GB2125243A

GB2125243A - Signal quantizer

Info

Publication number: GB2125243A
Application number: GB08315679A
Authority: GB
Inventors: Mark Gerard Butz; William Joseph Zacharias
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1982-08-03
Filing date: 1983-06-08
Publication date: 1984-02-29
Also published as: IT8322196A0; DE3327572A1; GB8315679D0; IL68277A0; FR2531553A1; SE8303777D0; SE8303777L; JPS5951622A

Abstract

A signal quantizer includes comparators (65) which compare an input signal on line 58 with a plurality of predetermined adjustable thresholds. Variable resistors (93) and amplifiers (96) associate with each threshold a potential output signal of predetermined adjustable magnitude. identification stages (53) identify the largest threshold exceeded by the input signal, and the corresponding output stage (50) produces as an output signal a signal representative of the potential output signal associated with the threshold identified. <IMAGE>

Description

SPECIFICATION Signal quantizer The invention relates to quantizers for signals and, more particularly, to such quantizers which provide adjustable quantizing thresholds and an adjustable output associated with each threshold.

There are many situations in which signals must be quantized. Quantizing is here defined by example: the numbers 0, 1, 2, 3, 4, 5, can represent the quantum levels (or threshold levels) used for quantizing a signal. The signal itself, however, may have any value between 0 and 5, including a fractional value such as 2.5.

Quantizing (sometimes called digitizing) ascribes a value to, or "rounds off", a signal whose value falls between, and not exactly on, the quantum levels. The value ascribed to the signal can be the value of the largest quantum level which the signal value equals or exceeds. Thus, signals of values 1.25, 2.75, and 4 would be ascribed values of 1, 2, and 4 as output signals, respectively.

In some situations, it would be desirable to provide a signal quantizer having adjustable threshold levels and, further, having a means for adjusting the quantized output signals.

For example, as shown in Figure 1, a machinetooled workpiece 3 can be scanned by a movable eddy current probe or other inspection transducer 6 which produces an electrical signal indicative of surface features contained on the workpiece 3.

This signal is carried by a conduit 9 to a signal processor 1 2 which converts the signal to a direct current signal 13 which is transmitted along conduit 15, through switches 1 6A and 1 6B, and to a power amplifier 19 which amplifies the direct current signal 1 3 and transmits an amplified signal 20 along conduit 22 to an electrode pen 25. A point 27 of electrode pen 25 is in contact with a record paper 30 which is connected to ground by a conduit 33. The current signal carried by conduit 22 and travelling through record paper 30 generates heat at the point of contact 27 between electrode pen 25 and record paper 30 and this heat produces a small burn mark in record paper 30.Variations in the signal present on conduit 22 induced by variations in the signal produced by the eddy current transducer 6 cause variations in the degree of burning and thus produce variations in the color of the mark burned into record paper 30.

In practice, the eddy current probe 6 is moved with respect to the machine-tooled workpiece 3 by mechanical devices (not shown) and, simultaneously, the electrode pen 25 is mechanically moved with respect to record paper scanning path of the probe 6 along workpiece 3 is mapped identically and to scale onto record paper 30 by the burn marks produced by electrode pen 25. Accordingly, variations in the surface features of workpiece 3 are mapped and indicated by burn marks present on record paper 30.

A problem arises in the use of this system because the signal, produced by the eddy current probe 6, is generally a continuously varying analog signal. Thus, the burn marks produced are similarly varying along a color spectrum ranging from white or light gray to dark gray or black. A particular problem found will be illustrated by example.

It is assumed that the color spectrum can be represented by a number sequence from 0 to 10 in which 0 represents white or light gray and 10 represents black or dark gray. Two colors, such as colors 5 and 6, can be adjacent on record paper 30, but the difference in grayness between them can be difficult to distinguish because the color darkens continuously from the location of color 5 to that of color 6. There is no clear line of demarcation. Thus, it is difficult to interpret the burn marks produced by eddy current probe 6 in this case.

Another problem arises in analyzing burn marks recorded upon different types of record papers or upon record papers of the same type but at different times. In the former situation, the differences in record papers can cause identical eddy current probe signals to produce different burn marks. In the latter situation, differences in the environment, such as humidity or temperature differences, occurring at the different times, can similarly cause nonuniform burn marks to result from identical probe signals. In both situations, it is difficult to compare the different records of eddy current signals.

