A Differential Ring Oscillator With Tail Current Source Control Scheme Using N-Type Oxide TFTs

In this article, a voltage-controlled oscillator (VCO) design using n-type metal oxide thin-film transistor (TFT) technology is proposed. The VCO has a differential structure delay cell based on a tail current source control scheme. The circuits were fabricated on a glass substrate using our ITO-stabilized ZnO TFT technology. According to tape-out test results, under a 15-V power supply voltage, the presented VCO can reach a 111.23–171-kHz tuning range, a 4.28-kHz/V tuning sensitivity, and 4% linearity error. When the control voltage changes from 2 to 15 V, the VCO gain range is 177.5–181.9 kHz/V. The phase noise performance was also analyzed. At 150 kHz, the phase noise of the VCO is −74.5 dBc/Hz at a frequency offset of 340 kHz. In addition, the circuit power consumption at the maximum oscillation frequency is 1.5 mW. These results indicate that the VCO can be applied to transparent and flexible sensors and digital signal processor (DSP) electronics with moderate speed requirements.