US2488417A - Pulse amplifier - Google Patents

Description

Nov. 15, 1949' R. LEE 2,488,417

PULSE AMPLIFIER Filed Aug. 26, 1945 wxTNEssEs: INVENTOR fw@ /Peabe L ee.\

Patented Nov. 15, 1949 PULSE AMPLIFIER Reuben Lee, Catonsville, Md., assignor to Westinghouse Electric Gorporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 2.6, 1943, Serial No. 500,066

l. Claim. 1

My invention relates to amplifiers and, in particular, relates to arrangements for amplifying voltages pulses which are substantially rectangular in Wave form.

In earlier radio practice, amplifiers were required to handle periodic waves which were either substantially sinusoidal in wave form or which differed therefrom largely through the imposition of periodic modulations of frequency considerably lower than that of sinusoidal carrier wave. A notable trend of the radio art, particularly in practical use of microwaves and ultra-high-frequency current, has been the employment of waves in the form of rectangular pulses, that is to say, Wave forms having nearly vertical leading and following edges connected at the top by a substantially flat crest of nearly constant amplitude. The properties of transformers are such that they are able at the secondary terminals to reproduce quite accurately the wave form of a sinusoidal wave impressed on their primary windings; but it is a different problem to make an arrangement which will cause the accurate reproduction of a rectangular Wave at the secondary terminals when a rectangular wave is impressed on the primary terminals of the transformer. Nevertheless, for many purposes such an accurate reproduction of a rectangular wave is extremely important.

One object of my invention is accordingly to provide a circuit arrangement capable of causing a transformer having a rectangular wave impressed upon its primary terminals to reproduce this rectangular wave form to scale at its secondary terminals.

Another object of my invention is to provide a circuit arrangement in which a rectangular Wave pulse accompanied by static or other noise voltage impressed upon the primary of a transformer will be reproduced with substantial accuracy of Wave form on the secondary terminals of this transformer without the noise or static being exaggerated or amplified to an undesirable degree.

Another object of my invention is to provide a transformer and circuit therefor which will amplify substantially without change of wave form between its primary and secondary terminals high-frequency waves which depart very substantially from a sinusoidal form.

Other objects of my invention will become apparent upon reading the following description taken in connection with the drawings, in which:

Figure 1 is a graph illustrating the wave form of the voltage to be amplied, and

Fig. 2 is a schematic diagram of a circuit embodying the principles of my invention.

Referring, in particular, to Fig. 1, rectangular wave pulses having substantially vertical sides and flat tops and approximating to sharp right angles at the junction of their sides with their crests and troughs have been shown in recent work to have great utility in the ultra-high-frequency radio art. The heavy line curve I in Fig. 1 illustrates a wave form of the type under discussion. However, in many practical radio systems, there is usually present in addition to the waves purposely generated and useful in the circuit an undesired but unavoidable voltage of smaller amplitude and frequency of varying frequency, due to static, tube noises, and the like. The dotted line 2 in Fig. 1 indicates such an undesired voltage. In Fig. 1, the length of the voltage pulse -is indicated by the quantity T1. while the periodic time between successive Waves is indicated by the quantity T2. The amplitude of the rectangular Wave is marked e1, while the amplitude of the undesired noise is marked ez.

The problem of which I have discovered a solution is the arrangement of a transformer which shall reproduce at its secondary terminals substantially without distortion such a wave form as is shown in Fig. 1 when the latter is impressed uoon its primary terminals.

Referring in detail to Fig. 2. a wave form of the character shown in Fig. 1 is impressed across a pair of input terminals 3 4 which are connected, respectively, to the control electrode and to the cathode of an amplifier 5 which may be of any type known to those skilled in the art as suitable for such service. The plate electrode of the tube 5 is connected through a suitable channel to the positive terminal of a direct-current source of which the negative terminal is grounded. Between the cathode of the tube 5 and the ground is connected a capacitor s across which. is shunted the primary winding 'l of a transformer having a transformation ratio apor imatelv euual to the amplification of magnitude desired for the wave form of Fig. 1. The primary windings 1 is associated with a secondary winding li to which it is coupled with as small an amount of leakage reactance as is feasible. For many purposes, it will be found possible to attain this close coupling between the windings 'i and s hv placing them upon a core containing powdered iron or very thinly laminated iron. 'The winding i! has one terminal connected to the one terminal of the diode or other rectifier fied replica of the wave in Fig. 1 at terminals" I have found that where a secondary winding such as 8 is connected directly ktoazzpairtof out'- put terminals like I2, I3 withoutthe 'additionof any such elements as 9, I0, Il, the impression of a wave of the form shown in 1*"ig.'v ltonfthe input' terminals 3, 4 will result in the production at thev terminals I2, I3 of a Wave form of substantially diierent type. I have found the presence of the rectifier 9 to be highly effective in 'eliminating this distortion ofthe wave formr however.

While Ihave shown the'rectier Sand its associated elements I andv I I as connected to the secondary winding, they `may be'connected'in I;

shunt with the primary winding T.

I have found'particularly that'where'undesired noise-voltage such as shown ini curve 2 of Fig. 1 is `present'on' the" :terminals 3, 4, it may be reprohigher'ratio Vto the xamplitudeflof the rectangular wave unless theresistor I9 and'capa'citorv II are connected 'in series with therectifler`9'in Fig. 2. In y*order tolimit the -amplitude of .the noise voltagefat the voutput terminalsIZ; I31to a value nota-1 greater than ethe sameorder as vit 'has at the' input `terminalsf'3,` 4, the'fresistor I0,"capacitor I I, and reciten 9. should be selected so that theinelec- I Vtrical constants' accord .fwith the following. formu- Ti=puise width (seconds.) Vc1:pulseyoltage amplituder ez=noise voltage amplitude T2=time interval between pulses (sec.)V

'R2=ohms.in resistor l0 T CL- capacitor I I in farads.`

' duced across the Vterminals I2, I3 'in substantially lio,

It will often be found satisfactory that the capacitor II be at least as great as the value indicated above, as a surplus above that value will do no harm.

While I have shown a particular embodiment of the principles of my invention in compliance with the patent statutes, those principles are typical of broader applications which will be evident to those skilled in the art.

I claim as my invention;

An amplifier comprising a tube having a control'electrode circuit and having an output circuit connected between its anode and its cathode including an impedance connected in the cathode lead of said tube, a transformer primary winding vconnected in shunt to said impedance, a secondary winding for said transformer having its terminals connected to an output circuit, and a rectiiier connected in series Witha resistor which is shunted by al capacitor `shunting lthe terminals o'f'one of said windings, said primary and secondary windings'being closely coupled, saidvresistor being equal in value to @gli @1 -6a T1 i Where T2 is the periodic timeof analternatingcurrent voltage impressedl onthe control electrode circuit'of said amplifier, T1 is the length in seconds of a rectangular wave impressed on said control electrode circuit, R1 is the resistance of said rectifier in ohms, e1 is the amplitudeof said rectangular waves, and e2 is the amplitudeof noise accompanying said rectangular waves.

REUBEN LEE.

REFERENCES CITED The following references areV of record inthe leof this patent: y

UNITED sTA'rEs'PA'rENTs Great Britain .Jan.. 7, 1938

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