OP183 Datasheet, PDF (10/12 Pages) Analog Devices – 5 MHz Single-Supply Operational Amplifiers

OP183/OP283
Low Noise Microphone Amplifier for Multimedia
The OP183 family is ideally suited as a low noise microphone
preamp for low voltage audio applications. Figure 40 shows a gain
of 100 stereo preamp for the AD1849 16-bit SoundPort Stereo
Codec chip. The common-mode output buffer serves as a “phan-
tom power” driver for the microphones.
Ω10kΩ
+5V
LEFT
ELECTRET
CONDENSER
MIC
INPUT
RIGHT
ELECTRET
CONDENSER
MIC
INPUT
10µF _{Ω50Ω}
Ω20Ω
Ω10kΩ
+5V
1/2 OP283
Ω100Ω
1/2 OP213
Ω20Ω
10µF
Ω10kΩ
Ω50Ω
Ω100Ω
1/2 OP283
17 _MINL
AD1849
19 ^CMOUT
15 MINR
Ω10kΩ
Figure 40. Low Noise Stereo Microphone Amplifier for
Multimedia Sound CODEC
A +3 Volt 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 oftentimes can
obscure low frequency physiological signals, such as heart rates,
blood pressures, EEGs, ECGs, et cetera.
Ω
R2
2.67kΩ
+3V
ΩR1
2.67kΩ
C1
C2
1/2 OP283
2
8
1µF
1µF
A1
1
5
V_IN
ΩR6
3
4
ΩR3
2.67kΩ
ΩR4
2.67kΩ
A2
7
V_O
6
10kΩ
1/2 OP283
×C3
2µF
(1µF × 2)
Ω_R5
1.33kΩ
(2.67kΩ ÷ 2)
ΩR8
1kΩ
ΩR7
1kΩ
ΩR11
10kΩ
+3V
ΩR9
75kΩ
C5
0.015µF
2
A3 ¹
ΩR12
70Ω
3
C4
ΩR10
OP183
1µF
25kΩ
A1, A2, AND A3 = 1/2 OP283
Ω
Q = 0.75
NOTE: FOR 50Hz APPLICATIONS
CHANGE R1–R4 TO 3.1k Ω
AND R5 TO 1.58k Ω (3.16kΩ ÷ 2).
0.75V
C6
1µF
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.
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 OP283’s common-mode range is 0.75 V. This notch
filter effectively squelches 60 Hz pickup at a filter Q of 0.75. To
reject 50 Hz interference, simply change the resistors in the twin-T
section (R1 through R5) from 2.67 kΩ to 3.16 kΩ.
The filter section uses an OP283 dual op amp in a twin-T configu-
ration 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.
A Low Voltage Frequency Synthesizer for Wireless
Transceiver
The OP183’s low noise and the low voltage operation capability
serves well for the loop filter of a frequency synthesizer. Figure 42
shows a typical application in a radio transceiver. The phase noise
performance of the synthesizer depends on low noise contribution
from each component in the loop as the noise is amplified by the
frequency division factor of the prescaler.
CRYSTAL
REFERENCE
OSCILLATOR
PHASE
DETECTOR
+3V
OP183
÷
PRESCALER
V_CONTROL
RF
OUT ^VCO
900MHz
VARACTER
DIODE
Figure 42. A Low Voltage Frequency Synthesizer for a
Wireless Transceiver
The resistors used in the low-pass filter should be of low to
moderate values to reduce noise contribution due to the input bias
current as well as the resistors themselves. The filter cutoff
frequency should be chosen to optimize the loop constant.
Figure 41. +3 Volt Supply 50 Hz/60 Hz Notch Filter with
Pseudo Ground
Figure 41 shows a 50 Hz/60 Hz active notch filter for eliminating
line noise in patient monitoring equipment. It has several kilohertz
–10–
REV. B