US 6,784,810 B2Granted

A/D converter with comparators and low-power detection mode for resistive matrix keyboards

AssigneeNational Semiconductor Corporation

InventorsOhad Falik, Victor Flachs

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Abstract

An apparatus and method is disclosed for providing a fast, low power consumption, detection of at least one depressed key in a resistive matrix keyboard. The common contact of each row of a resistive matrix is connected to a first input of each of a plurality of analog/digital comparators capable of switching between high and low voltage states. A common predetermined reference voltage is applied to a second input of each analog/digital comparator using a digital to analog converter. The output of a analog/digital comparator is in a first state if the voltage level applied to the first input is higher than the reference voltage, and in a second state if the voltage level applied to the first input is lower than the reference voltage. The reference voltage is varied to identify which analog/digital comparator has experienced a change of state.

Claims20

Dependent claims

A method for providing a fast, low power consumption, detection of at least one depressed key in a resistive matrix keyboard, comprising:

(a) connecting a common contact of each row of a resistive matrix to a first input of each of a plurality of analog/digital comparators capable of switching between high and low voltage states;
(b) generating, by using a digital to analog converter, a common predetermined reference voltage applied to a second input of each analog/digital comparator of said plurality of analog/digital comparators, wherein an output of each of said plurality of analog/digital comparators is in a first state if a voltage level applied to said first input of an analog/digital comparator is higher than said reference voltage, and is in a second state if a voltage level applied to said first input of said analog/digital comparator is lower than said reference voltage;
(c) simultaneously connecting contacts of all columns of a plurality of columns of said resistive matrix to a voltage level that enables current flow through at least one resistor of a plurality of resistors connected to said plurality of columns, and seeking first changes in an output state of at least one analog/digital comparator;
(d) periodically repeating step (b) and step (c) if no first change is detected;
(e) upon detecting a first change of state of at least one analog/digital comparator, using said digital to analog converter to vary said reference voltage at least once in one of:
an up-going direction and a down-going direction, so that said varied reference voltage is equal to a voltage that is applied to the first input of each analog/digital comparator;
and
(f) whenever said varied reference voltage reaches a voltage that is applied to an input of an analog/digital comparator, detecting a second change of state in that analog/digital comparator, and obtaining a digital word of said digital to analog converter, that corresponds to a value of the reference voltage reached that caused said second change of state in that analog/digital comparator.

5 more elements

An apparatus for providing a fast, low power consumption detection of at least one depressed key in a resistive matrix keyboard, said apparatus comprising:

(a) a plurality of analog/digital comparators, each analog/digital comparator of which having a first input connected to a common contact of a different row of a resistive matrix and capable of switching between high and low voltage states;
(b) a digital to analog converter, connected to a second input of each of said plurality of analog/digital comparators, for generating a common predetermined reference voltage and for applying said common predetermined reference voltage to said second input of each of said plurality of analog/digital comparators, wherein an output of each of said plurality of analog/digital comparators is in a first state if a voltage level applied to said first input of an analog/digital comparator is higher than said reference voltage, and is in a second state if a voltage level applied to said first input of said analog/digital comparator is lower than said reference voltage;
(c) circuitry for detecting a change of state in at least one of said plurality of said analog/digital comparators;
(d) a control circuit for controlling a frequency of detection of a change of state and for varying said reference voltage in one of:
an up-going direction and a down-going direction by inputting different digital words to said digital to analog converter at a desired rate;
and
(e) a data bus for outputting said digital words of said digital to analog converter that correspond to values of said reference voltage that cause a change of state in each of said plurality of analog/digital comparators, wherein the control circuit is capable of determining the digital words associated with the change of state in each of the analog/digital comparators.

4 more elements

A keyboard for providing a fast, low power consumption detection of at least one depressed key, said keyboard comprising:

a resistive matrix;
a plurality of analog/digital comparators, each analog/digital comparator of which having a first input connected to a common contact of a different row of the resistive matrix and capable of switching between high and low voltage states;
a digital to analog converter, connected to a second input of each of said plurality of analog/digital comparators, for generating a common predetermined reference voltage and for applying said common predetermined reference voltage to said second input of each of said plurality of analog/digital comparators, wherein an output of each of said plurality of analog/digital comparators is in a first state if a voltage level applied to said first input of an analog/digital comparator is higher than said reference voltage, and is in a second state if a voltage level applied to said first input of said analog/digital comparator is lower than said reference voltage;
circuitry for detecting a change of state in at least one of said plurality of said analog/digital comparators;
a control circuit for controlling a frequency of detection of a change of state and for varying said reference voltage in one of:
an up-going direction and a down-going direction by inputting different digital words to said digital to analog converter at a desired rate;
and
a data bus for outputting said digital words of said digital to analog converter that correspond to values of said reference voltage that cause a change of state in each of said plurality of analog/digital comparators, wherein the control circuit is capable of determining the digital words associated with the change of state in each of the analog/digital comparators.

5 more elements

Dependencies are inferred from the claim text.