waveform data compressing circuit

Download Waveform data compressing circuit

Post on 14-Feb-2017

219 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

  • United States Patent [191 [11] Patent Number: 4,755,960 Batson et al. [45] Date of Patent: Jul. 5 1988 9

    [54] WAVEFORM DATA COMPRESSING 0378868 4/1973 U.S.S.R. ............................ .. 364/715

    CIRCUIT 0686027 9/1979 U.S.S.R. 1107118 8/1984 U.S.S.R. ............................ .. 364/715

    [75] Inventors: Brian E. Batson, Lake Oswego; Gary , R. Fladstol, Portland, both of Greg. OTHER PUBLICATIONS

    [73] Assignee. Tektronix, Ind Beavenon, Greg Murthy, Digital Extremum Calculator, Wireless World, vol. 84, #1515, p. 76, Nov. 1978.

    [21] Appl. No.: 746,898 - _ Primary Examiner-Gary V. Harkcom

    [22] Filed Jun 20 1985 Assistant ExaminerDale M. Shaw [51] Int. Cl.4 ......................... .. G06F 7/08; G06F 7/02 Attorney, Agent, or Firm,-John P. Dellett; Daniel J. [52] US. Cl. ......................... .. 364/715; 340/ 146.2 Bedell; George T. Noe [58] Field of Search .......... .. 364/715, 200 MS File,

    364/900 MS File; 340/1462; 377/49 [57] ABSTRACT [56] References Cited A data compression circuit has a compression mode of

    US. PATENT DOCUMENTS

    3,845,465 10/1974 Hosick et a1. .................. .. 340/ 146.2

    operation where it determines and stores minimum and maximum values of successive sequences of applied data words and provides an output comprising a pair of data

    1%; Emir/am et a1 words representing the stored minimum and maximum , , ue sman . . . . . . . . . . . ..

    4,499,548 2/1985 Beebe ..................... .. 328/151 f. ejmh Sequence Offset by a selected amium' The c1rcu1t also has a transparent mode of operatlon where

    FOREIGN PATENT DOCUMENTS output data sequences match input data sequences.

    0112982 7/1984 European Pat. Off. .......... .. 364/715

    0230529 3/1969 U.S.S.R. ............................ .. 364/715 7 Claims, 6 Drawing Sheets

    DATA IN ._-"I MSEND. COUNT RESET 'CDATA

    INPUT 4O COUNTER MLATCH -> REG / Eoc- EOC LlMlT ~cF

    C/T GGJ 64 LAST X LAST Y

    FLAG DECODER 44 46

    x COMP P Y COMP / FLAG - FLAG Y

    FLAG X __ 5o 56 NULL E09

    -. _, CDATA LATCH

    MLATCH-P ".LATCH . MMUND

    VECTOR- COMP >MSEL I ALLNUL ADDAV- STATE -MMUND 52 58 EOC__ MACH_ _.AL_|_NU|_ X LATCH DECODER Y LATCH DECODER

    / >ADDLCH ' MSEL 2 ->MSEND 6 62

    /\

    CLK *i 32/ i I 1

    [x1 REGISTER I [Y1 REGISTER

    FLAG X

    \ / 48 54

    DATA X DATAY FLAG Y

  • US. Patent Jul. 5, 1988 Sheet 2 of6 4,755,960

    5 IO I5 20 25 3O 35 4O 45 50 TIME (m8)

    FIG. 2

    5 IO 15 2O 25 3O 35 4O 45 5O

  • US. Patent Jul. 5, 1988 Sheet 3 of6 4,755,960

    5 IO I5 20 25 3O 35 4O 45 50

    TIME (m8)

    5 IO 15 2O 25 3O 35 4O 45 5O

    TlME(mS)

  • US. Patent Jul. 5, 1988 Sheet 4 of6 4,755,960

    DATA IN

    32

    vEcToR- -IIIII_ATcH

    CF-- MINIMUM /MAXIMUM -MsI=_ND c/T-_- CIRCUIT

    ADDLATCH

    367 CLOCK FLXAG DTA DAYTA FLYAG

    ~ OFFSET ADDAV

    OFFSET> CIRCUIT -__-_.DLATH

    C/T~> n---DSEND

    / 1 K34 " DATAOUT

    ADDRESS CLK

    70 v G2 INPUT DATA STATE DATA _

    ROM REG ' OUTPUT

  • 4,755,960 1

    WAVEFORM DATA COMPRESSING CIRCUIT

    BACKGROUND OF THE INVENTION

    The present invention relates in general to data com pression circuits and in particular to a method and appa ratus for reducing sequences of data characterizing sampled waveform magnitudes to data pairs indicating the minimum and maximum data in each sequence. A digital sampling oscilloscope measures the magni

    tude of a voltage waveform at regular intervals, con verts the analog sample voltages to digital data, and then uses the digital data to control a display of the waveform on a screen. Typically such an oscilloscope is capable of displaying a ?xed maximum number of sam ple data points along a portion of the waveform. To increase the portion of the waveform displayed (i.e. compress the waveform), the sampling rate is re duced. This results in a loss of waveform display detail since high frequency, high magnitude oscillations be tween sampling points will be overlooked. What would be useful would be a method and appara

    tus for compressing a waveform image without decreas ing the sampling rate and without decreasing the ability to detect and indicate high frequency, high magnitude voltage swings.

