Static information storage and retrieval – Read/write circuit – Including reference or bias voltage generator
Reexamination Certificate
2002-09-20
2003-11-04
Nelms, David (Department: 2818)
Static information storage and retrieval
Read/write circuit
Including reference or bias voltage generator
C365S189011, C365S185210
Reexamination Certificate
active
06643193
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device having a circuit which is desired to perform as intended without being affected by any unevenness in device characteristics among lots/wafers/chips, temperature fluctuation or the like, for instance a microcomputer or a flash memory, and to a method of adjusting the characteristics of the semiconductor device, for instance a technique which can be effectively applied to a microcomputer with a built-in flash memory.
Semiconductor devices may run into performance deterioration as circuit characteristics deviate from the desired performance characteristics intended in the circuit design as a consequence of some unevenness in the manufacturing process. Remedies for such performance deterioration include, for instance a technique to make a constant amperage adjustable in a semiconductor device with a built-in constant amperage source, and the Japanese Published Unexamined Patent Application No. Hei 11(1999)-7783 describes an EEPROM for adjusting the programming time by setting a desired constant amperage according to trimming data. The Japanese Published Unexamined Patent Application No. Hei 11(1999)-145393 discloses a method by which the amperage ratio of a current mirror circuit is measured and a transistor is selected according to a mask pattern. Further, according to the Japanese Published Unexamined Patent Application No. Hei 10(1998)-214496, a trimming circuit for allowing fine adjustment of the output voltage of a voltage clamping means against process fluctuations of a semiconductor device, such as a microcomputer, and this trimming circuit is controlled with a trimming control means according to trimming adjustment information. The technique disclosed in the patent application further provides for a register in which the trimming adjustment information is to be set, and the trimming adjustment information is transferred from a specific area in a non-volatile memory to this register to perform trimming as desired with software.
SUMMARY OF THE INVENTION
However, according to the Japanese Published Unexamined Patent Application No. Hei 11(1999)-7783, a desired transistor is selected out of a plurality of transistors differing in threshold voltage according to trimming data to adjust the programming time and the output of a timer circuit is adjusted to keep the programming time constant all the time, but there is no mention of how to select the desired transistor. Regarding the method disclosed in the Japanese Published Unexamined Patent Application No. Hei 11(1999)-145393, by which the amperage ratio of a current mirror circuit is measured and a transistor is selected according to a mask pattern, but trimming to bring the amperage ratio, which is a characteristic of a current mirror circuit, into a desired state is often rather difficult. Therefore, the present inventor has found that this would invite elongation of the time required to acquire trimming data, i.e. the testing time, and the accuracy of adjustment by trimming tends to be poor. Nor is there any mention in the Japanese Published Unexamined Patent Application No. Hei 10(1998)-214496 as to how trimming information is to be determined.
Examination by the present inventor has revealed that it would not be easy to accurately monitor the output time of the timer circuit according to, for instance, the Japanese Published Unexamined Patent Application No. Hei 11 (1999)-7783. Though there is no mention of this point in its specification, it may be possible to acquire trimming data according to which a desired transistor is to be selected out of a plurality of transistors differing in threshold voltage by externally measuring the output time of the timer circuit via an I/O port or the like, but there are not a few parasitic capacitors and resistors on the path of measurement from the timer circuit to the I/O port via an internal bus, and the obtuseness or distortion of signal waveforms they give rise to is likely to make accurate measurement difficult. The testing system will be made complex, moreover. It is desirable to perform trimming lot by lot, wafer by wafer or chip by chip, and there is the remaining problem of an extended testing time.
In particular, within a chip, often there are a plurality of circuits to be trimmed apart from a timer circuit. In such a case, the testing time will be further extended if the characteristics are measured circuit by circuit and trimming data are acquired individually, resulting in a corresponding increase in testing cost.
An object of the present invention is to provide a semiconductor device, such as a microcomputer or a flash memory, facilitating measurement for acquisition of control data (trimming data) for use in the adjustment of circuit characteristics.
Another object of the invention is to provide a semiconductor device, such as a microcomputer or a flash memory, serving to reduce the time taken to acquire trimming data.
Still another object of the invention is to provide a semiconductor device, such as a microcomputer or a flash memory, making possible highly reliable adjustment of the characteristics of circuits which are desired to have intended characteristics unaffected by unevenness of device characteristics or the like.
The above-stated and other objects and novel features of the present invention will become apparent from the description in this specification and the accompanying drawings.
What follows is a brief summary of typical aspects of the present invention disclosed in this application.
[1] A semiconductor device according to the invention has, formed over one semiconductor chip, a control voltage generating circuit (
10
) for generating a control voltage on the basis of control data; circuits (
4
, etc.) using a constant current source generating a constant current on the basis of the control voltage; a current measuring transistor (
2
) whose control terminal is connected to a signal line for providing the control voltage to the constant current source; an external measuring terminal (
3
), connected to the current terminal of the current measuring transistor, for making possible external measurement of the current flowing in the current measuring transistor; and a memory means (
13
) for holding control data and providing them to the control voltage generating circuit. The control data are utilized for determining the characteristics of the circuits using the constant current source, and the choice of control data determines the characteristics of the pertinent circuit. When the characteristics of a given circuit are to be determined, control data are actually provided to the control voltage generating circuit to generate a control voltage, and the resultant current actually flowing in the current measuring transistor is observed at the external measuring terminal. The measurement is done either by connecting a current measuring apparatus to the external measuring terminal and measuring the amperage therewith, or applying a voltage to the external measuring terminal via a resistor having a known resistance and measuring the voltage with a voltage measuring apparatus arranged in parallel to the resistor. The measuring line within the semiconductor device has no intervening internal bus or I/O circuit and few undesirable parasitic capacitance components or wiring resistance components which distort observed signal waveforms to a substantial extent. The value of control data required for obtaining the desired constant current is acquired from the value of the control data at the time when the observed value has become equal to the target value or from the correlation between the observed value and the control data at the time. The value thereby obtained is stored into the memory means as the control data. The semiconductor device determines the constant current of the constant current source on the basis of the control data stored in the memory means. Therefore, the measurement for determining the constant current can be accomplished accurately and, moreover, in a s
Fujito Masamichi
Hirakii Mitsuru
Shinagawa Yutaka
Takeuchi Kan
Tanaka Toshihiro
Auduong Gene N.
Hitachi , Ltd.
Miles & Stockbridge P.C.
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