Abstract:
Integrated circuit devices include a comparator circuit and a fuse programmable input circuit. The fuse programmable input circuit generates first and second differential input signals at voltage levels that can be controlled through a pair of fuses. The comparator circuit generates an output signal based on the relative voltage levels exhibited by the first and second differential input signals. In particular, the output signal is driven to a first logic state when the voltage difference between the first and second differential input signals is positive and the output signal is driven to a second logic state, which is opposite the first logic state, when the voltage difference is negative. Because the comparator is responsive to the relative difference between the voltage levels of the first and second differential input signals and not the absolute magnitudes of the voltage levels, fuse remnants that may exist after the fuse programmable input circuit has been programmed (i.e., one or more fuses have been cut) typically do not affect the output signal.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 98-19869, filed May 29, 1998, the disclosure of which is hereby incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of integrated circuit devices, and, more particularly, to fuse programmable integrated circuit devices. 
     BACKGROUND OF THE INVENTION 
     In some integrated circuit memory devices, different operating modes can be selected on the semiconductor chip before packaging. For example, a memory device may be capable of operating in various modes, such as page mode, nibble mode, burst mode, and static mode. In such a memory device, the desired operation mode may be chosen by cutting a predetermined fuse or set of fuses. In addition, fuses can be used to select among other options relating to, for example, propagation delay adjustment, pulse width adjustment, transistor width adjustment, and current level adjustment. Fuses can also be used to repair memory devices, including defective memory cells. Thus, broadly stated, a semiconductor device can be programmed to exhibit a certain set of characteristics or features by selectively cutting or leaving intact various fuse elements. To determine the status of a particular fuse, a fuse signature circuit can be used to determine if the fuse element is cut or intact. 
     The aforementioned applications for fuses are described, for example, in U.S. Pat. No. 4,446,534 entitled “PROGRAMMABLE FUSE CIRCUIT,” U.S. Pat. No. 4,730,129 entitled “INTEGRATED CIRCUIT HAVING FUSE CIRCUIT,” U.S. Pat. No. 4,773,046 entitled “SEMICONDUCTOR DEVICE HAVING FUSE CIRCUIT AND DETECTING CIRCUIT FOR DETECTING STATES OF FUSES IN THE FUSE CIRCUIT,” U.S. Pat. No. 5,428,311 entitled “FUSE CIRCUITRY TO CONTROL THE PROPAGATION DELAY OF AN IC,” U.S. Pat. No. 5,491,444 entitled “FUSE CIRCUIT WITH FEEDBACK DISCONNECT,” U.S. Pat. No. 5,701,274 entitled “SEMICONDUCTOR DEVICE WITH SELECTABLE DEVICE INFORMATION,” U.S. Pat. No. 5,726,585 entitled “SWITCHING CIRCUIT FOR USE INA SEMICONDUCTOR MEMORYDEVICE,” U.S. Pat. No. 5,767,732 entitled “CIRCUIT FOR PERMANENTLY ADJUSTING A CIRCUIT ELEMENT VALUE IN A SEMICONDUCTOR INTEGRATED CIRCUIT USING FUSE ELEMENTS,” and U.S. Pat. No. 5,818,285 entitled “FUSE SIGNATURE CIRCUITS FOR MICROELECTRONIC DEVICES.” 
     In addition to these applications, fuse elements or fuse circuits have also been used to perform selection functions. With reference to FIG. 1, a conventional semiconductor device  10  is shown to comprise a selection circuit  15  and an internal circuit  20 . The selection circuit  15  typically has at least one fuse element (not shown), and controls the operation of the internal circuit  20  in accordance with a fuse cutting operation. 
     A circuit diagram of the selection circuit  15  according to the prior art is shown in FIG.  2 . The selection circuit  15  includes a master fuse MF, which is electrically connected between a power supply voltage VCC and an output terminal ND 1 , and a resistor R 1 , which is electrically connected between the output terminal ND 1  and a ground or common voltage VSS. The master fuse MF typically comprises a laser fuse. Before the master fuse MF is cut, the output terminal ND  1  is driven to a logically high level (hereinafter logic one level) that is approximately equal to the power supply voltage VCC, which thereby activates the internal circuit  20 . Conversely, after the master fuse MF is cut, the output terminal ND 1  is pulled down to a logically low level (hereinafter logic zero level) that is approximately equal to the ground or common voltage VSS, which thereby deactivates the internal circuit  20 . 
     If the master fuse MF is cut imperfectly, however, the operation of the internal circuit  20  and ultimately the semiconductor device  10  may not be reliably predicted. For example, after the master fuse MF is cut, remnants of the master fuse MF may act as a resistor. This may cause the voltage level at the output terminal NDI to fall between the standard logic one and logic zero voltage levels, which can cause the behavior of the internal circuit  20  to be indeterminate. 
