Noise Reduction in Transistor Oscillators: Part 3—Noise Shifting Techniques

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  • Author: Andrei Grebennikov
In modern wireless communication sys-tems, cross-coupled oscillators have been pre-ferred over other topolo-gies for monolithic inte-grated circuit implemen-tation because they are easily realized using CMOS technology and differential circuitry. However, because the current-source transis-tor is top or tail located, to improve the phase noise performance, it is necessary to use the special filtering techniques for second har-monic suppression. Therefore, the new oscilla-tor topologies based on classical types of oscil-lators can overcome this problem when one of the active device ports is grounded [28]. In addition, these topologies provide larger oscil-lation amplitude for a given bias current because there is no voltage drop of the DC cur-rent across the current-source transistor, sim-ilar to the differential voltage-biased VCO.