R11

1 MW

R8

4.3 kW

R6

10 kW

R5

10 kW

R7

10 kW

VBIAS

(from the

Level Shifter)

I

PHOTO

A2

A1

A3

A4

A5

V+

V-

VREF

VOUT

VREF

VLOGOUT

High-Current Linearity

Correction Signal

I

REF

+

VCC

5 V

C1

100 nF

I

I

2

1

V

=

LOGOUT

0.375 LOG

10

·

+ 2 V + I R

1

S

·

( (

LOG114EVM

www.ti.com

The V

combining with the high-current linearity correction section. Combining the input signal and linearity

correction signal is accomplished with amplifier A4 and resistors R5 and R6. Capacitor C1 is used to

bypass the power supply for the LOG114. The signal path circuit is shown in Figure 3.

Figure 3. LOG114EVM Signal Path

2.3

High-Current Linearity Correction

The LOG114 is capable of handling a wide dynamic range of currents, from less than 100 pA in a carefully

designed PCB to 10 mA in high-current applications. Because the LOG114 was designed for high speeds,

the transistors that provide feedback around amplifiers A1 and A2 within the LOG114 have a small series

resistance, R

input currents that exceed approximately 1 mA. The modified equation for V

deviation from the ideal is given in Equation 3.

(3)

4

LOG114EVM User Guide

SBOU110

– September 2011

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