Datasheet

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APPLICATION INFORMATION
Theory of Operation
IN– (2)
IN+(3)
NULL (1) NULL (8)
(6)OUT
(4)V
CC–
(7)V
CC+
S0276-01
Noise Calculations and Noise Figure
THS4021
THS4022
SLOS265C – SEPTEMBER 1999 – REVISED JULY 2007
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 f
T
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 .
Figure 30. THS4021 Simplified Schematic
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:
• 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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Product Folder Link(s): THS4021 THS4022