System For Processing Signal Data To Obtain Improved Contour Presentations On A Cathode-ray Display

Abstract

A system for processing analog signals representative of a parameter such as charge intensity, etc., along a scanned surface in contour mapping fashion. Monopolar and bipolar pulse patterns and a staircase signal are generated wherein the pulse spacing and staircase individual step widths are representative of corresponding input analog signal slopes at the corresponding points in real time. A variety of display intensity modulation signals is developed to permit a selection of contour presentations.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is filed under the provisions of 35 U.S.C. 119 with claim for the benefit of the filing of an application covering the same invention filed July 10, 1968 Ser. No. 32909/68 in Great Britain.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to cathode-ray displays of scanned information and more particularly to systems for processing analog intensity modulation signals for said displays.

2. Description of the Prior Art

In the prior art, the presentation of intensity modulated cathode-ray display patterns has been a widely used expedient for depicting variable amplitude analog signals resulting from the scan of a surface to be examined, such as by a scanning electron microscope or similar device.

One more specific example involves the generation of varying potentials resulting from scan (as by a raster type scan, for example) of a semi-conductor surface having a potential or work function condition and distribution to be investigated. A cathode-ray display used to present these data would be equipped with a raster scan synchronous with that scanning of the electron microscope beam over the said semi-conductor surface. In general, prior art systems applied the analog varying amplitude signals thus obtained more or less directly as intensity control signals to an intensity controlling element of the cathode-ray display. Biasing, d.c. level shifting and amplification were sometimes applied, however the signals were applied otherwise unmodified.

One basic requirement of a display of data from sources such as the aforementioned, is that it provide the observer with an image that is readily interpreted. Another important requirement is that it should allow quantitative recovery of measuring system outputs.

Practically, the first requirement is met by careful attention to scan linearity and correspondence between coordinates observed in the "pick-up" scan and those of the display.

The second requirement is not met by direct application of the aforementioned intensity modulation analog signal, since recovery of discrete "Z" coordinate values is difficult. The unique method and apparatus of the present invention provides for the availability of these "Z" coordinate values by encoding the said analog signal in discrete steps in the circuit path before it is displayed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a typical instrumentation of the device of the present invention.

FIG. 2 is a plot of various waveforms occurring during operation at various points in the device of FIG. 1.

SUMMARY OF THE INVENTION

In view of the indicated state of the prior art and its disadvantages, it was the general object of the present invention to generate several different types of "Z" (intensity modulation signals) for the selective presentation of the basic analog signal data in various forms resembling contour relief maps.

According to the invention, there is provided an electrical arrangement for processing an analog signal of the character described, for display on a cathode-ray tube display device.

The structure includes a dual input summing amplifier, to one input of which the analog signal is fed. The output of this amplifier is applied in parallel to upper and lower threshold detectors. Whenever the upper threshold is attained by the signal at this point, a reversible counter is stepped once in one direction and once in the other direction for a lower threshold attainment. A decoder responds to both of said counter outputs and produces a staircase output correspondingly "counted" both up and down. The said staircase output constitutes a reference signal applied to the other summing amplifier input and has the effect of holding the summing amplifier substantially within the limits set by the threshold detectors. The said staircase, as well as differentiated monopolar and bipolar forms of the leading and trailing edges of the individual staircase steps provide a variety of intensity control signals for the cathode-ray display device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In describing the invention with respect to FIG. 1, reference will be repeatedly made to waveforms of FIG. 2. It is to be understood that a waveform called out with reference to an identifying letter is the corresponding waveform of FIG. 2. The common abscissa of FIG. 2 is the sweep position of the scanning beam (of an electron microscope, for example) providing the basic analog data such as shown in waveform a. The abscissa could, in the case of a linear raster type scan, also be considered a (real) time base in the ordinary sense.

In FIG. 1, the element 2 comprises the summing amplifier, and as such, includes the series resistors at inputs 1A and 1B, and also the feedback resistor across the straight-forward differential type operational amplifier 18 operated as a single variable input device with its other input grounded. The inputs at 1A and 1B are seen to add at point 19 and thus the entire subcombination constitutes the said summing amplifier.

