DE2543777A1 - SAW TOOTH VOLTAGE GENERATOR - Google Patents

Description

DiPL-ING. KLAUS NEUBECKER

Patent application ^! t
4 Düsseldorf 1 - S chad ο /.- Platz 9

Drying. Ernst Straitnann

PF 2297
7557

Düsseldorf, Sept. 30, 1975

Tektronix, Inc.

Beaverton, Oregon, V. St. A. Sawtooth voltage controller

The invention relates to a sawtooth voltage generator.

In the case of a device for the precise examination or measurement of electrical processes, for example for an oscilloscope or similar equipment, the electrical process is usually described as a visual representation of the instantaneous voltage reproduced in time. In most cases the time relationship is provided by the device itself. E.g. produces a Deflection generator a sawtooth voltage, which after processing in a horizontal amplifier, the horizontal deflection plates the cathode ray tube, which results in a horizontal deflection. If the for a linear deflector voltage required of the electron beam (i.e. deflection factor) and the ramp rate of the sawtooth voltage are known quantities, the horizontal distance can be displayed on the screen of the oscilloscope Waveform can be converted into time units.

When accurate time measurements are to be made it is essential that that equal sections of horizontal distance represent equal time sections. When the shift of the electron beam proportional to that of the horizontal at all times

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Baffles applied voltage, it follows that the Deflection voltage must vary linearly with time. In addition, the electron beam must be returned to a rest position because otherwise there would be visible shifts in position of the deflection of the electron beam.

Two important requirements for a precision sawtooth generator are therefore the stability of the fundamental voltage before the sawtooth waveform is triggered and the absence of deviations, after the sawtooth voltage has been triggered.

Basically, all sawtooth generators for generating sawtooth voltages generate the sawtooth voltage by a Capacitor is charged and discharged by a # charge voltage. Limit previous arrangements for basic stabilization the charging current to a certain value, whereby longer periods of time were required for a recovery from negative Voltage spikes (such as overshooting the discharge) to recover. Tripping deviations due to the time interval necessary to turn on the current flowing into the time capacitor were made by others Reduced precautions, such as overdriving an emitter-coupled amplifier. However cause such measures also include deviations caused by stray capacities and device capacities.

The object of the invention is to create a sawtooth voltage generator, which does not have these disadvantages and shows even smaller deviations after the sawtooth release and at the same time maintains time base stability.

According to the invention, the object is provided by the main claim mentioned features solved.

The disadvantages described in known sawtooth voltage generators are eliminated in that the distortion the output by increasing or decreasing a counter current

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which is generated via feedback devices to charge a time capacitor in the direction or to discharge, which is necessary to get the desired time base, while the deviations after triggering the The sawtooth voltage can be reduced by a very fast current switch for the timing element from a power source causing a current sink of greater capacity.

The basis of the present invention is thus to provide a sawtooth voltage generator which is a Time element (capacitor) includes a "time" stream and a counter current is alternatively supplied or withdrawn in order to charge and discharge the time element (the capacitor) and thus to generate the sawtooth voltage. A current sink for deriving the "time" current and the counter current is through an emitter-coupled pair is provided which operates as a gate controlled by a gate control signal. A couple of bipolar or asymmetrical conductive devices, such as diodes, is associated with the gated components connected to carry the fault current and an additional Create current path.

Further details, advantages and possible applications of the invention emerge from the accompanying illustration of an exemplary embodiment and from the following description.

It shows:

1 shows a circuit according to the prior art for generating a linear sawtooth voltage;

2 shows the profile of the sawtooth voltage generated with the known device;

3 shows a preferred embodiment of the sawtooth voltage generator according to the invention; and

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4 shows the curve of the sawtooth voltage generator according to the invention generated sawtooth voltage.

In the drawings, FIG. 1 shows a sawtooth voltage generator known from US Pat. No. 3,723,762, which avoids some of the disadvantages initially indicated. The sawtooth voltage generator comprises a capacitor 14 and a switching diode 12 which is used to charge and discharge the capacitor 14, the voltage developing across the capacitor terminals being used as the sawtooth voltage. A signal source 10, which generates a switching signal P, is grounded at one end and connected at the other end to the cathode electrode of the switching diode 12, the anode electrode of which is connected to the connection point 13 between the output of a source for charging current 15 and a terminal of the capacitor 14. The polarity of the source 15 is chosen so that the current I .. flows into the capacitor 14 via the connection 13. The other connection of the capacitor 14 is grounded and the connection point 13 is still connected to an output connection 16. As is known, in the absence of a switching signal P supplied by the source 10, a current I _{1 flows} from the source via the diode 12 into the signal source 10. If a switching signal P is present, the switching diode 12 is reverse-biased, whereby the current I,. is enabled to charge the capacitor 14. It is also known that an exponentially running reverse current I ₁ (t) flows into the connection point 13 due to the stored charge, so that the capacitor is also charged due to this current. The effect of the additional exponential current leads to the sawtooth voltage source form 19 of FIG. 2, in which the switching signal P is also shown. As can be seen from FIG. 2, the waveform 19 is not linear and contains initial value deviations. In order to avoid these disadvantages, a series circuit with a source for constant voltage 22 and a second diode 17 are connected in parallel with the capacitor 14. The polarity of the second diode 17 and the positive terminal of the constant voltage source 11 are in the

