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THS4081 Datasheet, PDF (11/24 Pages) Texas Instruments – 175-MHz LOW-POWER HIGH-SPEED AMPLIFIERS | |||
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THS4081, THS4082
175-MHz LOW-POWER HIGH-SPEED AMPLIFIERS
SLOS274C â DECEMBER 1999 â REVISED MAY 2000
APPLICATION INFORMATION
theory of operation
The THS408x is a high-speed, operational amplifier configured in a voltage feedback architecture. It is built
using a 30-V, dielectrically isolated, complementary bipolar process with NPN and PNP transistors possessing
fTs of several GHz. This results in an exceptionally high performance amplifier that has a wide bandwidth, high
slew rate, fast settling time, and low distortion. A simplified schematic is shown in Figure 38.
(7) VCC +
IN â (2)
(6) OUT
IN + (3)
Figure 38. THS4081 Simplified Schematic
(4) VCC â
noise calculations and noise figure
Noise can cause errors on very small signals. This is especially true when amplifying small signals, where
signal-to-noise ratio (SNR) is very important. The noise model for the THS408x is shown in Figure 39. This
model includes all of the noise sources as follows:
⢠en = Amplifier internal voltage noise (nV/âHz)
⢠IN+ = Noninverting current noise (pA/âHz)
⢠INâ = Inverting current noise (pA/âHz)
⢠eRx = Thermal voltage noise associated with each resistor (eRx = 4 kTRx )
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