The Modified 'Switching-Modulator' for Generation of AM and DSB-SC: Theory and Experiment

The 'switching-modulator' or the 'square-law' modulator can be used for generating amplitude modulation (AM/DSB), while the 'ring-modulator' or the balanced modulator can be used to generate double-side-band-suppressed-carrier (DSB-SC) in the laboratory. For decades it has been accepted that different circuits are required for generating these two forms of AM, which differ only in the presence or absence of the independent carrier. In this work, we have modified the switching-modulator by introducing an additional active device. With this modification, the modulator becomes capable of generating AM with varying depths of modulation, including the DSB-SC. Thus a single circuit can be used to generate both the DSB and the DSB-SC. We give the theory and the experimental results of the modified 'switching modulator'. The simplicity of the proposed method makes it ideally suited for laboratory implementation.