Datasheet

14
LT1632/LT1633
sn1632 16323fs
Figure 4. RF Amplifier Control Biasing and DC Restoration
TYPICAL APPLICATIONS
U
A
R
R
R
R
RR
R
VVVA
V
OUT IN IN V
=++
+






=−






+−
4
3
1
2
1
32
5
•
Common mode range can be calculated by the following
equations:
Lower
V
V
A
R
R
V
Upper
V
V
A
R
R
VV
where V
CML
OUT
V
CMH
OUT
V
S
S
limit common mode input voltage
limit common mode input voltage
is supply voltage.
=






+








=






+−
()








2
5
01
10
11
2
5
015
10
11
.
.
.
.
.
.
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.
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.
Stopband attenuation is greater than 85dB at 10MHz.
–
+
A1
1/2 LT1632
V
OUT
1632/33 F04
5V
5V
HP-MSA0785
HP-MSA0785
R3
10k
L1
220µH
C5
0.01µF
L2
220µH
Q1
2N3906
Q2
2N3906
C6
0.01µF
R5
50Ω
R1
10Ω
R2
453Ω
R4
10Ω
C3
1500pF
–
+
A2
1/2 LT1632
C4
1500pF
C2
1500pF
C1
0.01µF
V
IN
L4
3.9µH
L3
3.9µH
+
+
+
RF1
RF2
Figure 2. Single Supply, 400kHz, 4th Order Butterworth Filter
FREQUENCY (Hz)
0.1k
GAIN (dB)
1k 10k 100k 1M 10M
1632/33 F03
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
V
S
= 3V, 0V
V
IN
= 2.5V
P-P
Figure 3. Frequency Response
–
+
1/2 LT1632
2.32k
V
IN
V
S
/2
V
OUT
1632/33 F02
220pF
2.32k 6.65k
–
+
1/2 LT1632
2.74k
22pF
470pF
5.62k
2.74k
47pF
With a 2.25V
P-P
, 100kHz input signal on a 3V supply, the
filter has harmonic distortion of less than –87dBc.
RF Amplifier Control Biasing and DC Restoration
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
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