Datasheet

MACROMODELS AND APPLICATIONS
OPERATING SUGGESTIONS
3
0
-3
-6
-9
-24
Frequency(MHz)
Gain(dB)
0 25 50 200
-12
-15
-18
-21
75 175150125100
V =1V
OUT PP
V = 0.5V-
G
V = 0.8V-
G
V =0V
G
V =+0.5V
G
V =+0.8V
G
DESIGN-IN TOOLS
DEMONSTRATION BOARDS
VCA822
www.ti.com
..................................................................................................................................... SBOS343C SEPTEMBER 2007 REVISED DECEMBER 2008
With the components shown, the circuit provides a
linear variation of the low-pass cutoff from 2MHz to SUPPORT
20MHz, using 1V V
G
+1V. Practical evaluation
Computer simulation of circuit performance using
shows that this circuit works from 8MHz to 16MHz
SPICE is often useful when analyzing the
with 0.8V < V
G
< +0.8V, as shown in Figure 87 .
performance of analog circuits and systems. This
principle is particularly true for video and RF amplifier
circuits where parasitic capacitance and inductance
can play a major role in circuit performance. A SPICE
model for the VCA822 is available through the TI web
page. The applications group is also available for
design assistance. The models available from TI
predict typical small-signal ac performance, transient
steps, dc performance, and noise under a wide
variety of operating conditions. The models include
the noise terms found in the electrical specifications
of the relevant product data sheet.
Operating the VCA822 optimally for a specific
application requires trade-offs between bandwidth,
input dynamic range and the maximum input voltage,
Figure 87. VCA822 as a Voltage-Control,
the maximum gain of operation and gain, output
Low-Pass Filter
dynamic range and the maximum input voltage, the
package used, loading, and layout and bypass
recommendations. The Typical Characteristics have
been defined to cover as much ground as possible to
describe the VCA822 operation. There are four
sections in the Typical Characteristics:
V
S
= ± 5V DC Parameters and V
S
= ± 5V DC and
Two printed circuit boards (PCBs) are available to
Power-Supply Parameters , which include dc
assist in the initial evaluation of circuit performance
operation and the intrinsic limitation of a VCA822
using the VCA822 in its two package options. Both of
design
these are offered free of charge as unpopulated
PCBs, delivered with a user's guide. The summary
V
S
= ± 5V, A
VMAX
= +2V/V Gain of +2V/V
information for these fixtures is shown in Table 2 .
Operation
V
S
= ± 5V, A
VMAX
= +10V/V Gain of +10V/V
Table 2. EVM Ordering Information
Operation
LITERATURE
V
S
= ± 5V, A
VMAX
= +100V/V Gain of +100V/V
BOARD PART REQUEST
Operation
PRODUCT PACKAGE NUMBER NUMBER
VCA822ID SO-14 DEM-VCA-SO-1B SBOU050
Where the Typical Characteristics describe the actual
VCA822IDGS MSOP-10 DEM-VCA-MSOP-1A SBOU051
performance that can be achieved by using the
amplifier properly, the following sections describe in
The demonstration fixtures can be requested at the
detail the trade-offs needed to achieve this level of
Texas Instruments web site (www.ti.com ) through the
performance.
VCA822 product folder.
Copyright © 2007 2008, Texas Instruments Incorporated Submit Documentation Feedback 23
Product Folder Link(s): VCA822