US3828205A

US3828205A - Memory circuit

Info

Publication number: US3828205A
Application number: US00361023A
Authority: US
Inventors: J Konopka
Original assignee: Thomas International Corp
Current assignee: Thomas International Corp
Priority date: 1971-10-15
Filing date: 1973-05-17
Publication date: 1974-08-06
Anticipated expiration: 1991-08-06

Abstract

A triggered neon lamp memory circuit selectively produces control voltages for an electrically tuned receiver. Each stage comprises a neon lamp and a control voltage potentiometer in series with a common source of sustaining potential. In one embodiment, when the neon lamp of a given stage is triggered by manually actuating a touch contact, a series transistor is turned on to effectively couple a fixed voltage to the potentiometer. When the neon lamp turns off, the transistor turns off to remove the fixed voltage from the potentiometer while also raising the voltage at one terminal of the neon lamp to reduce the voltage thereacross to substantially below trigger potential. In another embodiment, when the neon lamp of a given stage is triggered, a diode coupled to a reference potential clamps the voltage across the potentiometer to a fixed value.

Description

United States Patent [191 Konopka [451 Aug. 6, 1974 MEMORY CIRCUIT John G. Konopka, Mundelein, Ill.

[73] Assignee: Warwick Electronics Inc., Chicago,

Ill.

22 Filed: May 17, 1973 21 Appl. No.: 361,023

Related US. Application Data [63] Continuation-in-part of Ser. No. 189,637, Oct. 15,

1971, Pat. N0. 3,746,886.

[75] Inventor:

Primary Examiner-John Zazworsky Attorney, Agent, or FirmWegner, Stellman, McCord, Wiles & Wood [5 7] ABSTRACT A triggered neon lamp memory circuit selectively produces control voltages for an electrically tuned receiver. Each stage comprises a neon lamp and a control voltage potentiometer in series with a common source of sustaining potential. In one embodiment, when the neon lamp of a given stage is triggered by manually actuating a touch contact, a series transistor is turned on to effectively couple a fixed voltage to the potentiometer. When the neon lamp turns off, the transistor turns off to remove the fixed voltage from the potentiometer while also raising the voltage at one terminal of the neon lamp to reduce the voltage thereacross to substantially below trigger potential. In another embodiment, when the neon lamp of a given stage is triggered, a diode coupled to a reference potential clamps the voltage across the potentiometer to a fixed value.

12 Claims, 2 Drawing Figures PATENTED AUG 51974 3.828.205 sum; or 2- MEMORY CIRCUIT CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my copending application Ser. No. 189,637, filed Oct. 15, 1971, entitled Memory Circuit, now US. Pat. No. 3,746,886.

BACKGROUND OF THE INVENTION This invention relates generally to memory switching circuits and, more particularly, to a discrete control voltage developing circuit utilizing as a memory element a voltage breakdown device such as a gas discharge lamp.

DESCRIPTION OF THE PRIOR ART Many television receivers use Varactor tuners which select different channels electrically rather than mechanically. Varactor diodes, which exhibit a variable capacitance in response to different control voltages applied to the diodes, control the frequency characteristics of the tuner. Various circuits have been developed for selectively applying different discrete control voltages to the Varactor tuner. In some circuits, a neon lamp is utilized as the switching and memory element. Typically, the neon lamp is coupled from a source of sustaining potential to ground through a resistor. When the neon lamp assumes its low impedance state, a voltage at the junction between the lamp and the resistor actuates a transistor which couples a control voltage developing potentiometer across a source of power.

In such neon memory circuits, the sustaining voltage across a triggered or activated lamp plus the voltage drop across the series resistor is very close to the trigger potential of the extinguished lamps of the other stages. Due to the fact that the trigger potential of neon lamps varies from lamp to lamp, the resulting voltage across the extinguished lamps can cause inadvertent firing of nonselected stages.