     Consequently, there exists a need for improved integrated circuit devices that can be reliably programmed through the use of fuses. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide improved fuse programmable integrated circuit devices. 
     It is another object of the present invention to provide fuse programmable integrated circuit devices that can generate selection signals for controlling other circuits or devices with reduced susceptibility to fuse remnant defects. 
     These and other objects, advantages, and features of the present invention are provided by integrated circuit devices that include a comparator circuit and a fuse programmable input circuit. The fuse programmable input circuit generates first and second differential input signals at voltage levels that can be controlled through a pair of fuses. The comparator circuit generates an output signal based on the relative voltage levels exhibited by the first and second differential input signals. In particular, the output signal is driven to a first logic state when the voltage difference between the first and second differential input signals is positive and the output signal is driven to a second logic state, which is opposite the first logic state, when the voltage difference is negative. 
     Because the comparator is responsive to the relative difference between the voltage levels of the first and second differential input signals and not the absolute magnitudes of the voltage levels, fuse remnants that may exist after the fuse programmable input circuit has been programmed (i.e., one or more fuses have been cut) typically do not affect the output signal. 
     In accordance with an aspect of the invention, the fuse programmable input circuit may include a pair of voltage divider circuits that generate the first and second differential input signals. In accordance with another aspect of the invention, the comparator circuit may include a differential amplifier circuit. 
     Integrated circuit decoding devices according to the present invention include a redundant address generator that is operatively connected to a selection circuit. The redundant address generator includes a plurality of fuses that can be selectively cut to prevent signals from passing therethrough to reach an output terminal. 
     In accordance with an aspect of the invention, the selection circuit generates a control signal through a comparator circuit and a fuse programmable input circuit. The fuse programmable input circuit generates first and second differential input signals at voltage levels that can be controlled through a pair of fuses. The comparator circuit generates the control signal based on the relative voltage levels exhibited by the first and second differential input signals. In particular, the output signal is driven to a first logic state when the voltage difference between the first and second differential input signals is positive and the output signal is driven to a second logic state, which is opposite the first logic state, when the voltage difference is negative. 
     Thus, the redundant address generator, which can implement a decoding function through selective cutting of the appropriate fuses, can be activated or deactivated via the control signal from the selection circuit. Moreover, the control signal can be reliably controlled through the fuse programmable input circuit. In particular, the control signal is typically unaffected by fuse remnants that may remain after the fuse programmable input circuit is programmed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features of the present invention will be more readily understood from the following detailed description of specific embodiments thereof when read in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a block diagram of a semiconductor device including a selection circuit for controlling another circuit in accordance with the prior art; 
     FIG. 2 is an electrical schematic of the selection circuit of FIG. 1; 
     FIG. 3 is an electrical schematic of a selection circuit in accordance with the present invention; 
     FIG. 4A is a graphical representation of the input voltages generated by two fuse programmable voltage divider circuits used in the selection circuit of FIG. 3 before and after the fuses are cut; 
     FIG. 4B is a graphical representation of a selection signal generated by the selection circuit of FIG. 3; 
     FIG. 5 is a graphical representation of the selection signal generated by the selection circuit of FIG. 3 for several different values of resistance introduced by fuse remnants that may be produced after the fuses are cut; and 
     FIG. 6 is a schematic diagram of a redundancy circuit incorporating the selection circuit of FIG. 3 in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. Like reference numbers signify like elements throughout the description of the figures. 
     Referring now to FIG. 3, a preferred embodiment of a selection circuit  30 , according to the present invention, is shown as comprising a fuse programmable input circuit  32   a ,  32   b  and a comparator circuit  34 . The selection circuit  30  generates a selection or output signal at an output terminal ND 4 , which can be used to control the operation of another circuit (e.g., internal circuit  20  of FIG.  2 ). In particular, the selection signal exhibits a logic one voltage level before a pair of fuses F 1  and F 2  are cut and exhibits a logic zero voltage level after the fuses F 1  and F 2  are cut. 
     The comparator circuit  34  comprises a differential amplifier circuit having first and second input terminals ND 2  and ND 3  and the output terminal ND 4 . The comparator circuit  34  compares a difference between the voltage levels on the first and second input terminals ND 2  and ND 3  and generates the selection signal as the comparison result. The comparator circuit  34  includes two PMOS transistors MP 1  and MP 2  and four NMOS transistors MN 1  through MN 4  configured as follows: The PMOS transistor MP 1  has its source electrode electrically connected to the power supply voltage VCC and its drain electrode electrically coupled to the drain electrode of NMOS transistor MN 1  at the output terminal ND 4 . The PMOS transistor MP 2  has its source electrode electrically connected to the power supply voltage VCC and its gate and drain electrodes commonly tied to both the gate electrode of the PMOS transistor MP 1  and the drain electrode of the NMOS transistor MN 2 . The PMOS transistors MP 1  and MP 2  act as a current mirror and preferably have similar characteristics. 
