ssm2135p Analog Devices, Inc., ssm2135p Datasheet - Page 9

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

REV. E
APPLICATION CIRCUITS
Low Noise Stereo Headphone Driver Amplifier
Figure 1 shows the SSM2135 used in a stereo headphone driver
for multimedia applications with the AD1848, a 16-bit stereo
codec. The SSM2135 is equally well suited for the serial-bused
AD1849 stereo codec. The headphone’s impedance can be as
low as 25 W, which covers most commercially available high fidel-
ity headphones. Although the amplifier can operate at up to ±18 V
supply, it is just as efficient powered by a single 5 V. At this
voltage, the amplifier has sufficient output drive to deliver
distortion-free sound to a low impedance headphone.
Figure 2 shows the total harmonic distortion characteristics
versus frequency driving into a 32 W load, which is a very
typical impedance for a high quality stereo headphone. The
SSM2135 has excellent power supply rejection, and as a result,
is tolerant of poorly regulated supplies. However, for best sonic
quality, the power supply should be well regulated and heavily
bypassed to minimize supply modulation under heavy loads. A
minimum of 10 mF bypass is recommended.
Figure 2. Headphone Driver THD+N vs. Frequency into a
32 W Load (V
Figure 1. A Stereo Headphone Driver for Multimedia
Sound Codec
0.0005
AD1848
AUDIO PRECISION
0.010
0.001
0.1
R
L
V
GND
1
V
OUT
REF
OUT
20
CC
40
35/36
34/37
32
41
S
= 5 V, with 80 kHz Low-Pass Filter)
0.1 F
0.1 F
+5V
100
10k
10k
THD+(%) VS FREQ(Hz)
10 F
2
3
5
6
8.66k
8.66k
8
4
SSM2135
SSM2135
0.1 F
10 F
1k
1/2
1/2
1
7
470 F
470 F
R CH.
L CH.
10k
AGND
20k
–9–
Figure 3. Low Noise Microphone Preamp for Multimedia
Sound Codec
Figure 4. MIC Preamp THD+N Performance (V
A
Low Noise Microphone Preamplifier
The SSM2135’s 4.7 nV/÷Hz input noise in conjunction with
low distortion makes it an ideal device for amplifying low level
signals such as those produced by microphones. Figure 3 illus-
trates a stereo microphone input circuit feeding a multimedia
sound codec. As shown, the gain is set at 100 (40 dB), although
it can be set to other gains depending on the microphone output
levels. Figure 4 shows the preamplifier’s harmonic distortion
performance with 1 V rms output while operating from a single
5 V supply.
The SSM2135 is biased to 2.25 V by the V
codec. The same voltage is buffered by the 2N4124 transistor to
provide “phantom power” to the microphone. A typical electret
condenser microphone with an impedance range of 100 W to 1 kW
works well with the circuit. This power booster circuit may be
omitted for dynamic microphone elements.
R CHANNEL
L CHANNEL
V
MIC IN
MIC IN
= 40 dB, V
AUDIO PRECISION
0.010
0.1
1
20
2N4124
2k
2k
OUT
10 F
10 F
+5V
10k
10k
= 1 V rms, with 80 kHz Low-Pass Filter)
100
100
100
THD+(%) VS FREQ(Hz)
10 F
2
3
5
6
+5V
4
10k
10k
SSM2135
8
SSM2135
10 F
0.1 F
1/2
1/2
1
7
1k
0.1 F
REF
+5V
SSM2135
pin of the AD1848
35/36
34/37
S
29
32
28
10k
= 5 V,
LMIC
GND
V
RMIC
V
REF
CC
20k
AD1848