Abstract
In this thesis, we <a href="http://www.ntsearch.com/search.php?q=design&v=56">design</a> an operational transconductance amplifier (OTA) with low distortion and tunable transconductance (Gm). By applying current reusing and gain boosting techniques, the MOS devices in the input stage of the proposed OTA operate in the linear region and the high linear voltage-to-current conversion can be obtained. Using this OTA, a Gm-C filter which is suitable for high frequency operation is constructed. To overcome the process variations, the transconductance of the OTA is tunable so that the cutoff frequency of the Gm-C filter can be set properly. Moreover, an on-chip automatic bandwidth tuning loop is also designed to automatically decide the transconductance of the OTA and compensate most variation effects. To verify the designed circuits, an experimental chip is fabricated in UMC 0.18 mm CMOS process. The realized filter is a 6th-order Butterworth lowpass filter. The power supply voltage is 1.8 V. The measurement results of the filter show that the tuning range of the -3-dB bandwidth is among 5.8 MHz to 7.9 MHz and the DC gain is among –1 dB to –0.12 dB. The total harmonic distortion (THD) is small than –40 dBc when the input signal is 1 MHz sinusoidal waveform with 1.4 Vppd. The input third intercept point (IIP3) is 11 dBV, and the power consumption is 11.75 mW. When activate the on-chip automatic tuning loop, the error of the filter bandwidth is less than 5.3 %.