In this explanation a simple sine wave is taken as an assumed analog signal input (waveform a) into terminal 1A. That waveform may, as hereinbefore indicated, have been generated by an electron microscope scanning a surface charge pattern, although it could have resulted from any other scanning operation wherein the data is amenable to presentation as contour data on a synchronously scanned cathode-ray tube display device.

The 1B input to the summing amplifier 2 is reserved in this case for introduction of feedback as will be hereinafter understood. It will be noted that this feedback (or reference signal) is also provided to an output terminal 13. The precise nature of the said reference signal (waveform b ) and its generation will be more fully described and will be apparent as this description proceeds.

The output of the summing amplifier 2 is provided to an output terminal 14 as waveform c and in parallel to a pair of threshold detectors 3 and 4. These elements 3 and 4 are identified as upper and lower threshold detectors respectively. As the name implies, each is a circuit adapted to deliver a trigger at any time that its input attains its predetermined threshold. Various relaxation oscillators suitably biased or offset are available in the art for instrumentation of this particular function.

The analog signal input at 1A is inverted by the summing amplifier 2, so that, as the amplitude of the input signal falls, there is a rise in the output until the threshold level of detector 3 is attained and the said trigger is delivered via the synchronizing circuit 5 to the reversible binary counter 6.

Operation of the detector 3 causes the counter 6 to be advanced one step in a forward direction at a rate determined by pulses from a clock pulse generator 7. Actually the pulses from detector 3 (and in the opposite polarity from detector 4 as will be seen subsequently) are enabling pulses to the counter 6, the actual change of state being effected by clock pulses from 7 on line 23 via the gate 9.

Synchronizing circuit 5 is actually a logic type of circuit producing an inhibit control on lead 8 to the gate 9 to prevent clock pulses on 23 from operating the counter during any time when both detectors are pulsing in the same time period. The synchronizing circuit is also arranged with suitable logic circuitry to pass detector triggers from 3 or 4 only at times other than during the occurrence of any clock pulse.

The counter output is fed to a decoder 10, which is actually a digital-to-analog converter for generating the reversible "staircase" (waveform b ) at a level such that when this signal is fed back to the IB input of 2, the level of the output signal from 2 is reduced to a level intermediate that of the threshold levels of the two detectors 3 and 4. Waveform 6 graphically conveys this summing amplifier signal relationship. The upper and lower threshold levels are shown in dotted line in connection with waveform c.

Considering now the sequence resulting from lower threshold triggering from 4, an opposite process occurs, with counter 6 being stepped once in reverse direction upon each attainment of the said lower threshold level of detector 4.

Therefore, during operation, a stepped reference voltage (waveform b ) is subtracted from or added to the input signal within 2, the amplified algebraic difference or sum at the amplifier output is thereby kept within limits set by the said threshold detectors. See again the output of 2 at waveform c.

Referring now specifically to the four output terminals 11, 12, 13 and 14, the four varieties of cathode-ray device intensity modulating signals available may be summarized.

Terminal 11 provides the waveform f, which is actually the "flip-flop" signal of the first (least significant) stage of the counter 6 (waveform d ) via the differentiator 16 and the rectifier 15. After differentiation, the counter output is converted to waveform e, and rectification at 15 results in the waveform f as aforesaid at terminal 11. It may be said that successive changes of state of the first counter stage (which are the same whether the counter is stepped forward or backward) are available in leading edge form at terminal 11.

Terminal 12 will be seen to provide the mixed outputs of the threshold detectors 3 and 4 via the pulse adder 17. As previously indicated, one of the lines 20 or 21 will convey positive trigger pulses and the other negative pulses. Thus, after addition in 17, the waveform g is obtained at terminal 12. The significance of the two polarities of intensifying pulses will be more fully understood as this description proceeds.

Terminal 14 provides the waveform c, and terminal 13 the feedback (reference) signal of waveform b previously discussed.

In view of this available selection of cathode-ray display intensity control signals, four modes of system operation will be seen to follow. These modes are arbitrarily identified as modes A through D, as follows:

Mode A: By using the output from terminal 11 (waveform f ) as an intensity modulation function in a raster scanned system, the contours generated with gradient line much like in elevation contour mapping. The granularity of the contours (spacing of individual illuminations) will depend on the number of scan lines employed per unit of physical dimension, according to well understood principles.

