Tamper monitor circuit
First Claim
1. A tamper monitor circuit, comprising:
- a reference oscillator operable to supply a reference signal having a reference frequency;
a detection oscillator configured to operate at a circuit temperature and to be energized with a supply voltage, the detection oscillator operable to supply a detection signal having a frequency that varies with variations in the circuit temperature, variations in the supply voltage, or both; and
a comparison circuit coupled to receive the reference signal and the detection signal and operable, in response to the reference signal, to (i) selectively determine the frequency of the detection signal, (ii) determine a frequency difference between two or more of the determined frequencies, and (iii) supply a tamper detect signal if the determined frequency difference exceeds a predetermined difference threshold.
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Accused Products
Abstract
A tamper monitor circuit detects voltage, temperature, and/or clock variations that may be associated with a circuit tampering technique, and triggers an appropriate tamper response. The tamper monitor circuit includes a reference oscillator, a detection oscillator, and a comparison circuit. The reference oscillator supplies a reference signal having a reference frequency. The detection oscillator operates at a circuit temperature and is energized with a supply voltage, and supplies a detection signal having a frequency that varies with variations in the circuit temperature, variations in the supply voltage, or both. The comparison circuit receives the reference signal and the detection signal and, in response to the reference signal, selectively determines the frequency of the detection signal, determines a frequency difference between two or more of the determined frequencies, and supplies a tamper detect signal if the determined frequency difference exceeds a predetermined difference threshold.
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Citations
20 Claims
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1. A tamper monitor circuit, comprising:
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a reference oscillator operable to supply a reference signal having a reference frequency;
a detection oscillator configured to operate at a circuit temperature and to be energized with a supply voltage, the detection oscillator operable to supply a detection signal having a frequency that varies with variations in the circuit temperature, variations in the supply voltage, or both; and
a comparison circuit coupled to receive the reference signal and the detection signal and operable, in response to the reference signal, to (i) selectively determine the frequency of the detection signal, (ii) determine a frequency difference between two or more of the determined frequencies, and (iii) supply a tamper detect signal if the determined frequency difference exceeds a predetermined difference threshold. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A tamper monitor circuit, comprising:
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a reference oscillator configured to operate at a first circuit temperature and to be energized with a supply voltage, the reference oscillator operable to supply a reference signal having a frequency that varies, in accordance with a first sensitivity, with variations in the first circuit temperature, variations in the supply voltage, or both; and
a detection oscillator configured to operate at a second circuit temperature and to be energized with the supply voltage, the detection oscillator operable to supply a detection signal having a frequency that varies, in accordance with a second sensitivity that differs from the first sensitivity, with variations in the second circuit temperature, variations in the supply voltage, or both; and
a comparison circuit coupled to receive the reference signal and the detection signal and operable, in response to the reference signal, to (i) selectively determine the frequency of the detection signal, (ii) determine a frequency difference between two or more of the determined frequencies, and (iii) supply a tamper detect signal if the determined frequency difference exceeds a predetermined difference threshold. - View Dependent Claims (15, 16, 17, 18, 19)
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20. A tamper monitor circuit, comprising:
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a reference oscillator operable to supply a reference signal having a reference frequency;
a detection oscillator configured to operate at a circuit temperature and to be energized with a supply voltage, the detection oscillator operable to supply a detection signal having a frequency that varies with variations in the circuit temperature, variations in the supply voltage, or both;
a detection counter coupled to receive the detection signal and operable to generate a detection count value representative of a number of detection signal periods;
a reference counter coupled to receive the reference signal and operable to generate a reference count value representative of a number of reference signal periods;
a reference count comparator coupled to the reference counter, the reference count comparator operable to determine when the reference count value reaches a predetermined comparator count value and, upon determining that the reference count reaches the predetermined comparator count value, to supply a count capture command; and
a detection count capture circuit coupled to the detection counter and the reference count comparator, the detection count capture circuit coupled to receive the count capture command and operable, in response thereto, to capture the detection count value; and
a controller circuit coupled to the detection count capture circuit and operable to;
(i) selectively retrieve the detection count value from the detection count capture circuit, (ii) compare the retrieved detection count value to a baseline detection count value, and (iii) supply a tamper detect signal if the retrieved detection count value differs from the baseline detection count value by a predetermined threshold magnitude.
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Specification