Switching transistors or other three terminal devices have been used to maintain a fixed voltage across the control voltage developing potentiometer. Such a three terminal device has been thought necessary because of wide variations in the triggered impedance of a neon lamp, which would produce different voltage drops and hence different voltage outputs across the potentiometers. As a result, prior neon memory circuits have been complex and use a large number of components.

SUMMARY OF THE INVENTION In accordance with the present invention, the disadvantages of prior memory circuits for producing control voltages have been overcome. A plurality of individual memory stages, each containing a gas discharge device, are selectively energized by manual actuation of an associated touch contact. Each memory stage, when its associated neon lamp is extinguished, raises the potential at one junction of the neon lamp in order to decrease the voltage thereacross to a value substantially below the neon lamp trigger potential, preventing inadvertent triggering of the neon lamp.

When a neon lamp is actuated, current fiowsthrough the lamp also through a control potentiometer which develops a desired discrete tuning voltage. ln'one embodiment, a switching transistor located in a series path with the neon lamp and the potentiometer serves to bypass current to a regulated supply. In another embodiment, a diode coupled to a clamp voltage supply bypasses current from the actuated neon lamp. Both circuits thus maintain a fixed voltage drop across the potentiorneter.

One object of the present invention is the provision of a gas discharge memory stage which effectively clamps the voltage across an output voltage developing resistance.

Another object of the present invention is the provision of a gas discharge memory stage having a reduced number of components and having improved immunity to inadvertent triggering.

Other objects and features of the invention will be apparent from the following description, and from the drawings. While illustrative embodiments of the invention are shown in the drawings and will be described in detail herein, the invention is susceptible of embodiment in many different forms and it should be understood that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of one embodiment of the invention, using a three terminal switching device; and

FIG. 2 is a schematic diagram of another embodiment of the invention, using a two terminal switching device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, two embodiments of a plural stage memory circuit are illustrated, which circuits may be used as a channel selector for a Varactor tuner in a television receiver, or may be used in any application where one of a plurality of discrete voltages are to be selectively generated. For simplification, only two stages A and B of the memory circuit are shown in FIG. 1, and only one stage N is shown in FIG. 2, but any number of similar stages may be provided for each voltage level or channel to be selected. Since each stage is similar, corresponding elements have been identified by the same reference numeral, followed by a letter subscript which respectively corresponds to thestage in which the element is located. Each stage includes a memory element in the form of a voltage breakdown device, preferrably a gas discharge device (such as a neon lamp) since the light energy from the device provides a visualindication of the state of the stage.

Turning to FIG. 1, each stage of the memorycircuit is connected in parallel from a first voltage source V through a common series resistor 20 to a second-source of potential V the voltage difference V -V, of which may be approximately 200 volts. Neongas'discharge lamps suitable for use in this circuit mayhave a'trigger voltage or trigger level of approximately 1 10 volts, and a sustaining voltage or sustaining level of approximately volts. A second voltage source V maybe at a negative volts with respect to the second source of potential or ground reference potential V,,,.

When power is first applied, the voltage across all of the neon lamps including 22a and 22b will increase towards the trigger level. Due to inherent variations in the exact trigger level of the lamps, or due to purposeful selection, one neon lamp will have a lower trigger level than the others, and that lamp will be the first to turn on and assume a low impedance state. When this lamp turns on, it causes the voltage at terminal 24 to fall substantially below the trigger potential of the other lamps, thereby preventing the remaining lamps from becoming activated. The resistance value of resistor 20, coupled between the first voltage source V and terminal 24, is chosen relative to the total resistance of an activate stage to limit the current to a value which optimizes lamp life and light output.

Assuming lamp 22a of Stage A has a lower trigger level than that of lamp 22b of Stage B, the lamp 22a will be the first to turn on, thereby disabling activation of Stage B. When lamp 22a turns on, a sufficient amount of base current is coupled throughlamp 22a, a diode 28a, and a base bias resistor 30a to turn on a series three terminal device such as a clamping transistor 26a. The base of transistor 26a is directly coupled to a regulated source of clamp voltage V,.,.

