高頻互補式金氧半導體轉置電導-電容式連續時序濾波器

Abstract

對訊號處理系統而言，連續時序(continuous-time)濾波是非常重要的而 且常是決定整個系統性能優劣的主要因素。 本論文提出以轉置電導 --容(transconductance-C)積分器為組成元件， 所設計成可工作於高頻 的CMOS類比濾波器。首先，我們描述一應用交叉耦合(cross-coupled)的 飽和電晶體所組成的完全差洞(fully-differential) 運算轉置電導放大 器(operational transconductance amplifier) 。 由於採用交叉耦合的 架構，偶次和奇次的非線性效應，都可以大大地降低。 利用此一電路， 可以組成一線性具可調性的積分器，而運用此積分器就可以設計高頻濾波 器。 因為這一積分器的直流增益是可以調整的，因此由其組成的濾波器 的特性也是具可調性的。利用0.8um n-well CMOS製程所設計而成的高頻 互補式金氧半導體轉轉置電導-電容帶通(bandpass)濾波器的晶片已經製 做完成，它的中央頻率(center frequency)和特性值(quality factor)都 可經改變外界提供的控制電壓而達到調整的目的。頻率的可調範圍是從 10MHz 到 40MHz。當輸入訊號的峰值達到 2.1伏特時，總諧失真(total harmonic distor- tion)小於 -30dB。 整個晶片(不含pad) 為0.4平方釐 米，功率消耗為45毫瓦，電壓源為單一5伏特。 Continuous-time filtering is a crucible and often the limit- ing factor of performance of signal processing systems.The the- sis presents CMOS circuits for integrated analog filter at high frequencies, based on transconductance-C integrators. First,a fully-differential OTA (Operational Transconductance Amplifier) based on crosscoupled MOS transistors operated in sa- turation region is described.Due to the cross-coupled topology, both the even and odd nonlinearities could be eliminated. The OTA has a tunable transconductance, resulting in a adjustable resistance. With this circuit,a linear tunable integrator for HF filters can be made. The quality factor of the integrator is adjustable due to the availability of the variable-conductance transconductors. Experimental results of a HF CMOS transconductance-C bandpass filter realized in 0.8um n-well CMOS technology are given. Both the center frequency and the quality factor can be adjusted through the external control voltages. The center frequency can be varied in the range of 10 MHz to 40 MHz. The total harmonic distortion is less than -30dB with a peak-to-peak input amplit- ude of 2.1V. Active area is 0.4mm2 and the filter consumes 45mW from a single 5V power supply.