A Compact Low-Power Biquad for Active-RC Complex Filter

A low-power complex filter based on high-efficient biquad is presented under low-voltage application in this brief. In order to achieve higher shift frequency, one improved biquad is proposed to overcome the essential limitation of the original structure. It costs less power and becomes more compact compared to the Tow Thomas biquad. In order to further reduce the power consumption, an amplifier suitable for low-voltage application is employed. To overcome the variation of resistance and capacitance, a simple on-chip tuning strategy through the calibration of resistor is integrated. To validate the improved biquad, a fourth-order complex filter is fabricated in TSMC 0.13 mu m standard RFCMOS technology. The measured results show that the complex filter consumes 0.5 mA with a 0.7-V power supply. It is centered at 1.65 MHz with 0.9-MHz -0.5 dB-bandwidth and the image rejection is about 18.33 dB with the voltage gain of 8.1 dB.