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US 5,870,042 AGranted
Method of and apparatus for testing A-D converter with a source current measurement and reduced external test terminals
AssigneeMitsubishi Denki Kabushiki Kaisha
InventorHiroshi Noda
Life of this patent
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Abstract
When an upper reference voltage is erroneously reduced below a normal value in a subranging A-D converter, a resistance block of a ladder resistance having a voltage lower than a proper one is selected and a lower reference voltage is necessarily reduced below an analog input voltage, so that all outputs of lower bits go high. Namely, a region (B1) where a current flowing to a comparator becomes constant without depending on the value of an analog input voltage (Vin) appears. Presence of abnormality can be determined by detecting this. Thus, a functional test or a static linearity test of an A-D converter cell is made while remarkably reducing the number of external test terminals.
Claims20
A method of testing a subranging A-D converter, said subranging A-D converter
- having a plurality of upper reference voltages, a plurality of lower reference voltage groups each consisting of a plurality of lower reference voltages, and a first comparator array including a plurality of comparators,
- deciding an upper bit of a digital output on the basis of comparison between said plurality of upper reference voltages and an analog input in said plurality of comparators,
- selecting one of said plurality of lower reference voltage groups on the basis of said upper bit while deciding a lower bit by comparing said plurality of lower reference voltages belonging to said one of said plurality of lower reference voltage groups with said analog input;
- and
- A-D converting of said analog input to a digital output consisting of said upper and lower bits with predetermined resolution;
- said method comprising steps of:
- (a) supplying an analog signal being changed at an amount of change being smaller than said resolution;
- (b) measuring the relation between said analog signal and a current flowing at least to said first comparator array at the time of comparing said analog input with said plurality of lower reference voltages for obtaining a current waveform;
- (c) obtaining the number of points taking extreme values in said current waveform;
- and
- (d) determining nondefectiveness/defectiveness of said subranging A-D converter on the basis of whether or not said number is a prescribed number.
8 more elements
A method of testing a subranging A-D converter, said subranging A-D converter
- having a plurality of upper reference voltages, a plurality of reference voltage groups each consisting of a plurality of lower reference voltages, and a first comparator array including a plurality of comparators,
- deciding an upper bit consisting of W bits (W being positive integer) on a basis of comparison between said plurality of upper reference voltages and an analog input in said plurality of comparators,
- selecting one of said plurality of lower reference voltage groups on a basis of said upper bit while deciding a lower bit consisting of W bits by comparing said plurality of lower reference voltages belonging to said one of said plurality of lower reference voltage groups with said analog input;
- and
- A-D converting said analog input to a 2W-bit digital output consisting of said upper and lower bits, said method comprising steps of:
- (a) obtaining linear ideal A-D conversion characteristics being obtained in case of assuming that said A-D converter includes no quantization error and first resolution being a voltage of said analog input corresponding to the minimum unit of change of said digital output;
- (b) separating a first initial value corresponding to the minimum value of said voltage of said analog input defining said ideal A-D conversion characteristics and a first final voltage corresponding to the maximum value thereof every second resolution being (2.sup.W +1) times said first resolution for supplying 2.sup.W analog signals including said first initial voltage and said final voltage as said analog input;
- (c) measuring said analog input and 2.sup.W source currents flowing at least to said first comparator array at a time of comparing said analog input with said plurality of lower reference voltages;
- and
- (d) obtaining a current waveform corresponding to said ideal A-D conversion characteristics from said first initial value and said source current corresponding thereto and said first final voltage and said source current corresponding thereto for determining nondefectiveness/defectiveness of said A-D converter on a basis of whether or not all said source currents are within a prescribed range with respect to said current waveform.
7 more elements
A method of testing an A-D converter comprising a comparator array including a plurality of comparators for comparing a plurality of reference voltages with an analog input and outputting a digital output consisting of 2W bits (W being positive integer) on a basis of said comparison in said plurality of comparators thereby conducting A-D conversion of said analog input to said digital output, said method comprising steps of:
- (a) a measuring a relation between said analog input and a source current actually flowing to said comparator array at a time of comparing said analog input with said reference voltages, for obtaining an actual current waveform;
- (b) obtaining an initial voltage being a value of said analog input corresponding to a boundary as to whether a value of said digital output is minimum value or a value being larger than the same by 1;
- (c) obtaining a final voltage being said value of said analog input corresponding to a boundary as to whether said digital output is in a full scale or results in an overflow;
- (d) dividing a value obtained by subtracting said initial voltage from said final voltage by (2.sup.2W -1) for obtaining resolution;
- (e) obtaining first value as a current increment by dividing a changeable value of said source current by a changeable value of said analog input in a basic region and multiplying said first value by said resolution when said A-D converter ideally performs said A-D conversion, said basic region being in a range of said initial voltage to said final voltage, and said source current being monotonously increased following increase of said value of said analog input in said basic region;
- (f) obtaining an ideal current waveform indicating said source current being increased by said increment every time said value of said analog input is increased by said resolution when said A-D converter ideally performs said A-D conversion in said basic region;
- and
- (g) comparing said actual current waveform with said ideal current waveform for determining nondefectiveness/defectiveness of said A-D converter on basis of whether or not the difference therebetween is within a prescribed range.
5 more elements
An apparatus for testing an A-D converter comprising:
- (a) a subranging A-D converter having a comparator array consisting of a plurality of comparators for comparing an analog input with a plurality of upper reference voltages and further with a plurality of lower reference voltages for A-D converting said analog input to a digital output with predetermined resolution;
- (b) an analog signal source for supplying an analog signal being stepwise changed by an amount of change being smaller than said resolution;
- (c) a power source for supplying said comparator array with a voltage;
- (d) a current measure for measuring a current flowing from said power source at a time of comparing said analog input with said plurality of lower reference voltages;
- and
- (e) analyzing means for analyzing a relation between said analog signal and said current.
3 more elements
An apparatus for testing an A-D converter comprising:
- (a) an A-D converter having a comparator array consisting of a plurality of comparators for comparing an analog input with a plurality of reference voltages for A-D converting said analog input to a digital output;
- (b) a power source for supplying said comparator array with a voltage;
- (c) a current measurer for measuring a current flowing from said power source at a time of comparing said analog input with said plurality of lower reference voltages;
- (d) detection means detecting whether or not said A-D converter is in an overflow state and whether or not said digital output is at minimum value;
- and
- (e) operating means for obtaining an ideal waveform of said source current on a basis of the result in said detection means to compare said ideal waveform with a waveform of said source current obtained by said current measurer.
3 more elements
Dependencies are inferred from the claim text.