Method and apparatus for detection of non-linear electrical devices

• US 4,547,724 A
• Filed: 02/07/1983
• Issued: 10/15/1985
• Est. Priority Date: 02/07/1983
• Status: Expired due to Term

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Beazley, Todd M., Diller, Calvin D.
• Primary Examiner(s): Krawczewicz, Stanley T.
• Assistant Examiner(s): Harvey, Jack B.
• Application Number:
  US06/464,796
• Time in Patent Office: 981 Days
• Field of Search: 324/57 R, 324/158 D, 324/132, 324/57 PS, 324/63, 324/65 R
• US Class Current: 324/626
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00
• CPC Class Codes: G01R 27/14 Measuring resistance by measuring current or voltage obtained from a reference source G01R27/16, G01R27/20, G01R27/22 take precedence

Abstract

The present invention provides a system for applying a fixed level D.C. voltage and a square wave signal sequentially to a voltage divider including a resistor of a known impedance and the device under test. The square wave ranges from a value which is substantially equal to the ground level to a level that is substantially twice the nominal value of the fixed D.C. level, thus the average value of the square wave signal is substantially equal to the nominal value of the fixed level D.C. voltage.

With each of these signals applied on at a time to the voltage divider, the voltage across the device under test is applied to a voltage detector via a low pass filter. The output of the low pass filter for each applied voltage signal is the average of the voltage signal which appears across the device under test. The value of these average voltages are stored and then compared. If the average values are substantially equal, then the device under test is linear, and knowing the average voltage value, the nominal voltage value, and value of the known resistor, the resistance value of the device under test can be calculated. If the average values of the voltages across the device under test varies from the application of the fixed level D.C. voltage and the square wave signal, the device under test is non-linear, e.g. a diode or transistor junction.

Claims

1. A method for detecting linear and non-linear electrical characteristics in a device under test, comprising the steps of:

(a) connecting said device under test in series with a reference device having a known impedance value and a linear electrical characteristic thereby to form a voltage divider;

(b) applying a substantially fixed DC voltage across said voltage divider;

(c) measuring the DC voltage value across said device under test in response to said fixed DC voltage in step (b);

(d) applying a positively going, substantially square wave voltage signal having an average voltage that is substantially equal to the fixed DC voltage applied across said voltage divider;

(e) measuring the average voltage value across said device under test in response to said square wave voltage signal in step (d); and

(f) comparing the DC voltage value measured in step (c) with the average voltage value measured in step (e), wherein said device under test is determined to be linear if said compared values are substantially equal and non-linear if said compared values are substantially different.

2. A method in accordance with claim 1 further comprising the step of calculating the impedance value of the device under test if said compared values are substantially equal.

3. An apparatus for detecting linear and non-linear electrical characteristics in a device under test, comprising:

means for connecting said device under test in series with a reference device having a known impedance value and a linear electrical characteristic thereby to form a voltage divider;

means for applying a substantially fixed DC voltage across said voltage divider;

means for measuring the DC voltage value across said device under test in response to said fixed DC voltage;

means for applying a positive going square wave voltage signal having an average voltage that is substantially equal to said fixed DC voltage applied across said voltage divider;

means for measuring the average voltage value across said device under test in response to said square wave voltage signal; and

means for comparing the DC voltage value measured across said device under test with the average voltage value also measured across said device under test, wherein said device under test is determined to be linear if said compared values are substantially equal and non-linear if said compared values are substantially different.

4. An apparatus in accordance with claim 3 further comprising means for calculating the impedance value of the device under test if said compared values are substantially equal.