Digital phase shifter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Digital phase shifter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Digital technology

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The formation and detection of the SSB signal using phase-shifting devices attract the attention of radio amateurs in that this method can significantly simplify both the receiving and transmitting paths of the radio station. Of greatest interest to a radio amateur is the simplest two-phase method for generating an SSB signal, so we will talk about phase shifters that provide two voltages at the output, shifted in phase by 90 °. However, the principles outlined in this note can also be applied to multi-phase systems.

Digital phase shifter

To obtain good signal parameters using the phase method, greater accuracy and stability of both LF and HF phase shifters are required. In this case, it is often required that the RF phase shifter be a band shifter, that is, that the phase shift does not change when the frequency changes. These requirements are met by a discrete phase shifter based on binary digital elements. The principle of its operation is as follows: if rectangular signals of the same frequency with a duty cycle equal to two and a phase shift of 180 ° are applied to the counting inputs of two triggers, then signals of half the frequency, shifted in phase by 90 ° at any input frequency. Such a phase shifter provides very high accuracy and stability of the phase rotation, which are determined only by the parameters of the input signals, namely the duty cycle and phase shift. The stability of these parameters can be ensured by preliminary dividing the frequency of the master oscillator with another trigger, at the outputs of which the signals we need will be automatically generated.

The practical implementation of a discrete RF phase shifter, however, still encounters difficulties, since even with the use of modern integrated circuits at frequencies above 1 MHz, the delay in the switching moment of triggers already begins to affect, and due to its temperature instability and spread, it turns out to be impossible to provide the necessary accuracy of the phase shift. With an increase in the speed of microcircuits produced by the industry, this difficulty will certainly be overcome.

However, a discrete frequency phase shifter below 1 MHz can be used even now, for example, in the formation of an SSB signal by a phase-filter method. So, the phase shifter, the schematic diagram of which is shown in the figure, provides a phase rotation of 90 ° with an accuracy of more than 0,001% at a frequency of 1,5 kHz and 0,25% at a frequency of 100 kHz. The master oscillator circuit can be anything, it is only important that the fronts of its pulses are steep enough to trigger trigger D1. If the shape of the output signals of the master oscillator is close to sinusoidal, a pulse shaper must be connected between the generator and the trigger.

Authors:T. Krymshamkhalov (UA6XAC), V. Solodovnikov, Nalchik; Publication: N. Bolshakov, rf.atnn.ru

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