     The NMOS transistors MN 1  and MN 2  act as input transistors and preferably have similar characteristics. The source electrodes of transistors MN 1  and MN 2  are electrically connected together and are also electrically connected to the drain electrode of transistor MN 3 . Transistor MN 4  is connected in series between transistor MN 3  and a ground or common voltage VSS. More specifically, the drain electrode of transistor MN 4  is electrically connected to the source electrode of transistor MN 3  and the source electrode of transistor MN 4  is electrically connected to the ground or common voltage VSS. The gate electrode of transistor MN 2  serves as a first input terminal ND 2 . The gate electrodes of transistors MN 1 , MN 3 , and MN 4  are electrically connected together to serve as a second input terminal ND 3 . 
     Continuing to refer to FIG. 3, the fuse programmable input circuit comprises a first voltage divider circuit  32   a  that is electrically connected to the comparator circuit  34  and divides the power supply voltage VCC to generate a first division voltage A at the first input terminal ND 2 . The first voltage divider circuit  32   a  includes two resistors R 2  and R 3  and one fuse F 1  connected in series between the power supply voltage VCC and the ground or common voltage VSS. The fuse F 1  may be formed as a laser fuse (i.e., fabricated by use of polysilicon). The resistor R 2  has one terminal electrically connected to the power supply voltage VCC through the fuse F 1  and the other terminal electrically connected to the first input terminal ND 2 . The resistor R 3  has one terminal electrically connected to the first input terminal ND 2  and the other terminal electrically connected to the ground or common voltage VSS. 
     The fuse programmable input circuit further comprises a second voltage divider circuit  32   b  that is electrically connected to the comparator circuit  34  and divides the power supply voltage VCC to generate a second division voltage B at the second input terminal ND 3 . The second voltage divider circuit  32   b  includes two resistors R 4  and R 5  and one fuse F 2  connected in series between the power supply voltage VCC and the ground or common voltage VSS. The fuse F 2  may be formed as a laser fuse (i.e., fabricated by use of polysilicon). The resistor R 4  has one terminal electrically connected to the power supply voltage VCC and the other terminal electrically connected to the second input terminal ND 3 . The resistor R 5  has one terminal electrically connected to the second input terminal ND 3  and the other terminal electrically connected to the ground voltage VSS through the fuse F 2 . 
     The selection circuit  30  may further comprise a buffer circuit  36  electrically connected to the output terminal ND 4  and comprising two inverters INV 1  and INV 2  connected in series. The buffer circuit  36  can be used to amplify the voltage level of the selection signal at the output terminal ND 4  to a logic one voltage level (e.g., the power supply voltage level VCC) or to a logic zero level (e.g., the ground or common voltage level VSS). This amplified version of the selection signal is designated as the OUT signal in FIG.  3 . 
     In a preferred embodiment, the values of the resistors R 2  through R 5  are chosen so that the first division voltage A is higher than the second division voltage B before the fuses F 1  and F 2  are cut, and the first division voltage A is less than the second division voltage B after the fuses F 1  and F 2  are cut. Moreover, through careful selection of the resistance values for resistors R 2  through R 5 , the relationship between the first and second division voltages A and B can be reversed after the fuses F 1  and F 2  are cut as shown in FIG.  4 A. That is, after the fuses are cut, the second division voltage B is greater than the first division voltage A when the power supply voltage VCC is greater than the ground or common voltage VSS. 
     The resistors R 2  through R 5  preferably comprise linear circuit elements, which ensures that the first and second division voltages A and B will vary linearly in accordance with the power supply voltage level VCC. Moreover, as illustrated in FIG. 4A, the relationship between the first and second division voltages A and B (i.e., which division voltage is greater than the other) is also maintained as the power supply voltage VCC is increased from the ground or common voltage level VSS. 
     The operation of the selection circuit  30  is described hereafter. Before the fuses F 1  and F 2  are cut, the first input terminal ND 2  is maintained at a logic one voltage level and the second input terminal ND 3  is maintained at a logic zero voltage level due to the values selected for resistors R 2  through R 5  and application of a predetermined power supply voltage VCC. When the fuse programmable input circuit  32   a ,b is programmed to a first state in which the fuses F 1  and F 2  are intact, the comparator circuit  34  generates a logically high voltage level at the output terminal ND 4 . The buffer circuit  36  may then be used to amplify the voltage level exhibited at the output terminal ND 4  to a full logic one level corresponding approximately to the power supply voltage VCC as shown in FIG.  4 B. 
