www.ti.com

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

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

• IN+ = Noninverting current noise (pA/√Hz)

• IN– = Inverting current noise (pA/√Hz)

• e

Copyright © 1999–2007, Texas Instruments Incorporated

Submit Documentation Feedback

9

Product Folder Link(s): THS4021 THS4022