Abstract:
Apparatuses and methods for providing a current independent of temperature are described. An example apparatus includes a current generator that includes two components that are configured to respond equally and opposite to changes in temperature. The responses of the two components may allow a current provided by the current generator to remain independent of temperature. One of the two components in the current generator may mirror a component included in a voltage source that is configured to provide a voltage to the current generator.

Description:
BACKGROUND 
       [0001]    Current generators are electrical circuits used to produce currents with low variability that may be provided to other circuitry. It may be desirable for the current provided by the current generator to be insensitive to process, voltage, or temperature (PVT) variations. Electrical components&#39; physical properties may change with changing temperature. For example, a resistance of a resistor may increase with increasing temperature. If the resistor is included in a current generator circuit, it may cause variations in the output current as temperature changes. Operational amplifiers and transistors may be used to compensate for temperature variations. Often many additional components are necessary for PVT compensation. This may lead to increases in component costs and increased layout area for the current generator. It may also increase the power consumption of the current generator. 
       SUMMARY 
       [0002]    An example apparatus according to at least one embodiment of the disclosure may include a voltage generator that may be configured to provide a voltage, a current generator that may be coupled to the voltage generator and may be configured to provide a current based on the voltage from the voltage generator, wherein the current generator may include a first component that has a property that may increase as temperature increases and a second component that has the property that may decrease as temperature increases, wherein the second component may be configured to decrease the property at a rate equal to a rate the first component increases the property and wherein the second component may match a resistance of the voltage generator. 
         [0003]    An example apparatus according to at least one embodiment of the disclosure may include a voltage generator that may be configured to provide a voltage, an operational amplifier that may be coupled to the voltage generator and may be configured to receive the voltage at an inverting input, a first transistor, a gate of the first transistor may be coupled to an output of the operational amplifier, a second transistor, a gate of the second transistor may be coupled to the output of the operational amplifier, a first resistance may be coupled to a drain of the first transistor, a second resistance may be coupled to the drain of the first transistor, wherein the second resistance, the first resistance, and the drain of the first transistor may be further coupled to a non-inverting input of the operational amplifier, and a diode may be coupled in series with the second resistor, wherein the second resistance and the diode may be matched to a voltage generator diode and voltage generator resistance that may be included in the voltage generator. 
         [0004]    An example apparatus according to at least one embodiment of the disclosure may include a voltage generator that may include an operational amplifier, and a voltage generator resistance and a voltage generator diode coupled to the operational amplifier, the voltage generator may be configured to provide a voltage, and a current generator coupled to the voltage generator, wherein the current generator may be configured to provide a bias current based on the voltage; the current generator may include a first component including a first resistance that may increase as temperature increases; and a second component including a second resistance that may decrease as temperature increases, wherein the second component may be configured to decrease the second resistance at a rate equal to a rate the first component increases the first resistance and wherein the second component may match the voltage generator resistance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a block diagram of an apparatus according to an embodiment of the invention. 
           [0006]      FIG. 2  is a circuit diagram of a current generator according to an embodiment of the invention. 
           [0007]      FIG. 3  is a plot of currents in a circuit over a range of temperatures according to an embodiment of the invention. 
           [0008]      FIG. 4  is a block diagram of a portion of a memory according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    Certain details are set forth below to provide a sufficient understanding of embodiments of the disclosure. However, it will be clear to one having skill in the art that embodiments of the disclosure may be practiced without these particular details. Moreover, the particular embodiments of the present disclosure described herein are provided by way of example and should not be used to limit the scope of the disclosure to these particular embodiments. In other instances, well-known circuits, control signals, timing protocols, and software operations have not been shown in detail in order to avoid unnecessarily obscuring the disclosure. As used herein, apparatus may refer to, for example, an integrated circuit, a memory device, a memory system, an electronic device or system, a smart phone, a tablet, a computer, a server, etc. 
         [0010]      FIG. 1  is a block diagram of an apparatus  100  that includes a voltage generator  105  and a current generator  110  according to an embodiment of the disclosure. As used herein, apparatus may refer to, for example, an integrated circuit, a memory device, a memory system, an electronic device or system, a smart phone, a tablet, a computer, a server, etc. The voltage generator may provide a voltage Vin to the current generator  110 . The current generator  110  may provide an output current Iout, based at least in part on the voltage Vin. In some embodiments, the current Iout may be provided to an input buffer (not shown in  FIG. 1 ) of a memory device as a bias current or the current Iout may be provided to another circuit that may use a current as an input. 
