SSM2135SZ Datasheet, PDF (13/16 Pages) Analog Devices – Dual Single-Supply Audio Operational Amplifier

Digital Volume Control Circuit
Working in conjunction with the AD7528 dual 8-bit DAC,
the SSM2135 makes an efficient audio attenuator, as shown in
Figure 38. 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 internal R-2R ladder switches of the DACs operating prop-
erly. This voltage is also the optimal midpoint of the SSM2135
common-mode and output swing range. With the circuit as
shown in Figure 38, 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.
LEFT
AUDIO IN
AD7528
3
5V _{10µF + 0.1µF}
R_FBA
2
V_REFA
OUT A
1/2
DAC A
SSM2135
LEFT AUDIO
47µF ^OUT
DATA IN
CONTROL
SIGNAL
RIGHT
AUDIO IN
6 DAC A/
DAC B
15 _CS
16 _WR
18
V_REFB
R_FBB
OUT B
DACB
19
20
1/2
1
SSM2135
RIGHT AUDIO
OUT
47µF
2kΩ
V_DD
17
DGND
5
0.1µF
5V
0.1µF
100Ω
2V
1µF
5V
5V
1/2
SSM2135
7.5kΩ
2V
5kΩ
Figure 38. Digital Volume Control
SSM2135
Logarithmic Volume Control Circuit
Figure 39 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 attenuation levels
for each input code.
5V
0.1µF
LEFT AUDIO
IN
47µF
3
14 16
DGND V_DD
V_IN
AD7111
R_{FB 1}
I_OUT
D1
10
AGND ₂
5V
0.1µF
5V _{10µF + 0.1µF}
1/2
SSM2135
LEFT AUDIO
OUT
47µF
RIGHT AUDIO
IN
DATA IN
AND
CONTROL
47µF
3
14 16
DGND V_DD R_{FB 1}
V_IN
I_OUT
AD7111
D1
10
AGND
2
1/2
SSM2135
2kΩ
RIGHT AUDIO
OUT
47µF
10
5V
5V
0.1µF
100Ω
2V
1/2
SSM2135
7.5kΩ
2V
1µF
5kΩ
Figure 39. Single-Supply Logarithmic Volume Control
Rev. G | Page 13 of 16