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ADL5306ACP-R2 Datasheet(PDF) 1 Page - Analog Devices |
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ADL5306ACP-R2 Datasheet(HTML) 1 Page - Analog Devices |
1 / 16 page 60 dB Range (100 nA to 100 µA) Low Cost Logarithmic Converter ADL5306 Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective companies. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 © 2003 Analog Devices, Inc. All rights reserved. FEATURES Optimized for fiber optic photodiode interfacing Measures current over 3 decades Law conformance 0.1 dB from 100 nA to 100 μA Single- or dual-supply operation (3 V to ±5.5 V total) Full log-ratio capabilities Temperature stable Nominal slope of 10 mV/dB (200 mV/decade) Nominal intercept of 1 nA (set by external resistor) Optional adjustment of slope and intercept Rapid response time for a given current level Miniature 16-lead chip scale package (LFCSP 3 mm × 3 mm) Low power: ~5 mA quiescent current APPLICATIONS Low cost optical power measurement Wide range baseband logarithmic compression Measurement of current and voltage ratios Optical absorbance measurement GENERAL DESCRIPTION The ADL5306 ∗ is a low cost microminiature logarithmic converter optimized for determining optical power in fiber optic systems. The ADL5306 is derived from the AD8304 and AD8305 translinear logarithmic converters. This family of devices provides wide measurement dynamic range in a versatile and easy-to-use form. A single-supply voltage between 3 V and 5.5 V is adequate; dual supplies may optionally be used. Low quiescent current (5 mA typical) permits use in battery-operated applications. IPD, the 100 nA to 100 µA input current applied to the INPT pin, is the collector current of an optimally scaled NPN transistor that converts this current to a voltage (VBE) with a precise logarithmic relationship. A second converter is used to handle the reference current, IREF, applied to IREF. These input nodes are biased slightly above ground (0.5 V). This is generally acceptable for photodiode applications where the anode does not need to be grounded. Similarly, this bias voltage is easily accounted for in generating IREF. The logarithmic front end’s output is available at VLOG. The basic logarithmic slope at this output is 200 mV/decade (10 mV/dB) nominal; a 60 dB range corresponds to a 600 mV output change. When this voltage (or the buffer output) is applied to an ADC that permits an external reference voltage to be employed, the ADL5306’s 2.5 V voltage reference output at VREF can be used to improve scaling accuracy. FUNCTIONAL BLOCK DIAGRAM TEMPERATURE COMPENSATION BIAS GENERATOR 451 Ω 14.2k Ω 80k Ω 20k Ω RREF 200k Ω 6.69k Ω COMM COMM COMM VNEG VSUM VPOS INPT VREF NC IREF 0.5V +5V 2.5V 0.5V VBE1 ILOG VBE2 VOUT SCAL BFIN VLOG 03727-0-001 0.2 log10 ( ) IPD 1nA 1k Ω 1k Ω 1nF 1nF 1nF VBIAS IPD Q2 Q1 Figure 1. Functional Block Diagram The logarithmic intercept (reference current) is nominally positioned at 1 nA by using the externally generated, 100 µA IREF current provided by a 200 kΩ resistor connected between VREF, at 2.5 V, and IREF, at 0.5 V. The intercept can be adjusted over a narrow range by varying this resistor. The part can also operate in a log-ratio mode, with limited accuracy, where the numerator and denominator currents are applied to INPT and IREF, respectively. A buffer amplifier is provided to drive substantial loads, raise the basic 10 mV/dB slope, serve as a precision comparator (threshold detector), or implement low-pass filters. Its rail-to-rail output stage can swing to within 100 mV of the positive and negative supply rails, and its peak current-sourcing capacity is 25 mA. A fundamental aspect of translinear logarithmic converters is that small-signal bandwidth falls as current level diminishes, and low frequency noise-spectral density increases. At the 100 nA level, the ADL5306’s bandwidth is about 100 kHz; it increases in proportion to IPD up to a maximum of about 10 MHz. The increase in noise level at low currents can be addressed by using a buffer amplifier to realize low-pass filters of up to three poles. The ADL5306 is available in a 16-lead LFCSP package and is specified for operation from–40°C to +85°C. ∗ Protected by US Patents 4,604,532 and 5,519,308; other patents pending. |
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