Digital amplitude modulator - transmitter

摘要

A digital amplitude modulator for use in transmitting information signals in the context of AM audio and AM video. The amplitude modulator/transmitter basically consists of a predetermined number of quadrature hybrid power devices configured as combiners and arranged in cascade so that the output of one combiner becomes one of the inputs of its adjacent combiner. An analog signal source such as a microphone or a video generator, produces an analog signal that passes through an analog- to-digital converter. The output of the A/D converter appears on datelines. The data consists of four-bit words. However, it is contemplated that in order to improve the quality of the signals being transmitted, 12- or 16-bit words or any arbitrary n are employed. Each of the bits from the least significant bit (LSB) to the most significant bit (MSB) is fed into a gate. In turn, each of the gates has its output connected to one of the input ports of one of the combiners. The gate is also connected to the output of an amplifier which receives an RF signal from an RF signal generator. The output of the gate representing the LSB has a value that is placed into an input port of the LSB combiner. The output of the gate to the left of the LSB gate contains a value that is twice that of the output of the LSB gate. In fact, the output of each advanced gate is twice that of the preceding gate. Thus, the output of each gate represents a binary weighted power signal and the combined signal appearing at the output of the MSB combiner represents the sum of the power signals fed into the various combiners. This output signal is fed to a load for transmission. Typically, the load consists of an antenna with conventional filtering.