Abstract:
A circuit configuration includes two signal path sections that are used to program the delay of a signal path, in particular in DRAMs. The two signal path sections have different delays and can be driven in parallel at the input end. The two signal path sections can be connected to an output terminal via a multiplexer. A selection circuit includes two signal path sections which are connected between supply voltage potentials. The selection circuit has two complimentary transistors which are connected in series and has source-end programmable elements. These transistors can be driven by complimentary control signals. This permits the delay to be programmed flexibly with little expenditure on circuitry.

Description:
BACKGROUND OF THE INVENTION  
       FIELD OF THE INVENTION  
         [0001]    The invention relates to a circuit configuration for programming a delay in a signal path.  
           [0002]    In integrated circuits, in particular in semiconductor memories of the dynamic type, what are referred to as DRAMs (Dynamic Random Access Memories), it is necessary for the same circuit design to be configured for different application purposes. In addition, there is a need to set functional properties in dependence on fluctuations in the manufacturing process. To do this, programmable connections, referred to a fuses, are conventionally used. These fuses can either be programmed to be switched on via an additional metal conductor track or programmed to be switched off by means of energy pulses. As a result, it is possible to set delays in signal paths within the DRAM, or a circuit design can be adapted to different module variants. The metal-programmable or fusible connections are referred to as metal options or fusible options.  
           [0003]    Published German Patent Application DE 199 22 712 A1 discloses a phase interpolator with a delay interpolation circuit. Various signal paths whose delay can be varied are disclosed. The delay is achieved by means of respectively assigned currents with different current strengths. The currents are made available by thermometer digital/analog converters.  
           [0004]    Published German Patent Application DE 41 12 077 A1 discloses a programmable logic module in which a delay stage is connected between a combinatorial logic operation circuit and the macro cell. The delay of the delay stage can be switched between two levels as a function of a control signal.  
         SUMMARY OF THE INVENTION  
         [0005]    It is accordingly an object of the invention to provide a circuit for programming a delay in a signal path which overcomes the above-mentioned disadvantageous of the prior art apparatus of this general type. In particular, it is an object of the invention to provide such a circuit, which includes a particularly small number of components and which can be easily programmed.  
           [0006]    With the foregoing and other objects in view there is provided, in accordance with the invention, a circuit configuration for programming a delay in a signal path, which includes: an input terminal for receiving an input signal; an output terminal for providing an output signal; a first signal path section with a first delay, the first signal path section having an input end connected to the input terminal and having an output end; a second signal path section with a second delay that is different from the first delay of the first signal path section, the second signal path section having an input end connected to the input terminal and having an output end; and a multiplexer having an input connected to the output end of the first signal path section and the output end of the second signal path section, the multiplexer having an output connected to the output terminal. The circuit configuration also has a drive circuit that includes supply terminals for receiving a supply voltage, and a first path connected between the terminals for receiving the supply voltage. The first path includes two transistors connected together to define a first node. The first path includes a first programmable path section and a second programmable path section. One of the first programmable path section and the second programmable path section is programmed to be switched on and the other one of the first programmable path section and the second programmable path section is programmed to be switched off. The drive circuit also includes a second path that is connected between the terminals for receiving the supply voltage. The second path includes two transistors connected together to define a second node. The second path includes a first programmable path section and a second programmable path section. One of the first programmable path section of the second path and the second programmable path section of the second path is programmed to be switched on and another one of the first programmable path section of the second path and the second programmable path section of the second path is programmed to be switched off. The two transistors of the first path are controllable by complimentary control signals. The two transistors of the second path are also controllable by the complimentary control signals. The multiplexer has a control input that is connected to the first node and the second node.  
           [0007]    The circuit configuration according to the invention has a small number of components. The two signal path sections have a different signal transit time are thus driven in parallel at the input end and each generate an output signal in accordance with their set delay. At the output end, just one of the two delayed signals made available is tapped. The multiplexer is used for this, and it selects one signal path section or the other by means of metal options or fusible options. The selection circuit is space-saving. The selection circuit includes four metal options or fusible options and four transistors having paths connected in the center. By means of a preset control signal, a setting of the drive circuit is selected and accordingly a setting of the multiplexer is selected. The significant factor is that just one of the options per path section is programmed to be switched on and the other is switched off.  
