Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsLinear ICsLinear IC - Op-amp Logarithmic TQFN 16 (4x4)

General Description

The MAX4207 logarithmic amplifier computes the log

ratio of an input current relative to a reference current

(externally or internally generated) and provides a cor-

responding voltage output with a default -0.25V/decade

scale factor. The device operates from dual ±2.7V to

±5.5V supplies and is capable of measuring five

decades of input current across a 10nA to 1mA range.

The MAX4207’s uncommitted op amp can be used for

a variety of functions, including filtering noise, adding

offset, and adding additional gain. A 0.5V reference is

also included to generate an optional precision current

reference using an external resistor, which adjusts the

log intercept of the MAX4207. The output-offset voltage

and the adjustable scale factor are also set using exter-

nal resistors.

The MAX4207 is available in a space-saving 16-pin thin

QFN package (4mm x 4mm x 0.8mm), and is specified

for operation over the -40°C to +85°C extended temper-

ature range.

Applications

Photodiode Current Monitoring

Portable Instrumentation

Medical Instrumentation

Analog Signal Processing

Features

♦ ±2.7V to ±5.5V Dual-Supply Operation

♦ 5 Decades of Dynamic Range (10nA to 1mA)

♦ Monotonic Over a 1nA to 1mA Range

♦ -0.25V/Decade Internally Trimmed Output Scale

Factor

♦ Adjustable Output Scale Factor

♦ Adjustable Output Offset Voltage

♦ Internal 10nA to 10µA Reference Current Source

♦ Input Amplifiers Summing Nodes at Ground

♦ Small 16-Pin Thin QFN Package (4mm x 4mm x

0.8mm)

♦ -40°C to +85°C Operating Temperature Range

♦ Evaluation Kit Available (Order MAX4206EVKIT)

MAX4207

Precision Transimpedance Logarithmic

Amplifier with Over 5 Decades of Dynamic Range

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

MAX4207

GND

REFIIN

REFIOUT

LOGIIN

REFISET

SCALE

LOGV2

LOGV1

OSADJ

CMVIN

CMVOUT

REFVOUT

COMP

SET

0.1µF

OUT

0.1µF

COMP

Typical Operating Circuit

19-3070; Rev 1; 6/04

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

PART TEMP RANGE PIN-PACKAGE

MAX4207ETE -40°C to +85°C 16 Thin QFN-EP*

*EP = Exposed paddle.

16 15 14 13

CMVIN

LOGIIN

REFIIN

REFIOUT

N.C.

REFISET

CMVOUT

GND

REFVOUT

N.C.

5678

LOGV1

OSADJ

SCALE

LOGV2

MAX4207

TOP VIEW

(LEADS ON BOTTOM)

THIN QFN

Pin Configuration

Summary of content (15 pages)

