A low power quadrature and divide-by-two frequency VCO design mixer with charge-injection for biomedical applications

A new fully integrated, low power complementary cross-coupled quadrature voltage-controlled oscillator (QVCO), divide-by-two frequency divider and double-balance mixer for biomedical applications are presented. The features of our proposed circuit are using charge recycling technique to reduce current from the divider, employing adaptive body-biasing technique (ABB) to drop the minimum voltage clearance of the VCO and achieving two quadrature frequencies which are 2.0 GHz and 4.0 GHz bands. The VCO use differentially tuned MOS varactors can diminish the bad effect of high varactor sensitivity by excluding the common-mode noise. The proposed QVCO and double-balance mixer were implemented in 0.18 um CMOS process with 1.8 V supply voltage, is employed to modulate a wireless communication signal for proposed interactive intelligent healthcare monitoring system (IIHMS). Measured results indicate the divider output frequency is tunable from 1.91 GHz to 2.07 GHz and the QVCO output is from 3.82 GHz to 4.14 GHz, corresponding to 8.05 %. The phase noise of the QVCO operating at 2.02 GHz is -121.8 dBc/Hz at 1 MHz offset. This QVCO draws 2.61 mA and 4.7 mW power consumption. The output power is -17.15 dBm with a 50-Ω load at the frequency of 2.02 GHz. The broadband CMOS double-balance mixer input return loss is higher than 8.5 dB.