US2486789A

US2486789A - Unsymmetrical rectangular wave generator

Info

Publication number: US2486789A
Application number: US520247A
Authority: US
Inventors: Louis L Lakatos
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1944-01-29
Filing date: 1944-01-29
Publication date: 1949-11-01
Anticipated expiration: 1966-11-01

Description

@V- l 1949 l.. l.. LAKA-ros UNSYMMETRICAL RECTANGULAR WAVE GENERATOR Filed JemY 29, 1944 Snventor ZM@ fw [faam Bu Cttorneg atented Nov. l, 1949 UN SYMMETRICAL RECTANGULAR WAVE GENERATOR Louis L. Lakatos, Bala-Cynwyd, Pa., assigner to Radio Corporation of America, a corporation of Delaware Application January 29, 1944, Serial No. 520,247

(Cl. Z50- 27) 2 Claims.

This invention relates to a generator for the production of rectangular waves, and in particular to a generator for the production of unsymmetrical rectangular waves. In any one complete cycle, a rectangular wave has two substantially horizontal portions, one in the positive half of the cycle and the other in the negative half of the cycle. An unsymmetrical rectangular wave is a Wave in which these two horizontal portions are of unequal length or duration.

Square or rectangular waves are applied to the deecting circuits of cathode ray tubes in television equipment, range finders, and similar apparatus employing cathode ray tubes, and have many other applications. It is essential in many of such applications that the length or duration of the two respective horizontal portions of one cycle of such a Wave (at a given frequency) should be accurately fixed.

, Prior art devices for the production of waves having the features described employ a plurality of tubes, often of the gaseous type, and consequently they are expensive, occupy considerable space and require complicated circuits for their proper operation. i

It is, therefore, an object of the invention to provide an improved method of, and apparatus for, the production of unsymmetrical rectangular waves.

It is a further object of the invention to provide an improved method of, and apparatus for, the production of rectangular waves, the length or duration of the respective horizontal portions whereof may be accurately predetermined.

It is a further object of the invention to provide a simple, inexpensive and compact circuit for the production of rectangular waves of the character described.

A further object of the invention is to provide an improved rectangular wave generator which may be easily constructed, and which is stable in operation.

In accordance with the invention, the rectangular wave is produced from a simple sine voltage wave. Two paths are provided for the sine wave, and the phase of the wave in one of such paths is shifted. The waves in each path are then limited, amplified and again limited sothat each assumes a substantially rectangular shape. The outputs of the two paths are then added (in an algebraic sense), and this results in a rectangular wave having two horizontal portions per cycle, the length or duration of such portions being determined by the amount of phase shift originally provided in one of the paths or channels.

The invention may be better understood from the following description of an embodiment thereof, when read in conjunction with the accompanying drawing, in which:

Figure 1 is a circuit diagram of a rectangular 2 wave generator in accordance with the invention, and

Figures 2 to 9, inclusive, are graphs plotted on a horizontal time `base, which represent the shape of voltage waves at various points, more particularly described later, in the circuit of Figure 1.

Referring to Figure 1, a sine voltage wave is supplied by a generator 40, which may include an oscillator, with or without one or more stages of amplication. In the embodiment described, the sine wave may have a frequency of 200 cycles per second and an amplitude of 50 to 60 volts R. M. S. Two vchannels 6 and 8 are provided for this wave. One channel 6 includes a capacitor l0, and the other channel 8 a capacitor Ill. The various resistance and capacitance values of the elements of the circuit are indicated on the drawing in ohms and inicrcfarads, respectively.

As shown in the drawing, the capacitor I0 is connected to ground through a resistor l2, and to the grid 28 of a tube I8 through a resistor 54. Similarly, the capacitor i4 is connected to ground through a resistor I6 and to the grid 32 of a tube 20 through a resistor 56. While the tubes i8 and 2B are shown in one envelope, they may be included in separate envelopes.

The capacitance of the capacitor I4 is small by comparison with that of the capacitor lil. The difference between the impedances presented to the wave in the respective channels results in a substantial phase shift in the wave in the one channel 8, but a comparatively negligible phase shift in the wave in the other channel 5. This effect is best seen from a comparison of Figs. 2, 3 and 4. Fig. 2 shows the shape of the wave produced by the generator 40; Fig. 3 gives the shape of the wave which has passed through the capacitor IG, and shows that that capacitor has had little effect onit; while Fig. 4 gives the shape of the wave which has passed through the capacitor I4, and shows the substantial phase shift which has taken place in that wave lowing to the relatively high impedance ci the capacitor to that of the parallel resistors I6 and 56. The resistors I2 and I6, in addtion to their function in procuring phase shift (in combination with the capacitors I0 and I4, respectively), also provides a path to ground for the current which flows in channels 6 and 8, as hereinafter explained.

