US2879392A - Electric wave generating circuit arrangements - Google Patents

Description

United States Patent 9 ELECTRIC WAVE GENERATING CIRCUIT ARRANGEMENTS Ronald Mudie, .larvis Brook, England, assignor to Servomex Controls Limited, Jarvis Brook, Sussex, England Application April 1, 1957, Serial No. 649,993

' Claims priority, application Great Britain April 3, 1956 12 Claims. (Cl. 250-36) This invention relates to electric wave generators of the type comprising a square-wave generator feeding an integrating circuit arrangement.

The object of one form of the present invention is to provide a novel electric wave generator for generating square, triangular, sawtooth and like waves, having good time accuracy for repetition frequencies as low as 1 per 1,000 seconds.

The object of another form of the invention is to provide a wave generator the output voltage of which varies symmetrically about earth or other common fixed potential for such waves.

The object of another form of the invention is to provide a wave generator able to generate square, triangular, sawtooth and like waves either continuously or parts thereof comprising either a single voltage excursion or a forward and return voltage excursion.

According to the present invention, in an electric wave generator of the type described, the square-wave generator is a Schmitt trigger and the integrating circuit is a Miller integrator.

The Schmitt trigger is a known circuit arrangement comprising first and second valves having a common cathode load, the first valve having an anode load, a tapped impedance connected in parallel with both the first valve and the common cathode load and the second valve having its control grid connected to the tap of the tapped impedance. Although the Schmitt trigger was originally described in the Journal of Scientific Instruments, 193 8, No. 15, page 24 as comprising two triodes, the term is herein applied also to a combination of multi-electrode valves.

one terminal of said integrating capacitor and its anode connected to the control grid of a second valve, said second valve having a common cathode load with a third valve and said third valve having its control grid maintained at a fixed potential and its anode connected to the other terminal of said integrating capacitor.

A form of the invention adapted to generate saw-tooth and like unsymmetrical waves has the resistor of the integrator circuit in two parts, one part of which can be bridged by a diode which may be connected in either conducting sense.

To control the voltage excursion-s at various points of the generator and to provide a symmetrical voltage output, the Schmitt trigger valves and integrator amplifier valves are connected between positive and negative voltage sources and the anodes thereof are connected to di- 2,879,392 Patented Mar. 24, 195a ICE ode pairs in anti-parallel arrangement to limit the voltage excursions at these points in the circuit.

The wave generator can be made to run continuously by deriving positive-going and negative-going pulses from the integrator circuit and feeding these back to operate the trigger. By the inclusion of a series diode in the feedback line, connected in one conductive sense or the other, the wave generator canbe limited to forward and return voltage excursions in either sense.

In order that the invention may be readily carried into effect, one embodiment will now be particularly described with reference to the accompanying drawing, which is a schematic circuit diagram of a wave generator comprising a square wave generator feeding an integratingcircuit arrangement.

In the drawing, a two-way switch 1 has a moving contact 1a and fixed contacts 1b and 1c connected respec' tively to a positive potential source at terminal 3 and to a negative potential source at terminal 4. A twoway switch 2 has a moving contact 2a and fixed contacts 211, 2c connected respectively to contact 1a and to a feedback line 5.

Two pentode valves '6, 7 comprisea Schmitt trigger circuit and have a common cathode load 8 connected to negative 350 volts supply at terminal 9. Both valves 6, 7 have their screens connected to earth and the suppressor grids connected to the respective cathode. For simplicity, this connection is omitted in the drawing in the case of every pentode. The anode of valve 6 is connected through an anode load 10 to a positive 300 volts supply at terminal 11. A tapped impedance comprising series connected resistors 12, '13 is connected in parallel with both valve 6 and the common cathode load 8, the control grid of valve 7 being connected to the tap. A capacitor 14 is connected across resistor 12.

The anode of valve 6 is connected to a pair of diodes 15, 16, diode 15 having its cathode connected to the anode of valve 6 and its anodev connected to a negative volts supply at terminal 17. Diode 16 has its anode connected to the anode of valve 6 and its cathode connested to a positive 75 volts supply at terminal 18.