           [0008]    In accordance with an added feature of the invention, the drive signal, which operates the drive circuit, is set by means of what is referred to as a bonding option. To do this, the drive signal is tapped by a terminal face, referred to as a bond pad, which is connected by a bonded connection to a terminal for the positive pole of the supply voltage or alternatively to a terminal for the negative pole of the supply voltage. In this way, the signal which presets the drive circuit has a predefined high level or low level.  
           [0009]    To carry out the configuration, the drive circuit is first programmed with a metal option by means of the last mask while the semiconductor chip is being manufactured. Instead of the metal option, the fusible option can be used in which a connection is melted with a laser. After the integrated circuit has been tested, the precise desired delay is finally set by means of the bonding option. Overall, a flexible setting of a delay for a signal path is set with the possibility of intervening at various points in the manufacturing process of the integrated circuit.  
           [0010]    In accordance with an additional feature of the invention, there is provided, capacitors and third programmable path sections for connecting the capacitors in either the first signal path section or the second signal path section.  
           [0011]    In accordance with another feature of the invention, the two transistors of the first path include an n-type channel MOS transistor and p-type channel MOS transistor, and the two transistors of the second path include an n-type channel MOS transistor and p-type channel MOS transistor.  
           [0012]    In accordance with a concomitant feature of the invention, the circuit configuration includes: a first metal line and a second metal line. The first programmable path section of the first path includes a first terminal connected to the first metal line when the first programmable path section is programmed to be switched on. The first terminal is not connected to the first metal line when the first programmable path section is programmed to be switched off. The second programmable path section of the second path includes a second terminal connected to the second metal line when the second programmable path section is programmed to be switched on. The second terminal is not connected to the second metal line when the second programmable path section is programmed to be switched off.  
           [0013]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0014]    Although the invention is illustrated and described herein as embodied in a circuit configuration for programming a delay in a signal path, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0015]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 shows a circuit portion of a DRAM that includes two signal paths;  
         [0017]    [0017]FIG. 2 shows a drive circuit that generates drive signals for the multiplexer; and  
         [0018]    [0018]FIG. 3 shows a bonding option that is used for generating signals for the drive circuit.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a portion of a circuit of a DRAM. The signal path whose delay is to be set lies between the terminals  1  and  2 . A digital input signal IN is fed in at the terminal  1 , and a correspondingly delayed output signal OUT is tapped at the output  2 . Two signal paths  3 ,  4  are provided which are connected at the input end to the terminal  1 . At the output end, the signal paths  3 ,  4  are connected to the input terminals of a multiplexer  6 . The multiplexer  6  is driven by a control signal which includes complimentary components. The output terminal of the multiplexer  6  is connected to the output  2  of the circuit.  
         [0020]    [0020]FIG. 2 shows a drive circuit  5  that generates the control signal W, bW of the multiplexer. The drive circuit  5  includes two signal paths which are connected between terminals for the supply voltage VDD, VSS and are coupled to a central node in order to make available the signal W or bW. The signal paths  51 ,  52  include transistors  511 ,  512  or  521 ,  522 , respectively, the drain-source paths of which are connected in series. The source terminals of the transistors are connected via a metal option to the respective terminal for one of the supply potentials VDD, VSS. In the exemplary embodiment illustrated in FIG. 2, the transistor  512  is connected to the terminal for the supply potential VDD via a metal option  513  constituting a conductive connection, and the transistor  521  is connected to the terminal for the supply voltage VSS by means of a metal option  523  which is also programmed to be on. The other metal options are not programmed, i.e. they are switched off. The source terminal of the transistor  522  is thus connected to the terminal for the positive supply potential VDD via the non-programmed metal option  524  which is switched off, and the transistor  511  is connected to the terminal for the negative supply potential VSS via the metal option  514  which is switched off.  