PAGE 1
9-3070; Rev 1; 6/04 KIT ATION EVALU E L B A AVAIL Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range The MAX4207 logarithmic amplifier computes the log ratio of an input current relative to a reference current (externally or internally generated) and provides a corresponding voltage output with a default -0.25V/decade scale factor. The device operates from dual ±2.7V to ±5.5V supplies and is capable of measuring five decades of input current across a 10nA to 1mA range.
PAGE 2
MAX4207 Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range ABSOLUTE MAXIMUM RATINGS (All voltages referenced to GND, unless otherwise noted.) VCC ...........................................................................-0.3V to +6V VEE............................................................................-6V to +0.3V Supply Voltage (VCC to VEE) .............................................. +12V REFVOUT ....................................................(VEE - 0.
PAGE 3
Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range (VCC = +5V, VEE = -5V, GND = 0, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ, TA = -40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.
PAGE 4
Typical Operating Characteristics (VCC = +5V, VEE = -5V, GND = 0V, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ, TA = +25°C, unless otherwise noted.) VLOGV1 vs. ILOG 0.50 0.25 0.75 0 0.50 -0.25 -0.50 -0.50 -0.75 -0.75 -1.00 0 -0.25 TA = -40°C TO +85°C VCC = +2.7V VEE = -2.7V -1.00 TA = -40°C TO +85°C -1.25 1µ 10µ 100µ ILOG (A) 1m 10m -0.75 1n 10n 1mA 1.5 100µA 10µ 100µ 1m 10m 1n 100nA 20 1µA 15 10nA 0.
PAGE 5
Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range 10 10 5 5 0 -5 4 0 -5 3 2 1 0 -1 -2 -10 -10 -3 -15 -15 -4 -20 -5 -20 1n 10n 100n 1µ 10µ 100µ IREF (A) 1m 10m MAX4207 toc12 (VCC = +2.7V, VEE = -2.7V) (VCC = +5V, VEE = -5V) (VCC = +5.5V, VEE = -5.5V) 15 ERROR (mV) ERROR (mV) 20 VLOGIIN - VCMVIN (mV) ILOG = 10nA, 100nA, 1µA, 10µA, 100µA, 1mA 15 MAX4207 toc10 20 INPUT OFFSET VOLTAGE (VLOGIIN - VCMVIN vs.
PAGE 6
Typical Operating Characteristics (continued) (VCC = +5V, VEE = -5V, GND = 0V, IREF = 1µA, ILOG = 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, RSET > 1MΩ, TA = +25°C, unless otherwise noted.) VLOGV2 VOLTAGE-NOISE DENSITY vs. FREQUENCY TOTAL WIDEBAND VOLTAGE NOISE AT VLOGV2 vs. ILOG 1 10µA 0.
PAGE 7
Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range REFERENCE POWER-SUPPLY REJECTION RATIO vs. FREQUENCY REFERENCE OUTPUT VOLTAGE (VREFVOUT) vs. SUPPLY VOLTAGE (VCC - VEE) MAX4207 toc24 1.240 CREFVOUT = 0.1µF IREFVOUT = 1mA -10 -20 REFERENCE PSRR (dB) 1.235 1.230 1.225 1.220 1.215 VCC - VEE 5V/div -30 0V -40 -50 -60 -70 VREFVOUT 200mV/div -80 1.210 1.205 -90 1.200 -100 5 6 7 8 9 10 1.
PAGE 8
Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range MAX4207 Pin Description PIN NAME FUNCTION 1, 9 N.C. 2 REFVOUT No Connection. Not internally connected. 3 GND Ground 4 VEE Negative Power Supply. Bypass VEE to GND with a 0.1µF capacitor. 5 LOGV1 Logarithmic Amplifier Voltage Output 1. The output scale factor of LOGV1 is -0.25V/decade. 6 OSADJ Offset Adjust Input.
PAGE 9
Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range VCC VBE1 LOGIIN CMVIN VEE IREF VCC VBE2 REFIIN VEE where: k = scale factor (V/decade) ILOG = the input current at LOGIIN Figure 2. Simplified Model of a Logarithmic Amplifier Detailed Description Theory Figure 2 shows a simplified model of a logarithmic amplifier.
PAGE 10
IDEAL TRANSFER FUNCTION WITH VARYING K VOUT = K LOG (ILOG/IREF) K=1 K = 0.5 K = 0.25 1 0 -1 K = -0.25 K = -0.5 K = -1 -3 -4 0.001 IREF = 100µA 0.5 0 -0.5 -1.0 IREF = 10nA IREF = 1µA -1.5 0.01 0.1 1 10 100 1000 CURRENT RATIO (ILOG/IREF) Figure 3.
PAGE 11
Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range Applications Information Input Current Range Five decades of input current across a 10nA to 1mA range are acceptable for ILOG and IREF. The effects of bias currents increase as I LOG and I REF fall below 10nA. Bandwidth decreases at low ILOG values (see the Frequency Response and Noise Considerations section). As ILOG and IREF increase to 1mA or higher, transistors become less logarithmic in nature.
PAGE 12
MAX4207 Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range Table 1. MAX4207 Example Configurations LOGV2 AMPLIFIER CONFIGURATION Inverting Noninverting INPUT CONDITIONS VLOGV1 ILOG > IREF (constant) Negative Positive ILOG < IREF (constant) Positive Negative ILOG > IREF (constant) Negative Negative ILOG < IREF (constant) Positive Positive Output Offset The inverting configuration utilized by the MAX4207 facilitates large output-offset voltage adjustments.
PAGE 13
Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range MAX4207 VCC 2.2µH 2.7V TO 76V PHOTODIODE BIAS 2.2µF 0.22µF 0.1µF BIAS VCC CLAMP OUTPUT 0.1µF REFVOUT LOGV2 REFIOUT SCALE REFIIN MAX4007 MAX4207 32pF LOGV1 OSADJ 330Ω REFISET IAPD/10 IAPD 5MΩ LOGIIN OUT REF GND FIBER CABLE APD 32pF CMVOUT 330Ω CMVIN GND TIA TO LIMITING AMPLIFIER VEE VEE 0.1µF HIGH-SPEED DATA PATH Figure 6.
PAGE 14
MAX4207 Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range Layout and Bypassing Bypass V CC and V EE to GND with ceramic 0.1µF capacitors. Place the capacitors as close to the device as possible. Bypass REFVOUT and/or CMVOUT to GND with a 0.1µF ceramic capacitor for increased noise immunity and a clean reference current. For lowcurrent operation, it is recommended to use metal guard rings around LOGIIN, REFIIN, and REFISET. Connect this guard ring to CMVOUT.
PAGE 15
Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range 24L QFN THIN.EPS PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm 21-0139 C 1 2 PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm 21-0139 C 2 2 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.