SSM2135_03 Datasheet, PDF (11/16 Pages) Analog Devices – Dual Single-Supply Audio Operational Amplifier

SSM2135
R1
5k⍀
R2
5k⍀
V_S+ = 5V Æ 12V
R3
2.5k⍀
C1
0.1␮F
1/2
SSM2135
R4
100k⍀
V_S+
2
OUTPUT
C2
1␮F
Figure 8. Pseudo-Reference Generator
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.
L AUDIO
IN
AD7528/PM7528
FB
REFA
OUTA
DAC A
3
+5V _{10␮F+0.1␮F}
2
1/2
SSM2135
L AUDIO
47␮F ^OUT
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.
L AUDIO
IN
+5V
0.1␮F
47␮F
3
14
DGND V_DD
V_IN
AD7111
FB ₁
OUTA
10
AGND ₂
+5V
0.1␮F
+5V _{10␮F+0.1␮F}
1/2
SSM2135
L AUDIO
47␮F ^OUT
R AUDIO
IN
DATA IN
AND
CONTROL
47␮F
3
14
DGND V_DD FB ₁
V_IN
OUTA
AD7111
AGND
10
2
1/2
SSM2135
2k
R AUDIO
47␮F ^OUT
10
+5V
+5V
0.1␮F
100⍀
2.0V
1/2
SSM2135
7.5k
2.0V
1␮F
5k
Figure 10. Single-Supply Logarithmic Volume Control
DATA IN
CONTROL
SIGNAL
R AUDIO
IN
6 DACA/
DACB
15 _CS
16 _WR
18
REFB
FB
OUTB
DACB
V_DD
17
DGND
5
0.1␮F
+5V
19
20
1/2
1
SSM2135
R AUDIO
47␮F ^OUT
2k⍀
0.1␮F
100⍀
2.0V
1␮F
+5V
+5V
1/2
7.5k⍀
SSM2135
2.0V
5k⍀
Figure 9. Digital Volume Control
REV. E
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