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Arranged so that the diode 17 in the absence of one Switching signal P from the signal source 10 is conductive. If both diodes have similar characteristics, an additional one is used Exponential current i ~ (t) generated in the illustrated Direction flows when the switching pulse P is supplied. As a result, the exponential currents are effectively eliminated and the sawtooth voltage waveform 18 is generated. However, there remain initial deviations and inaccuracies due to from temperature fluctuations, diode mismatches, etc.

In US Pat. No. 3,621,282 a sawtooth generator is described which includes a bistable comparator in order to the sawtooth voltage with a reference voltage for discharge of a capacitor, through which the sawtooth voltage is generated, to a stabilized sawtooth voltage to deliver. However, the output of such a circuit does not return to an accurate reference voltage as the Output of the comparator can shift significantly due to the parameters of the comparator.

According to a preferred embodiment of the invention, which is shown in detail in FIG. 3, a sawtooth voltage generator is provided which is further improved over the known sawtooth voltage generators and at the same time keeps the time base at a reference level. The sawtooth voltage generator of the present invention includes a capacitor 50 which is charged and discharged to provide the sawtooth voltage waveform. A time control power source 52 is connected between the source of a suitable potential and one terminal of capacitor 50, so that a current I_ _T flows into the capacitor 50th The other terminal of the capacitor is grounded. The current flowing into the capacitor 50 or flowing out from this stream generated across the capacitor a terminal voltage V_ _T, which is an output terminal 54 is supplied by an amplifier 56, whose non-inverting input also connected to the non-grounded terminal of the capacitor 50

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while the inverting input is connected to its single output terminal and the output terminal 54. An amplifier connected in this way represents a voltage follower amplifier. As a result, the output sawtooth voltage at the output terminal 54 is conventionally defined by -sr = £ -, where -rr represents the first derivative or linear slope of the timing current I_ which charges the capacitor 50 (C_ in the above formula corresponds to capacitor 50). A next amplifier 58 is connected to the output terminal 54 and compares the output ramp voltage VO applied to its inverting input with a reference voltage, V ₀₇ ^ ₇ , applied to its non-inverting input during the idle period. It should be noted that the voltage V _{REF is} usually of the same magnitude as the level desired for the time base of the generated ramp voltage, typically zero volts. The only output of the amplifier 50 is therefore a counter current which is controlled by the difference between the output sawtooth voltage VO and the reference voltage V _n ^ _x. Between

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the non-grounded terminal of the capacitor 50 and the output of the amplifier 58 is an asymmetrically conducting device or a unipolar device such as a diode 60, which is polarized so that it allows a current flow I _D6O in the direction shown when it is biased in the forward direction.

A pair of transistors 62, 64 are connected with their emitters in common to a source for a suitable potential as shown in the drawing, namely via a series-connected current sink 66 in order to absorb the current I "flowing in the direction shown. The collectors of the transistors 62, 64 are led to the anode or cathode of the diode 60, while the base connections of the transistors are connected to a gate source V _GATE and a voltage source V. The generator will be completed

through a diode 68, the cathode of which is connected to the collector of transistor 62, while the anode is grounded.

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In Fig. 4 details are with the invention Waveforms associated with sawtooth voltage generator circuitry are shown. Waveform 80 represents the gate source voltage If ν.-.- ™, -, at least several tenths of a volt more negative

is than the potential of the voltage source V (82 in the drawing), the transistor 64 conducts the entire current Is. (pie transistors 62, 64 are connected to one another in the known emitter-coupled manner and their mode of operation is not explained in detail here). Since the transistor 64 conducts the entire current Is, the voltage V _{CT runs} across the capacitor 50 and thus VO at the output terminal 54 under the influence of I ™ according to Kirchoff's law according to the relationship:

