GB1313771A - Intelligence transducing beam modulation method and apparatus - Google Patents

Abstract

1313771 Facsimile systems AMPEX CORP 18 Feb 1970 [20 Feb 1969] 7734/70 Heading H4F In a facsimile or other display system an analogue signal is converted to a pulse width modulated signal comprising transition delimiting consecutive pairs of intervals, of which the aggregate duration of each pair is constant and of which the intervals within each pair are modulated in duration complementally, by comparison with a ramp signal (linear, convex or concave) of a frequency at least twice that of the highest frequency of the analogue signal which is to be reproduced, and the pulse width modulated signal is used to switch a beam of radiation between a high and low or zero intensity level, e.g. that from a C.R.T. Appropriate choice of ramp shape and limiting voltages compensates non-linearity in the system and the use of pulse width modulation means that the gamma characteristic of the C.R.T. does not affect reproduction. The modulated signal may be (a) used to switch an oscillator on and off, its output being coupled via a transformer and detector to a C.R.T.; (b) sent via a transformer to a full wave rectifier feeding a bi-stable controlling the C.R.T.; (c) passed via a light emitting diode to a detector controlling the C.R.T. Such circuits are said to be useful when operating with a " depressed " cathode, i.e. anode at earth potential.