THS4051 Datasheet, PDF (14/30 Pages) Texas Instruments – 70-MHz HIGH-SPEED AMPLIFIERS

THS4051, THS4052
70-MHz HIGH-SPEED AMPLIFIERS
SLOS238C– MAY 1999 – REVISED MAY 2000
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)
(4) VCC –
NULL (1)
NULL (8)
Figure 42. THS4051 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 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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