op183gbc Analog Devices, Inc., op183gbc Datasheet - Page 14

• Manufacturer Part Number: op183gbc
• Description: 5 Mhz Single-supply Operational Amplifiers
• Manufacturer: Analog Devices, Inc.

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.
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.
CONDENSER
CONDENSER
AD1849
LOUT1R
LOUT1L
CMOUT
Figure 36. Headphone Output Amplifier for Multimedia Sound Codec
ELECTRET
ELECTRET
RIGHT
INPUT
INPUT
LEFT
MIC
MIC
21
19
20
Figure 37. Low Noise Stereo Microphone Amplifier for
V
10kΩ
10kΩ
REF
10μF
10μF
V
REF
20Ω
20Ω
OPTIONAL
R VOLUME
CONTROL
10μF
10μF
GAIN
L VOLUME
CONTROL
1kΩ
Multimedia Sound Codec
OP219
5V
1kΩ
1/2
V
REF
50Ω
50Ω
OPTIONAL
GAIN
10kΩ
10kΩ
OP183
OP183
OP183
5V
5V
5kΩ
5kΩ
100Ω
100Ω
OP183
OP183
16Ω 220μF
16Ω 220μF
5V
10kΩ
10kΩ
47kΩ
47kΩ
17
19
18
MINL
CMOUT
MINR
AD1849
HEADPHONE
LEFT
HEADPHONE
RIGHT
Rev. D | Page 14 of 16
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.
V
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.
IN
10kΩ
R6
1μF
Figure 38. 3 V Supply 50 Hz/60 Hz Notch Filter with Pseudo Ground
C4
75kΩ
OP183
R9
2
3
3V
A1
R10
25kΩ
3V
4
5
2.67kΩ
3
4
1
R1
A3
OP183
(1μF × 2)
0.015μF
2.67kΩ
C5
1μF
C1
R3
1μF
C3
10kΩ
1
R11
R12
70Ω
2.67kΩ
R5
1.33kΩ
(2.67kΩ ÷ 2)
2.67kΩ
1μF
R2
C2
R4
0.75V
C6
1μF
Q = 0.75
NOTE:
FOR 50Hz APPLICATIONS
CHANGE R1–R4 TO 3.1Ω
AND R5 TO 1.58Ω (3.16Ω ÷ 2).
R8
1kΩ
6
8
A2
OP183
1kΩ
R7
OP183
7
V
O