00L 9, 1962 w. SHOCKLEY 3,058,009 TRIGGER CIRCUIT SWITCHING FROM STABLE OPERATION IN THE REGION TO UNSTABLE OPERATION Filed July 15, 1959 2 Sheets-Sheet l

F/G/ B2

STABLE LOAD LINE

UNSTABLE LOAD

2 v /'6 T T l3 TIME» TIME—+ * F_/.Q-_§A FIG. 3B

O

+Bl

_ /| 2

CONTROL {—.s|GNA|_ INVENTOR F/ 6‘_ 4 WILL/AM SHOCKLEY BY EMEZJW A TTORNEYS Oct. 9, 1962 W. s HOCKLEY ' TRIGGER CIRCUIT SWITCHING F ROM STABLE OPERATION IN3,058,009 THE NEGATIVE RESISTANCE REGI Filed July 15, 1959 ON TO UNSTABLE OPERATION 2 Sheets-Sheet 2

------~ 4

v ———— —"-3 F/G'. 5 I ______2 I ._____

I R F \/ + m Bl H /2? 28 + 29 /'2 ‘ - >3 B2 7 /26 - CONTROL |"‘SIGNAL R {C I v + / CC F / 6.7 B ' |—— /3| flz " 6 " ' SIGNALCONTROL

