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Frequency Shift Signal Generator

IP.com Disclosure Number: IPCOM000074047D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 44K

Publishing Venue

IBM

Related People

Croisier, A: AUTHOR [+3]

Abstract

The purpose of this signal generator is to generate two or more frequencies. It is based on the principle of storing in a read-only memory or in any equivalent circuits, a pattern of bits corresponding to the sampling of one period of a sine (or cosine) curve.

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Frequency Shift Signal Generator

The purpose of this signal generator is to generate two or more frequencies. It is based on the principle of storing in a read-only memory or in any equivalent circuits, a pattern of bits corresponding to the sampling of one period of a sine (or cosine) curve.

Conventionally in a two-frequency keyed generator, the frequencies are generated by a keyed oscillator which can be a sinusoidal oscillator or a multivibrator followed by a filter. The stability problem and the constraint to have a continuous output waveform are two of the main difficulties encountered in conventional generators. The described generator avoids these disadvantages.

As mentioned, the basic operating principle is to store in a read-only memory (ROM) a pattern of bits corresponding to the sampling of one period of a sine curve; then the continuous scanning of the memory permits the generation after conversion by a digital-to-analog converter, of a continuous sine wave form. A change of the scanning rate results in a change of the time interval during which the sine wave form period is obtained, i.e., it results in a change of the frequency of the generated sine wave. Whatever instant the rate change occurs the wave form continuity remains, since the bit pattern is not interrupted or modified, but is only more or less fast. To decrease the complexity of the system a Delta code can be used. The signal-to-noise ratio of the demodulated Delta signal is related to the speed of the clock and the characteristics of the integrating network used in the demodulator. When a steady sine wave form is coded by an ideal Delta modulator, a steady pattern of 1's and 0's is generated. By simulation, it is possible to optimize the characteristics of the Delta modulator...