using inductors instead of the FBAR. In their work, they also propose a gm-boosting method by replacing the inductor with a transformer to increase the gain. Fig. 38 shows a method proposed by [85] to create a complementary cross-coupled oscillator. In this circuit, the two FBARs are replaced with a single FBAR and the NMOS transistor MN2 is replaced by the PMOS MP2 and connected to VDD. A mass sensing circuit using FBAR based on this configuration is presented in [95]. In [96], they propose a complementary Colpitts oscillator that takes advantage of this configuration to boost the gain of the complementary Colpitts oscillator as shown in Fig. 39. FBAR2 FBAR1 Vout1 MN2 MN1 Vout2 Vbias2 MN3 (a) FBAR Vbias2â² MP2 C2 Vbias1â² MP1 C1 Vout1 MP1 MN1 Vout2 (b) Vout1 FBAR FBAR MP1 Vout2 Vbias1 MN1 C1 Vbias2 MN2 C2 Vout2 FBAR Vout1 MN1 (c) Figure 36. By stacking a PMOS and NMOS version of CG Colpitts, a complementary differential common gate Colpitts oscillator can be created [84]. Figure 38. Evolution of the cross-coupled to complementary. Vbiasâ² Vbias2 â² Vbias1â² MP2 C2 MP1 C1 Vout1 FBAR FBAR C1 Vbias2 MN2 C2 Figure 37. A complementary differential common gate Colpitts oscillator. 20â Vout2 Vout2 MN1 C1 MP1 Vout1 Vbias1 C2 MP2 Vbias MN1 C1 MN2 C2 Figure 39. Complementary gm-boosted common gate differential Colpitts topology [96]. IEEE CIRCUITS AND SYSTEMS MAGAZINE FOURTH QUARTER 2020