OP183_05 Datasheet, PDF (14/16 Pages) Analog Devices – 5 MHz Single-Supply Operational Amplifier

LOW VOLTAGE HEADPHONE AMPLIFIERS
Figure 36 shows a stereo headphone output amplifier for the
AD1849 16-bit SoundPort® Stereo Codec device. The
pseudoreference voltage is derived from the common-mode
voltage generated internally by the AD1849, thus providing a
convenient bias for the headphone output amplifiers.
OPTIONAL
GAIN
1kΩ
V_REF
5kΩ
5V
10μF
LOUT1L 21
10kΩ
L VOLUME OP183
CONTROL
16Ω ^220μF
47kΩ
HEADPHONE
LEFT
AD1849
5V
V_REF
OP183
CMOUT 19
10kΩ
LOUT1R 20
10μF
R VOLUME
CONTROL
OP183
5kΩ
16Ω ^220μF
47kΩ
HEADPHONE
RIGHT
1kΩ
OPTIONAL
GAIN
V_REF
Figure 36. Headphone Output Amplifier for Multimedia Sound Codec
LOW NOISE MICROPHONE AMPLIFIER FOR
MULTIMEDIA
The OP183 is ideally suited as a low noise microphone preamp
for low voltage audio applications. Figure 37 shows a gain of 100
stereo preamp for the AD1849 16-bit SoundPort Stereo Codec
chip. The common-mode output buffer serves as a phantom
power driver for the microphones.
10kΩ
5V
LEFT
ELECTRET
CONDENSER
MIC
INPUT
RIGHT
ELECTRET
CONDENSER
MIC
INPUT
10μF
50Ω
20Ω
10kΩ
5V
1/2
OP219
20Ω
10μF
10kΩ
50Ω
OP183
100Ω
100Ω
OP183
17 MINL
AD1849
19 CMOUT
18 MINR
10kΩ
Figure 37. Low Noise Stereo Microphone Amplifier for
Multimedia Sound Codec
OP183
3 V 50 HZ/60 HZ ACTIVE NOTCH FILTER WITH
FALSE GROUND
To process ac signals, it may be easier to use a false-ground bias
rather than the negative supply as a reference ground. This
would reject the power line frequency interference which can
often obscure low frequency physiological signals, such as heart
rates, blood pressures, EEGs, and ECGs.
Figure 38 shows a 50 Hz/60 Hz active notch filter for
eliminating line noise in patient monitoring equipment. It has
several kilohertz bandwidth and is not sensitive to false-ground
perturbations. The simple false-ground circuit shown achieves
good rejection of low frequency interference using standard off-
the-shelf components.
R2
2.67kΩ
3V
R1
2.67kΩ C1
C2
2
4
1μF
1μF
A1
1
OP183
6
V_IN
R6
10kΩ
3
5
OP183
R3
2.67kΩ
R4
2.67kΩ
A2
7
V_O
8
R7
C3
R5
1kΩ
1μF
(1μF × 2)
1.33kΩ
(2.67kΩ ÷ 2) ^R8
1kΩ
R11
10kΩ
Q = 0.75
3V
3
R9
75kΩ
4
C4
R10
1μF
25kΩ
C5
0.015μF
A3
1
OP183
NOTE:
FOR 50Hz APPLICATIONS
CHANGE R1–R4 TO 3.1Ω
R12
AND R5 TO 1.58Ω (3.16Ω ÷ 2).
70Ω _0.75V
C6
1μF
Figure 38. 3 V Supply 50 Hz/60 Hz Notch Filter with Pseudo Ground
Amplifier A3 biases A1 and A2 to the middle of their input
common-mode range. When operating on a 3 V supply, the
center of the common-mode range of the OP183 is 0.75 V. This
notch filter effectively squelches 60 Hz pickup at a filter Q of
0.75. To reject 50 Hz interference, change the resistors in the
twin-T section (R1 through R5) from 2.67 kΩ to 3.16 kΩ.
The filter section uses OP183 op amps in a twin-T
configuration whose frequency selectivity is very sensitive to
the relative matching of the capacitors and resistors in the twin-
T section. Mylar is the material of choice for the capacitors, and
the relative matching of the capacitors and resistors determines
the filter’s pass-band symmetry. Using 1% resistors and 5%
capacitors produces satisfactory results.
Rev. D | Page 14 of 16