United States Patent [19] [li] Patent Number: 5,072,168
Ferguson [45] Date of Patent: Dec. 10, 1991
[54] AUTOMATIC SCALING FOR DISPLAY OF MODULATION DOMAIN MEASUREMENTS
[75] Inventor: Keith M. Ferguson, Saratoga, Calif.
[73] Assignee: Hewlett-Packard Company, Palo Alto, Calif.
[21] Appl. No.: 612,036
[22] Filed: Not. 9,1990
[51] Int. CI.' G01R 23/16
[52] U.S. CI 324/77 B; 324/77 C;
324/121 R; 364/485
[58] Field of Search 364/484, 485, 521, 518;
324/77 B, 77 C, 77 CS, 121 R, 77 A
[56] References Cited
U.S. PATENT DOCUMENTS
4,321,680 3/1982 Bertrand 324/77 B
4,399,512 8/1983 Soma 364/521
4,794,324 12/1988 Tracey 324/77 B
4,801,873 1/1989 Takano 324/77 B
4,802.098 1/1989 Hansen 324/77 B
4,825,449 4/1989 McKissock 364/521
4,897,800 1/1990 Nakanishi 364/521
Primary Examiner—Kenneth A. Wieder
Assistant Examiner—Jose M. Solis
Attorney, Agent, or Firm—James M. Williams
[57] ABSTRACT
A method for examining an input signal and setting a modulation domain measuring instrument to a state which will produce a measurement and a stable, centered, properly scaled display of the signal, automatically. After finding the 50 percent voltage threshold of the input signal, an iterative process determines the minimum and maximum input frequency, then checks the ratio of these two frequencies against instruments limits, and adjusts the display values, if necessary to show only the higher frequencies. The method then varies the measurement parameters to seek the best frequency resolution while maintaining the measurement and display of frequency modulation. The display frequency scale is set to display the signal in the center half of the display, using values with no more than two significant digits for the center and span. The time scale is set to display a selected number of modulation cycles.
1 Claim, 5 Drawing Sheets