When transistor 26a turns on, the collector 26a is clamped to the regulated supply voltage V by the diode action of the transistors base-collector junction. The collector is coupled to ground reference potential V through a potentiometer resistor 32a which develops the tuning control voltage. The control voltage, having a value dependent on the setting of a wiper contact 34a of potentiometer 32a is coupled through an isolation diode 36a to a Varactor tuning output V Diode 36a isolates the tuning voltage output V from the tuning voltage potentiometer 32a when it is not energized. The clamp transistor 26 serves to bypass a portion of the current flow through neon lamp 22 and thus produces a fixed voltage drop across the potentiometer 32 regardless of tolerance variations in the neon lamp.

When a pair of touch contacts 38b of Stage B is now manually touched, memory Stage B is activated and memory Stage A, in response thereto, is deactivated. Specifically, when the touch contacts 38b are touched, a circuit is completed from negative supply voltage .V' through a current limiting supply resistor 40, common terminal 42, touch contacts 38b, and series resistor 44b, to a second junction 46b of neon lamp 22b. Junction 46b is also coupled to a third source of potential V a, which may be ground potential, through a capacitor 50b. When this circuit is completed, capacitor 50b. discharges toward negative supply voltage V through the circuit until the voltage across

junctions

24b and 46b of neon lamp 22b exceeds the trigger level thereof.

Neon lamp 22b then assumes a low impedance or high conduction state to provide base drive current for a switching transistor 26b, which is in series through an isolation diode 28b.

When either gas discharge lamp 22a or 22b turns on, it remains on while the voltage thereacross exceeds the sustaining level, even though the touch contacts are subsequently opened. The neon lamp acts as a memory element which also serves as a visual indicator. Diode 28 isolates the regulated supply voltage V to allow the decrease of the potential at junction 46.

When neon lamp 22b and transistor 26b turn on due to closure of touch contacts 38b, the common sustaining potentialon bus 24 is momentarily pulled down to the voltage at junction 46b, minus the sustaining voltage of neon lamp 22b. This decreases the total potential across neon lamp 22a sufficiently below the sustaining level to cause neon lamp 22a to assume a high impedance state. Base drive is now removed from transistor 26a, which turns off and thereby removes regulated voltage source V, from potentiometer 32a.

An advantage resulting from use of the switching transistor in series with the neon lamp is that when the transistor, or any other suitable switching device, turns off, a high impedance is developed between the second junction of the lamp and the second source of potential V thus allowing a voltage approximately equal to the regulated source voltage V to be developed at the second junction. This limits the voltage across the lamp to a value substantially below the requisite trigger level. When neon lamp 22a and its series switching transistor 26a turn off, for example, the charge on capacitor 50a is held at supply voltage V through a resistor 45a, such as 33 megohms.

If transistor 26a, for example, were eliminated from the circuit and replaced by a short circuit, the impedance between junction 46a and the second source of potential V would be so small in comparison with the high impedance of resistor 45a that capacitor 50a would be unable to maintain a charge from current therethrough. Under these circumstances, the neon lamp, when in its off-state, would have a voltage thereacross dangerously close to the trigger level. Due to variable tolerances in trigger levels from lamp to lamp, a very unstable situation would exist. However, with transistor 26a in series with lamp 22a, the potential at junction 46a is maintained at a high level V such that the total voltage across neon lamp 22a is safely below the trigger level.

When touch contacts 38a are touched, with lamp 22a in a high impedance state and lamp 22b in a low impedance state, capacitor 50a discharges toward the negative trigger potential at junction 42 until the voltage across neon lamp 22a again exceeds the trigger level and turns on in response thereto. Neon lamp 22b is then turned off in identical fashion as described with regard to the turning off of lamp 22a. Also, transistor 26b will turn off and remove the regulated voltage source V from potentiometer 32b while maintaining the voltage at junction 46b at V to avoid inadvertent triggering of lamp 22b.

