LOG200 Precision, High-Speed Logarithmic Amplifier

With Integrated Photodiode Bias

1 Features

• Ultra-fast transient response to low current levels:

– Settling time for 10

‑nA to 100‑nA step:

220

‑ns rising, 630‑ns falling (typ)

– Settling time for 100

‑nA to 1‑μA step:

80

‑ns rising, 240‑ns falling (typ)

• Wide dynamic current range:

100 pA to 10 mA (160 dB)

• High signal bandwidth:

– 6 MHz at 1 μA to 10 mA

– 120 kHz at 1 nA

• High-accuracy transfer function:

– 0.2 % max log conformity error

• Integrated reference current (1 μA) and reference

voltages (2.5 V and 1.65 V) for accurate ratio

calculation

• Low reference drift: 20 ppm/°C (typ)

• Additional auxiliary high-speed op amp for

differential ADC drive, single-ended gain or filter

blocks, and other peripheral functions

• Single supply (4.5 V to 12.6 V) or

dual supply (±2.25 V to ±6.3 V) operation

• Low quiescent current: 9.5 mA

• Specified temperature range: –40°C to +125°C

• Small package: 3 mm × 3 mm VQFN

2 Applications

• Optical modules

• Inter-DC interconnect

• Optical network terminal unit

• Chemistry/gas analyzer

• Erbium-doped fiber optic amplifier (EDFA)

+

–

+

–

+

–

I2

I1

PD

Bias

IBIAS

VCM

+

–

REFGND

+

–

2.5 V

1.65 V

REF25

REF165

+

–

REFA

OUTA

OUTB

–IN

+IN

VS+

VS–

VS+

1 μA

IREF

LOG200 Device Schematic

3 Description

The LOG200 is a wide-dynamic-range current-to-

voltage amplifier specifically designed to optimize

current measurements across 160 dB of dynamic

range

with

unparalleled

accuracy

and

speed

for optical communications, medical diagnostics,

and industrial process control measurements. The

LOG200 features two logarithmic amplifiers followed

by a high-accuracy differential amplifier that convert

current signals into a voltage representing the log-

compressed ratio of the two currents. The current

inputs are designed to feature a high-speed response

from one input, and a highly accurate reference

signal on the other input, allowing for a unique

combination of fast transient response and high

logarithmic conformity.

The LOG200 ratio is internally set to 250 mV/

decade of current-to-voltage conversion. The device

integrates an uncommitted high-speed amplifier to

allow the output to be configured for differential or

filtered responses, with a fast settling time to drive

successive approximation analog-to-digital converters

(SAR ADCs). The LOG200 also features a separate

reference current and reference voltage designed to

configure the device for optimized input current and

common-mode voltages.

The LOG200 can be powered in a single-supply

(4.5 V to 12.6 V) or dual-supply (±2.25 V to ±6.3 V)

configuration and is specified from –40°C to +125°C.

Package Information

PART NUMBER

PACKAGE(1)

PACKAGE SIZE(2)

LOG200

RGT (VQFN, 16)

3 mm × 3 mm

(1)

For all available packages, see the orderable addendum at

the end of the data sheet.

(2)

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

includes pins, where applicable.

LOG200

SBOSA28 – AUGUST 2023

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. ADVANCE INFORMATION for preproduction products; subject to change

without notice.