OP281GSZ Analog Devices Inc, OP281GSZ Datasheet - Page 13

• Manufacturer Part Number: OP281GSZ
• Description: IC OPAMP GP R-R 105KHZ LP 8SOIC
• Manufacturer: Analog Devices Inc

Specifications of OP281GSZ

• Slew Rate: 0.028 V/µs
• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Gain Bandwidth Product: 105kHz
• Current - Input Bias: 3nA
• Voltage - Input Offset: 100µV
• Current - Supply: 3.3µA
• Current - Output / Channel: 12mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 12 V, ±1.35 V ~ 6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Op Amp Type: Low Power
• No. Of Amplifiers: 2
• Bandwidth: 105kHz
• Supply Voltage Range: 2.7V To 12V
• Amplifier Case Style: SOIC
• No. Of Pins: 8
• Operating Temperature Range: -40°C To
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

The OP281-A op amp provides about 29 dB of gain for audio
signals coming from the microphone. The gain is set by the
300 kW and 11 kW resistors. The gain bandwidth product of the
amplifier is 95 kHz, which, for the set gain of 28, yields a –3 dB
rolloff at 3.4 kHz. This is acceptable since telephone audio is band
limited for 300 kHz to 3 kHz signals. If higher gain is required
for the microphone, an additional gain stage should be used, as
adding any more gain to the OP281 would limit the audio band-
width. A 2.2 kW resistor is used to bias the electret microphone.
This resistor value may vary depending on the specifications on
the microphone being used. The output of the microphone is ac-
coupled to the noninverting terminal of the op amp. Two 1 MW
resistors are used to provide the dc offset for single-supply use.
The OP281-B amplifier can provide up to 15 dB of gain for the
headset speaker. Incoming audio signals are ac-coupled to a
10 kW potentiometer that is used to adjust the volume. Again,
two 1 MW resistors provide the dc offset with a 1 mF capacitor
establishing an ac ground for the volume control potentiometer.
Because the OP281 is a rail-to-rail output amplifier, it would have
difficulty driving a 600 W speaker directly. Here, a class AB buffer
is used to isolate the load from the amplifier and also provide
the necessary current drive to the speaker. By placing the buffer
in the feedback loop of the op amp, crossover distortion can be
minimized. Q1 and Q2 should have minimum betas of 100. The
600 W speaker is ac-coupled to the emitters to prevent any qui-
escent current from flowing in the speaker. The 1 mF coupling
capacitor makes an equivalent high-pass filter cutoff at 265 Hz
with a 600 W load attached. Again, this does not pose a problem,
as it is outside the frequency range for telephone audio signals.
The circuit in Figure 10 draws around 250 mA of current. The
class AB buffer has a quiescent current of 140 mA while roughly
100 mA is drawn by the microphone itself. A CR2032 3 V lithium
battery has a life expectancy of 160 mA hours, which means this
circuit could run continuously for 640 hours on a single battery.
SPICE Macro-Model
Single OPx81 Channel SPICE Macro-model
* 9/96, Ver. 1
*
* Copyright 1996 by Analog Devices
*
* Refer to “README.DOC” file for License Statement. Use of this
* model indicates your acceptance of the terms and provisions in the
* License Statement.
*
* Node Assignments
*
*
*
*
*
*
*
.SUBCKT OPx81
*
* INPUT STAGE
*
Q1
Q2
I1
REV. B
99
4
6
1
7
8
3
5
1.28E-6
noninverting input
|
|
|
|
|
|
1
PIX
PIX
inverting input
|
|
|
|
|
2
99
positive supply
|
|
|
|
50
negative supply
|
|
|
45
output
|
|
–13–
EOS
IOS
RC1
RC2
RE1
RE2
V1
V2
D1
D2
*
* CMRR 76dB, ZERO AT 1kHz
*
ECM1 11 98
R1
C1
R2
*
* POLE AT 900kHz
*
EREF 98 0
G1
R3
C2
*
* POLE AT 500kHz
*
E2
R4
C3
*
* GAIN STAGE
*
CF
R5
G3
D3
D4
V3
V4
*
* OUTPUT STAGE
*
ISY
RS1
RS2
M1
M2
EG1 99
EG2 47
*
* MODELS
*
.MODEL POX PMOS (LEVEL=2, KP=25E-6, VTO=-0.75,
LAMBDA=0.01)
.MODEL NOX NMOS (LEVEL=2, KP=25E-6, VTO=0.75,
LAMBDA=0.01)
.MODEL PIX PNP (BF=200)
.MODEL DX D(IS=1E-14)
.ENDS
99
99
45
40
98
40
42
99
42
99
99
90
45
45
7
1
4
6
3
5
3
5
11 12
11 12
12 98
98 20
20 98
20 98
21 98
21 22
22 98
50
50
13
14
13
14
40
98
40
41
40
41
50
50
90
50
46
47
46
50
2
2
8
8
POLY(1) (12, 98) 80E-6 1
1E-10
500E3
500E3
108
108
DC .9
DC .9
DX
DX
POLY(2) (1, 98) (2, 98) 0 .5 .5
1.59E6
100E-12
283
(90, 0)
(4, 6)
1E6
177E-15
(20, 98)
1E6
320E-15
8. 5E-12
65. 65E6
(22, 98)
DX
DX
DC 0.5
DC 0.5
1.375E-6
10E6
10E6
99
50
POLY(1)
POLY(1)
99
50
1
1E-6
1
4.08E-7
POX L=1.5u
NOX L=1.5u
(98, 40)
(40, 98) 0.77 1
OP281/OP481
0.77 1
W=300u
W=300u