_ B2 + W /C + R H " [-7615 E] / 32 33 '-|2

u CONTROL 6% % EESIGNAL INVENTOR lav/3M1, agumim, ATTORNEYS 3,058,009 United States Patent O?tice Patented Oct. 9, 1952 1 2 3,058,009 as indicated by the dotted line 13, FIGURE 2. TRIGGER CIRCUIT SWITCHING FROM STABLE This is illustrated in FIGURES 3A and 3B. As the im OPERATION IN THE NEGATIVE RESISTANCE pedance Z decreases, the device remains in its stable con~ REGION TO UNSTABLE OPERATION dition for a period of time until the impedance is lowered William Shockley, 23466 Corta Via, Los Altos, Calif. to a point where the device is unstable. The device sud Filed July 15, 1959, Ser. No. 827,331 denly draws a relatively large current and the voltage 11 Claims. (Cl. 307-—88.5) drops to the position shown by the line 13. Thus, a sharp voltage step 16 is generated in response to the small This invention relates generally to a pulse generating or change in impedance. trigger circuit and more particularly to a pulse generating Referring to FIGURE 4, one means of accomplish~ circuit employing devices exhibiting negative resistance. ing the change in impedance in response to a small con In many switching ‘applications only relatively small trol signal is illustrated. A conventional high imped control signals are available. These control signals are ance 21 is connected between the common terminal not suitable for controlling associated switching devices of the load R and the device 11. The other end or circuits. It is often desirable to amplify or otherwise of the diode 21 is connected to the variable tap of the form new switching signals of su?icient magnitude for potentiometer 22 which is connected across a battery B2. driving associated switching devices. By varying the position of the tap from the positions indi It is a general object of the present invention to pro vide a circuit which generates pulses in response to small cated by numerals 1, 2, 3 and 4, the load lines shown in control signals. FIGURE 5 and designated 1, 2, 3 and 4 are obtained. 20 When the potential ‘at the common terminal is more posi It is another object of the present invention to provide tive than the potential at the tap, the diode 21 will draw a pulse generating circuit which includes negative re sistance devices. negligible current, while on the other hand, when the po tential at the tap is more positive than that at the common It is a further object of the present invention to provide terminal, then the diode will draw relatively large cur a pulse generating circuit which employs a negative re rents. As the potential on the potentiometer is progres sistance element which is biased into a stable region to sively raised, the load line represented by the impedance gether with means for causing the device to operate in of the conventional diode plus potentiometer will vary its unstable region to form output pulses. as represented by the dotted lines in FIGURE 5. When These and other objects of the invention will become the potential reaches a point V4, the load line becomes more clearly apparent from the following description tangent to the operating characteristics of the negative when taken in conjunction with the accompanying drawing. resistance device, and the device will increase its current Referring to the drawing: exponentially along the line 4. That is, it switches to relatively high currents. By the device to a volt FIGURE 1 illustrates a circuit in accordance with the age near the unstable point, a small signal applied at the 35 invention; control terminals will serve to switch the device and form FIGURE 2 shows the voltage current characteristics an output pulse at the terminals 12. of a typical negative resistance device; The circuit of FIGURE 3 is illustrative and in actual FIGURES 3A and 3B show operation of the circuit of practice might result in the destruction of the diode unless FIGURE 1 in response to changes in impedance; current limiting features 'are incorporated. This might FIGURE 4 shows another pulse generating circuit in arise from the ?nite resistance of the potentiometer accordance with the invention; whereby the intersection of large positive currents, load FIGURE 5 shows the operation of the circuit of FIG URE 4; and line, and the characteristics of the diode may occur in a non-destructive region. FIGURES 6—8 show other pulse generating circuits incorporating the invention. FIGURE 6 illustrates another means of accomplishing the same purpose in a non-destructive fashion. In this FIGURE 2 shows the current-voltage characteristics case, the impedance Z is replaced by the diode 26 and of a suitable negative resistance device. The illustrated capacitor 27 connected in series. A voltage source is characteristics are for a four layer device of the type de shown for varying the voltage across the diode 26. The scribed in Patent No. 2,855,524. The stable load line for source comprises a pair of potentiometers 28 and 29 con a resistive load is represented by the line S, while the nected in parallel across the voltage source B2 and having unstable load line is represented by the letter U. The their taps connected to opposite ends of the diode 26 unstable load line is obtained by other types of loading. through the control signal terminals. If the device is biased at the point of intersection of the If the condenser is large enough, it will present a rela load line U and the current-voltage characteristic curve, tively low impedance for switching transients of the de a slight disturbance in voltage will build up exponentially vice 11. As the potential is varied across the conventional in an unstable manner. diode, its impedance will vary from very high values to Referring to FIGURE 1, a four layer diode 11 is shown very low values in the neighborhood of zero volt across connected through a load resistance R to a power source the diode. When this occurs, the dynamic load line seen B1. An impedance Z connected in series with a second by the device 11 will shift from stable to unstable and power source B2 is connected in shunt with the device 11. the device 11 will build up its current rapidly to a high A coupling capacitor C serves to couple the output termi value and generate a sharp voltage front at the output nal 12 to the device 11. Alternatively an output may be terminals 12. It is evident that the potentiometer and obtained across a low impedance fraction of R or a series battery may be replaced by any other voltage generator resistance in series with Z. 65 which initially has a negative voltage and changes to a If the impedance Z is suf?ciently high, it will not slightly positive voltage. affect the load line of the device 11 and a stable con The circuit of FIGURE 6 can be used to cause a small dition as represented by the load line S, FIGURE 2, re voltage signal to produce switching of the four layer diode sults. However, if the impedance Z is varied, it may from the voltage represented by the line S of FIGURE 2 alter the load line from the form S to the form U. When 70 to approximately the holding voltage. This voltage will the impedance Z is sufficiently low, the current through be maintained while the condenser is discharged. After the device 11 will increase and the voltage will drop to a: this, the process will repeat periodically, as long as the 3,058,009 3 4 control signal is present, at a rate which depends upon load, said load and voltage being selected whereby the the time constants associated with the and capac element is biased to operate stably in its negative resist itor C. ance region, and means responsive to a control signal A circuit like FIGURE 6 is particularly suitable for for shifting the element from stable to unstable operation generating a series of sharp voltage pulses from a small in its negative resistance region whereby the current input signal. It should be noted that the DC. level of through the element increases rapidly to a high value and the input signal can be established at any arbitrary value the voltage across the element drops to a relatively low by providing a suitable bias source at one side of the con value. ventional diode. ' 8. A trigger circuit comprising a negative resistance FIGURE 7 represents an alternative means for varying 10 element, a source of potential coupled to said negative impedance. In this case, a saturable reactor 31 is repre resistive element, means coupled with said source of ented which presents a high A.C. impedance and thus leads potential and said negative resistance element for pro to a stable situation when no current ?ows in the control viding a substantially constant minimum current to said winding of the reactor. When current flows through the negative resist-ance element from said source of potential control winding, the saturable reactor may be made to sat 15 whereby the negative resistance element is biased stably urate in such a direction that increasing current flow cor in its negative resistance region, variable impedance means responding to turn-on of the four layer diode may occur connected to the negative resistance element, and means at low impedances. By this means, the device 11, which for reducing the variable impedance whereby the operat may be a four layer diode, may be made to switch at a. ing point of said negative resistance element changes from predetermined current level through the primary of the a stable to an unstable point. saturable core reactor. 