I =

R + R

+

=

+

R + R

R + R

R + R

+

Z

LOAD

R

R

R

R

V

+

V

+

V

-

V

-

+

-

-

LMP7701, LMP7702, LMP7704

www.ti.com

SNOSAI9I – SEPTEMBER 2005 – REVISED NOVEMBER 2015

8.4 Device Functional Modes

8.4.1 Precision Current Source

The LMP770x can each be used as a precision current source in many different applications. Figure 46 shows a

typical precision current source. This circuit implements a precision voltage controlled current source. Amplifier

bandwidth of amplifier A2 is greater then the closed loop bandwidth of amplifier A1. If A1 and A2 are the same

type of amplifiers, then the feedback around A1 will reduce its bandwidth compared to A2.

Figure 46. Precision Current Source

The equation for output current can be derived as shown in Equation 4.

(4)

Solving for the current I results in the Equation 5.

(5)

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

9.1.1 Low Input Voltage Noise

The LMP770x have the very low input voltage noise of 9 nV/

√Hz. This input voltage noise can be further reduced

by placing N amplifiers in parallel as shown in Figure 47. The total voltage noise on the output of this circuit is

divided by the square root of the number of amplifiers used in this parallel combination. This is because each

individual amplifier acts as an independent noise source, and the average noise of independent sources is the

quadrature sum of the independent sources divided by the number of sources. For N identical amplifiers, this

means:

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