Electricity: power supply or regulation systems – External or operator controlled – Using an impedance as the final control device
Utility Patent
2000-04-27
2001-01-02
Berhane, Adolf Deneke (Department: 2838)
Electricity: power supply or regulation systems
External or operator controlled
Using an impedance as the final control device
Utility Patent
active
06169393
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a trimming circuit, and more particularly, to a trimming circuit having a fuse that breaks electrically when adjusting the characteristics of a semiconductor integrated circuit.
During fabrication of a semiconductor integrated circuit, the electrical characteristics of the circuit are adjusted or corrected to include the circuit within a standardized range. In this process, a trimming circuit having fuses is used.
Each of the fuses is broken electrically or by a laser apparatus. A laser apparatus is normally not employed due to its relatively large size. The fuse is normally broken electrically since the fuse can easily be broken by applying a large amount of current or voltage.
In the prior art, the characteristics of a semiconductor integrated circuit subsequent to fuse breakage could not be confirmed before the fuse breakage. Thus, if the fuse is inadvertently broken, the semiconductor integrated circuit becomes defective. To prevent the fabrication of defective circuits, utmost caution is required before breaking the fuse when carrying out the breaking procedures and when testing the fuse.
Accordingly, there is a need for a trimming circuit that can easily confirm the characteristics of a semiconductor integrated circuit prior to fuse breakage. Such a trimming circuit includes an n number of polysilicon fuses (hereafter referred to a polyfuses), a transistor connected in series to each polyfuse, a control terminal for providing a control signal to each of the transistors, and trimming terminals, the number of which is two times greater than the number of polyfuses (2×n). The trimming circuit selectively deactivates the transistors and hypothetically breaks the corresponding fuses. The characteristics of the semiconductor integrated circuit when a transistor is deactivated is substantially the same as that when the fuse is actually broken. Thus, the characteristics of the semiconductor integrated circuit can be confirmed before actually breaking the fuse.
However, even if a transistor connected in series to a certain polyfuse is deactivated, a large voltage or current for breaking the other polyfuses is applied to the deactivated transistor. Thus, large transistors, which occupy a large amount of space, are required to resist high voltages or a large amount of current.
For accurate and fine adjustment of the characteristics of the semiconductor integrated circuit, the trimming circuit is provided with many polyfuses. Accordingly, the dimensions of the trimming circuit, and consequently, the chip incorporating the trimming circuit increases.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a relatively compact trimming circuit that enables hypothetical breakage of a fuse.
To achieve the above object, the present invention provides a trimming circuit for performing hypothetical fuse breakage and actual fuse breakage by selectively short-circuiting an adjusted device. The trimming circuit includes a switch circuit connected to the adjusted device for short-circuiting the adjusted device. A first external terminal is connected to the switch circuit. A first fuse circuit is connected between a first power supply and a second power supply. A second external terminal is connected to the first fuse circuit. The first fuse circuit includes a fuse connected to one of the first and second external terminals and a current limiting element connected to the other one of the first and second terminals and connected in series to the fuse. The current limiting element is connected to permit the flow of current in a forward direction from the first power supply to the second power supply. The potentials at the first and second external terminals are controlled so that the fuse is provided with a predetermined breakage current during the actual fuse breakage and the current limiting element impedes the breakage current during the hypothetical fuse breakage.
Another aspect of the present invention provides a trimming circuit for performing hypothetical fuse breakage and actual fuse breakage by selectively short-circuiting an adjusted device. The trimming circuit includes a switch circuit connected in parallel to the adjusted device and a fuse circuit including a fuse connected in series with a current limiting element. The fuse circuit is connected to the switch circuit and between a high potential power supply and a low potential power supply. The current limiting element is connected in a forward direction to permit the flow of current from the high potential power supply to the low potential power supply. A control terminal is connected to the fuse circuit and the high potential power supply. The control terminal is provided with a first control signal having a predetermined potential. A trimming terminal is connected to the fuse circuit and the switch circuit. The trimming terminal is provided with a second control signal having a predetermined potential. The potential of the second control signal is set to be less than the potential of the first control signal so that the current limiting element permits current to break the fuse during the actual breakage. The predetermined potential of the second control signal is equal to or greater than a set potential of the first control signal so that the current limiting element prevents current from breaking the fuse during the hypothetical breakage.
A further aspect of the present invention provides a trimming circuit for performing a simulated fuse breakage and an actual fuse breakage by short-circuiting a selected adjusted device. The trimming circuit includes a plurality of switch circuits. Each switch circuit is connected to an associated adjusted device. A plurality of fuse circuits are connected between a high potential power supply and a low potential power supply. Each fuse circuit is connected to an associated one of the switch circuits. The trimming circuit further includes a plurality of trimming terminals, each trimming terminal connected to a respective one of the fuse circuits and its associated switch circuit, for providing trimming signals to the fuse circuits and the switch circuits. For a simulated breakage, the trimming signals operate the respective switch circuits to selectively bypass the associated adjusted device without breaking one of the fuses circuits. A control terminal is connected to the each of the fuse circuits for providing a control signal to the fuse circuits. A selected one of the fuse circuits is broken by applying the control signal to the selected fuse circuit and simultaneously not applying the associated trimming signal to the selected fuse circuit such that a current passes through and breaks the fuse. Breaking the fuse circuit operates the switch circuit connected to the fuse circuit to bypass the associated adjusted device.
A further aspect of the present invention provides a trimming circuit having a first terminal and a second terminal. The trimming circuit includes a plurality of adjusted devices connected in series between the first and second terminals and a plurality of switch circuits. Each switch circuit is connected to an associated one of the adjusted devices. The trimming circuit further includes a plurality of fuse circuits. Each fuse circuit is connected to an associated one of the switch circuits. The trimming circuit also includes a high potential, constant-current power supply having a first output terminal and a second output terminal, the first output terminal being connected to each of the fuse circuits, and a low potential, constant-current power supply, having a plurality of first terminals and one second terminal, each first terminal being connected to an associated one of the switch circuits and the fuse circuit to which the associated switch circuit is connected, and the second terminal being connected to the second output terminal of the high potential power supply. A plurality of trimming terminals, each trimming terminal being connected to a respective one of the fuse circuits and
Arent Fox Kintner & Plotkin & Kahn, PLLC
Berhane Adolf Deneke
Fujitsu Limited
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