In accordance with the present invention there is provided a quantizer comprising comparator means for comparing an output signal with a plurality of predetermined thresholds, potential output signal means for associating a potential output signal of adjustable predetermined value with each input threshold, and identification means coupled to the comparison means and to the potential output signal means for producing as an output signal the potential output signal associated with the largest input threshold exceeded by the input signal.

The thresholds are preferably adjustable and the quantizer preferably allows adjustment of the output signal corresponding to each quantum level.

In the accompanying drawings, by way of example only: Figure 1 is a schematic block diagram of signal processing equipment including a quantizer embodying the invention, and Figure 2 is a schematic circuit diagram of the quantizer of Fig. 1.

Figure 2 illustrates three identical comparator stages, one of which is contained within a dashed region 50. The Figure also shows fouridentical identification stages, one of which is contained within a dotted region 53 and also shows four identical stages for generating the potential output signals, one of which is contained within a dotted region 56. The actual number of each of the above type of stages to be used will depend upon the number of quantum thresholds desired by the user. The quantizing circuit of Figure 2 is shown as block 61 in Figure 1 and switches 1 6A and 1 6B are used to splice block 61 into the system of Figure 1.

The structures of the stages contained in the dotted regions 50, 53 and 56 are described as follows. With respect to comparator stage 50, an input signal bus 59, which is connected to conduit 1 5A in Figure 1, is connected to one input 63B of a comparator 65B by means of an input resistor 67B. Comparator 65Bis preferably an analog comparator. The other input 69B of comparator 65Bis connected to a tap 72B of a variable resistor 74B. The variable resistor 74B is connected between a voltage source Vs and ground. The output 768 of comparator 65B is connected to the voltage source V5 by means of a pull-up resistor 788.

With respect to identification stage 53, the output 76B of comparator 65B is connected to an input of AND gate 81 B, the other input of which is connected to the output of an inverter 83A, the input of which is connected to the output of a comparator in another comparison stage, such as the output 76A of a comparator 65A. The output of the AND gate 81 8 is connected to one terminal of a light emitting diode (LED) 85B by means of an inverter 87B. The other terminal of LED 85B is connected to terminal A which is, as shown in the upper right corner of the Figure, connected to a voltage source Vs by a resistor 89.

With respect to the potential output signal stage 56, a voltage divider network 92 comprising a resistor 91 B and a variable resistor 938 is connected between ground and the output of AND gate 818. A tap 94B on variable resistor 938 is connected to an input 97B of an operational amplifier (op-amp) 96B by means of a resistor 99B. The input 978 of op-amp 968 is connected to the output 101B of the op-amp by means of a resistor 1038. The output 1018 of opamp 96B is connected to a potential output bus 105 by means of a resistor 1078. The other input 109B of op-amp 968 is connected to ground.

The potential output bus 105 its connected to an input 112 of an op-amp 1 15, the output 117 of which is connected to an output signal terminal 15B (shown also in Figure 1) as well as fed back to the input 112 by means of a resistor 119. The other input 121 of op-amp 115 is connected to ground. The output signal terminal 1 58 is to be connected through the switch 1 6B to the input of power amplifier 19 in Figure 1 as discussed above.

It is to be noted that, as shown in Figure 2, the number of both the identification stages 53 and the potential output signal stages 56 exceeds the number of comparator stages 50 by one stage.

One reason for this is that the excess stage is used to produce a potential output signal when the input signal 58 exceeds no threshold. Further, AND gates 81A and 81 D are connected differently than the rest of AND gates 818-C: while one input of each of AND gates 81 A-C is connected directly to a respective comparator output 76A-C, AND gate 81 D is not so connected. Instead, one input of AND gate 81 D is connected to comparator output 76C by means of inverter 83C and the other input is connected to the voltage source Vs. Moreover, while one input of each of AND gates 818-81D is connected to a respective comparator output through inverters 83A-C, AND gate 81A is not so connected.

Instead, one input of AND gate 81A is connected to the voltage source Vs and the other input is connected to comparator output 76A.

The operation of the above-described circuitry is explained as follows. The taps 72A-C on adjustable resistors 74A-C are set to the desired thresholds. For example, if the voltage supply V5 is established at +5 volts, taps 72A-C can be set so that the inputs 69A-C to comparators 65A C are established respectively at 4.5, 3.5, and 2.5 volts. This establishes the voltage thresholds to which the input signal 58 as transmitted to comparator inputs 63A-C is compared.

The outputs 76A-C of comparators 65A-C will normally be at logical zero (or low) when the signal applied to inputs 63A-C fails to exceed the voltage thresholds. Thus, the outputs of AND gates 81 A-C will similarly be zero. Since the inputs to AND gate 81 D are both at logical one (or high), it provides a logical one as an output. This indicates that the input signal 58 is below the threshold of variable resistor 74C. If this threshold is the lowest, then the high output of AND gate 81 D indicates that no threshold has been exceeded.