         [0021]    The respective transistors of the signal paths  51 ,  52  are MOS transistors of the complimentary channel type. The transistors  512 ,  522  are n-type channel MOS transistors, and the transistors  511 ,  521  are p-type channel MOS transistors. The transistors of one of the signal paths are driven by complimentary components of a control signal. The transistors of the same type of transistor (respectively p-type channel or respectively n-type channel transistors) of different signal paths are also driven by the complimentary components of this control signal. The transistors  521 ,  512  are thus controlled by the signal bHSPEED, and the transistors  522 ,  511  are controlled by the HSPEED control signal which is complimentary thereto. By suitably programming the programmable path sections  513 ,  514 ,  523 ,  524  and suitably setting the drive signals HSPEED, bHSPEED, a multiplicity of programming and setting possibilities are obtained for generating the drive signal W, bW for the multiplexer  6 . Either only the option  513  is programmed to be switched on and the option  514  switched off, or vice versa. The same applies to the options  523  and  524 .  
         [0022]    The metal options shown in the drive circuit  5  are individualized by the application of the last metal layer to the layered structure of the integrated circuit. Alternatively, instead of metal options, it is possible to provide meltable fuses that are switched on in the preset state and are disconnected by means of an energy pulse, for example, laser or fusing current. Generally, the metal options and fuses are programmable path sections which are permanently set to be switched on or switched off. The signal HSPEED or bHSPEED is then set, preferably by means of what is referred to as a bonding option. FIG. 3 shows a bonding option for setting the signals HSPEED and bHSPEED. A terminal face  71  is provided which is connected in the example shown to a terminal face  73  for the reference potential VSS by means of a bonding wire  72 . Alternatively, it is possible to connect the terminal face  71  to the terminal face  74  for the positive supply potential VDD.  
         [0023]    The two signal paths  3 ,  4  have different signal transit times for the signal IN fed in to them at the terminal  1  at the input end. The delayed signals IN′, IN″ which are present at the output of the signal path sections  3 ,  4  are generated in parallel. One of the signals is then selected by means of the multiplexer  6  and passed on to the output terminal  2 . The signal path section  3 ,  4  have a different number of inverters  31  or  41 ,  42 ,  43  which are connected in series with respect to the input/output signal paths. Moreover, metal options or fusible options are provided in order to connect capacitors, which are connected to terminals for the supply voltage, to the signal path section  3  or  4 . As a result, a different delay can be set for the signal path sections  3 ,  4 . Capacitors  32 ,  33 ,  34 ,  35 , which can be connected to the signal path section via a metal option  36  or  37 , are thus provided. The metal option  36  is programmed to be switched on as a metal conductor track, and the metal option  37  remains switched off in the initial state. Corresponding capacitors and metal options are made available for the signal path section  4 . There, the metal options are always switched off. Moreover, it is advantageous, if appropriate, to connect further inverters into the signal path  4  by means of metal options. Two inverters  44 ,  45  connected in series are provided as spares, and can be connected to the signal path section  4  by means of two options  461 ,  462 . In the example shown, the metal options  461 ,  462  are embodied in the switched off state, and instead the input of the inverter  44  is connected to the terminal for reference potential VSS via a metal option  463  which is embodied in the switched on state.  
         [0024]    In the exemplary embodiment illustrated, the signal HSPEED has a low level. The signal bHSPEED has a high level. The transistor  512  is thus switched on and the transistor  521  is switched off. The signal W has a high level and selects the signal path section  3  in the multiplexer  6 . There, the input signal IN is passed on to the output terminal  2  as an output signal OUT with a delay due to inversion by means of the inverter  31  and due to additional delay by the capacitors  32 ,  33 .  
         [0025]    The circuits illustrated in FIGS.  1 - 3  are part of a semiconductor memory module. It is now possible to configure the same semiconductor memory for other application purposes. To do this, the fuses  36 ,  37 ,  461 ,  462 ,  463  and  513 ,  514 ,  523 ,  524  are, if appropriate, to be programmed in a desirable fashion. The ultimate setting of the multiplexer  6  is then set by means of the bonding option  71 ,  72 ,  73 ,  74 .