Datasheet ADL5304 (Analog Devices)

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High Speed, 200 dB Range, Logarithmic Converter Data Sheet ADL5304 FEATURES
A single positive supply of 5 V is al that is required for operation
Optimized for very fast response at all input currents
over a specified 1 pA to 3 mA input range. Dual-supply operation
Overall bandwidth of >4 MHz for inputs >1 µA
extends the specified input current range to 10 mA.
Bandwidth: 25 kHz at input of 1 nA and 350 kHz at 10 nA
The ADL5304 accepts two current inputs to the logarithmic
10 decades of input range: 1 pA to 10 mA
argument. The numerator input, INUM, flows in the collector of an
Law conformance: ±0.25 dB from 100 pA to 100 µA
NPN transistor, connected in a feedback path around a low offset
Log ratio or fixed-intercept operation
JFET amplifier. The denominator current, IDEN, is treated in the
Precision voltage references and reference current
same way, which al ows for log ratio operation. The input summing
Adaptive photodiode (PD) bias for low dark current
nodes (INUM and IDEN) operate at a constant default voltage of
Programmable log slope and intercept
1.5 V. The VSM1 to VSM4 pins flank the INUM and IDEN inputs
Default log slope of 10 mV/dB at VLOG pin
to provide a guard voltage to minimize leakage currents.
Single- or dual-supply operation
Adaptive photodiode biasing is provided for optical measurements.
APPLICATIONS
A monitor current 1.1 times INUM is output at the IMON pin, and
High accuracy optical power measurement
an external resistor, RMNTR, at 10 times the photodiode series
Wide range baseband log compression
resistance (RS) applies a voltage across the photodiode that
Versatile detector for high speed APC loops
1st order keeps the internal PD junction at 0 V to minimize dark current.
GENERAL DESCRIPTION
The VLOG output is buffered and can be rescaled through The ADL5304 is a high speed logarithmic converter with fast internal gain setting resistors. The internal ILOG varies from response and low noise over a 200 dB (1 pA to 10 mA) measure- −400 µA to +400 µA as INUM changes over 10 decades from 1 pA ment range. The ADL5304 provides a nominal logarithmic slope of to 10 mA. This corresponds to 0.5 V to 2.5 V at the VLOG pin 10 mV/dB (200 mV/decade); other values are easily configured. in the default configuration shown in Figure 1. Logarithmic intercept can be programmed over a wide range with the internal 100 nA current source or external y for log ratio Accurate 1.5 V (Pin 1P5V) and 2.0 V (Pin 2VLT) reference outputs applications. The default intercept value of 3.162 fA places the al ow precise repositioning of the intercept using external resistors. midpoint of the measurement range of 100 nA at VLOG = 1.5 V. The ADL5304 is available in a 32-lead, 5 mm × 5 mm LFCSP and specified for operation from −40°C to +85°C.
SIMPLIFIED BLOCK DIAGRAM IMON VNUM INNM 1P5V BSDC 2VLT VPOS DCBI 30 32 31 26 28 17 29 27 INPS 1.5V 24 2V MONITOR AND RMNTR PD BIAS INMS VSM1 100nA BIAS AND 23 2 (1.1× INUM) VREF VSM2 1.5V VLOG 3 22 ADL5304 INUM 4 SCL1 VNUM ILOG 21 5kΩ 5kΩ IDEN 5 TEMPERATURE SCL2 20 COMPENSATION 7.5kΩ IREF 6 19 SCL3 VDEN VSM3 7 ACOM 18 VSM4 1.5V 8 COMM NMFS VNEG DNFS ACOM HFCP 9 10 11 12 13 14 15 16 VDEN INDN 1kΩ 1kΩ
001
V
09459-
NEG
Figure 1.
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Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION SIMPLIFIED BLOCK DIAGRAM TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS TEST CIRCUITS TERMINOLOGY THEORY OF OPERATION BASIC CONCEPTS OPTICAL MEASUREMENTS Decibel Scaling CIRCUIT DESCRIPTION Bandwidth vs. Current Noise vs. Current Filtering to Improve Noise and Dynamic Behavior Photodiode Bias Reference Outputs Buffer Amplifier Setting the Log Slope and Intercept Slope Inversion Log Ratio Operation APPLICATIONS INFORMATION USING THE ADL5304 Using the Adaptive Bias Summing Node Voltage Leakage VLOG Output Dynamic Response USING A NEGATIVE SUPPLY EVALUATION BOARD SCHEMATIC AND SILKSCREENS OUTLINE DIMENSIONS ORDERING GUIDE