     After the fuses F 1  and F 2  are cut, the first input terminal ND 2  is maintained at a logic zero voltage level and the second input terminal ND 3  is maintained at a logic one voltage level. That is, after the fuses F 1  and F 2  are cut, the voltage levels on the first and second input terminals ND 2  and ND 3  are logically reversed from their previous state when the fuses were intact. As a result of the fuse cutting procedure, remnants of the fuses F 1  and F 2  may be produced that are electrically conductive and thus have some resistance. Thus, it may not be possible to model the cut fuses as open circuits. Nevertheless, the values of the resistors R 2  through R 5  can be selected such that the effective impedance of R 2  and the remnants of fuse F 1 , and R 5  and the remnants of fuse F 2 , are greater than the impedances of R 3  and R 4  respectively. When the fuse programmable input circuit  32   a ,  32   b  is programmed to this second state in which the fuses F 1  and F 2  are cut, the comparator circuit  34  generates a logically low voltage level at the output terminal ND 4 . The buffer circuit  36  may then be used to amplify the voltage level exhibited at the output terminal ND 4  to a full logic zero level corresponding approximately to the ground or common voltage VSS as shown in FIG.  4 B. 
     Advantageously, the selection circuit  30  according to the present invention provides improved reliability as remnants that may remain from programming the selection circuit  30  (i.e., cutting the fuses F 1  and F 2 ) will typically not affect the selection signal generated at the output terminal ND 4 . 
     FIG. 5 provides a graph of the selection signal OUT versus the power supply voltage VCC for a variety of resistance values assigned to the remnants of fuses F 1  and F 2 . In the examples shown, when the fuses F 1  and F 2  are intact, they exhibit a nominal resistance of 0.10 Ω. Assuming the remnants of the fuses F 1  and F 2  each act as a resistor of 20 Ω, the selection signal OUT is driven to a logic zero level at a power supply voltage level of 2.5 volts. As illustrated by the examples, even if the fuses F 1  and F 2  are cut imperfectly (i.e., the remnants act as a resistor), the selection signal OUT can still be reliably controlled for typical power supply voltage levels. 
     A selection circuit  30  in accordance with the present invention can be used in a variety of applications. One such application is in a redundancy decoding circuit. Typically, a semiconductor memory device includes redundant memory cells, which are substituted for defective memory cells in the device. To substitute a redundant memory cell for a defective memory cell, a redundancy decoding circuit is used to generate a redundant address, which designates the substituted redundant memory cell instead of the defective memory cell. A circuit diagram of a redundancy decoding circuit  40  incorporating the selection circuit  30  of the present invention is shown in FIG.  6 . 
     With reference to FIG. 6, a redundancy decoding circuit  40 , in accordance with the present invention, comprises a selection circuit  30  and a redundant address generator  42 . The selection circuit  30  was described hereinabove with reference to FIG.  3 . The redundant address generator  42  includes a series of NMOS transistors MN 5  through MN 10  that have their drain electrodes electrically connected to an output terminal ND 5  through a series of fuses F 3  through F 8  respectively. The transistors MN 5  through MN 10  receive redundant address signals, RA 0 , RA 0 B through RAi, RAiB, at their gate electrodes respectively. By selectively cutting or leaving intact the fuses F 3  through F 8 , the redundant address signals can either be blocked or passed through to the output terminal ND 5 . Thus, the redundant address generator  42  can be programmed to operate as a decoder for the redundant address signals RA 0 , RA 0 B through RAi, RAiB. 
     As shown in FIG. 6, the redundancy decoding circuit  40  may also include a driving unit  44 , which is comprised of PMOS transistors MP 3  and MP 4  and NMOS transistor MN 11  and supplies a driving current to the output terminal ND 5  of the redundant address generator  42 . A signal RCSxB can be applied in common to the gate electrodes of the PMOS transistors MP 3  and the NMOS transistor MN 11  to activate or deactivate the driving unit  44 . In the embodiment illustrated in FIG. 6, the signal RCSxB is driven to a logic zero level to activate the driving unit  44  when decoding redundant address signals. 
     The selection circuit  30 , sometimes referred to as “a switching control signal generator” or “an enable fuse circuit,” allows the driving unit  44  to drive the redundant address generator  42  by applying a control signal OUT to the gate of the PMOS transistor MP 4 . As discussed hereinbefore, the selection circuit  30  can be programmed to generate the control signal OUT by cutting or leaving intact fuses contained therein. Moreover, the control signal OUT is typically unaffected by any fuse remnants that may remain from the fuse cutting operation. Consequently, the reliability of the redundancy decoding circuit is improved as the control signal OUT can be reliably driven to a desired logic level where it can be maintained. 
     In concluding the detailed description, it should be noted that many variations and modifications can be made to the preferred embodiment without substantially departing from the principles of the present invention. All such variations and modifications are intended to be included herein within the scope of the present invention, as set forth in the following claims.