The anode of valve 7 :is connected through a resistor 19 to a positive 300 volts supply at terminal 20. The anode of valve 7, similarly to that of valve 6, is connected also to a pair of diodes 21, 22, in anti-parallel arrangements, having anode and cathode respectively connected to negative and positive 75 volts supplies at terminals 23, 24 respectively.

A series combination of resistor 25, potentiometer 26 and resistor 27 is connected between the anode of valve 7 and earth. The variable tap of" potentiometer 26 is connected through the series combination of a fixed resistor 28 and a variable resistor .29 to the control grid of a pentode valve 30. The variable resistor 29' is variable in decade steps and has its ends connected to the moving contacts 31a, 32a of ganged three-way switches 31, 32. Fixed contacts 31b, 32b are open circuit and a diode 33 is connected, in opposite conducting senses, between contacts 310, 32c and between contact 31d, 32d. The grid of valve 30 is also connected to one terminal of a variable, integrating capacitor 34, the other terminal of which is connected to the anode of a pentode valve 35. The integrating capacitor 34 is also variable in decade steps.

The screen of valve 30 is connected to the junction of two resistors 36, 37 connected between a positive 300 volts supply at terminal 38 and earth. A capacitor 39 is connected from the screen to earth in parallel with resistor 37. A common cathode load 40 is connected between a negative 350 volts supply at terminal 41 and the cathodes of valve 30 .and a .triode valve 42.. The anode of valve 42 is connected to a positive 300 volts supply at terminal 73. A series combination of resistor 43, potentiometer 44 and resistor 45 are connected between a positive 75 volts supply at terminal 46 and a negative 75 volts supply at terminal 47. The variable tap of potentiometer 44 is connected to the grid of valve 42.

The anode of valve 30 is connected through a registor 48 to a positive 300 volts supply at terminal 49. The anode of valve 30 is also connected to the cathode of a diode 50, the anode of which is connected to a positive 75 volts supply at terminal 51.

The anode of valve 30 is also connected to the grid of a triode 52, the anode of which is connected to earth. The cathode of valve 52 is connected to the cathode of valve 35 and through a common cathode load 53 to a negative 350 volts supply at terminal 54. The screen of valve 35 is connected to earth. The anode of valve 35 is connected through resistor 55 to a positive 300 volts supply at terminal 56. The anode of valve 35 is also connected to the cathode and anode respectively of a pair of diodes 57, 58, the anode and cathode of which diodes are respectively connected to a negative 75 volts supply at terminal 59 and a positive 75 volts supply at terminal 60. The control grid of valve 35 is connected to the junction of two resistors 61, 62 connected in series between earth and a negative 350 volts supply at terminal 63.

The anode of valve 35 is also connected to one output terminal 64, the other output terminal 65 being connected to earth.

The anode of valve 30 is also connected to the grid of a triode 66 having its anode connected to earth. The cathode of valve 66 is connected through a series combination of a potentiometer 67 and a resistor 68 to a negative 350 volts supply at terminal 69. The variable tap of potentiometer 67 is connected by a feedback line 70 to the fixed contact 71a of a three-way switch 71. The switch 71 is ganged with a three-way switch 72, the moving contact 72a of which is connected to the feedback line 5. Fixed contacts 71b, 72b are connected together and a diode 73 is connected, in opposite conducting senses, between contacts 71c, 72c and between contacts 71d, 72d.

The two valves 6 and 7 operate as a Schmitt trigger circuit in known manner as, for example, described in Time Bases by O. S. Puckle, 2nd edition, pages 82-83. The anode voltages of the two valves 6 and 7 vary in the form of square waves in antiphase. The excursions of valve 6 are limited by diodes and 16 respectively at the values 75 volts and +75 volts. The excursions of valve 7 corresponding thereto are limited respectively by diodes 21 and 22 to the values +75 volts and 75 volts. The anode voltages are held at the values :75 volts as soon as the appropriate diodes conduct and the anode voltages are held at these values until a further control pulse is received at the grid of valve 6, in the manner described below, whereupon the potentials of the anodes are reversed and held, as the other pair of diodes become conducting.

