THS4051 Datasheet, PDF (14/36 Pages) Texas Instruments – 70-MHz HIGH-SPEED AMPLIFIERS

THS4051
THS4052
SLOS238D − MAY 1999 − REVISED AUGUST 2008
www.ti.com
APPLICATION INFORMATION
THEORY OF OPERATION
The THS405x 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_Ts 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 42.
(7) VCC +
IN − (2)
(6) OUT
IN + (3)
NULL (1)
NULL (8)
Figure 42. THS405x Simplified Schematic
(4) VCC −
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 THS405x is shown in Figure 43. 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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