
SCLK
DIN
DD
SS
A
B
AD5292
20kΩ
W
GND
–15V
+15V
V–
V+
U5
V
OUT
AD5291/AD5292