DISTORTION AND INTERMODULATION QUALITIES OF A RING MODULATOR WITHOUT TRANSFORMERS FOR HIGH-FREQUENCY BROAD-BAND SYSTEMS

Drawing up a television fibre optic distribution system the distortion qualities of diode modulators, which look well suited for linear translators, were studied theoretically and numerically. Symmetry of the classic ring modulator using differential transformers at high frequencies cannot be produced sufficiently. The deterioration of the linearity because of additional distortions (also of even-numbered order) can be avoided by increasing the carrier amplitude. But the parasitic influence of carrier disturbances cannot be eliminated in this way. Therefore a variant of circuitry, better and more symmetrically realizable, is treated here. If parasitic capacities and inductivities can be neglected, the influence of the non-linear diode characteristics under working conditions can be estimated very exactly also in multichannel systems, using a derived formula. Because of the not neglectible barrier-layer capacitances of the diodes in high frequency applications further distortion and intermodulation products are generated, which are able to reduce the S/N ratio considerably. Such parasitic effects were studied using a special analysis program in conjunction with a flexible simulation system.