| Summary: | 碩士 === 國立清華大學 === 電機工程學系 === 96 === In this thesis, a 4th-order Butterworth Gm-C filter with low power consumption and high linearity performance for wireless communication applications is designed and implemented in two different structures: common lossless-integrator-based structure and novel lossy-integrator-based one. To increase the linearity of the filter, an operational transconductance amplifier (OTA) with high linearity is introduced. Furthermore, the multi-input OTA structure is employed to reduce the power consumption and the active area. Due to the adjustability of the OTA transconductance, an offline frequency tuning system is also added to overcome the bandwidth inaccuracy which is caused by the process variation.
In order to evaluate the performances of the designed filters, two test chips are fabricated with TSMC 0.18_μm CMOS process and the supply voltage is 1.8 V. The measurement results of the lossless-integrator-based 4th-order filter show that the filter bandwidth is varied from 10 MHz to 8.8 MHz and the DC gain is about -0.74 dB. The total harmonic distortion (THD) is smaller than -40 dBc when the input signal frequency is 1 MHz and the amplitude is less than 1.5 Vppd. Besides, the power consumption of the filter is about 5.5 mW.
According to simulation results, the lossy-integrator-based 4th-order filter has better linearity performance than the lossless-integrator-based one. Its THD is smaller than -40 dBc when the input signal frequency is 1 MHz and the amplitude is less than 1.9 Vppd. Moreover, the power consumption of the lossy-integrator-based 4th-order filter is only 4 mW. By enabling the offline tuning loop, the frequency tuning error is less than 5%.
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