¹ CT ^{= 1} T ^{+ 1} DOO " ^Is '

where I_, I _D6 Q and Is have already been defined. By choosing Is greater than I_ (ie Is> I ™), I _{D6O is determined} ^from the difference between VO and V., ™ until I „ _m = 0. When I _om = 0. becomes V0 << V _n ™ and there is no excess current available for charging or discharging the capacitor 50 and VO is thus defined as a potential which is close to the value ν_ ™. It is now clear that, under the conditions described above, the fault current IjmgQn ^{= 1} DoO ^{= 1} DOe ~ ¹ T - * - ^st * Distortions in the voltage VO are corrected by an increase or a decrease in the fault current, whereby I ™ is caused assume a non-zero value that charges or discharges the capacitor in the direction necessary to restore the correct time base. This method is a significant improvement on the prior art because capacitor 50 (C_) can be charged or discharged by a current many times greater than current I _T , rather than applying this charging or discharging current to the current I _T itself is limited. The latter would require a longer time to allow recovery after negative voltage spikes (e.g. discharge overshoot), etc.

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At a time to, in order to switch on the sawtooth voltage 86, the gate voltage source V_ is from a potential which is several tenths of a volt more negative than the voltage source Vs, switched to a potential that is several tenths Volts is more positive than the voltage source Vs. During this transition period

^Is " ^I C62 ^{+ I} C64 '

^{= 1} ERROR " ^I C62 ^{and 1} CT ¹ T ^{+ 1} DoO ~ ^Σ Ο64 ¹ T ^{+ 1} ERROR

Since, as you can remember, before the transition I _ERRO r = Is - IT, it must now follow that I ™ = O. In this way, the capacitor 50 is not charged or discharged by a residual current. If there is a decrease in current ^I C64 k ^ ^{s to} a point where Ip ₆₄ = I ™, ¹ DoO ⁼ ° · ^D: * - ^e current conduction through diode 60 ceases and changes in fault current I _13n , .. - no longer affect I-,. Diode 68 now conducts, preventing transistor 62 from saturating. As a result, I ™ = I »- Ip ₆ 4 and Vu„, and with this VO begin to increase. While the current 1 ^ ₆₄ drops to zero, the sawtooth voltage increases more slowly than would be ideal during a time interval in which I_, ~> I _{C g4 ^ 0.} By choosing Is much larger than I _m (i.e., Isi >> I _m ), such a time interval is only a fraction of the total rise time of ^V _GATE / thereby providing a very fast and "clean" current switch for capacitor 50 (C _m ) is effected. The present invention thus represents an improvement over the prior art, since the time interval which is necessary to effectively switch the current flowing into the time capacitor is essentially limited by the rise time of the gating waveform or by the loop bandwidth of the operational integrator sawtooth generator Circuit, such as "Miller integrators".

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It should be noted that the present embodiment represents only an example and changes can be made by those skilled in the art without departing from the concept of the invention is deviated.

Claims ;

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Claims (5)

P a "f e η f a η s ρ r ü c h e; J sawtooth voltage generator, characterized by a Time element (50) over which the sawtooth voltage (V _CT , VO) is generated; by a time current source (52) for supplying a time current (I) for the time element (50); by means (58) for supplying additional current (! "_," __) for the time element (50); by a current sink (66) for taking up the time current (I ") and the additional current (!""" _ ") and by means of ÜKKUK lines (60 _r 62, 64, 68) for controlling the time current and the additional current in the current sink (66) in order to alternately charge and discharge the time element (50) and thus generate a sawtooth voltage. 2. sawtooth voltage generator according to claim 1, characterized characterized in that the current sink (66) draws substantially more current (I) than from the time current source (52) is delivered. 3. sawtooth voltage generator according to claim 1, characterized in that the devices for supplying the "additional current comprise a first amplifier device (56), which _{follows the sawtooth voltage (ν_, φ} ), and a second amplifier device (58), the Difference between the following sawtooth voltage (V) and an external reference voltage (V_ ^) reacts, which is fed to the second amplifier device (58) in order to deliver the additional current (! """__.). EKKUK 4. sawtooth voltage generator according to claim 1, characterized in that the control means comprise a pair of emitter-coupled transistors (62, 64) which are related to a pair of voltage sources ' ^we i ^ter a switching diode (60) which between 609815/1004 the collectors of the two emitter-coupled transistors (62, 64) are connected, and one is asymmetrical conductive device (68) between the collector of one of the two emitter-coupled transistors (62) and a voltage source (ground) is connected. 5. sawtooth voltage generator according to claim 4, characterized in that a device for changing at least one of the two voltage sources for the emitter-coupled transistors is variable. ES / hs 3 609815/1004 At L e r s e i t e