AD745KR-16-REEL7 Analog Devices Inc, AD745KR-16-REEL7 Datasheet - Page 10

• Manufacturer Part Number: AD745KR-16-REEL7
• Description: IC OPAMP BIFET 20MHZ ULN 16SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD745KR-16-REEL7

• Rohs Status: RoHS non-compliant
• Amplifier Type: J-FET
• Number Of Circuits: 1
• Slew Rate: 12.5 V/µs
• Gain Bandwidth Product: 20MHz
• -3db Bandwidth: 20MHz
• Current - Input Bias: 150pA
• Voltage - Input Offset: 100µV
• Current - Supply: 8mA
• Current - Output / Channel: 40mA
• Voltage - Supply, Single/dual (±): 9.6 V ~ 36 V, ±4.8 V ~ 18 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.300", 7.5mm Width)
• Output Type: -

AD745
TWO HIGH PERFORMANCE ACCELEROMETER
AMPLIFIERS
Two of the most popular charge-out transducers are hydrophones
and accelerometers. Precision accelerometers are typically cali-
brated for a charge output (pC/g). Figures 14 and 15 show two
ways in which to configure the AD745 as a low noise charge
amplifier for use with a wide variety of piezoelectric accelerom-
eters. The input sensitivity of these circuits will be determined
by the value of capacitor C1 and is equal to:
The ratio of capacitor C1 to the internal capacitance (C
transducer determines the noise gain of this circuit (1 + C
The amplifiers voltage noise will appear at its output amplified
by this amount. The low frequency bandwidth of these circuits
will be dependent on the value of resistor R1. If a “T” network
is used, the effective value is: R1 (1 + R2/R3).
A dc servo loop (Figure 15) can be used to assure a dc output
<10 mV, without the need for a large compensating resistor
when dealing with bias currents as large as 100 nA. For optimal
pC = Picocoulombs
g = Earth’s Gravitational Constant
∆V
OUT
EQUIVALENT
=
B AND K
4370 OR
∆Q
EQUIVALENT
B AND K
4370 OR
C1
OUT
(5
110M
R1
(5
22M )
110M
AD745
1k
R1
R3
22M )
1250pF
AD711
AD745
C1
1250pF
C1
2.2 F
C2
R3
1k
9k
R2
9k
R2
18M
18M
C3
2.2 F
R5
R4
OUTPUT
0.8mV/pC
OUTPUT
0.8mV/pC
T
) of the
T
/C1).
low frequency performance, the time constant of the servo loop
(R4C2 = R5C3) should be:
A LOW NOISE HYDROPHONE AMPLIFIER
Hydrophones are usually calibrated in the voltage-out mode.
The circuit of Figures 16 can be used to amplify the output of a
typical hydrophone. If the optional ac coupling capacitor C
used, the circuit will have a low frequency cutoff determined by
an RC time constant equal to:
where the dc gain is 1 and the gain above the low frequency
cutoff (1/(2π C
of Figure 17 uses a dc servo loop to keep the dc output at 0 V
and to maintain full dynamic range for I
time constant of R7 and C1 should be larger than that of R1
and C
The transducer shown has a source capacitance of 7500 pF. For
smaller transducer capacitances (≤300 pF), lowest noise can be
achieved by adding a parallel RC network (R4 = R1, C1 = C
in series with the inverting input of the AD745.
Time Constant ≥10 R1 1+
Time Constant ≥
B AND K TYPE 8100 HYDROPHONE
T
for a smooth low frequency response.
100
100
C
C
R3
C
T
R3
C
DC OUTPUT
(100 Ω))) is equal to (1 + R2/R3). The circuit
C
OPTIONAL DC BLOCKING CAPACITOR
OPTIONAL, SEE TEXT
T
10 1
R4
10
10
R4
8
R1
8
10
R
8
R1
OPTIONAL, SEE TEXT
2
INPUT SENSITIVITY = –179dB RE. 1V/mPa



1mV FOR IB (AD745)
π
C1
R6
1M
100k
C1
×
1900
R5
R2
1900
AD745
C
R2
R3
R2
C
AD745
1

 C1

×
100
AD711K
0.27 F
B
’s up to 100 nA. The
C2
Ω
16M
R4
100nA
OUTPUT
16M
OUTPUT
C
T
is
)