SSM2135P データシートの表示（PDF） - Analog Devices
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SSM2135P Datasheet PDF : 12 Pages
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SSM2135
An 18-Bit Stereo CD-DAC Output Amplifier
The SSM2135 makes an ideal single supply stereo output
amplifier for audio D/A converters because of its low noise and
distortion. Figure 33 shows the implementation of an 18-bit ste-
reo DAC channel. The output amplifier also provides low-pass
filtering for smoothing the oversampled audio signal. The filter’s
cutoff frequency is set at 22.5 kHz and it has a maximally flat
response from dc to 20 kHz.
As mentioned above, the amplifier’s outputs can drive directly
into a stereo headphone that has impedance as low as 25 Ω with
no additional buffering required.
+5V SUPPLY
1 VL
LL
2
3 DL
CK
4
DR
5
6 LR
18-BIT
DAC
18-BIT
SERIAL
REG.
VREF
18-BIT
SERIAL
REG.
AD1868
VREF
7 DGND
8 VBR
18-BIT
DAC
VBL
16
15
VOL 14
13
AGND 12
11
VOR
10
VS 9
7.68kΩ
330pF
7.68kΩ
330pF
1/2
SSM2135
3
9.76kΩ
2
8
220µF
1
4
47kΩ
7.68kΩ 100pF
7.68kΩ
9.76kΩ
100pF
6
220µF
7
5
1/2 47kΩ
SSM2135
LEFT
CHANNEL
OUTPUT
RIGHT
CHANNEL
OUTPUT
Figure 33. +5 V Stereo 18-Bit DAC
A Single Supply Differential Line Driver
Signal distribution and routing is often required in audio
systems, particularly portable digital audio equipment for
professional applications. Figure 34 shows a single supply line
driver circuit that has differential output. The bottom amplifier
provides a 2 V dc bias for the differential amplifier in order to
maximize the output swing range. The amplifier can output a
maximum of 0.8 V rms signal with a +5 V supply. It is capable
of driving into 600 Ω line termination at a reduced output
amplitude.
AUDIO
IN
100µF
10kΩ
1kΩ
+5V
10µF+0.1µF
2
3
1kΩ
8
1
1/2
4 SSM2135
1kΩ
DIFFERENTIAL
AUDIO OUT
2.0V
1µF
6
7
5
1/2
SSM2135
2.5kΩ
0.1µF
100Ω
+5V
82
1
1/2
3
SSM2135 4
+5V
7.5kΩ
5kΩ
A Single Supply Differential Line Receiver
Receiving a differential signal with minimum distortion is
achieved using the circuit in Figure 35. Unlike a difference
amplifier (a subtractor), the circuit has a true balanced input
impedance regardless of input drive levels. That is, each input
always presents a 20 kΩ impedance to the source. For best
common-mode rejection performance, all resistors around the
differential amplifier must be very well matched. Best results
can be achieved using a 10 kΩ precision resistor network.
DIFFERENTIAL
AUDIO IN
10kΩ
+5V
10µF+0.1µF
20kΩ
28
1
3
1/2
4 SSM2135
10kΩ
20kΩ
20kΩ
2.0V
1µF
6
7
10Ω 10µF
5
1/2
SSM2135
AUDIO
OUT
+5V
100Ω
8
1
3
2
4
0.1µF
1/2
SSM2135
2.5kΩ
7.5kΩ
+5V
5kΩ
Figure 35. Single Supply Balanced Differential Line
Receiver
A Pseudo-Reference Voltage Generator
For single supply circuits, a reference voltage source is often
required for biasing purposes or signal offsetting purposes. The
circuit in Figure 36 provides a supply splitter function with low
output impedance. The 1 µF output capacitor serves as a charge
reservoir to handle a sudden surge in demand by the load as
well as providing a low ac impedance to it. The 0.1 µF feedback
capacitor compensates the amplifier in the presence of a heavy
capacitive load, maintaining stability.
The output can source or sink up to 12 mA of current with
+5 V supply, limited only by the 100 Ω output resistor. Reduc-
ing the resistance will increase the output current capability.
Alternatively, increasing the supply voltage to 12 V also
improves the output drive to more than 25 mA.
VS+ = +5V → +12V
R3
2.5kΩ
C1
0.1µF
R1
5kΩ
2
8
R4
1/2
SSM2135 1
100Ω
VS+
OUTPUT
C2 2
3
4
1µF
R2
5kΩ
Figure 34. Single Supply Differential Line Driver
Figure 36. Pseudo-Reference Generator
REV. D
–9–
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