Mode B: In this mode, the bipolar intensity pulses of waveform g are employed to inject the increasing and decreasing slope concept into the presentation. Thus, not only more, but also less intensified successive marking points are presented. The observer may interpret the resulting display by supposing that a light shines over the contoured surface, being scanned and displayed, in the direction of scan and is reflected or casts a shadow depending on the sign of the incremental slope of the variable with respect to the direction of scan. This produces an illusion of three dimensionality and can be helpful in interpreting the parameter distribution on the scanned surface unambiguously.

Mode C: In this mode, the output from terminal 13 (waveform b ) is employed as the intensity function. The advantage of this mode of display over the prior art direct intensity modulation (by the analog signal of scanned surface parameter variation) technique is that the stepped (discontinuous) changes in brightness enables the observer to appreciate progressive change of brightness (instantaneous value of parameter presented) without calibration equipment.

Mode D: By using the upper and lower threshold limited summary amplifier output (waveform c ) available from terminal 14 as the intensifying function, the result is a display of a contour map in which the background brightness is controlled by details of the way the signal changes between discrete contour points or levels. This mode of display has the effect of providing improved tone quality of the display since the transition from light to dark (display dynamic range) need correspond only to a change in signal value of one contour level rather than to a relatively large peak-to-peak amplitude range of the intensifying function (as in waveform b, for example).

It will be realized that various modifications in the instrumentation illustrated could be made within the spirit of the invention. Also, displays provided in accordance with the described modes could be combined. That is, Mode A intensity signals might be combined with a fraction of the Mode D signals, thereby affording some of the advantage of each. The drawings and description herein are illustrative only and not intended to be limiting as to the scope of the invention.

Claims

What is claimed is:

1. A device for processing electrical analog signals representative of the distribution of a parameter over said processing to adapt said analog signals for application as intensity controlling signals for a correspondingly scanned cathode-ray display device, comprising:

Summing means for accepting said analog signal and also a reference signal as inputs, to produce an output which is a continuous algebraic sum of said analog and reference signals;

Threshold detection means connected to said summing means output for providing a trigger pulse, of a first polarity whenever said output increases by a predetermined threshold amount, and a second polarity whenever said output decreases by a second predetermined threshold amount;

Clock means for generating a series of equally spaced clock pulses of a frequency high with respect to the frequency of said analog signals;

A reversible binary counter responsive to said clock pulses and to said trigger pulses to advance by one step during each of said trigger pulses of said first polarity and to reverse by one step during each of said trigger pulses of second polarity;

A digital-to-analog decoder connected to receive the output digital words of said counter to operate as a staircase generator having individual steps which are each the analog of a corresponding value of said digital word, thereby to produce said reference signal;

And means connecting said reference signal to said summing amplifier, thereby to produce a closed loop circuit having a plurality of signal points therein each providing a corresponding discrete form of said intensity control signals.

2. The invention set forth in claim 1 in which said threshold detection means includes upper and lower threshold detectors fed in parallel from said summing means for developing said trigger pulses of first and second polarity respectively.

3. The invention set forth in claim 1 in which said reference signal is provided to an output terminal as a cathode-ray device intensity control signal.

4. The invention set forth in claim 1 in which the output of said summing amplifier is supplied to an output terminal as a cathode-ray device intensity control signal.

5. The invention defined in claim 2, further defined in that there is included a pulse adder connected to add said pulses of first and second polarity, and means are included to supply the output of said pulse adder to an output terminal as a cathode-ray device intensity control signal.

6. The invention set forth in claim 1 in which counter operated means are included for deriving and supplying to an output terminal, a signal representative in time of the change of state of the least significant stages of said counter, as a cathode-ray device intensity control signal.

7. The invention defined in claim 6 in which said counter operated means includes a differentiator connected to the bistable signal of said first stage and a rectifier is connected between said differentiator and said output terminal, thereby to provide said cathode-ray device intensity control signal in unipolar form.