Turning to FIG. 2, an intermediate memory stage N is illustrated which is simplified with respect to the circuit of FIG. 1. Corresponding elements have been identified by the same reference number, followed by the subscript n which corresponds to stage N. Representative values for the potential sources are illustrated and representative component values will be given herein, but it should be understood that such values are merely representative and are not critical. The neon lamp 22n may have a trigger or firing potential of not less than the highest holding potential of any other lamp plus the clamp voltage of 30v DC. The three terminal switching device of FIG. 1 has been eliminated and a substantially simpler, two terminal switching device is used in place thereof.

The unidirectional conduction diode 28n is coupled between junction 46n and a clamp line 62n which is directly connected to the top of a 50 kilohm potentiometer 32n. Clamp line 62n is shunted to reference ground 65 through a capacitor 67n, having a value such as 0.1 microfarad. The clamp line 62n is coupled through a second unidirectional conduction device, in the form of a diode 76in, to a source of clamp potential, at +30 volts DC.

In operation, diode 70n and its associated clamp circuit serves a purpose similar to the three terminal switching device 26 and its associated circuit in FIG. 1. When neon lamp 22n is triggered by manually touching the pair of contacts 38n, current flows through the neon lamp and diode 28n to potentiometer 32n. Due to wide tolerance variations in neon lamps, the actual impedance of neon lamp 22n will typically differ from the impedance of other neon lamps in the other stages. This results in different voltages appearing on clamp line 62 in different stages, absent the effect of the clamp circuit to be described. Such different voltages would produce different output voltages V for the same setting of wiper 34, producing an unsatisfactory circuit.

However, the illustrated clamp circuit including diode 70n bypasses some of the current which flows through the actuated neon lamp 22n, maintaining clamp line 62n at a clamped voltage equal to the clamp potential plus the breakover potential of the semiconductor diode 70n. As a result, a fixed regulated voltage is switched across potentiometer 32, regardless of the particular voltage drop characteristic of the neon lamp 22.

I claim:

1. In a memory circuit having an individually selectable memory stage for generating a variable DC output voltage, the improvement, comprising:

a voltage breakdown device triggerable from a first state to a second state of conduction;

trigger means for triggering said voltage breakdown device;

a variable device having a variable element adjustable to vary the DC output voltage;

series circuit means responsive when said voltage breakdown device is triggered for coupling at least a portion of the current through said voltage breakdown device to said variable device to generate said variable DC output voltage; and

clamp circuit means coupled to said series circuit means for clamping at least some of the current to said variable device to produce a repeatedly constant DC output voltage for each same adjustment of said variable element.

2. The improvement of claim 1 wherein said series circuit means includes diode means for passing the current flowing through said variable device.

3. The improvement of claim 1 wherein said trigger means comprises a source of trigger potential, touch contact means, and resistive means effectively coupling said touch contact means between said trigger potential source and a junction located in said series circuit means between said voltage breakdown device and said variable device.

4. The improvement of claim 3 wherein said voltage breakdown device comprises a gas discharge lamp triggerable from a low to a high state of conduction when the voltage thereacross exceeds said trigger potential, whereby said gas discharge lamp serves as a memory element and is a visual indicator of the state of the memory element.

5. The improvement of claim 1 wherein said clamp circuit means comprises a source of clamp potential, diode means connected between said clamp potential source and one side of said variable device, said diode means being poled to conduct when said voltage breakdown device is triggered in order to clamp said one side of said variable device to substantially said clamp potential.

6. The improvement of claim 1 wherein said clamp circuit means includes a semiconductor device having first, second, and third terminals, said first and second terminals being located between said voltage breakdown device and said variable device, a source of regulating potential, said third terminal being coupled to said regulating potential source, and resistive means located between said third terminal and one of said first and second terminals for actuating said semiconductor device when said voltage breakdown device is triggered.

