70MHz Band-Pass Gm-C Filter with Automatic Frequency Tuning

• Main Authors: Chien-Fu Chen, 陳建輔
• Other Authors: 余繁
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/24174057631605508721

碩士 === 淡江大學 === 電機工程學系碩士班 === 93 === The analog filter is the primary element of electronic circuit. Nowadays, signal processing system had been forced to design the digital circuit, but we are living in the analog world actually. As the result, the analog filter is necessary as an interface between analog and digital. Because the integrated circuit is growing quickly, the high frequency circuits and SOC (system on a chip) is designed. Based on these two techniques, the high frequency integrated filter is more needed in the future. In the development of integrated filter circuit, which can be differentiated between passive filter technique and active filter technique. Based on the SOC, the integrated active filter would be preferred, because the integrated active filter has small chip size and low active power. In order to achieve high operation frequency, we choose the continuous-time filters which is made by operational transconductance amplifier (OTA) and capacitors. The research of this thesis is to design a new operational transconductance amplifier (OTA) which can achieve a 70MHz band-pass filter. The band-pass filter has simulated by TSMC 181P6M technology model. The property of integrated active-filter is decided by its transconductance value, linearity and linear Range. Those will affect frequency response, total harmonic distortion (THD) and input signal range. In this new operational transconductance amplifier, the fully differential structure is preferred, because it has better noise immunity and distortion properties. We use cross-coupling and unbalanced differential pairs as input stages which can increase and compensate transconductance value, linearity and linear range. In order to solve process variation, the automatic frequency tuning is used. It utilizes the phase characteristic of band-pass filter to product Vtune, the error voltage Vtune can be applied to control the frequency. As the result, the center frequency of fourth order band-pass can operate at 70MHz.