BC447 Datasheet, PDF (22/36 Pages) ON Semiconductor – High Voltage Transistors

THS4271
THS4275
SLOS397E − JULY 2002 − REVISED JANUARY 2004
3.3 V 3.3 V
100 Ω
100 Ω
1 nF
THS4271
+
_
CF
DAC5675
14-Bit,
400 MSps
249 Ω
100 Ω
249 Ω
249 Ω
249 Ω
1 nF
_
CF
1 nF
IF+
49.9 Ω
49.9 Ω
RF(out)
IF−
1 nF
+
THS4271
Figure 81. Differential Mixer Drive Circuit Using
the DAC5675 and the THS4271
Active Filtering With the THS4271
High-frequency active filtering with the THS4271 is
achievable due to the amplifier’s high slew-rate, wide
bandwidth, and voltage feedback architecture. Several
options are available for high-pass, low-pass, bandpass,
and bandstop filters of varying orders. A simple two-pole
low pass filter is presented here as an example, with two
poles at 100 MHz.
50 Ω Source
VI
249 Ω
61.9 Ω
6.8
pF
249 Ω
5V
_
THS4271
+
−5 V
49.9 Ω
VO
33 pF
Figure 82. A Two-Pole Active Filter With Two
Poles Between 90 MHz and 100 MHz
A Low-Noise Receiver With the THS4271
A combination of two THS4271 amplifiers can create a
high-speed, low-distortion, low-noise differential receiver
circuit as depicted in Figure 83. With both amplifiers
operating in the noninverting mode of operation, the circuit
presents a high load impedance to the source. The
designer has the option of controlling the impedance
through termination resistors if a matched termination
impedance is desired.
22
100 Ω
VI+
+
_
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49.9 Ω
VO+
249 Ω
499 Ω
249 Ω
100 Ω
_
100 Ω
VI−
+
49.9 Ω
VO−
Figure 83. A High Input Impedance, Low
Noise, Differential Receiver
A modification on this circuit to include a difference
amplifier turns this circuit into a high-speed instrumenta-
tion amplifier, as shown in Figure 84.
100 Ω
VI−
+
THS4271
_
Rf1
Rg1
100 Ω
VI+
_ ^Rf1
THS4271
+
Rg2
Rf2
_
Rg2
THS4271
+
Rf2
49.9 Ω
VO
49.9 Ω
Figure 84. A High-Speed Instrumentation
Amplifier
ǒ Ǔ ǒ Ǔ V_O +
1
2
1
)
2R_f1
R_g1
ǒ_{Vi)–Vi–}Ǔ
R_f2
R_g2
(1)
THEORY AND GUIDELINES
Distortion Performance
The THS4271 provides excellent distortion performance
into a 150-Ω load. Relative to alternative solutions, it
provides exceptional performance into lighter loads, as
well as exceptional performance on a single 5-V supply.
Generally, until the fundamental signal reaches very high
frequency or power levels, the 2^nd harmonic dominates the
total harmonic distortion with a negligible 3^rd harmonic
component. Focusing then on the 2^nd harmonic,
increasing the load impedance improves distortion