    SUMMARY OF THE INVENTION

    According to a ?rst aspect of the invention, a wave form data compression circuit converts waveform sam ple data obtained during a series of waveform} sampling intervals to a series of data pairs indicating the minimum and maximum magnitudes of the waveform sample data measured during each sampling interval. If these data pairs are then provided as input data to a vertical raster scan display system similar to the system described in copending US. Pat. application Ser. No. 07/102,802, ?led Sept. 21, 1987, which is a continuation of US. Pat. application Ser. No. 06/746, 815, now abandoned by Bowne and Larson entitled Vertical Raster Scan Con troller, the waveform may be displayed on a screen as a series of vertical bars, one bar corresponding to each waveform sampling period. The vertical positions of the top and bottom of each bar are determined by the value of the maximum and minimum data pairs gener ated by the compression circuit. The portion of the waveform displayed on the screen may then be ex panded by increasing the number of sample points in cluded in a sampling interval without necessarily de creasing the sampling rate. With a suitably high sam pling rate, any large voltage swings between the begin ning and end of a sampling period would affect the length of the corresponding vertical display line. According to a second aspect of the invention, the

    waveform data compression circuit may selectively generate as the minimum sample data of the pair, either the smallest data obtained during a sampling interval or the maximum value outputted during the preceding sampling interval, whichever is smaller. The compres sion circuit may also selectively output as the maximum value of the pair either the largest data obtained during the sampling interval or the minimum value obtained during the preceding sampling interval, whichever is larger. When such vectorized minimum/maximum data pairs are provided as input to a vertical raster scan display system, there is at least one point of overlap between successive vertical bars of the waveform dis

    35

    45

    55

    65

    2 play, thereby yielding the smoothest possible waveform image. According to a third aspect of the invention, the

    waveform data compression circuit increases or de creases the minimum and maximum data pairs by a selected offset amount. This feature is useful when the circuit is used in conjunction with a vertical raster scan display system because it permits vertical shifting of a waveform image display. According to a fourth aspect of the invention, the

    waveform data compression circuit may be used in conjunction with a digitizer which generates over or under range indicating codes when a sampled wave form is outside selected limits. In such case the maxi mum or minimum waveform compressor output data comprises these codes. Thus when the waveform data compressor circuit provides waveform sample data input to a vertical raster scan display system, the system can recognize the over and under range conditions and appropriately suppress or clip the waveform display. According to a ?fth aspect of the invention, the

    waveform data compression circuit may be set to selec tively pass data sequences through without compres sion or offset. When the circuit is used to provide input to a vertical raster scan display system, this feature permits control and graphics data to be sent to the sys tem over the same input channels as waveform sample data.

    In a preferred embodiment of the invention, from 1 to 255 sixteen bit_ data words may be mapped into a single data pair at the rate of 2>

  • 4,755,960 3

    FIG. 5 is a block diagram of the minimum/maximum detection circuit of FIG. 4; FIG. 6 is a block diagram of the state machine of

    FIGS. 5 and 7; and FIG. 7 is a block diagram of the offset circuit of FIG.

    4.

    DETAILED DESCRIPTION

    Referring to FIG. 1, there is depicted in block dia gram form, an oscilloscope system 10 employing a data compressor circuit 11 according to the present inven tion adapted to permit digitized waveforms to be dis played on screen 20 of a vertically scanned cathode ray tube (CRT) 22. A digitizer 14 samples and digitizes an analog voltage waveform at regular intervals and trans mits digitized waveform data obtained to a memory management unit 15 which stores the sample data in a random access waveform memory 18. A typical sampled waveform is depicted in FIG. 2.

    The voltage of the waveform is scaled along the verti cal axis while time is scaled along the horizontal axis. Vertical grid lines bound sampling intervals while hori zontal grid lines represent measurable voltages. For purposes of illustration, the digitizer 14 is assumed to have a measurement resolution of 1 mV and a sampling interval of 1 m5 although other resolutions and sam pling intervals may be used. The waveform may be sampled several times during each sampling interval. In the instant case, the digitizer output data at, for instance .the beginning of sampling interval 1, indicates that the magnitude of the waveform is 11 mV, while the digi

    ltizer output data at the beginning of sampling interval 2 would be 13 mV. An image of the sampled waveform of FIG. 2 is

    displayed as being displayed on a cathode ray tube (CRT) 22 screen 20 of FIG. 1. A portion of the screen

    vis illustrated in FIG. 3A. The screen is divided into ~rows and columns of pixel

Recommended

View more >