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LOG114 Single-Supply, High-Speed, Precision Logarithmic Amplifier

1 Features

•Advantages:

–Tiny for high density systems

–Precision on one supply

–Fast over eight decades

–Fully-tested function

•Two scaling amplifiers

•Wide input dynamic range: eight decades, 100pA

to 10mA

•2.5V reference

•Stable over temperature

•Low quiescent current: 10mA

•Dual or single supply: ±5V, 5V

•Package: Small QFN-16 (4mm × 4mm)

•Specified temperature range: −5°C to 75°C

2 Applications

•Optical modules

•Inter-DC interconnect

•Optical network terminal unit

•Chemistry/gas analyzer

•Erbium-doped fiber optic amplifier (EDFA)

3 Description

The LOG114 is specifically designed for measuring

low-level and wide dynamic range currents in

communications, lasers, medical, and industrial

systems. The device computes the logarithm or

log-ratio of an input current or voltage relative

to a reference current or voltage (logarithmic

transimpedance amplifier).

High precision is verified over a wide dynamic range

of input signals on either bipolar (±5V) or single

(5V) supply. Special temperature drift compensation

circuitry is included on-chip. In log-ratio applications,

the signal current can be from a high impedance

source such as a photodiode or resistor in series

with a low impedance voltage source. The reference

current is provided by a resistor in series with a

precision internal voltage reference, photo diode, or

active current source.

The output signal at V

LOGOUT

has a scale factor

of 0.375V/decade of input current, which limits the

output so that the output fits within a 5V or 10V

range. The output can be scaled and offset with one

of the available additional amplifiers, so the output

matches a wide variety of ADC input ranges. Stable

DC performance allows accurate measurement of

low-level signals over a wide temperature range. The

LOG114 is specified over a −5°C to 75°C temperature

range and can operate from −40°C to 85°C.

Package Information

PART NUMBERPACKAGE

(1)

PACKAGE SIZE

(2)

LOG114RGV (VQFN, 16)4mm × 4mm

(1)For more information, see Section 10.

(2)The package size (length × width) is a nominal value and

includes pins, where applicable.

+

–

+

–

+

–

I2

I1

V

CM IN

COM

+

–

V

O4

–IN

4

+IN

4

V+

V

REF GND

I

2

I

1

LOG114

V

LOGOUT

REF

V

REF

–

+

V

O5

+IN

5

–IN

5

V–

A.Thermally dependent R

1

and R

3

provide temperature compensation.

B.V

LOGOUT

= 0.375 × log(I

1

/I

2

).

C.V

O4

= 0.375 × K × log(I

1

/I

2

), K = 1 + R

6

/R

5

.

D.Differential Amplifier (A

3

) Gain = 6.25

Functional Block Diagram

LOG114

SBOS301C – MAY 2004 – REVISED DECEMBER 2025

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,

intellectual property matters and other important disclaimers. PRODUCTION DATA.

Produktspecifikationer