LT1632/LT1633
TYPICAL APPLICATIONS
A
V
=
R4
R3

ï£ï£¬1+
R2
R1
+
R3 + R2
R5 
VOUT
=

ï£ï£¬
VIN+
−
VIN−
•
AV
Common mode range can be calculated by the following
equations:
Lower limit common mode input voltage
VCML
=

ï£ï£¬
VOUT
AV


R2
R5
+

0.1V

1.0
1.1
Upper limit common mode input voltage
( ) VCMH
=

ï£ï£¬
VOUT
AV


R2
R5
+
VS − 0.15V



1.0
1.1
where VS is supply voltage.
10
0
–10
–20
–30
– 40
– 50
– 60
– 70
– 80
VS = 3V, 0V
VIN = 2.5VP-P
–90
0.1k 1k
10k 100k 1M 10M
FREQUENCY (Hz)
1632/33 F03
Figure 3. Frequency Response
With a 2.25VP-P, 100kHz input signal on a 3V supply, the
filter has harmonic distortion of less than – 87dBc.
RF Amplifier Control Biasing and DC Restoration
For example, the common mode range is from 0.15V to
2.65V if the output is set at one half of the 3V supply. The
common mode rejection is greater than 110dB at 100Hz
when trimmed with resistor R1. The amplifier has a
bandwidth of 550kHz.
Taking advantage of the rail-to-rail input and output, and
the large output current capability of the LT1632, the
circuit shown in Figure 4 provides precise bias current for
the RF amplifiers and restores the DC output level. To
ensure optimum performance of an RF amplifier, its bias
point must be accurate and stable over the operating
Single Supply, 400kHz, 4th Order Butterworth Filter
The circuit shown in Figure 2 makes use of the low voltage
operation and the wide bandwidth of the LT1632 to create
a 400kHz 4th order lowpass filter with a single supply. The
amplifiers are configured in the inverting mode to mini-
mize common mode induced distortion and the output
can swing rail-to-rail for the maximum dynamic range.
Figure 3 displays the frequency response of the filter. C1 +
0.01µF
Stopband attenuation is greater than 85dB at 10MHz.
2.32k
VIN
2.32k
6.65k
220pF
47pF
–
1/2 LT1632
+
VS/2
2.74k
2.74k
5.62k
470pF
22pF
–
1/2 LT1632
+
VIN
VOUT
1632/33 F02
5V
R2
453Ω
R3
10k
5V
–
A1
+1/2 LT1632
HP-MSA0785
C2
1500pF
RF1
L3
3.9µH
R5
50Ω
R1
10Ω
Q1
2N3906
+
C5
0.01µF
L1
220µH
HP-MSA0785
C3
1500pF
RF2
+
A2
1/2 LT1632
–
R4
10Ω
Q2
2N3906
+
L2
220µH
C6
0.01µF
C4
1500pF
VOUT
L4
3.9µH
1632/33 F04
Figure 2. Single Supply, 400kHz, 4th Order Butterworth Filter
14
Figure 4. RF Amplifier Control Biasing and DC Restoration