Apparatus and method for range control and supply voltage compensation in a dual slope analog to digital converter
AssigneeHoneywell Inc.
InventorDavid C. Ullestad
Life of this patent
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Abstract
Apparatus for control of the range of input voltage values to be measured and for compensation of the changes in the supply voltage of an analog to digital dual slope converter circuit is described. The selection of a range for input voltage measurements in the analog to digital converter circuit permits the conversion to take place over a relatively long time period, thereby increasing the resolution of the resulting conversion. Changes in the supply voltage are combined with the input analog signal (during the capacitance charging period) and with the reference voltage (during the capacitance discharge cycle) providing compensation for the effects of time, temperature and the tolerance of the supply voltage.
Claims22
A dual slope analog to digital converter circuit comprising:
- a first operational amplifier with a capacitor coupled thereto configured as an integrating circuit;
- a second operational amplifier having an output terminal coupled to an inverting input terminal of said first operational amplifier;
- a switch responsive to control signals for coupling a known voltage to an inverting terminal of said second operational amplifier when said switch is in a first state, said switch coupling an analog voltage to said inverting terminal of said second operational amplifier when said switch is in a second state;
- and
- resistor network means for applying a reference signal to a non-inverting terminal of said first operational amplifier, said resistor network means applying a predetermined portion of a reference signal applied to a non-inverting terminal of said first operational amplifier to a non-inverting input terminal of said second operational amplifier.
The method of converting an analog signal to a digital quantity, the method comprising the steps of:
- applying said analog signal to a first terminal of a first operational amplifier configured as an integrator for a predetermined period of time;
- applying a known signal to said first terminal of said first operational amplifier;
- applying a portion of a reference voltage to a second terminal of said first operational amplifier;
- applying an output signal from said first operational amplifier to a first terminal of a second operational amplifier;
- applying said reference voltage to a second terminal of said second operational amplifier;
- and
- applying an output signal from said second operational amplifier to a timer means, wherein said known signal is applied to said first amplifier until said second operational amplifier output signal reaches a predetermined value and an output signal of said timer means provides said digital quantity representative of said analog signal.
An analog to digital converter circuit comprising:
- an integrating circuit having a reference signal applied to a first terminal thereof;
- an operational amplifier having a output terminal coupled to a second input terminal of said integrating circuit, said operational amplifier having a reference signal portion coupled to a first input terminal;
- a switch responsive to control signals for selectively applying a input signal and a known signal to a second terminal of said operational amplifier;
- timer means coupled to an output terminal of said integrating circuit for providing a count related to a time said input voltage was applied to said operational amplifier first terminal, said timer means providing control signal to said switch.
Dependencies are inferred from the claim text.