基于普通调幅方式的信号传输电路的设计.doc

Signal transmission circuit design of ordinary AM 1 Signal Generators Principles of Signal Generators A signal generator is an electronic instrument that generates repeating voltage waveforms. An ideal signal generator can simply be modeled .A practical signal generator is modeled as an ideal signal generator connected to a series source resistance (output resistance) Rs . The terminal voltage, v(t), is the output of the signal generator and depends on the terminal current, i(t), and Rs. Vs(t) can be, in general, a sine wave, a square wave, a triangular wave or a pulse train. The first three are characterized by three parameters: frequency (or period), amplitude, and DC (Offset) value. The pulse train is associated with frequency, amplitude and pulse duration. These parameters can be set to any value in the operation range of the signal generator, using the external controls. In general, amplitude ranges of signal generators vary from 10 mV to 20 V, and frequency ranges vary from 1μHz to 40 MHz. This means signals for which the amplitude and frequency can be set to any value in these ranges can be generated using these signal generators. Signal generators usually produce more than one type of signals. Different signal types can be obtained by proper connection and/or switching. A sine wave oscillator is the heart of the signal generator. It generates a sine wave of fixed amplitude and adjustable frequency, which is set by the external frequency control. This signal is fed to both attenuator I and squarer. The signal amplitude is set to the desired value determined by external controls, by attenuator I. The output of attenuator I is a sine wave with desired amplitude and frequency. The squarer generates a square wave of fixed amplitude and at the same frequency with the sine wave. The output of the squarer is fed to attenuator II which acts similar to attenuator I. The output is the square wave with amplitude and frequency which are determined e