7. In a memory circuit having an individually selectable memory stage with output means for producing a desired DC output voltage and a gas discharge device triggerable from a low to a high state of conduction when the desired DC output voltage is to be produced, the improvement, comprising:

means for maintaining said gas discharge device in said high state of conduction to cause the gas discharge device to form a memory element;

circuit means effective when the gas discharge device is in the high state of conduction for causing at least a portion of the current flow through said gas discharge device to flow through said output means to produce said desired DC output voltage;

diode means;

a source of clamp potential; and

means connecting said diode means between said clamp potential source and said circuit means for clamping the voltage across said output means to substantially said clamp potential regardless of the voltage drop produced across said gas discharge device.

8. The improvement of claim 7 including second diode means, and said circuit means connects said second diode means in series with the gas discharge device and the output means to cause said current portion to flow through said second diode means.

9. The improvement of claim 7 wherein said output means comprises a potentiometer having a fixed resistance and a wiper movable thereacross, said circuit means connects said fixed resistance in series with said gas discharge device, said connecting means connects said diode means between said clamp potential source and one side of said fixed resistance, and said wiper is movable to develop different desired DC output voltages when said gas discharge device is triggered to said high state of conduction.

10. The improvement of claim 7 wherein the circuit means includes capacitive means, a ground source, a source of elevated potential for providing current to said gas discharge device, said circuit means connects said gas discharge device and said output means in series between said elevated potential source and said ground source, and said capacitive means is coupled between said ground source and a junction, in said circuit means located between said gas discharge device and said output means.

11. The improvement of claim 10 wherein said connecting means connects said diode means between said clamp potential source and the same junction in said circuit means to which said capacitor means is coupled. and said output means, and isolation means connected bet e do t ut means and other selectabl sta s 12. The improvement of claim 11 including second we n Sal u p e ge diode means, said circuit means connects said second of the memory clrcult' diode means in series with said gas discharge device

Claims

1. In a memory circuit having an individually selectable memory stage for generating a variable DC output voltage, the improvement, comprising: a voltage breakdown device triggerable from a first state to a second state of conduction; trigger means for triggering said voltage breakdown device; a variable device having a variable element adjustable to vary the DC output voltage; series circuit means responsive when said voltage breakdown device is triggered for coupling at least a portion of the current through said voltage breakdown device to said variable device to generate said variable DC output voltage; and clamp circuit means coupled to said series circuit means for clamping at least some of the current to said variable device to produce a repeatedly constant DC output voltage for each same adjustment of said variable element.

7. In a memory circuit having an individually selectable memory stage with output means for producing a desired DC output voltage and a gas discharge device triggerable from a low to a high state of conduction when the desired DC output voltage is to be produced, the improvement, comprising: means for maintaining said gas discharge device in said high state of conduction to cause the gas discharge device to form a memory element; circuit means effective when the gas discharge device is in the high state of conduction for causing at least a portion of the current flow through said gas discharge device to flow through said output means to produce said Desired DC output voltage; diode means; a source of clamp potential; and means connecting said diode means between said clamp potential source and said circuit means for clamping the voltage across said output means to substantially said clamp potential regardless of the voltage drop produced across said gas discharge device.

10. The improvement of claim 7 wherein the circuit means includes capacitive means, a ground source, a source of elevated potential for providing current to said gas discharge device, said circuit means connects said gas discharge device and said output means in series between said elevated potential source and said ground source, and said capacitive means is coupled between said ground source and a junction in said circuit means located between said gas discharge device and said output means.

11. The improvement of claim 10 wherein said connecting means connects said diode means between said clamp potential source and the same junction in said circuit means to which said capacitor means is coupled.

12. The improvement of claim 11 including second diode means, said circuit means connects said second diode means in series with said gas discharge device and said output means, and isolation means connected between said output means and other selectable stages of the memory circuit.