THS3202 Datasheet, PDF (19/32 Pages) Texas Instruments – 2-GHZ, LOW DISTORTION, CURRENT FEEDBACK AMPLIFIERS

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THS3202
SLOS242D − SEPTEMBER 2002 − REVISED JANUARY 2004
+6 V
THS3202(a)
VI+
+
_
0.1 µF
+
10 µF
499 Ω
0.1 µF
210 Ω
RS
RLine
2n2
1:n
Telephone Line
RLine
THS3202(b)
VI−
+
_
499 Ω
−6 V
0.1 µF
10 µF
+
RS
RLine
2n2
Figure 90. Simple Line Driver With THS3202
Due to the large power supply voltages and the large current drive capability, power dissipation of the amplifier must
not be neglected. To have as much power dissipation as possible in a small package, the THS3202 is available only
in a MSOP−8 PowerPAD package (DGN) and SOIC−8 package (D). Again, power dissipation of the amplifier must
be carefully examined or else the amplifiers could become too hot and performance can be severely degraded. See
the Power Dissipation and Thermal Considerations section for more information on thermal management.
NOISE CALCULATIONS
Noise can cause errors on very small signals. This is especially true for amplifying small signals coming over a
transmission line or an antenna. The noise model for current-feedback amplifiers (CFB) is the same as for voltage
feedback amplifiers (VFB). The only difference between the two is that CFB amplifiers generally specify different
current-noise parameters for each input, while VFB amplifiers usually only specify one noise-current parameter. The
noise model is shown in Figure 91. This model includes all of the noise sources as follows:
• e_n = Amplifier internal voltage noise (nV/√Hz)
• IN+ = Noninverting current noise (pA/√Hz)
• IN− = Inverting current noise (pA/√Hz)
• e_Rx = Thermal voltage noise associated with each resistor (e_Rx = 4 kTR_x )
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