OP27GZ Analog Devices Inc, OP27GZ Datasheet - Page 17

• Manufacturer Part Number: OP27GZ
• Description: Amplifier IC
• Manufacturer: Analog Devices Inc

Specifications of OP27GZ

• Peak Reflow Compatible (260 C): No
• Leaded Process Compatible: No
• Amplifier Type: General Purpose
• Number Of Circuits: 1
• Slew Rate: 2.8 V/µs
• Gain Bandwidth Product: 8MHz
• Current - Input Bias: 15nA
• Voltage - Input Offset: 30µV
• Voltage - Supply, Single/dual (±): ±4 V ~ 18 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Supply: -
• Output Type: -
• Current - Output / Channel: -
• -3db Bandwidth: -
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant, Contains lead / RoHS non-compliant

While the tape equalization requirement has a flat high
frequency gain above 3 kHz (T2 = 50 μs), the amplifier need
not be stabilized for unity gain. The decompensated
provides a greater bandwidth and slew rate. For many applica-
tions, the idealized time constants shown can require trimming
of R1 and R2 to optimize frequency response for nonideal tape
head performance and other factors (see the References
section).
The network values of the configuration yield a 50 dB gain at
1 kHz, and the dc gain is greater than 70 dB. Thus, the worst-
case output offset is just over 500 mV. A single 0.47 μF output
capacitor can block this level without affecting the dynamic
range.
The tape head can be coupled directly to the amplifier input,
because the worst-case bias current of 80 nA with a 400 mH,
100 μ inch head (such as the PRB2H7K) is not troublesome.
Amplifier bias-current transients that can magnetize a head
present one potential tape head problem. The OP27 and
are free of bias current transients upon power-up or power-
down. It is always advantageous to control the speed of power
supply rise and fall to eliminate transients.
In addition, the dc resistance of the head should be carefully
controlled and preferably below 1 kΩ. For this configuration,
the bias current induced offset voltage can be greater than the
100 pV maximum offset if the head resistance is not sufficiently
controlled.
A simple, but effective, fixed gain transformerless microphone
preamp (Figure 43) amplifies differential signals from low
impedance microphones by 50 dB and has an input impedance
of 2 kΩ. Because of the high working gain of the circuit, an
OP37
OP37
dummy resistor, R
unplugged. Otherwise, the 100% feedback from the open input
can cause the amplifier to oscillate.
Common-mode input noise rejection will depend upon the
match of the bridge-resistor ratios. Either close tolerance (0.1%)
types should be used, or R4 should be trimmed for best CMRR.
All resistors should be metal film types for best stability and low
noise.
helps to preserve bandwidth, which is 110 kHz. As the
is a decompensated device (minimum stable gain of 5), a
HEAD
TAPE
Figure 42. Tape Head Preamplifier
p
R
, may be necessary if the microphone is to be
A
C
A
10Ω
+
–
5kΩ
OP27
R2
33kΩ
R1
0.01µF
0.47µF
T1 = 3180µs
T2 = 50µs
15kΩ
OP37
OP37
Rev. F | Page 17 of 20
Noise performance of this circuit is limited more by the Input
Resistors R1 and R2 than by the op amp, as R1 and R2 each
generate a 4 nV/√Hz noise, while the op amp generates a
3.2 nV/√Hz noise. The rms sum of these predominant noise
sources is about 6 nV/√Hz, equivalent to 0.9 μV in a 20 kHz
noise bandwidth, or nearly 61 dB below a 1 mV input signal.
Measurements confirm this predicted performance.
MICROPHONE INPUT
For applications demanding appreciably lower noise, a high
quality microphone transformer coupled preamplifier (Figure
44) incorporates the internally compensated OP27. T1 is a JE-
115K-E 150 Ω/15 kΩ transformer that provides an optimum
source resistance for the OP27 device. The circuit has an overall
gain of 40 dB, the product of the transformer’s voltage setup and
the op amp’s voltage gain.
Gain can be trimmed to other levels, if desired, by adjusting R2
or R1. Because of the low offset voltage of the OP27, the output
offset of this circuit is very low, 1.7 mV or less, for a 40 dB gain.
The typical output blocking capacitor can be eliminated in such
cases, but it is desirable for higher gains to eliminate switching
transients.
(Z = 50Ω TO 200Ω)
LOW IMPEDANCE
Figure 44. High Quality Microphone Transformer Coupled Preamplifier
SOURCE
Figure 43. Fixed Gain Transformerless Microphone Preamplifier
150Ω
R3
R1
=
R4
R2
T1
1
1kΩ
1kΩ
R1
R2
121Ω
Figure 45. Burn-In Circuit
R1
100Ω
2
3
R3
R
30kΩ
OP27
P
8
–18V
+18V
4
2
3
OP27/
+
–
OP37
OP27
1800pF
316kΩ
316kΩ
1100Ω
A1
7
R3
R4
C2
R2
1
T1 – JENSEN JE – 115K – E
JENSEN TRANSFORMERS
6
6
5mF
C1
R7
10kΩ
100Ω
OUTPUT
R6
OP27
OUTPUT