ssm2135p Analog Devices, Inc., ssm2135p Datasheet - Page 11

• Manufacturer Part Number: ssm2135p
• Description: Dual Single-supply Audio Operational Amplifier
• Manufacturer: Analog Devices, Inc.

Digital Volume Control Circuit
Working in conjunction with the AD7528/PM7528 dual 8-bit
D/A converter, the SSM2135 makes an efficient audio attenuator,
as shown in Figure 9. The circuit works off a single 5 V supply.
The DACs are biased to a 2 V reference level, which is sufficient
to keep the DACs’ internal R-2R ladder switches operating prop-
erly. This voltage is also the optimal midpoint of the SSM2135’s
common-mode and output swing range. With the circuit as
shown, the maximum input and output swing is 1.25 V rms.
Total harmonic distortion measures a respectable 0.01% at 1 kHz
and 0.1% at 20 kHz. The frequency response at any attenuation
level is flat to 20 kHz.
Each DAC can be controlled independently via the 8-bit parallel
data bus. The attenuation level is linearly controlled by the
binary weighting of the digital data input. Total attenuation
ranges from 0 dB to 48 dB.
REV. E
CONTROL
DATA IN
R AUDIO
L AUDIO
SIGNAL
IN
IN
5k
5k
R1
R2
Figure 8. Pseudo-Reference Generator
15
16
6
18
Figure 9. Digital Volume Control
DACA/
DACB
CS
WR
V
S
REFA
REFB
+ = 5V Æ 12V
AD7528/PM7528
V
+5V
DD
SSM2135
17
DAC A
DACB
0.1 F
1/2
0.1 F
DGND
OUTB
C1
OUTA
FB
FB
5
2.5k
R3
100k
1 F
2.0V
R4
3
2
19
20
1
0.1 F
100
SSM2135
SSM2135
+5V 10 F+0.1 F
1/2
1/2
1 F
C2
V
S
2
+
2k
OUTPUT
SSM2135
1/2
+5V
47 F
47 F
7.5k
R AUDIO
OUT
L AUDIO
OUT
2.0V
5k
+5V
–11–
Logarithmic Volume Control Circuit
Figure 10 shows a logarithmic version of the volume control
function. Similar biasing is used. With an 8-bit bus, the AD7111
provides an 88.5 dB attenuation range. Each bit resolves a
0.375 dB attenuation. Refer to the AD7111 data sheet for attenua-
tion levels for each input code.
CONTROL
R AUDIO
L AUDIO
DATA IN
Figure 10. Single-Supply Logarithmic Volume Control
AND
IN
IN
10
47 F
47 F
10
10
DGND
DGND
V
V
3
3
IN
IN
0.1 F
0.1 F
AD7111
AD7111
14
14
+5V
V
+5V
V
DD
DD
AGND
AGND
OUTA
OUTA
FB
FB
1 F
2.0V
1
2
1
2
0.1 F
100
SSM2135
SSM2135
+5V 10 F+0.1 F
1/2
1/2
SSM2135
2k
SSM2135
1/2
+5V
47 F
47 F
R AUDIO
OUT
L AUDIO
OUT
2.0V
7.5k
5k
+5V