Digital testing of analog memory devices
First Claim
1. An integrated circuit comprising:
- an array of analog memory cells;
an analog write circuit coupled to the array;
an analog read circuit coupled to the array;
an analog comparator having a first input terminal and a second input terminal, the analog comparator generating an output signal having a digital state indicating whether a first input voltage is greater than a second input voltage level, a first input terminal of the analog comparator being connected to an output terminal of the read circuit when the read circuit reads a test value from the analog memory array; and
a reference voltage generator coupled to provide a first voltage to the analog write circuit during writing of the test value and a second voltage to a second input terminal of the analog comparator during reading of the test value, wherein the first voltage represents the test value.
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Accused Products
Abstract
An analog memory has comparison logic and a reference voltage generator built on-chip for testing of analog write and read processes. During a test, the reference voltage generator, which may be a resistor tree structure, provides a set of intermediate voltages. One of the intermediate voltages VIN is written to a selected memory cell. The comparison logic compares other intermediate voltages VH and VL to an analog output signal generated by reading the selected memory cell. A digital control signal from an external digital tester selects the levels of voltages VIN, VH, and VL. Typically, voltages VH and VL are equal VIN ±ΔV where ΔV represents an acceptable resolution for stored analog data. If the signal from reading the selected memory cell falls within a desired range VIN ±ΔV, an output digital result signal is set; otherwise, the test result signal is cleared. A low-cost digital tester which generates the digital control signals and observes the digital result signal can test all the circuits associated directly with write and read processes. Since the analog signals for the test are generated on-chip, the effect of noise is minimized, and a high accuracy resolution test is achieved.
103 Citations
25 Claims
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1. An integrated circuit comprising:
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an array of analog memory cells; an analog write circuit coupled to the array; an analog read circuit coupled to the array; an analog comparator having a first input terminal and a second input terminal, the analog comparator generating an output signal having a digital state indicating whether a first input voltage is greater than a second input voltage level, a first input terminal of the analog comparator being connected to an output terminal of the read circuit when the read circuit reads a test value from the analog memory array; and a reference voltage generator coupled to provide a first voltage to the analog write circuit during writing of the test value and a second voltage to a second input terminal of the analog comparator during reading of the test value, wherein the first voltage represents the test value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An integrated circuit comprising:
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an array of analog memory cells; means for writing in the array a value represented by an analog input signal; means for reading the array to generate an analog output signal representing a value read from the array; and digitally operable test circuitry comprising; means for using the writing means to write a test value to the array; and means for generating a digital output signal indicating whether the analog output signal from the reading means accurately represents the test value. - View Dependent Claims (14, 15, 16)
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17. A method for testing an analog memory, comprising the steps of:
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providing resistor tree structure incorporated on-chip with the analog memory; writing to a selected memory cell in the analog memory a value represented by a first voltage from the resistor tree structure; reading the selected memory cell to generate an analog output signal representing a value read from the selected memory cell; comparing the analog output signal to a second voltage from the resistor tree structure; and generating a digital signal which indicates whether the analog output signal is at a voltage level greater than the second voltage. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24)
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25. An integrated circuit comprising:
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analog circuitry which generates an analog output signal from an analog input signal; a reference voltage generator coupled to the analog circuitry, the reference voltage generator generating a first intermediate voltage, a second intermediate voltage, and a third intermediate voltage, wherein during testing of the analog circuitry, the reference voltage generator provides to the analog circuitry the first intermediate voltage in place of the analog input signal; a first analog comparator coupled to the analog circuitry and the reference voltage generator, wherein during testing of the analog circuitry, the first analog comparator generates a first digital signal indicating whether the analog output signal from the analog circuitry is greater than the second intermediate voltage; a second analog comparator coupled to the analog circuitry and the reference voltage generator, wherein during testing of the analog circuitry, the second analog comparator generates a second digital signal indicating whether the analog output signal from the analog circuitry is less than the third intermediate voltage; and a gate coupled to generate a digital result signal which is a logical AND of the first and second digital signals.
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Specification