9. A trigger circuit comprising a negative resistance FIGURE 8 illustrates an alternative way of making a element, impedance means, potential source means op variable impedance. In this case, the variable impedance eratively coupled to said negative resistance element consists of a variable condenser. Variable capacity arises through said impedance means, said impedance means from the silicon p-n junction of the diode 32 whose capacity 25 having a high impedance state and a low impedance state, decreases with increasing reverse bias. In this case, the said impedance means in conjunction with said potential diode is reverse biased by the voltage across the four layer source means being such that said negative resistance ele diode. Variations of the voltage applied to the diode 32 ment is biased stably in its negative resistance operating are achieved by the potentiometer 33. When the capacity region when the impedance means is in the high impe of the diode rises to suf?ciently high values, oscillations 30 dance state and said negative resistance element is op of the four layer diode will occur. These oscillations erated unstably when said impedance means is in the low will lead to an increase in the capacity of the conventional impedance state, and means for changing said impedance diode and may even bring it to a condition of positive means from the high impedance to the low impedance bias. If this occurs, the four layer diode will in eifect state. encounter a load line which lies above its negative re 35 10. A trigger circuit comprising a negative resistance sistance characteristics and it will again switch to high element, a ?rst source of potential, ?rst impedance means, currents. said ?rst source of potential being coupled to said nega It is evident that these principles apply to other current tive resistance element through said ?rst impedance controlled negative resistance devices such as therrnistors means, said ?rst impedance means in conjunction with or gas . 40 said ?rst source of potential being such that the load line It is also evident that similar principles may be used therefor crosses the characteristic curve of said negative for making sensitive devices using voltage controlled resistance element in the negative resistance region and negative resistance devices such as the Eralsi or tunnel at one point only, second impedance means, a second diode described in the Physical Review volume 109, 603, source of potential, said second source of potential being 1958. Such circuits may readily be derived using principle 45 coupled to said negative resistance element through said of duality as discussed by R. L. Wallace and G. Raisbeck second impedance means, said second impedance means Bell, Supt. Technical Institute, April 1951, volume 30, page being variable and having at least a high impedance state 381-418. and a low impedance state, the high impedance state of Thus, it is seen that there is provided an improved cir said second impedance means in conjunction with said cuit for generating switching pulses. The circuit generates 50 second source of potential being such that insigni?cant‘ sharp, relatively high power pulses in response to rela current is passed to the negative resistance element for tively small control signals. said second source of potential *When the second impe I claim: dance means is in its high impedance state, the low impe 1. A trigger circuit comprising a negative resistance dance state of said second impedance means in conjunc element, a ?xed source of constant current potential sup 55 tion with said second source of potential being such that ply which biases the negative resistance element stably in the load line therefor crosses the characteristic curve its negative resistance operating region, a variable im of said negative resistance element at at least two points pedance and a second source of potential serially con whereby operation of the negative resistance element is nected between the terminals of the negative resistance unstable, and means for change said second impedance element, and means for reducing the variable impedance 60 element from its high impedance state to its low impe so that the operating point changes from a stable to an dance state. unstable condition. 11. A trigger circuit comprising a negative resistance 2. A trigger circuit as in claim 1 wherein the variable element, a ?rst source of potential, impedance means, impedance is resistive. said ?rst source of potential being coupled to said negative 3. A trigger circuit as in claim 1 wherein the variable 65 resistance element through said impedance means, said impedance is capacitive. impedance means in conjunction with said ?rst source of 4. A trigger circuit as in claim 3 wherein the variable potential being such that the load line therefor crosses impedance includes a p-n junction. the characteristic curve of said negative resistance ele 5. A trigger circuit as in claim 1 wherein the variable ment in the negative resistance region and at one point impedance is inductive. 70 only, a unidirectional current transmitting device, a sec 6. A trigger circuit as in claim 5 wherein the variable ond source of potential coupled to said negative resistance impedance includes a saturable reactor. element through said unidirectional current transmit 7. A trigger circuit comprising a negative resistance ting device, the voltage of said second source of potential element, a load, a ?rst source of voltage serving to apply being less than the voltage at the intersection of the a voltage to said negative resistance element through said 75 characteristic curve of the negative resistance element 3,058,009 6 and the load line corresponding to the ?rst impedance 2,666,977 Pfann ______Jan. 26, 1954 means and the ?rst source of potential, the polarity of 2,740,940 Becker et al. ______Apr. 3, 1956 the connection of the unidirectional element being such 2,843,765 Aigrain ______._ July 15, 1958 that the unidirectional element is back biased by the 2,909,659 Woo ______Oct. 20, 1959 diiferenee in the voltage across the negative resistance 2,912,599 Abraham ______Nov. 10, 1959 element and that of second source of potential, whereby the unidirectional device presents a high impedance to FOREIGN PATENTS the negative resistance element, and means for applying 166,800 Australia ______Feb. 6, 1956 additional voltage to said second potential source where 217,799 Australia ______-_ Apr. 30, 1956 by the unidirectional element becomes forward biased 10 1,058,550 Germany ______June 4, 1959 and presents a low impedance to the negative resistance OTHER REFERENCES element, said low impedance being such that the load line therefor crosses the characteristiecurve of the nega “Germanium Crystal Diodes,” by Cornelius, Elec tive resistance element at at least two points to cause tronics, February 1946, pages 118-123. unstable operation. Negative Resistance in Germanium Diodes, by Kauke, 15 Radio~Electronic Engineering, April 1953, pages 840. References Cited in the ?le of this patent “The Application of The Dynistor Diode to Oft~On Cont-rollers,” by Pittman, I.R.E. Professional Group on UNITED STATES PATENTS Circuit Theory, and Solid State Circuit Con 2,577,803 Pfann ______Dec. 11, 1951 ference, 1958, pages 55-56. 2,581,273 Miller ______Jan. 1, 1952 20