9 In this letter, a novel current-mode operational amplifier (COA) is proposed. The proposed COA can operate at 2 V (4-1 V) supply voltage. For high frequency operation it has only an npn transistor in signal path. Finally, SPICE simulation are shown to verify the performance of the proposed COA.
In this paper, a 1-MHz 7th-order Butterworth lowpass filter is designed. The filter is composed of very low distortion CMOS OTAs. The linearity of the OTA is free from mobility reduction and body effect. This is the reason that the OTA shows low distortion characteristics. Thus, the lowpass filter also has low distortion. We confiimed that the filter exhibited very low distortion by simulation. When an input signal with lV(peak-peak) and 333kHz is applied, THD of the lowpass filter becomes only 0.094%.
A linear-in-dB VGA is fabricated in 0.18-pm CMOS technology. It is composed of three cascaded VGAs. Each of them is based on a conventional VGA and a proposed gain control circuit. To avoid devices parameters and temperature behavior on gain characteristics of VGA, a bias circuit is adapted to a proposed gain control circuit. The gain range of 73dB, the gain error of within rt2dB, the NF of 5dB are obtained at 380MHz by measurement, and the maximum current consumption is 6 mA under a single 1.8V power supply.
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