Assuming that an input signal 58 of 4.0 volts is applied to conduit 15A, the signal present at inputs 63A-C will similarly be approximately 4.0 volts, subject to the voltage drop across input resistors 67A-C. This 4.0 volt input signal exceeds both the thresholds at comparator inputs 698-C, but not that at 69A. Accordingly, the comparators 658-C (and not comparator 65A) are triggered and their outputs are pulled high by pull-up resistors 788-C. However, only one of the AND gates (namely, AND gate 818) among AND gates 81A-D produces a high output, and for the following reasons.

Regarding AND gate 81A, it produces an output of logical zero because comparator 65A has not been triggered: this comparator provides a logical zero to one input of AND gate 81A.

Regarding AND gates 81 C-D, they similarly produce an output of logical zero because they respectively receive as inputs the inverted (hence, logical zero) comparator outputs 768-C.

However, regarding AND gate 81 B, it produces an output of logical one in receiving the output 76B (logical one) of triggered comparator 65B and the inverted output 76A (logical one) of nontriggered comparator 65A.

The output of AND gate 81 B is applied both to LED 85B (indirectly) and to the voltage divider network 92 comprising resistor 91 8 and variable resistor 93B. In the case of LED 858, the output of AND gate 818 is inverted by inverter 87B to a low voltage (logical zero) and then applied to terminal 130 of LED 85B causing a current to flow from voltage supply V5 through resistor 89 to terminal A and through LED 85B. LED's 85 will preferably have associated with them printed markings (not shown) indicating their respective thresholds so that the illumination of LED 858 indicates the highest threshold which is crossed by the input signal 58.

In the case of the voltage divider network 92, a predetermined voltage as determined by the setting of tap 94B on variable resistor 938 is applied to the input 978 of op-amp 96B. This voltage is predetermined for two reasons. First, AND gates 81A-D are preferably identical, with the result that the output voltage produced by each when driven to logical one is a known voltage, such as 5 volts. Second, the tap 948 on variable resistor 938 selects a certain fraction of this output voltage, depending upon the values of resistor 91 B and variable resistor 93B, and applies it to the input 97B of op-amp 96B by means of resistor 99B.Op-amp 96B amplifies the voltage at tap 94B in accordance with the feedback network comprising resistors 99B and 103B. Thus, the amplified voltage at output 1018 is also predetermined. This amplified voltage (a potential output voltage) is fed to the potential output signal bus 105 by means of resistor 1 07B and this voltage is further amplified by the output amplification stage comprising op-amp 11 5 and resistors 107B and 119. (In some applications, the potential output voltage signal fed to the bus 105 may be desired itself and further amplification by op-amp 11 5 may not be necessary).The output of op-amp 11 5 is fed to the output signal terminal 1 5B for further amplification by power amplifier 1 9 in Figure 1 and subsequent transmission thereby to electrode pen 25.

Figure 2 illustrates one form of calibration circuitry for use in establishing the desired threshold voltages.

The calibration circuitry consists of a voltage divider network 201 comprising a resistor 203 and a variable resistor 205 connected between the voltage source V5 and ground. A tap 207 on variable resistor 205 is connected to a conduit 209 for developing a calibration signal 211. The calibration signal 211 can be connected to the input signal bus 59 by connecting conduit 15A with conduit 209. The operation of the calibration circuitry is as follows.

All taps 72A-C on variable resistors 74A-C are set to their V5 side while tap 207 on variable resistor 205 is set to its ground side. Under these conditions, LED's 85A-C will be off and LED 85D will be on since the calibration signal 211 on the input signal bus 59 does not exceed any of the voltage thresholds 69A-C. One of the comparators' threshold voltages, such as that at input 69C, is established by initially adjusting tap 207 until the calibration signal 211 equals the desired threshold voltage for that comparator.

This voltage can be read on a meter (not shown) connected to tap 207, or the tap 207 can be set to a predetermined position to achieve the voltage desired. Then tap 72C is adjusted until LED 85D goes out and LED 85C comes on. This indicates that the voltage threshold level at 69C is equal to that of the calibration signal 211. The next comparator stage is calibrated in the same manner by increasing the calibration signal 211 to the next desired voltage level and then adjusting tap 72B until LED 85B comes on and LED 85C goes out. The calibration procedure continues in the same manner for each stage.