When the control grid of valve 6 is connected by way of switch control 2a to contact 2c, control pulses are derived from valve 66 in the manner to be described later. When the control grid of valve 6 is connected to contact 2b, it is further connected to switch contact 11:. Operation of switch 1 connects contact In to either contact lb or 10, which provides respectively either a positive-going or a negative-going step function voltage to the control grid of valve 6. In either case, a single operation of the trigger circuit is initiated, resulting in a single changeover of the anode potentials of valves 6 and 7 in the sense determined by the polarity of the voltage applied to the control grid of valve 6.

The output voltage of valve 7 is fed to the potentiometer comprising resistors 25, 26 and 27, the voltage being represented at A. Part of this voltage is taken off at the tap of potentiometer 26 and applied to the input of the Miller integrator to be described.

A Miller integrator consists essentially of an amplifier having a resistance connected in series with an input terminal of the amplifier and.a capacitance connected between the input terminal and an output terminal. A step function input to the integrator provides a linear ramp output wave for so long as the step function persists and within the operating range of the amplifier. The basic circuit is widely described in the technical literature, for example in Time Bases, O. S. Puckle, pages 340-344. The present wave-generator employs a novel and 1mproved form of Miller integrator, two essential features of which are the provision of more than one amplifying stage and the provision of a pulse feedback circuit connected to an amplifying stage other than the last stage.

As shown in the accompanying drawing, the Miller integrator has two amplifying stages D.C. coupled, the first stage comprising valves 30 and 42, operating together as a difference amplifier, known as a long-tailed pair. The second stage comprises valves 35 and 52 similarly comprising a long-tailed pair. The input resistance is provided by resistors 28, 29, the capacitance connected between input and output is provided by the capacitor 34 and the pulse feedback circuit includes valve 66, acting as a cathode-follower, connected to the output of the first amplifying stage.

In operation, the square wave A is applied by way of resistors 28, 29 to the control grid of valve 30. Because of the limits between which the anode voltage excursions of valve 7 are maintained by diodes 21, 22, the square wave is alternately positive-going and negative-going with respect to a point in the circuit of zero voltage potential, shown as earth.

The control grid of valve 42 is taken to a constant potential at the tap of potentiometer 44 which is adjustable between fine limits on either side of zero volts potential. This compensates for small differences of grid bias voltages between valves 30 and 42, so that the input to valve 30 is always centered accurately about zero volts.

Assuming that the input to valve 30 is positive-going, the anode circuit of valve 30 increases so that the anode potential falls from a value near +300 v. towards +75 v. The anode current of valve 42 correspondingly falls. When valve 30 is fully conducting and valve 42 is out 01f, valve 30 carries the whole current flowing through resistor 40. This it is able to do without running into grid current by a current which flows from the +75 v. source through the diode 50, when the diode becomes conducting.

The output of the first amplifier stage thus appears across resistor 40 and is applied to the control grid of valve 52. Simultaneously with the earlier part of the anode potential drop of valve 30 described above, so will the grid potential of valve 52 also fall. In consequence, the anode current of valve 52 will fall and the anode current of valve 35 will rise correspondingly.

In the case of the second amplifier stage, the anode of valve 52 is connected to earth potential. The anode potential of valve 35 falls, by reason of the increasing voltage drop in resistor 55, from the value of +75 v. towards the value 75 v. When this potential is reached, the diode 57 becomes conductive and the anode potential is held at 75 v.

Diode 58 becomes conductive and similarly arrests the anode potential at +75 v. at the other limit of the anode potential excursion.

During the time the anode potentials of valves 30 and 35 have been falling, negative feedback has been applied, by way of capacitor 34, to the control grid of valve 30, opposing the positive-going input voltage, opposing the falling anode potentials of valves 30 and 35 and producing a linear fall of these potentials in the known manner of Miller integrator circuits.

The output of the second amplifier stage appears across resistor 55. The anode terminal of valve 35 is the output terminal of the Miller integrator and is connected to terminal 64, the output terminal of the'wavegeneratorr The output wave C thus appears between terminal64andearth terminal 65.

As soon as the anode potential .of valve 35 is held by conduction of one or otherof the diodes 57, 58, the large negative feedback to the grid of valve 30 immediately ceases. Because the square waveinput voltage to the integrator is still maintained ata positive value, current will still flow through the resistors 28, 29 and the voltage across capacitor 34 will stillc'hange to carry the control grid of valve 30 further positive. Because this produces no corresponding negative feedback, the grid potential will move positive much more rapidly than before. In fact, the rate of grid potential change will be the previous rate of change, before the anode potential of valve 35 was held, multiplied 'by'the former gain of the two-stage amplifier.

