LMH6523 Datasheet, PDF (19/31 Pages) Texas Instruments – High Performance Quad DVGA

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CASCADE OPERATION
0.01 F
V_CC
1H
VIN
100
¼ LMH6523
0.01 F
1H
LMH6523
SNOSC88 – DECEMBER 2012
0.01 F
100
0.01 F
V_CC
1H
40.2
0.01 F
¼ LMH6523
VOUT
40.2 0.01 F
1H
Figure 49. Schematic for Cascaded Amplifiers
SVA-30206583
With four amplifiers in one package the LMH6523 is ideally configured for cascaded operation. By using two
amplifiers in series additional gain range can be achieved. The schematic in Figure 49 shows one way to
connect two stages of the LMH6523. The resultant frequency response is shown below in Figure 50. When using
the LMH6523 amplifiers in a cascade configuration it is important to keep the signal level within reasonable limits
at all nodes of the signal path. With over 40dB of total gain it is possible to amplify signals to clipping levels if the
gain is not set correctly.
50
40
30
20
10
0
-10
-20
1
10
100
FREQUENCY (MHz)
1000
SVA-30206584
Figure 50. Frequency Response of Cascaded Amplifiers
DIGITAL CONTROL
The LMH6523 will support two modes of control, parallel mode and serial mode (SPI compatible). Parallel mode
is fastest and requires the most board space for logic line routing. Serial mode is compatible with existing SPI
compatible systems.
The LMH6523 has gain settings covering a range of 31 dB. To avoid undesirable signal transients the LMH6523
should not be powered on with large inputs signals present. Careful planning of system power on sequencing is
especially important to avoid damage to ADC inputs.
The LMH6523 was designed to interface with 2.5V to 5V CMOS logic circuits. If operation with 5V logic is
required care should be taken to avoid signal transients exceeding the DVGA supply voltage. Long, unterminated
digital signal traces are particularly susceptible to these transients. Signal voltages on the logic pins that exceed
the device power supply voltage may trigger ESD protection circuits and cause unreliable operation.
Some pins on the LMH6523 have different functions depending on the digital control mode. These functions will
be described in the sections to follow.
Copyright © 2012, Texas Instruments Incorporated
Product Folder Links: LMH6523
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