The value of this internal calibration signal circuitry is at least threefold. The circuitry provides a rapid and simple method of calibrating the input comparator stages without the requirement of any other equipment. Also, the circuitry simulates an input signal 58 which can check the operation of the signal quantizer 61, the power amplifier 19, and the record paper 30 without having to set up a workpiece inspection.

Finally, this calibration circuitry has the advantage that it is independent of the signal processor 12 of Figure 1.

A quantizer has been described which compares an input signal with a plurality of predetermined, adjustable thresholds and identifies the largest threshold crossed by the input signal by illuminating a LED. Each threshold has associated with it in advance a predetermined adjustable potential output signal. The potential output signal corresponding to the largest threshold identified is amplified and applied to an output signal terminal. In this manner, adjustable quantum levels can be selected, as an example, for quantizing an eddy current probe signal and the output signal associated with each quantum level is further adjustable to accommodate conditions which affect the degree of burning of a record paper by an electrode pen. The quantizer has been described in connection with positive logic implementation. Of course, negative logic (in which a negative voltage is taken as logical one and a less negative, or zero, voltage is taken as logical zero) or other binary logic systems can be used.

The use of the present quantizer with an eddy current probe is more fully described and separately claimed in our copending application serial number , entitled "Eddy Current Microscope", filed concurrently herewith.

Claims

1. A quantizer for an input signal comprising: (a) comparator means for comparing the input signal with a plurality of predetermined thresholds, (b) potential output signal means for associating a potential output signal of adjustable predetermined value with each input threshold, and (c) identification means coupled to the comparison means and to the potential output signal means for producing as an output signal the potential output signal associated with the largest input threshold exceeded by the input signal.

2. A quantizer for an analog input signal comprising: (a) n thresholding means for providing n adjustable signal thresholds, (b) n comparator means coupled to the respective n threshold means for receiving and comparing the input signal with each of the n thresholds, (c) n potential output signal means coupled to the respective n comparator means, each for associating a potential output signal of adjustable value with one of the thresholding means, and (d) identification means coupled to the n thresholding means for identifying the largest threshold exceeded by the input signal and for activating the potential output signal means associated with that threshold.

3. Apparatus in accordance with claim 1 or 2 in which the thresholding means comprise variable resistors.

4. Apparatus in accordance with claim 1 or 2 in which the comparator means comprise analog comparators.

5. Apparatus in accordance with claim 1 or 2 in which the potential output signal means each comprise variable resistors coupled to an input of an operational amplifier.

6. Apparatus according to claim 1 or 2 and further comprising an amplifier coupled to the potential output signal means for amplifying the preliminary output signal.

7. Apparatus according to claim 1 or 2 in which the identification means comprise sources of illumination.

8. Apparatus according to claim 7 and further comprising printed markings associated with the sources of illumination.

9. A quantizer for an analog input signal which may be present on an input signal bus, comprising: (a) n thresholding means for providing n adjustable signal thresholds, (b) n analog comparator means for receiving at a first input of each a different one of the signal thresholds, (c) n resistance means, each connected between the input signal bus and the second input of a different analog comparator means, (d) n pull-up resistors, each connected between the output of a different digital comparator and a voltage supply, (e) n inverters, the input of each being connected to the output of a different digital comparator, (f) (n-2) two-input AND gates, one input of each being connected to the output of a different digital comparator and the other input of each being connected to the output of a different one of the inverters, (g) one two-input AND gate having one input connected to a voltage source and the other input connected to the unconnected inverter, (h) one two-input AND gate having one input connected to a voltage source and the other input connected to the remaining comparator means, (i) n adjustable voltage divider networks each connected between the output of a different AND gate and ground, (j) n amplifier means, each connected to a different voltage divider network and each supplying an input to an output amplifier.

10. Apparatus in accordance with claim 9 and further comprising n illumination means, each activated by a different one of the AND gate means and each associated with printed markings.

11. Apparatus according to claim 1,2 or 9 and further comprising calibration means for simulating an input signal.

12. Apparatus according to claim 11 in which the calibration means comprises a voltage source and a voltage divider network comprising a variable resistor.

13. Method of quantizing an input signal, comprising the steps of: (a) comparing the magnitude of the input signal with a plurality of predetermined adjustable thresholds, (b) associating with each threshold a potential output signal of predetermined adjustable magnitude, (c) identifying the largest threshold exceeded by the input signal, (d) producing as an output signal the potential output signal associated with the threshold identified.

1 4. A signal quantizer substantially as herein described with reference to the accompanying drawings.