- 學位論文
應用於麥克風自動增益控制放 大器之電路設計
Design of a Microphone Automatic Gain Control Amplifier
摘要
應用於麥克風等的自動增益控制放大器之互補式金氧半場效電晶體所構成的可變增益放大器之設計為本論文的研究核心，藉由一個單電源的軌對軌運算放大器來實現此可變增益放大器。由於是應用在音頻系統，此軌對軌運算放大器需著重於低雜訊、低偏移以及高電源拒斥比。調控增益之方式是使用線性金氧半場效電晶體電阻電路，可使用此系統之輸出電壓回授控制金氧半場效電晶體電阻電路之電阻值，藉此克服原本使用一般電阻而增益無法連續調變之問題。可變增益放大器之增益調變範圍為0dB至20dB，其特點包含輸入信號動態範圍為33dB、線性度佳、總諧波失真小於1%與功率消耗只有1.4mW。並使用0.35um TSMC 2P4M製成與MIMOS 2P3M CMOS製成來設計本論文之電路，以及比較使用不同製程其電路特性之差異。 一般而言，輸入信號有著寬動態範圍，如聲音作為信號源，聲音的大小會使的訊號振福也跟著改變，而在麥克風(電容式麥克風)之應用電路，其目的是讓輸出信號不論原本聲音的大小如何變化，都呈現穩定的輸出振幅(也就是讓聲音大小一致)，因此需要一個平均電路，將變動的交流訊號轉換成一個與交流訊號振幅成正比的直流訊號，並將此直流訊號回授控制可變增益放大器內的金氧半場效電晶體電阻電路。當輸入信號振幅較大時，改變金氧半場效電晶體電阻電路之等效電阻值使可變增益放大器之增益下降，反之，則使之上升，以達到自動回授控制之目的。
並列摘要
This research describes the design of a CMOS variable gain amplifier for use in the microphone AGC amplifier and can be used in similar applications. The VGA is realized by a single supply rail-to-rail input and output CMOS operational amplifier (OPA). The OPA is designed to be with low noise, low offset and high PSRR. Variable gain is realized by using linearized MOS resistive circuits (MRC) as voltage-controlled resistors thereby overcoming discrete gain step limitation set by using resistors. These MRC has excellent controllability as well as high linearity in spite of MOSFET nonlinearity. The VGA which is designed at gain setting of 20dB has a variable gain range from 20dB to 0 dB. It exhibits an input signal dynamic range of 33dB and exhibits a good linearity and a total harmonic distortion (THD) of less than 1%. The VGA also exhibits a simulated power consumption of 1.4mW. This robust circuit is designed and compared in both 0.35um TSMC 2P4M and 0.35um MIMOS 2P3M CMOS technologies. Input signal having a wide dynamic range coming from different sources (i.e. voice), will be fed through an electret condenser microphone (ECM). With the wide dynamic range of the input signal, an averaging circuit is used to convert the AC signal from the output of the first stage amplifier (VGA) to DC voltage which will then be used as the control voltage to vary the resistance of MRC. The VGA acts in such manner that when the input signal is low, gain becomes high and while the input signal is high, the gain becomes low.