Electron Beam Deflection Tube for Pulse Code Modulation 



By R.W. SEARS 



Introduction 



pULSE code transmission systems^ in which successive signal ampHtude 

 -*- samples are transmitted by pulse code groups require special modulators. 

 The essential operational requirements of a pulse code modulator are: (1) 

 to quantize or measure the signal amplitude sample to the nearest step in 

 the discrete amplitude scale transmitted by the pulse code system, and (2) 

 to generate the group of on-off pulses identifying the step. 



Several methods have been proposed^ • ^ • ^ in which quantization and pulse 

 formation were performed with circuits employing conventional electron 

 tubes. The circuits involved sequential and comparison operations and 

 were not easily adapted to a multi-channel time division system because of 

 limitations in coding speeds and the complexity of the equipment. An 

 electron beam deflection tube has been developed which, together with as- 

 sociated beam positioning and sweep circuits, performs the modulation 

 rapidly, making possible the sequential modulation of a number of channels 

 in time division multiplex. 



The electronic principles, design and characteristics of the experimental 

 tube are described in the present paper. 



Conversion from Signal Input to Pulse Code Output 



An electrical input voltage may be converted into an output code pulse 

 group with the electron beam deflection tube shown in Fig. la. An aperture 

 or code masking plate is arranged perpendicular to the axis of the electron 

 gun at the focal point. The coordinates of the aperture plate are aligned 

 with the deflection axes of the X and Y deflector plate pairs. The electron 

 beam strikes the output plate when it passes through an opening in the 

 aperture plate. 



An input voltage of appropriate value applied to the Y deflector plates 

 will deflect the beam to point "a" of the aperture plate as indicated in Fig. 

 la. A linear sweep voltage applied to the X deflection plates, while the 



^ An Experimental Multi-Channel Pulse Code Modulation System of Toll Quality, 

 L, A. Meacham and E, Peterson, this issue. 



2 A. H. Reeves, U. S. Patent M 2,272,070, Feb. 3, 1942. 



3 H. S. Black and J. O. Edson, paper presented June 11, 1947 at A. I. E. E. meeting; 

 Montreal, Canada. 



* W. M. Goodall, Bell System Technical Journal, July 1947. 



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