Dual slope integration circuit

• US 4,082,998 A
• Filed: 03/14/1977
• Issued: 04/04/1978
• Est. Priority Date: 06/30/1975
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Marriott, Joe E.
• Primary Examiner(s): Rolinec, Rudolph V.
• Assistant Examiner(s): Karlsen, Ernest F.
• Application Number:
  US05/777,297
• Time in Patent Office: 386 Days
• Field of Search: 324/99 D, 324/99 R, 324/130, 324/111, 340/347 AD, 340/347 NT, 340/347 CC, 330/9, 328/127, 307/296
• US Class Current: 324/99.00D
• CPC Class Codes: G01R 19/255 using analogue/digital converters of the type with counting of pulses during a period of time proportional to voltage or current, delivered by a pulse generator with fixed frequency
• CPC Class Codes: G01R 21/133 by using digital technique
• CPC Class Codes: H03M 1/406 using current mode circuits, i.e. circuits in which the information is represented by current values rather than by voltage values

Abstract

A circuit for performing dual slope integration to provide a digital measurement of an input voltage of either positive or negative polarity employs a single source of reference potential in combination with a switchable resistive network as a source of reference current.

Claims

1. A dual polarity current source and biasing circuit comprising:

circuit means having an input for producing an output signal responsive to a net current applied to the input thereof;

single polarity step variable current source means coupled to the input of said circuit means for supplying an output current to the input of said circuit means having an amplitude selectable from first, second and third amplitudes where the second amplitude is non-zero, the first amplitude is less than the second amplitude, and the third amplitude is greater than the second amplitude;

sample holding means coupled to said circuit means for selectively sampling the output signal therefrom when the second amplitude output current is selected from said source means and for concurrently and subsequently applying to the input of said circuit means a feedback current responsive to the output signal selectively sampled which alters the output signal produced by said circuit means to substantially equal a reference value during the selective sampling.

2. A circuit as in claim 1 wherein said source means comprises:

a single source of reference voltage; and

a plurality of resistors switchably connectable between the source of reference voltage and the input of said circuit means of supplying thereto the output current having the first, second and third amplitudes.

3. A dual slope integration circuit for operating on an input voltage of either positive or negative polarity, the circuit comprising:

input means having an input for receiving the input signal and operable in first and second operating modes for selectively producing either a reference output current or an output current responsive to the input signal during operation in the first and second operating modes, respectively;

single polarity step variable current source means for controllably supplying an output current having one non-zero amplitude during initial operating of the input means in the first and second operating modes and having an amplitude which is selectively less than or greater than the one non-zero amplitude during subsequent operation of the input amplifier means in the first operating mode;

current integration means having an input coupled to receive the output currents from said input means and from said source means for producing an output signal representative of the time integral of currents applied to the input thereof;

sample holding means coupled to said current integration means for selectively sampling the output signal produced therefrom during operation of said input means in the first operating mode and for concurrently and subsequently applying to the input of said current integration means a feedback current in response to the output signal selectively sampled which alters the output signal produced by said current integration means to substantially equal a reference value during the selective sampling;

logic means cooperating with said current integration means, cooperating with said input amplifier means, cooperating with said source means and cooperating with said sample holding means for controlling the operations thereof in first and second operating modes and for establishing a relationship between the durations of such modes which is representative of the value of the input signal.

4. A circuit as in claim 3 wherein said source means comprises:

means for applying a single source of reference voltage; and

a plurality or resistors switchably connectable between the source of reference voltage and the input of said current integration means for supplying thereto the output current having the first, second and third amplitudes.

5. The method of measuring an applied voltage of either polarity using dual-slope integration which establishes a time relationship between equal time integrals produced during a signal-responsive cycle and a reference cycle, the method comprising the steps, performed in selected sequence of:

combining a compensating current with a single polarity first reference current which is initially non-zero and adjusting the compensating current to produce a first resultant net current which is substantially zero during an auto-zeroing cycle;

establishing a current representative of the applied signal;

combining the current representative of the applied signal, the first reference current, and the compensating current to produce a signal-responsive net current;

integrating the time integral of the signal-responsive net current during a signal-responsive cycle;

determining the polarity of the applied signal;

altering the magnitude of the first reference current by a predetermined amount in response to the determined polarity;

combining the altered first reference current and the compensating current to produce a reference net current; and

integrating the time integral of the reference net current during a reference cycle.