Datasheet

+
-
+
-
V
OCM
12 Bit/80 MSps
IN
IN
5 V
CM
5 V
-5 V
V
S
10 µF 0.1 µF
10 µF 0.1 µF
THS4503
R
f
R
f
C
F
C
F
1 µF
R
g
R
g
0.1 µF
R
T
R
S
ADS5410
Using the THS4503 With the ADS5410
R
iso
R
iso
+
-
+
-
V
OCM
14 Bit/40 MSps
IN
IN
5 V
CM
5 V
V
S
10 µF 0.1 µF
THS4501
R
f
R
f
C
F
C
F
1 µF
R
g
R
g
R
T
R
S
ADS5421
0.1 µF
Using the THS4501 With the ADS5421
R
iso
R
iso
THS4502
THS4503
www.ti.com SLOS352E –APRIL 2002–REVISED OCTOBER 2011
common-mode voltage control.
• Do not terminate the output unless required. Many
open-loop, class-A amplifiers require 50-Ω
termination for proper operation, but closed-loop
fully differential amplifiers drive a specific output
voltage regardless of the load impedance present.
Terminating the output of a fully differential
amplifier with a heavy load adversely effects the
amplifier's linearity.
• Comprehend the V
OCM
input drive requirements.
Determine if the ADC's voltage reference can
provide the required amount of current to move
V
OCM
to the desired value. A buffer may be
needed.
• Decouple the V
OCM
pin to eliminate the antenna
effect. V
OCM
is a high-impedance node that can
Figure 97.
act as an antenna. A large decoupling capacitor
on this node eliminates this problem.
• Be cognizant of the input common-mode range. If
the input signal is referenced around the negative
power supply rail (e.g., around ground on a single
5 V supply), then the THS4500/1 accommodates
the input signal. If the input signal is referenced
around midrail, choose the THS4502/3 for the
best operation.
• Packaging makes a difference at higher
frequencies. If possible, choose the smaller,
thermally enhanced MSOP package for the best
performance. As a rule, lower junction
temperatures provide better performance. If
possible, use a thermally enhanced package,
even if the power dissipation is relatively small
compared to the maximum power dissipation
rating to achieve the best results.
Figure 98.
• Comprehend the effect of the load impedance
seen by the fully differential amplifier when
performing system-level intercept point
FULLY DIFFERENTIAL LINE DRIVERS
calculations. Lighter loads (such as those
presented by an ADC) allow smaller intercept
The THS4500 family of amplifiers can be used as
points to support the same level of intermodulation
high-frequency, high-swing differential line drivers.
distortion performance.
Their high power supply voltage rating (16.5 V
absolute maximum) allows operation on a single 12-V
or a single 15-V supply. The high supply voltage,
EXAMPLE ANALOG-TO-DIGITAL
coupled with the ability to provide differential outputs
CONVERTER DRIVER CIRCUITS
enables the ability to drive 26 V
PP
into reasonably
The THS4500 family of devices is designed to drive
heavy loads (250 Ω or greater). The circuit in
high-performance ADCs with extremely high linearity,
Figure 99 illustrates the THS4500 family of devices
allowing for the maximum effective number of bits at
used as high speed line drivers. For line driver
the output of the data converter. Two representative
applications, close attention must be paid to thermal
circuits shown below highlight single-supply operation
design constraints due to the typically high level of
and split supply operation. Specific feedback resistor,
power dissipation.
gain resistor, and feedback capacitor values are not
specified, as their values depend on the frequency of
interest. Information on calculating these values can
be found in the applications material above.
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