ZHCSSH5A August 2023 – December 2024 LOG200
PRODMIX
- 1
- 1 特性
- 2 應(yīng)用
- 3 說明
- 4 Pin Configuration and Functions
- 5 Specifications
- 6 Detailed Description
- 7 Application and Implementation
- 8 Device and Documentation Support
- 9 Revision History
- 10Mechanical, Packaging, and Orderable Information
封裝選項(xiàng)
請(qǐng)參考 PDF 數(shù)據(jù)表獲取器件具體的封裝圖。
機(jī)械數(shù)據(jù) (封裝 | 引腳)
- RGT|16
散熱焊盤機(jī)械數(shù)據(jù) (封裝 | 引腳)
- RGT|16
訂購(gòu)信息
7.1.1 Logarithmic Transfer Function
The LOG200 uses a differential amplifier to compare the voltage outputs of two logarithmic amplifiers. Logarithmic amplifiers rely on the feedback transistor relation of the base-emitter voltage (VBE) to the collector current IC, according to the principle:
where
- k = the Boltzmann constant, 1.381 × 10-23J/K
- T = absolute temperature in kelvins (K)
- q = the elementary charge, 1.602 × 10-19C
- IS = the transistor reverse saturation current
For the basic logarithmic amplifier implementation shown in Figure 7-1, the following expression holds:
Figure 7-1 Basic Logarithmic
AmplifierWhen a difference amplifier with reference voltage VREF is implemented to compare the outputs of two logarithmic amplifiers with input currents I1 and I2,
As IS1 is approximately equivalent to IS2 by design, this equation is equivalent to:
Figure 7-2 LOG200 Difference AmplifierIn the LOG200, the internal input resistors of the difference amplifier have a positive temperature coefficient to compensate for the temperature dependence of the above expression. The difference amplifier also gains up the nominal output, such that the output of the LOG200 is:
where K is the device scaling factor, nominally 250mV/decade. Thus, for each decade or order of magnitude shift in the difference of I1 and I2, the device output is correspondingly shifted by 250mV (such as by 250mV for I1 = 10μA and I2 = 1μA, or by –500mV for I1 = 10nA and I2 = 1μA).