This will lead to a rapid fall in the .anode potential of valve 30, still moving down towards :a +75 v., which,

compared with the previous slow'movement of potential,

appears as a pulse at the valve :anode. Although this pulse is applied to the input of the second amplifier stage,

it does not affect theoutput thereof, because the anode potentialof valve 35 canno'tchange further. However, the

pulse is applied to the grid of cathode-follower valve 66 and appears across thecathode load 67, 68 where it is taken off at the tap of potentiometer 67.

With switches 71, 72 and 2 in the positions shown in the drawing, the pulse is appliedto the grid of valve 6, so that the trigger circuit comprising valves 6, 7 is reset. The input to the integrator circuit is changed to a negative valueand the outputof the wave generator rises linearly to the value +75 v. When the anodepotential of valve 35 is held at this'upper limit, thegrid potential of valve .30 continuesto fall, now doing so rapidly to producea positive-going anode pulse which again serves to reset the trigger circuit. Hence with these settings of switches 71, 72 and 2, the wave genera'tor genera'tes linear waves continuously, the trigger square-wave output being as shown'at A, the generator output being as shown at C and the feedback pulses to the trigger circuit being as shown at B.

As shown, the D.C. coupled cathode follower valve 66 has its cathode load 67, 68 returned to a potential of -350 v. As the grid, and hence the cathode, moves in potential between +75 v. and nearly +300 v., feedback pulses taken off from potentiometer 67 are at the required D.C. level for application to the grid of valve 6.

It will be appreciated that a single excursion of the wave A produces a single excursion of the wave C, a return excursion of the wave A produces a return excursion of the wave C and a continuous wave A produces a continuous wave C. With switches 31, 32 in the position shown in the drawing, the value of the resistor combination 28, 29 is the same during both forward and return strokes. In the alternative positions of the switch the variable resistor 29 is shunted by the diode 33 during either the forward stroke or the return stroke at will, and a sawtooth wave output is thereby produced.

Continuous running of the wave generator may be effected by feeding back pulses appearing across the cathode load 67, 68 and supplying them to the grid of valve 6, when switch 2 is in the position shown in the drawing. The pulses appearing on line 70 are both positive-going and negative-going as shown at B and, with switches 71, 72 in the position shown in the drawing, both positive and negative pulses are supplied through line 5 and switch 2 to the grid of valve 6. However, in the alternative positions of switches 71, 72, only the negative-going pulses or only the positive-going pulses can be supplied, according to the conductive sense of diode 73 chosen. In this case only single forward and return strokes of the waves A and C in one sense or the other, are made by the generator.

If preferred, the points shown in the drawing as connected toearth may be connected to some other common point. In this case, the various supply potentials must be with respect to this common point instead of to earth and the output wave will then be symmetrical about the potential of the common point.

I claim:

1. A wave generator comprising a trigger circuit and an integrator circuit of the Miller integrator type, .said trigger circuit having an output terminal and an input terminal, the potential of said output terminal being changed by the trigger action of the circuit rapidly between upper and lower potentials upon application of trigger initiating potentials to said input terminal, said integrator circuit comprising a resistor, an amplifier vhaving input and output terminals, and a feedback capacitor, said resistor being connected between said output terminal of said trigger circuit and an input terminal of said amplifier, said capacitor being connected between an output terminal of said amplifier and said .inputterminal thereof .to supply negative feedback to said input terminal, said amplifier comprising a plurality of stages, a pulse feedback path being provided from the output of one of said plurality of stages other than the last stage thereof, to supply said trigger initiating potencircuit.

3. A Wave generator as claimed in claim 2, in which the anode of said-first valve and the anode of said second valve each have connected thereto a pair of diodes, a firstand the second diodes of eachpair being connected in reverse conducting sense, the free anode terminal of the first diode being connected to a lower potential than the free cathode terminal of the second diode.

4. A wave generator as claimed in claim 3 in which the anode of said first and second trigger valves have their anodes connected by way of an anode load to a source of positive potential, said common cathode load is connected to a source of negative potential and of said pair of diodes said first diode has its anode connected to a source of negative potential and said second diode has its cathode connected to a source of positive potential.

