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本帖最后由 meinhard8 于 2014-2-8 15:37 编辑
国外一个个人网站上提供了如下的电感测试电路,测试档位为,200纳亨,2000纳亨,20微亨,200微亨,2000微亨,5个档位,主要是测量高频电路中的电感元件。自己估测测试原理大概是矢量测量方法。下面提供原文的说明和图纸。请高手帮忙解析下,测量原理,以及提供出后面运放增益的定量计算。
this inductance meter is simple. The meter operates by forcing a constant 100kHz sinusoidal current through the inductor (Lx) and measuring the magnitude of the quadrature voltage generated across it. This voltage leads the current by 90º. The amplitude of the quadrature component of the voltage across Lx may be recovered by synchronous demodulation, with the demodulator's reference signal provided by a +90º phase-shifted version of the current source signal. When the demodulator output is integrated, the out-of-phase components cancel and the in-phase (quadrature)components add to create a DC signal which is proportional to the peack amplitude of the in-phase component.
The reference sine wave is generated by a 100kHz crystal oscillator using a gate of an CD4011.This reference is used by the demodulator and after amplitude scaling by the range switch, to the voltage-controlled current source, which drives the inductor.
The currents through inductor is low enough to not cause saturation of sensitive ferrite core. 20mA pk/pk on 200nH and 2uH ranges, and 200uA on the 2mH range. The voltage generated across inductor is amplified by two amplifiers, separated by a range switch attenuator. This amplifiers are part of a TL084.
The synchronous demodulation is performed by MC1496, an RF double balanced modulator/demodulator. The phase-shifted reference signal through a passive RLC network, drives the top differential pairs into saturation, while the bottom differential pair is driven linearly by the amplified signal Vx, across Lx. When the reference signal is the same frequency as Vx (across Lx) and is saturating the top pairs, the output of the demodulator is a function of the amplitude and phase of Vx. The output of MC1496 is used differentially to avoid DC drift problems, is filtered and drives the digital voltmeter. The range of the inductance meter is 1nH to 2mH.
当下,我已经按图纸进行了实物装配,100KHZ振荡器以及后续TL062组成的恒流电路都已经调试正常,MC1496构成的同步整流电路也调试正常,但是由TL084的4个运放构成的测试信号放大电路,我理解不透彻,这里烦请高手定量解析一下,方便我对这个适配器的校准工作。
清晰一些的讲,我的疑问是1:TL084构成电路的电压增益是多少,2:以及这个电压增益是如何计算出来的。3:测试的信号整流出来以后是100KHZ的有效值还是平均值,以及这个值和被测电感的对应关系?
烦请论坛内,对测试电路精通的朋友给以解答。 |
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曾经有一段真挚的爱情摆在我的面前,我没有珍惜,现在想起来,还好我没有珍惜……
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