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A multiloop method is presented for highly nonlinear ring oscillators in this paper. This circuit permits lower tuning gain through the use of coarse/fine frequency control, which also translates into a lower sensitivity to the voltage at the control lines. A 8-GHz VCO in SMIC 0.18ȝm 1P6M CMOS technology is designed. The linear tuning range of VCO is from 7.95 to 8.45GHz with the tuning voltage vary from 0 to 1.8V. The post simulation result shows that the power consumption is 48mW, the phase noise of the proposed VCO is -88.24dBc/Hz at 1MHz and -113.2dBc/Hz at 10MHz, and core chip area is 130 ȝm × 120 ȝm.

We present both a theoretical and experimental demonstration of a fully differential variable gain amplifier (VGA) with small total harmonic distortion (THD) for an electrocardiogram (ECG) acquisition system. Capacitive feedback technology is adopted to reduce the nonlinearity of VGA. The fully differential VGA has been fabricated in SMIC 0.18-m CMOS process, and it only occupies 0.11 mm 2 . The measurements are in good agreement with simulation results. Experimental results show that the gain of VGA changes from 6.17 to 43.75 dB with a gain step of 3 dB. The high-pass corner frequency and low-pass corner frequency are around 0.22 Hz and 7.9 kHz, respectively. For each gain configuration, a maximal THD of 0.13% is obtained. The fully differential VGA has a low THD and its key performance parameters are well satisfied with the demands of ECG acquisition system application in the UWB wireless body area network.