5. In a wave generator comprising a trigger circuit and an integrator circuit of the Miller type having input and output terminals, comprising a resistor, an amplifier having input and output terminals and a feedback capacitor, said resistor being connected between said input terminal of said amplifier and the output terminal of said trigger circuit, said capacitor being connected between an output terminal of said amplifier and said input terminal thereof to supply negative feedback to said input terminal, said amplifier comprising a plurality of stages, a pulse feedback path being provided from the output of one of said plurality of stages other than the last stage thereof to the input of said trigger circuit.

6. A wave generator comprising a trigger circuit and an integrator circuit of the Miller integrator type, said trigger providing rapid transitions of potential at its output upon application of trigger initiating impulse to its input and having its output connected to the input of said integrator circuit, said integrator circuit comprising a resistor, an amplifier, having input and output terminals, and a feedback capacitor, said resistor being connected between said output of said trigger circuit and an input terminal of said amplifier, said capacitor being connected between an output terminal of said amplifier and said input terminal thereof to supply negative feedback to said input terminal, said amplifier comprising a plurality of 7 stages, a pulse feedback path being provided from the "outputof one 'of said plurality of stages otherthan the last stage thereof, to supply trigger'initiating impulses "to 'the input'of said trigger circuit and the output terminal of the last of said plurality of amplifier stages having a pair of diodes connected thereto, a first diode and the second diode of said pair being connected in reverse conductive sense, the free anode terminal ofthe first diode being connected to a lower potential than the free cathode terminal of the second'diode.

7. A wave generator as claimed in claim 6, in which the last of said plurality of amplifier stages comprises a ,valve having an anode load connected to a source of positive potential, a cathode load connected to a source of negative potential and said first diode has its anode connected to a source of negative potential and said second diode has its cathode connected to a source of positive potential.

8. A wave generator as claimed in claim 7, in which the first of said plurality of amplifier stages comprises a valve having connected to its anode the cathode of a diode, the anode of which diode is connected to a source of positive potential.

9. A wave generator as claimed in claim 6,- in which the said pulse feedback path includes a valve connected as a cathode follower and having its control grid con nected to the output of said one amplifier stage.

10. A Wave generator as claimed in claim 9, in which the said pulse feedback path includes a diode connected across a two-pole three-position switch, the three posi- .transition of potential from one value to another to the integrator circuit, said integrator circuit comprising a resistor, an amplifier having input and output terminals and afeedback capacitor, said resistor being connected be "tween the output of said trigger circuit and an input terminal of said amplifier, said capacitor being connected between anoutput terminal of said amplifier and said input terminal thereof tosupply negative feedback to said terminal,'said resistor comprising two parts connected in series, one part thereof being connected across a two-pole threeposition switch.-tbe three positions thereof connecting a diode across said resistor part in one conducting sense, connecting said diode across said resistor part in the reverse conducting sense and disconnecting said diode from said resistor part, said amplifier comprising a plurality of stages,'a pulse feedback path being provided from the output of one of said plurality of stages other than the last stage thereof to supply trigger initiating potential to the input of said trigger circuit. I 12. A wave generator comprising a trigger circuit and an integrator circuit of the Miller integrator type, said trigg'r'cir'cuit having an' output terminal and an input terminal, the potential ofsaid output terminal being changed by the trigger action of the circuit rapidly between upper and lower potentials upon application of trigger initiating potentials to said input terminal, said "integrator circuit comprising a resistor, an amplifier having input and output terminals, and a feedback capacitor, said resistor being directly connected between said output terminal of said trigger circuit and an input terminal of said amplifier, said capacitor being connected between an output terminal of said amplifier and said input terminal thereof to supply negative feedback to said input terminal, said amplifier comprising a plurality of stages, a pulse feedback path being provided from the outputof one of said plurality of stages other than the last stage thereof, to supply said trigger initiating potentials to the input of said trigger circuit, and means connected to the cathode of said amplifier to provide zero grid bias in the absence of signal voltage.

References Cited in the file of this patent Time Bases by O. S. Puckle, 1955, second edition, published by Wiley & Sons Inc., pages 82 and 170.

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