ltc6244hv Linear Technology Corporation, ltc6244hv Datasheet - Page 20

• Manufacturer Part Number: ltc6244hv
• Description: Dual 50mhz, Low Noise, Rail-to-rail, Cmos Op Amp
• Manufacturer: Linear Technology Corporation

LTC6244
APPLICATIO S I FOR ATIO
20
Figure 9a. Low Noise Fully Differential Buffer/Amplifi er
(f
–3dB
V
V
IN
IN
Figure 9b. Design Equations for Figure 9a Circuit
+
–
= 970kHz, Gain = 5, R
R
R
Input Impedance = 2 • R
Gain
Maximum
C
C
2k
2k
f
3
IN
IN
IN
F
dB
=
=
=
=
439 9 8
10k
10k
R
R
C
82pF
C
82pF
8 977
G
G
IN
IN
V
.
U
OUT
4000
V
I
Gain =
N N
•
+
+
2k
2k
•
f
3
Gain
Gain R
U
–
–
dB
•
V
V
π
IN
1
•
OUT
IN
2
5MHz
= 4k)
(
+
•
f
–
Gain
–
–
3dB
•
+
+
1
LTC6244
LTC6244
2
R
–
IN
1/2
1/2
G
W
V
V
=
2k
2k
IN
+
•
+
–
•
f
R
C
R
2
3 3
33pF
33pF
C
C
IN
)
dB
F
G
F
F
•
C
6244 F09a
IN
U
V
V
OUT
OUT
+
–
A Low Noise AC Difference Amplifi er
In the signal conditioning of wideband sensors and trans-
ducers, a low noise amplifi er is often used to provide gain
for low level AC difference signals in the frequency range
of a few Hertz to hundreds of kilo-Hertz. In addition, the
amplifi er must reject common mode AC signals and its input
impedance should be higher than the differential source
impedance. Typical applications are piezoelectric sensors
used in sonar, sound and ultrasound systems and LVDT
(linear variable differential transformers) for displacement
measurements in process control and robotics.
The Figure 11a circuit is a low noise, single supply AC
difference amplifi er. The amplifi er’s low frequency –3dB
bandwidth is set with resistor R5 and capacitor C3, while
the upper –3dB bandwidth is set with R2 and C1. The
input common mode DC voltage can vary from ground to
V
The amplifi er’s gain is the ratio of resistors R2 to R1 (R4
= R2 and R3 = R1). The component values in the circuit
of Figure 11a implement an 800Hz to 160kHz AC ampli-
fi er with a gain equal to 10 and 12nV/√Hz input referred
voltage noise density shown in Figure 11b. The total input
referred wideband noise is 4.5µV
of 500Hz to 200kHz.
+
and the output DC voltage is equal to the V
Figure 10. Differential Input Referred Noise
32
28
24
20
16
12
8
4
10k
f
GAIN = 5
R
–3dB
IN
= 4k
= 970kHz
FREQUENCY (Hz)
100k
RMS
, in the bandwidth
6244 F10
REF
1M
voltage.
6244f