A study of the transfer function of contact-modulated amplifiers
F. H. Krantz, O. M. Salati, R. S. Berkowitz · Transactions of the American Institute of Electrical Engineers Part II Applications and Industry · 1957
CONTACT MODULATORS, or “choppers,” are frequently used in modern circuit design where modulation (or demodulation) at a fixed frequency is required. Their advantages for this service include extremely high ratios of open-circuit to closed-circuit resistance, almost negligible internal noise, and excellent stability and reproducibility. These properties make the contact modulator particularly suitable for use in several types of d-c and a-c amplifiers as well as in d-c servomechanisms employing a-c control elements.