In [97], the authors emphasize the amplitude imbalance of the output signal of this configuration, which is relatively larger than the conventional cross-coupled oscillators due to the asymmetric configuration of this oscillator. They propose a feedback method to compensate for this by biasing the transistors MN2 and MP2 by a voltage taken in middle of the inductor in the tank. V. Common Source Colpitts Oscillator Fig. 40 shows a single-ended common source Colpitts oscillator, where the inductor L1 is connected between the input and the output of a common source amplifier. L1 forms a tank with capacitors C1 and C2. A coupling capacitor in series with L1 is normally needed, as shown in Figs. 1 and 2 to avoid DC short circuit between input and the output of the amplifier. This capacitor is omitted in the following figures for simplifying the description and understanding. The common source topology is the one that resembles the circuit proposed by Colpitts in 1918. [33] presents one of the first CS amplifiers, where a JFET is used to realize the oscillator. The Metal Oxide Semiconductor Field Effect Transistor (MOSFET) implementation of this configuration was proposed as early as 1956 [33]. This configuration is the only one Vbias using an inverting amplifier and can also be realized using a digital inverter as the gain stage [98]-[100] as shown in Fig. 41. Fig. 42 shows a cascoded CS oscillator realized by stacking two amplifiers, i.e. a common gate amplifier (transistor MN1) on a common source amplifier to increase the gain and improve the circuits output immunity to the load. Authors in [101] present a bipolar version of this circuit and a comparison of this circuit with a common collector with a emitter follower as buffer is presented in [102]. A. Differential Push-Push Common Source Colpitts Oscillator Fig. 43 shows a gm-boosted differential common source Colpitts oscillator proposed by [103]. The circuit is made of two single-ended common source oscillators connected to each other using a PMOS cross-coupling between transistors Mp1 and Mp2. The cross-coupling gives the oscillator gm-boosting and also makes the outputs of the circuit differential. The capacitors between the gates of the NMOS transistors are replaced by a single capacitor C3. C3 can be made variable for tuning the resonance frequency of the oscillator. Vbias1 Mp L1 Vout Mn C1 Vbias2 L1 C2 Vout Mn1 Mn C2 Figure 40. A single-ended common source Colpitts oscillator. Mp C1 Figure 42. Common source Colpitts oscillator connected to a common gate output stage formed by transistor Mn1. Mp MP1 Vout L C1 Mn C2 MP2 Vout2 Vout1 C1 L2 L1 MN1 MN2 C2 C3 Figure 41. Inverter-based Colpitts oscillator. FOURTH QUARTER 2020 Figure 43. gm-boosted common source Colpitts differential oscillator. IEEE CIRCUITS AND SYSTEMS MAGAZINE 21