Compact CMOS VCO using a transistor for frequency control

A compact CMOS voltage-controlled relaxation oscillator circuit is presented in this paper. The frequency control is fulfilled by using a single MOSFET to control the charging and discharging currents of a timing capacitor. This paper investigates and demonstrates the proposed control mechanism. The proposed VCO was fabricated using 0.18 μm CMOS technology and the fabricated VCO has a compact core size of only 80μm × 200μm, or 0.016mm². A linear tuning range from 650 MHz to 840 MHz, or a 28% range was achieved by the single MOSFET's control from a 1.8V DC supply voltage. The output power was −14.5 dBm with only ±1 dB variation in this tuning range. The corresponding power consumption was measured to be 5.4mW. Moreover, the VCO free-running frequency can be increased beyond 1.1 GHz by using higher DC supply.