# US 5,708,379 A · Electronically programmable output impedance circuit

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- Number: US 5,708,379 A
- Document ID: US5708379A
- Status: Granted
- Kind: A
- Application number: 08/790,233
- Filed: 1997-01-28
- Granted: 1998-01-13
- Earliest claimed: 1995-07-21
- Assignees: Hewlett-Packard Company
- Inventors: Neil J. Yosinski
- Web page: https://patentgrep.com/patent/US5708379A

## CPC

- G01R 31/00: Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere ({measuring superconductive properties G01R33/1238;} testing line transmission systems H04B3/46; testing or measuring semiconductors or solid state devices during manufacture {H10P74/00})
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

A method and apparatus for generating an AC voltage with user defined inductance and resistance values in series therewith is described. The output voltage of the AC source is sampled and a signal indicative of the total current being generated is derived. The signal is scaled to model a series resistance and scaled and differentiated to model a series inductance. The modelled series resistance and inductance are then combined with the output voltage. Different inductances and resistances can be modelled merely by changing the user's input to the microcontroller that controls the operation of the present invention.

## Claims

### Claim 1

An alternating current source for producing an alternating current output voltage, the source having a programmable output resistance characteristic and inductance characteristic, the source comprising:
an alternating current source with a first voltage feedback loop, the alternating current source with a first voltage feedback loop comprising:
an input sinusoidal reference signal source;
a first summer coupled to the reference signal source and a programmable output inductance characteristic and resistance characteristic circuit;
a second summer coupled to the first summer;
an error amplifier coupled to the second summer;
a pulse width modulated power amplifier coupled to the error amplifier;
a plurality of filters coupled to the pulse width modulated power amplifier, the output voltage across a last filter comprising the alternating current output voltage; and
a first differential amplifier with a positive and negative input coupled across the output voltage and a first output coupled to the second summer; and
the programmable output inductance characteristic and resistance characteristic circuit coupled to the alternating current source with a first voltage feedback loop for providing a user-selected first inductance characteristic and first resistance characteristic independently of one another in series with the output voltage generated by the alternating current source, the programmable output inductance characteristic and resistance characteristic circuit further comprising:
a first differentiator coupled to the output of a first filter;
a second differentiator coupled to the output of a second filter;
a second differential amplifier with a positive and negative input and a second output, the positive and negative inputs being coupled respectively to a first and second terminal of a sensing resistor, the sensing resistor coupled in series to the negative terminal of the alternating current output voltage;
a third summer coupled to the first and second differentiator and to the second output of the second differential amplifier;
a first bandpass filter coupled to the output of the third summer;
a first and a second multiplier, the multipliers each being coupled to the first bandpass filter;
a first and second digital to analog converter, each having an input and an output, the input of the first digital to analog converter being coupled to a microcontroller, the output of the first digital to analog converter being coupled to the first multiplier, the input of the second digital to analog converter being coupled to the microcontroller, the output of the second digital to analog converter being coupled to the second multiplier;
a third differentiator coupled to an output from the first multiplier;
a second bandpass filter coupled to an output of the third differentiator; and
a fourth summer coupled to an output of the second bandpass filter and to an output of the second multiplier, an output of the fourth summer being coupled to the first summer.