THS4031 datasheet(20/38 Pages) TI

20 / 38 page

THS4031, THS4032

100-MHz LOW-NOISE HIGH-SPEED AMPLIFIERS

SLOS224C – JULY 1999 – REVISED APRIL 2000

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

theory of operation

The THS403x 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 fTs 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 43.

IN – (2)

IN + (3)

NULL (1)

NULL (8)

(6) OUT

(4) VCC –

(7) VCC +

Figure 43. THS4031 Simplified Schematic

noise calculations and noise figure

Noise can cause errors on very small signals. This is especially true when amplifying small signals. The noise

model for the THS403x, shown in Figure 44, 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 (eRx = 4 kTRx )

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