THS4501 Datasheet, PDF (34/48 Pages) National Semiconductor (TI) – WIDEBAND, LOW-DISTORTION, FULLY DIFFERENTIAL AMPLIFIERS

THS4500
THS4501
SLOS350F – APRIL 2002 – REVISED OCTOBER 2011
R_F
V_S
R_S
R_G
+
V_S
-
R_T
+
-
-V_S
R_ISO
C_L
R_ISO
Riso = 10 - 25 W
R_F
R_G
Figure 115. Use of Isolation Resistors With a
Capacitive Load
POWER-SUPPLY DECOUPLING
TECHNIQUES AND RECOMMENDATIONS
Power-supply decoupling is a critical aspect of any
high-performance amplifier design process. Careful
decoupling provides higher quality ac performance
(most notably improved distortion performance). The
following guidelines ensure the highest level of
performance.
1. Place decoupling capacitors as close to the
power-supply inputs as possible, with the goal of
minimizing the inductance of the path from
ground to the power supply.
2. Placement priority should be as follows: smaller
capacitors should be closer to the device.
3. Use of solid power and ground planes is
recommended to reduce the inductance along
power-supply return current paths.
4. Recommended values for power-supply
decoupling include 10-μF and 0.1-μF capacitors
for each supply. A 1000-pF capacitor can be
used across the supplies as well for extremely
high frequency return currents, but often is not
required.
EVALUATION FIXTURES, SPICE MODELS,
AND APPLICATIONS SUPPORT
Texas Instruments is committed to providing its
customers with the highest quality of applications
support. To support this goal, an evaluation board
has been developed for the THS4500 family of fully
differential amplifiers. The evaluation board can be
obtained by ordering through the THS4500 or
www.ti.com
THS4501 product folder on the Texas Instruments
web site, www.ti.com, or through your local Texas
Instruments sales representative. A schematic for the
evaluation board is shown in Figure 116 with the
default component values. Unpopulated footprints are
shown to provide insight into design flexibility.
C4 _C0805
R4
R0805
J1
C1
R2
V_S
PD
U1
1
3
_
7
THS450X
4
R6
C5
J2
C0805
J2
C0805 _R0805
R1
C2
R1206
R0805
C0805
R3
8+
26
R0805
C7
C0805
5 ^R0805
PwrPad R7
C6
J3
J3
V_OCM^-VS
C0805
R5 R0805
C3
C0805
J2
R8
43
J4
R0805
R9 5
J3
R0805
R0805
R11
R1206
R9
61
T1
Figure 116. Simplified Schematic of the
Evaluation Board
Computer simulation of circuit performance using
SPICE is often useful when analyzing the
performance of analog circuits and systems. This
practice is particularly true for video and RF amplifier
circuits where parasitic capacitance and inductance
can have a major effect on circuit performance. A
SPICE model for the THS4500 family of devices is
available through either the Texas Instruments web
site (www.ti.com) or as one model on a disk from the
Texas Instruments Product Information Center
(1-800-548-6132). The PIC is also available for
design assistance and detailed product information at
this number. These models do a good job of
predicting small-signal ac and transient performance
under a wide variety of operating conditions. They are
not intended to model the distortion characteristics of
the amplifier, nor do they attempt to distinguish
between the package types in their small-signal ac
performance. Detailed information about what is and
is not modeled is contained in the model file itself.
34
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