Datasheet

LMH6714
2
OUTPUT
20 MHz,
0.1 V
PP
-5V
R
1
20:
3
1
6
7
4
R
F
LMH6609
LMH6714
LMH6505
R
G
100:
R
10
500:
R
9
4.22 k:
1N5712
SCHOTTKY
R
2
25:
C
1
1.0 µF
C
2
680 pF
C
3
40 pF
+
+
+
+
-
-
-
-
V
IN
INCLUDES SCOPE
PROBE CAPACITANCE
R
6
300:
R
5
25:
R
3
300:
R
4
300:
R
7
300:
R
8
500:
U4
U3
U2
U1
LMH6505
SNOSAT4E –DECEMBER 2005–REVISED APRIL 2013 www.ti.com
Figure 49. Automatic Gain Control Circuit
Signal frequencies must not reach the gain control port of the LMH6505, or the output signal will be distorted
(modulated by itself). A fast settling AGC needs additional filtering beyond the integrator stage to block signal
frequencies. This is provided in Figure 49 by a simple R-C filter (R
10
and C
3
); better distortion performance can
be achieved with a more complex filter. These filters should be scaled with the input signal frequency. Loops with
slower response time, which means longer integration time constants, may not need the R
10
– C
3
filter.
Checking the loop stability can be done by monitoring the V
G
voltage while applying a step change in input signal
amplitude. Changing the input signal amplitude can be easily done with an arbitrary waveform generator.
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