         [0011]    The current generator  110  may include components  115   a,    115   b  that respond equally, but inversely to changes in temperature. The equal and inverse responses of these components may allow current Iout to be independent of temperature. The responses may include a change in a property of the component, for example, resistance, capacitance, and/or impedance. Other component properties may also be designed to respond to temperature changes. 
         [0012]      FIG. 2  illustrates a circuit  200  according to an example embodiment of the disclosure. The circuit  200  includes a current generator  210  and a voltage generator  205 , which may be used for the current generator  110  and voltage generator  105  previously described with and illustrated in  FIG. 1 . The circuit  200  may provide an output current Iout that is independent of temperature. The current generator  210  may receive a voltage Vin from the voltage generator  205 . The voltage Vin may be received by the inverting input of an operational amplifier (op-amp)  235 . The output of the op-amp  235  may be provided to the gate of a transistor  240 . The transistor  240  may be a p-channel transistor or other transistor type. The drain of the transistor  240  may be coupled to a resistance  260 . The resistance  260  may be coupled in parallel to a leg  280 . The leg  280  includes a second resistance  250 , which is coupled in series with a diode  255 . The diode  255  is coupled to a voltage reference, for example, ground. The drain of transistor  240  may be further coupled to the non-inverting input of the op-amp  235 . A voltage Vfb may be measured at the non-inverting input of the op-amp  235 . A second transistor  245  may be coupled to the gate of transistor  240 . The second transistor  245  may be a p-channel transistor or other transistor type. The sources of the transistors  240 ,  245  may be coupled to a voltage source. An output current Iout may be provided by the transistor  245 . The output current Iout may be temperature independent, as will be described below. 
         [0013]    Still referring to  FIG. 2 , the voltage generator  205  may be a temperature independent voltage generator known in the art or a novel voltage generator. In the example embodiment of a voltage generator  205  illustrated in  FIG. 2 , the voltage generator  205  is a band gap voltage generator. Resistance  204  is coupled to resistance  212  and the inverting input of operational amplifier  230 . Resistance  204  is further coupled to the output of op-amp  230  and leg  270 , which includes resistance  220  and diode  225 . Resistance  212  is coupled to the inverting input of op-amp  230  and is further coupled to the diode  215 . Resistance  220  is coupled to the non-inverting input of op-amp  230  and diode  225 . The magnitude of resistance for the resistances  204 ,  212 ,  220  may be chosen to provide the desired value of the voltage Vin. For example, if the desired voltage Vin=1.25 V, resistance  212  may be selected to be 10KΩ, and resistances  204 ,  220  may be selected to be 100KΩ. The resistance  250  and diode  255  in leg  280  of the current generator  210  may be selected to match the resistance  220  and diode  225  in leg  270  of the voltage generator  205 . That is, the electrical characteristics of the resistance  250  are similar to the electrical characteristics of the resistance  220 , and the electrical characteristics of diode  225  are similar to the electrical characteristics of the diode  255 . This may allow Vfb to equal Vin. In some embodiments, the resistance  250  and diode  255  in leg  280  and the resistance  220  and diode  225  in leg  270  may have identical electrical characteristics. 
         [0014]    The resistances  250 ,  260  may represent components of the current generator  210 . The resistances  250 ,  260  may correspond to the components  115   a,    115   b  included in the current generator  110  of  FIG. 1 . The resistance of resistance  250  may decrease with increases in temperature. This may cause a resistor current Iptat across resistance  250  to increase as temperature increases. However, output current Iout may be prevented from changing in response to changes in resistance current Iptat by resistance  260 . In contrast to resistance  250 , the resistance of resistance  260  may increase as temperature increases. This may cause a resistance current Ictat across resistance  260  to decrease as temperature increases. 
         [0015]    In some embodiments, resistance  250  and diode  255  correspond to component  115   a.  Resistances  250 ,  260  may respond similarly to changes in temperature. A voltage drop across the diode  255  may change as temperature changes. For example, the voltage drop across the diode  255  may decrease as temperature increases, and the resistance of resistances  250 , 260  may both increase as temperature increases. The rate of the voltage drop across the diode  255  in response to the increase in temperature may be such that the resistance current Iptat may increase as temperature increase. The resistance current Icat may decrease with increase in temperature as described in the previous paragraph. This may prevent output current Iout from changing in response to changes in temperature. 
