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THS4021 Datasheet, PDF (9/22 Pages) Texas Instruments – 350-MHz LOW-NOISE HIGH-SPEED AMPLIFIERS
THS4021, THS4022
350-MHz LOW-NOISE HIGH-SPEED AMPLIFIERS
SLOS265B – SEPTEMBER 1999 – REVISED FEBRUARY 2000
APPLICATION INFORMATION
theory of operation
The THS402x 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
fT s 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 30.
(7) VCC +
IN – (2)
(6) OUT
IN + (3)
(4) VCC –
NULL (1)
NULL (8)
Figure 30. THS4021 Simplified Schematic
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 THS402x is shown in Figure 31. This
model includes all of the noise sources as follows:
• en = Amplifier internal voltage noise (nV/√Hz)
• IN+ = Noninverting current noise (pA/√Hz)
• IN– = Inverting current noise (pA/√Hz)
• eRx = Thermal voltage noise associated with each resistor (eRx = 4 kTRx )
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