SSM2135_03 Datasheet, PDF (9/16 Pages) Analog Devices – Dual Single-Supply Audio Operational Amplifier

SSM2135
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.
40
L_OUT
35/ 36
V_CC
34/ 37
GND
10k⍀
+5V
0.1␮F
32
V_REF
0.1␮F
10␮F
AD1848
8.66k⍀
2
470␮F
1
3
1/ 2
SSM2135
10␮F
L CH.
R CH.
5 ^{8 0.1␮F}
7
AGND
6
1/ 2
4 ^SSM2135
470␮F
41
R_OUT
10k⍀
8.66k⍀
Figure 1. A Stereo Headphone Driver for Multimedia
Sound Codec
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.
AUDIO PRECISION
1
THD+(%) VS FREQ(Hz)
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_REF pin of the AD1848
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.
L CHANNEL
MIC IN
10␮F
2k⍀ 10k⍀
+5V
2N4124
R CHANNEL
10k⍀
MIC IN
2k⍀ _10␮F
10k⍀
+5V 10␮F
100⍀ ₂
8
1
3
1/ 2
4 ^{SSM2135 +5V}
0.1␮F
10␮F
0.1␮F
5
7
6
1/ 2
SSM 2135
29
LMIC
35/ 36
V_CC
34/ 37
GND
32
V_REF
AD1848
28
RMIC
100⍀
10k⍀
Figure 3. Low Noise Microphone Preamp for Multimedia
Sound Codec
AUDIO PRECISION
1
THD+(%) VS FREQ(Hz)
0.1
0.1
0.010
0.001
0.0005
20
100
1k
10k 20k
Figure 2. Headphone Driver THD+N vs. Frequency into a
32 W Load (V_S = 5 V, with 80 kHz Low-Pass Filter)
0.010
20
100
1k
10k 20k
Figure 4. MIC Preamp THD+N Performance (V_S = 5 V,
A_V = 40 dB, V_OUT = 1 V rms, with 80 kHz Low-Pass Filter)
REV. E
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