         [0016]    When resistance current Ictat changes at the same rate resistance current Iptat changes, but in the opposite direction, the output current Iout may be constant over a range of temperatures. This principle is illustrated in  FIG. 3 . The resistance currents Ictat and Iptat are illustrated over a range of temperatures. Although both resistance currents Ictat and Iptat vary over the temperature range, the sum of currents Ictat and Iptat remains constant, resulting in output current Iout that is independent of temperature. 
         [0017]    The resistance of resistance  260  may be chosen such that its change in resistance with temperature directly mirrors the change in resistance with temperature of resistance  250 . The resistances  250  and  260  may include different materials that respond differently to changes in temperature. The resistance value chosen for resistance  260  may depend on the material properties of resistances  250 ,  260 . For example, the resistance  250  may be 100 kΩ and cause resistance current Iptat to increase by 0.35 uA/100° C. Resistance  260  may be a long path of N +  doping in a p-substrate, often referred to as a “Naa” resistance. The resistance  260  may cause resistance current Ictat to decrease by −1.6 uA/100° C. Resistance current Ictat may counteract resistance current Iptat when the resistance of resistance  260  is 450KΩ. In some embodiments, the current generator  210  may be manufactured with a trimmable resistance  260 . This may allow for the resistance of resistance  260  to be tuned to the properties of resistance  250  after manufacture of the current generator  210 . Resistance  260  may be trimmed as part of the manufacturing process of a product or may be left untrimmed to allow a user to tune resistance  260  at a later time. 
         [0018]    The circuit  200  may consume less power and layout area than other temperature independent current generators. The circuit  200  may also provide an output current with less variability than other current generators. For example, for the resistance values of the example previously described in reference to  FIG. 2 , the circuit  200  may consume approximately 20 uA of current and 200 um×100 um of layout area. Different current consumption and layout areas may be possible based, at least in part, on the components chosen for the voltage and current generators. 
         [0019]      FIG. 4  is a block diagram of a portion of a memory which may contain the circuit  200  according to an embodiment of the present invention. The memory  400  includes an array  402  of memory cells, which may be, for example, volatile memory cells (e.g., DRAM memory cells, SRAM memory cells, etc.), non-volatile memory cells (e.g., flash memory cells, PCM cells, etc.), or some other types of memory cells. 
         [0020]    The memory  400  includes a command decoder  406  that receives memory commands through a command bus  408  and generates corresponding control signals within the memory  400  to carry out various memory operations. The command decoder  406  responds to memory commands applied to the command bus  408  to perform various operations on the memory array  402 . For example, the command decoder  406  is used to generate internal control signals to read data from and write data to the memory array  402 . Row and column address signals are applied to the memory  400  through an address bus  420  and provided to an address latch  410 . The address latch then outputs a separate column address and a separate row address. 
         [0021]    The row and column addresses are provided by the address latch  410  to a row address decoder  422  and a column address decoder  428 , respectively. The column address decoder  428  selects bit lines extending through the array  402  corresponding to respective column addresses. The row address decoder  422  is connected to word line driver  424  that activates respective rows of memory cells in the array  402  corresponding to received row addresses. The selected data line (e.g., a bit line or bit lines) corresponding to a received column address are coupled to a read/write circuitry  430  to provide read data to a data output buffer  434  via an input-output data bus  440 . Write data are applied to the memory array  402  through a data input buffer  444  and the memory array read/write circuitry  430 . The memory may include a circuit  442  that provides a bias current for an input buffer of the memory  400  such as input buffer  444 . For example, the circuit  442  may include the circuit  200  of  FIG. 2 , or any circuit according to an embodiment of the disclosed invention. 
         [0022]    Those of ordinary skill would further appreciate that the various illustrative logical blocks, configurations, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software executed by a processor, or combinations of both. Various illustrative components, blocks, configurations, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or processor executable instructions depends on the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure. 
         [0023]    The previous description of the disclosed embodiments is provided to enable a person skilled in the art to make or use the disclosed embodiments. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the principles defined herein may be applied to other embodiments without departing from the scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope possible consistent with the principles and novel features as defined by the following claims.