THS4503-EP_17 Datasheet, PDF (24/40 Pages) Texas Instruments – WIDEBAND, LOW-DISTORTION FULLY DIFFERENTIAL AMPLIFIERS

THS4503−EP
SGLS291A − APRIL 2005 − JANUARY 2012
D Decouple the V_OCM pin to eliminate the antenna
effect. V_OCM is a high-impedance node that can act as
an antenna. A large decoupling capacitor on this node
eliminates this problem.
D 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.
D 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.
D Comprehend the effect of the load impedance seen by
the fully differential amplifier when performing
system-level intercept point calculations. Lighter
loads (such as those presented by an ADC) allow
smaller intercept points to support the same level of
intermodulation distortion performance.
EXAMPLE ANALOG-TO-DIGITAL
CONVERTER DRIVER CIRCUITS
The THS4500 family of devices is designed to drive
high-performance ADCs with extremely high linearity,
allowing for the maximum effective number of bits at the
output of the data converter. Two representative circuits
shown below highlight single-supply operation and split
supply operation. Specific feedback resistor, 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.
C_F
R_S
R_g
R_f
5V
V_S
R_T
5V
10 μF
+_−
V_OCM
0.1 μF
R_iso
IN _ADS5410
12 Bit/80 MSps
1 μF
−⁺
THS4503
IN
R_iso
CM
R_g
−5 V ^{10 μF 0.1 μF}
R_f
0.1 μF
C_F
Using the THS4503 With the ADS5410
Figure 98
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C_F
R_S
R_g
R_f
5V
V_S
R_T
5V
10 μF 0.1 μF
R_iso
+_−
IN ^ADS5421
V_OCM
14 Bit/40 MSps
1 μF
−⁺
THS4501
IN
R_iso
CM
R_g
R_f
C_F
Using the THS4501 With the ADS5421
Figure 99
0.1 μF
FULLY DIFFERENTIAL LINE DRIVERS
The THS4500 family of amplifiers can be used as
high-frequency, high-swing differential line drivers. 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, coupled with the
ability to provide differential outputs enables the ability to
drive 26 V_PP into reasonably heavy loads (250 Ω or
greater). The circuit in Figure 100 illustrates the THS4500
family of devices used as high speed line drivers. For line
driver applications, close attention must be paid to thermal
design constraints due to the typically high level of power
dissipation.
R_S
C_G
R_g
R_f
V_S
R_T
15 V
R_iso ^CS
V_OCM
+_−
THS4500
V_DD
R_L
0.1 μF
−⁺
R_{iso CS}
R_f
R_g
C_G
V_OD = 26 V_PP
Fully Differential Line Driver With High Output Swing
Figure 100
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