In one device, a twin triode, RCA type GSNIGT or GSL'ZGT, was used. Tube i8 has a cathode 22, an anode 24, and a control electrode or grid 2B. Tube 20 has a cathode 28, an anode 3D, and a control electrode or grid 32. The

anodes

24 and 30 are connected to a common B supply (not shown) through common resistors 36 and 38.

The voltage applied to the two anodes may be kept low-at say, 15 to 20 voltsfor reasons which will appear hereinafter. If the device is included in equipment containing tubes whose anodes requre a high voltage, the required voltage is ob tained by including the dropping resistor or bleeder 38 between the source 'of potential and the anode resistor 36.

The grids 26 and 32, respectively, are maintained at zero bias; however, the comparatively large amplitude of the input Wave causes current to flow in the circuits which include these grids, and by reason of such current flow, the tubes develop self-biases.

On the positive half of the applied signal cycle, the grid currents cause the voltage applied to the grids in excess of the steady state grid bias to be clipped, so that the tubes act as limiters. The shape of the voltage wave applied to the grids 26 and 32 is shown in Figs. 5 and 6, respectively. The tubes amplify the signals applied to their grids and invert their phase; since the anode voltages are low, limiting occurs in the anode circuits as Well as the grid circuits, so that the output of the two tubes have the shapes shown in Figs. 7 and 8, respectively. These outputs are, however, combined or added in the anode resistor 36 and take the shape shown in Fig. 9.

The portion of the wave shown in Fig. 9 which vr of the final output wave is that Shown in Fig. 9

by the letters abcdefghz'.

The comparative lengths of the horizontal portions of the output wave in any one cycle depend on the relative phase shift in the two channels 6 and 8. With the constants shown, a phase shift of approximately 65 may be obtained, resulting in a ratio of 1:2 for the comparative lengths of portions cd and ef in Fig. 9.

The capacitor lll causes negligible phase shift in the wave passing through channel 6; and, therefore, if this capacitor were omitted from the circuit, the omission would not substantially affect the relative phase shift of the waves in the two channels 6 and 8. Since it is this relative phase shift which determines the length of the two horizontal portions of the output wave, the capacitor l0 may, if desired, be omitted.

Certain other alternatives to the preferred embodiment will suggest themselves to those skilled in the art. For example, the invention has been described with a sine Wave as the input, and this is probably the most practical; but any periodic wave, for example, a square wave, may be used for this purpose. Since, however, a square wave is rich in harmonics it should be borne in mind that in channel 6 (the channelin which comparatively negligible phase shift occurs) the reactance of the condenser I0, at the fundamental frequency of the input wave, should be small by comparison with the resistance of the parallel resistors I2 and 54 in that channel.

A further alternative within the scope of the invention lies in the replacement of the triodes i3 and 20 by tetrodes or pentodes. Such multielectrode tubes may be used where better control is desired, or where it is not desired to use an input wave with as large an amplitude as before described.

While an input frequency of 200 cycles per second is often a useful one for the purposes before mentioned, other frequencies may be employed if desired. The circuit illustrated will operate with satisfaction through the whole range of audio frequencies, down to as low as I0 cycles per second; and, in the other direction, beyond the audio range up to 30 to 40 kilocycles per second, at which frequencies tube capacities may begin to interfere with the proper operation of the circuit. By the substitution of pentodes for the tubes I8 and 20, higher frequencies may be employed.

Similarly, the invention is not intended to be restricted to an amplitude of to 60 volts R. M. S. for the input signal. Very low voltage amplitudes may be employed if desired, although pentodes should then be used in place of the triodes I8 and 20, as explained before; the circuit will also work satisfactorily at high input amplitudes, up to the point where voltage breakdown occurs.

There has thus been described a method for the production of rectangular Waves, the respective horizontal portions of which may be accurately predetermined; the method employing simple, inexpensive and compact apparatus, and a circuit which is extremely stable in operation.

What I claim is:

1. An unsymmetrical rectangular wave generator, comprising in combination a pair of vacuum tubes, each of said tubes having at least one electrode in addition to a cathode and an anode; a common source of potential for the anodes of said tubes, said potential being sufficiently low to enable plate current to be cut off at a low negative grid voltage; a common impedance connecting said source of potential to said anodes; a source of periodic wave voltage; and a pair of channels connecting said source of periodic Wave voltage to said control electrodes, each of said channels including a resistor and capacitor, the impedance of the capacitor in one of said channels relatively to that of the resistor in the same channel being different from the impedance of the capacitor in the other of said channels relatively to that of the resistor in said other channel.

2. A circuit for converting a sine voltage Wave into an unsymmetrical rectangular wave, comprising in combination two channels for said sine Wave, one of said channels including means for altering the phase of the Wave passing therethrough, each of said channels including only one REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,223,840 Wolff Dec. 3, 1940 2,226,459 Bingley Dec. 24, 1940 FOREIGN PATENTS Number Country Date 117,784 Australia 1943