ssm2135p Analog Devices, Inc., ssm2135p Datasheet - Page 10

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

SSM2135
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 5 shows the implementation of an 18-bit
stereo 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 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 W with
no additional buffering required.
Single Supply Differential Line Driver
Signal distribution and routing is often required in audio systems,
particularly portable digital audio equipment for professional
applications. Figure 6 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 W line termination at a reduced output amplitude.
AUDIO IN
Figure 6. Single-Supply Differential Line Driver
100 F
10k
2.0V
1k
1 F
SSM2135
SSM2135
0.1 F
+5V
100
1k
2.5k
1/2
1/2
1k
10 F+0.1 F
CK
DGND
V
VBR
L
DL
LL
DR
LR
SSM2135
18-BIT
SERIAL
SERIAL
18-BIT
18-BIT
18-BIT
DAC
DAC
REG.
REG.
1/2
+5V
AD1868
V
V
REF
REF
Figure 5. 5 V Stereo 18-Bit DAC
DIFFERENTIAL
+5V
AUDIO OUT
AGND
VBL
VOL
VOR
7.5k
5k
V
S
5V SUPPLY
7.68k
7.68k
330pF
330pF
–10–
Single-Supply Differential Line Receiver
Receiving a differential signal with minimum distortion is achieved
using the circuit in Figure 7. Unlike a difference amplifier (a
subtractor), the circuit has a true balanced input impedance
regardless of input drive levels. That is, each input always pre-
sents a 20 kW 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 kW precision resistor network.
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 8 provides a supply splitter function with low
output impedance. The 1 mF 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 mF 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 a
5 V supply, limited only by the 100 W output resistor. Reducing
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.
DIFFERENTIAL
9.76k
9.76k
AUDIO IN
Figure 7. Single-Supply Balanced Differential
Line Receiver
7.68k
7.68k
SSM2135
SSM2135
1/2
1/2
100pF
100pF
20k
20k
220 F
220 F
SSM2135
1 F
+5V 10 F+0.1 F
10k
1/2
47k
47k
LEFT
CHANNEL
OUTPUT
RIGHT
CHANNEL
OUTPUT
2.0V
100
2.5k
SSM2135
0.1 F
20k
1/2
SSM2135
1/2
+5V
10
REV. E
10 F
7.5k
5k
AUDIO
OUT
+5V