VCA810
www.ti.com
SBOS275F –JUNE 2003–REVISED DECEMBER 2010
DESIGN-IN TOOLS MACROMODELS AND APPLICATIONS
SUPPORT
DEMONSTRATION BOARDS
Computer simulation of circuit performance using
A printed circuit board (PCB) is available to assist in SPICE is often useful when analyzing the
the initial evaluation of circuit performance using the performance of analog circuits and systems. This is
VCA810. This evaluation board (EVM) is available particularly true for video and RF amplifier circuits
free, as an unpopulated PCB delivered with where parasitic capacitance and inductance can play
descriptive documentation. The summary information a major role in circuit performance. A SPICE model
for this board is shown in Table 1. for the VCA810 is available through the TI web page.
The applications group is also available for design
Table 1. EVM Ordering Information assistance. The models available from TI predict
typical small-signal ac performance, transient steps,
LITERATURE
dc performance, and noise under a wide variety of
BOARD PART REQUEST
PRODUCT PACKAGE NUMBER NUMBER
operating conditions. The models include the noise
VCA810ID SO-8 DEM-VCA-SO-1A SBOU025 terms found in the electrical specifications of the
relevant product data sheet.
Go to the Texas Instruments website (www.ti.com) to
request an evaluation board through the VCA810
product folder.
OPERATING SUGGESTIONS
Output overdriving occurs when either the maximum
output voltage swing or output current is exceeded.
INPUT/OUTPUT RANGE
The VCA810 high output current of ±60mA ensures
The VCA810’s 80dB gain range allows the user to
that virtually all output overdrives will be limited by
handle an exceptionally wide range of input signal
voltage swing rather than by current limiting. Table 2
levels. If the input and output voltage range
summarizes these overdrive conditions.
specifications are exceeded, however, signal
distortion and amplifier overdrive will occur. The
Table 2. Output Signal Compression
VCA810 maximum input and output voltage range is
LIMITING TO PREVENT, OPERATE
best illustrated in the Typical Characteristics plot,
GAIN RANGE MECHANISM DEVICE WITHIN:
Input/Output Range vs Gain (Figure 11). This chart
−40dB < G < Input Stage
plots input and output voltages versus gain in dB.
Input Voltage Range
−10dB Overdrive
The maximum input voltage range is the largest at full
−10dB < G < Internal Stage
Output Voltage Range
attenuation (−40dB) and decreases as the gain
+10dB Overdrive
increases. Similarly, the maximum useful output
+5dB < G < Output Stage
Output Voltage Range
voltage range increases as the input decreases. We
+40dB Overdrive
can distinguish three overloading issues as a result of
the operating mode: high attenuation, mid-range
OVERDRIVE RECOVERY
gain-attenuation, and high gain.
As shown in the Typical Characteristics plot,
From –40dB to –10dB, gain overdriving the input
Input/Output Range vs Gain (Figure 11), the onset of
stage is the only method to overdrive the VCA810.
overdrive occurs whenever the actual output begins
Preventing this type of overdrive is achieved by
to deviate from the ideal expected output. If possible,
limiting the input voltage range.
the user should operate the VCA810 within the linear
regions shown in order to minimize signal distortion
From –10dB to +40dB, overdriving can be prevented
and overdrive delay time. However, instances of
by limiting the output voltage range. There are two
amplifier overdrive are quite common in automatic
limiting mechanisms operating in this situation. From
gain control (AGC) circuits, which involve the
–10dB to +10dB, an internal stage is the limiting
application of variable gain to input signals of varying
factor; from +10dB to +40dB, the output stage is the
levels. The VCA810 design incorporates circuitry that
limiting factor.
allows it to recover from most overdrive conditions in
200ns or less. Overdrive recovery time is defined as
the time required for the output to return from
overdrive to linear operation, following the removal of
either an input or gain-control overdrive signal. The
overdrive plots for maximum gain and maximum
attenuation are shown in the Typical Characteristics.
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Product Folder Link(s): VCA810
