Datasheet

13
LT1113
1113fb
U
SA
O
PP
L
IC
AT
ITY
P
I
CA
L
Accelerometer Amplifier with DC Servo
Paralleling Amplifiers to Reduce Voltage Noise
8
5V TO 15V
–5V TO –15V
4
1113 • TA03
OUTPUT
R1
100M
C1
1250pF
R3
2k
C3
2µF
R2
18k
C2
2µF
6
5
R4
20M
–
+
1/2 LT1113
7
R5
20M
ACCELEROMETER
B & K MODEL 4381
OR EQUIVALENT
1
3
2
–
+
1/2 LT1113
R4C2 = R5C3 > R1 (1 + R2/R3) C1
OUTPUT = 0.8mV/pC* = 8.0mV/g**
DC OUTPUT ≤ 2.7mV
OUTPUT NOISE = 6nV/√Hz AT 1kHz
*PICOCOULOMBS
**g = EARTH’S GRAVITATIONAL CONSTANT
1. ASSUME VOLTAGE NOISE OF LT1113 AND 51Ω SOURCE RESISTOR = 4.6nV/√Hz
2. GAIN WITH n LT1113s IN PARALLEL = n • 200
3. OUTPUT NOISE = √n • 200 • 4.6nV/√Hz
4. INPUT REFERRED NOISE =
OUTPUT NOISE
=
4.6
nV/√Hz
n • 200 √n
5. NOISE CURRENT AT INPUT INCREASES √n TIMES
6. IF n = 5, GAIN = 1000, BANDWIDTH = 1MHz, RMS NOISE, DC TO 1MHz =
9µV
= 4µV
√5
8
15V
–15V
4
8
15V
–15V
4
1113 • TA04
1k
7
6
5
1k
1k
1
2
3
–
+
A2
1/2 LT1113
–
+
1k
51Ω
51Ω
51Ω
1
2
3
A1
1/2 LT1113
10k
7
5
6
–
+
1/2 LT1113
–
+
An
1/2 LT1113
1k
1k
OUTPUT