LMH6639_14 Datasheet, PDF (16/26 Pages) National Semiconductor (TI) – LMH6639 190MHz Rail-to-Rail Output Amplifier with Disable

LMH6639
SNOS989G – JANUARY 2002 – REVISED MARCH 2013
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MULTIPLEXING 5 AND 10MHz
The LMH6639 may be used to implement a circuit which multiplexes two signals of different frequencies. Three
LMH6639 high speed op-amps are used in the circuit of Figure 46 to accomplish the multiplexing function. Two
LMH6639 are used to provide gain for the input signals, and the third device is used to provide output gain for
the selected signal.
FREQ 1
FREQ 2
330:
50
330:
5V
2_-
7
IC1
6
3₊
8
4
330:
50
330:
5V
-
IC2
+
4
7
6
8
1k
5V
1k
2_-
7
6 OUT
IC3
3
8
+
2k
4 _5V
V_REF
SD
SD
Note: Pin numbers pertain to SOIC-8 package
Figure 46. Multiplexer
Multiplexing signals “FREQ 1” and “FREQ 2” exhibit closed loop non-inverting gain of +2 each based upon
identical 330Ω resistors in the gain setting positions of IC1 and IC2. The two multiplexing signals are combined
at the input of IC3, which is the third LMH6639. This amplifier may be used as a unity gain buffer or may be used
to set a particular gain for the circuit.
1.5
SHUTDOWN
1
0.5
0
-0.5
-1
TIME (400 ns/DIV)
Figure 47. Switching between 5 and 10MHz
1k resistors are used to set an inverting gain of −1 for IC3 in the circuit of Figure 46. Figure 47 illustrates the
waveforms produced. The upper trace shows the switching waveform used to switch between the 5MHz and
10MHz multiplex signals. The lower trace shows the output waveform consisting of 5MHz and 10MHz signals
corresponding to the high or low state of the switching signal.
16
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