23.97GHz CMOS Distributed Voltage Controlled Oscillators with Inverter Gain Cells and Frequency Tuning by Body Bias and MOS Varactors Concurrently

Tunable VCOs operating around 24 GHz in 0.18 ¿m CMOS are reported. Simple CMOS inverters are used as gain stages and tuning is achieved with a novel method using both body-bias as well as MOS varactors concurrently and compared for performances. The novel tuning method allows for a wider tuning range than using a single method. Here forward body bias (FBB) type tuning of p-FETs has 9-10 times higher tuning bandwidth as compared to MOS varactors tuning when the latter is connected in series (before output collection point) but equal or nearly equal tuning when the varactor pair is connected in parallel (to drain transmission line). Six monolithically integrated novel distributed voltage controlled oscillators (D-VCOs) with a novel gain cell comprising of CMOS inverter are designed. Top Layer metal is used for coplanar waveguide (CPW) for onchip inductors. First D-VCO OSC-1 has 3-stages of the gain cell and oscillating at 23.97 GHz, the second D-VCO OSC-2 has 4-stages of gain cell and oscillating at 18.64 GHz, both K-band oscillators use body bias variation of p-FETs for wide frequency tuning. For further tuning after body bias type of tuning, MOS Varactors are added in series to OSC-1 and OSC-2 resulting in designs respectively OSC-3 and OSC-4, while in parallel resulting in designs respectively OSC-3a and OSC-4a. OSC-3 is oscillating at 23.53 GHz and OSC-4 is oscillating at 18.09 GHz. OSC-3a is oscillating at 22.79 GHz with 340 MHz tuning by each of these two tuning techniques (doubling of tuning bandwidth as total tuning is 680 MHz). OSC-4a is oscillating at 17.77 GHz (resulting Ku-band VCO from K-band for substantial design reuse) with 240 MHz tuning by FBB and 200 MHz tuning by varactor pair (total tuning of 440 MHz). The phase noise is reported at 1 MHz offset from the carrier, for example it is -102.4 dBc/Hz for 18.64 GHz D-VCO. These oscillators are emitting very low power in 2nd and 3rd harmonics.