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ADI 公司的確ADL5304是高速200dB測量范圍的對數(shù)轉(zhuǎn)換器,具有快速響應(yīng)和低噪音,正常對數(shù)斜率10 mV/dB(200 mV/decade),單電源工作的輸入電流在1pA到3mA,雙電源工作的輸入電流可擴(kuò)展至10mA,輸入電流大于1uA時(shí)的帶寬大于4MHz,主要用在高精度光功率測量,寬范圍基帶對數(shù)壓縮和高速APC回路的檢測.本文介紹了ADL5304主要特性,簡化方框圖,多種參數(shù)測量電路圖以及單電源工作基本連接圖,評估板電路圖和PCB布局圖. The ADL5304 is a high speed logarithmic converter with fast response and low noise over a 200 dB (1 pA to 10 mA) measurement range. The ADL5304 provides a nominal logarithmic slope of 10 mV/dB (200 mV/decade); other values are easily configured. Logarithmic intercept can be programmed over a wide range with the internal 100 nA current source or externally for log ratio applications. The default intercept value of 3.162 fA places the midpoint of the measurement range of 100 nA at VLOG = 1.5 V. A single positive supply of 5 V is all that is required for operation over a specified 1 pA to 3 mA input range. Dual-supply operation extends the specified input current range to 10 mA. The ADL5304 accepts two current inputs to the logarithmic argument. The numerator input, INUM, flows in the collector of an NPN transistor, connected in a feedback path around a low offset JFET amplifier. The denominator current, IDEN, is treated in the same way, which allows for log ratio operation. The input summing nodes (INUM and IDEN) operate at a constant default voltage of 1.5 V. The VSM1 to VSM4 pins flank the INUM and IDEN inputs to provide a guard voltage to minimize leakage currents. Adaptive photodiode biasing is provided for optical measurements. A monitor current 1.1 times INUM is output at the IMON pin, and an external resistor, RMNTR, at 10 times the photodiode series resistance (RS) applies a voltage across the photodiode that 1st order keeps the internal PD junction at 0 V to minimize dark current. The VLOG output is buffered and can be rescaled through internal gain setting resistors. The internal ILOG varies from −400 μA to +400 μA as INUM changes over 10 decades from 1 pA to 10 mA. This corresponds to 0.5 V to 2.5 V at the VLOG pin in the default configuration shown in Figure 1. Accurate 1.5 V (Pin 1P5V) and 2.0 V (Pin 2VLT) reference outputs allow precise repositioning of the intercept using external resistors. The ADL5304 is available in a 32-lead, 5 mm × 5 mm LFCSP and specified for operation from −40°C to +85°C. ADL5304主要特性: Optimized for very fast response at all input currents Overall bandwidth of >4 MHz for inputs >1 μA Bandwidth: 25 kHz at input of 1 nA and 350 kHz at 10 nA 10 decades of input range: 1 pA to 10 mA Law conformance: ±0.25 dB from 100 pA to 100 μA Log ratio or fixed-intercept operation Precision voltage references and reference current Adaptive photodiode (PD) bias for low dark current Programmable log slope and intercept Default log slope of 10 mV/dB at VLOG pin Single- or dual-supply operation ADL5304應(yīng)用: High accuracy optical power measurement Wide range baseband log compression Versatile detector for high speed APC loops 
圖1.ADL5304簡化方框圖
圖2.ADL5304測量對數(shù)/斜率/失調(diào)一致性電路圖
圖3.ADL5304測量帶寬電路圖
圖4.ADL5304測量脈沖設(shè)定電路圖
圖5.ADL5304測量光電二極管脈沖響應(yīng)電路圖
圖6.ADL5304測量輸出電路圖
圖7.ADL5304測量IMON脈沖響應(yīng)電路圖
圖8.ADL5304測量噪音定電路圖: INUM = 100 pA, INUM = 1 nA,和INUM = 10 nA
圖9.ADL5304單電源工作基本連接圖
圖10.ADL5304評估板電路圖
圖11.ADL5304評估板PCB布局圖 詳情請見: 
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