Abstract:
Provided is an analog digital converter (ADC). The ADC includes: a capacitor array generating a level voltage; a comparator outputting a compare signal by comparing the level voltage; and a logic circuit determining digital bits of an analog signal based on the compare signal, wherein the logic circuit determines at least one digital bit among digital bits of the analog signal while a sampling operation of the analog signal is performed in the capacitor array.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 of Korean Patent Application No. 10-2010-0127115, filed on Dec. 13, 2010, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention disclosed herein relates to an analog digital converter (ADC), and more particularly, to a Successive Approximation Register (SAR) ADC. 
     Recently, as a mixed-mode system is increasingly used, an ADC becomes more necessary. Especially, researches on fabricating one chip at a low price through a Complementary Metal-Oxide Semiconductor (CMOS) process in a system such as a Digital Video Disk Player (DVDP) or a Direct Broadcasting for Satellite Receiver (DRSR) are actively in progress. For this, a design technology of the ADC capable of directly processing a Radio Frequency (RF) signal becomes the biggest issue. 
     Various types of ADCs are suggested until now. For example, a flash 
     ADC, a pipeline ADC, and an SAR ADC are introduced and are used in application fields according to their characteristics. The flash ADC operates at a relatively high speed but has an area increased by 2 N  according to its resolution. The pipeline ADC has a fast operating characteristic and supports a high resolution but has high power consumption. The SAR ADC has low power consumption and a simple circuit configuration but operates at a relatively slow speed. 
     SUMMARY OF THE INVENTION 
     The present invention provides an analog digital converter (ADC) guaranteeing a fast operating characteristic. 
     Embodiments of the present invention provide ADCs including: a capacitor array generating a level voltage; a comparator outputting a compare signal by comparing the level voltage; and a logic circuit determining digital bits of an analog signal based on the compare signal, wherein the logic circuit determines at least one digital bit among digital bits of the analog signal while a sampling operation of the analog signal is performed in the capacitor array. 
     In some embodiments, the ADCs may further include a connection circuit connected between the comparator and an input node of the analog signal, wherein the connection circuit is turned on while the sampling operation of the analog signal is performed in the capacitor array. 
     In other embodiments, the ADCs may further include: a first connection circuit connected between the comparator and an input node of the analog signal; and a second connection circuit connected between the comparator and the capacitor array, wherein the first connection circuit is turned on and the second connection circuit is turned off while the sampling operation of the analog signal is performed in the capacitor array. 
     In still other embodiments, after the sampling operation of the analog signal may be completed in the capacitor array, the first connection circuit is turned off and the second connection circuit is turned on. 
     In even other embodiments, the ADCs may further include a sub analog digital converting circuit connected to an input node of the analog signal and the logic circuit, wherein the sub analog digital converting circuit determines at least one bit of digital bits of the analog signal while the sampling operation of the analog signal is performed in the capacitor array. 
     In yet other embodiments, the sub analog digital converting circuit may be realized with a flash ADC. 
     In further embodiments, the capacitor array may include: a plurality of capacitors sampling the analog signal; and a plurality of switches connected to the plurality of capacitors, wherein after a sampling operation is completed, the plurality of switches selectively connect the plurality of capacitors to input nodes of first and second reference voltages to generate the level voltage. 
     In other embodiments of the present invention, ADCs include: a first successive approximation register (SAR) ADC converting an analog input signal into a digital signal of a predetermined bit; and a second SAR ADC converting a reaming voltage of the first SAR ADC into a digital signal of a predetermined bit, wherein the first SAR ADC converts the analog input signal into a digital signal while a sampling operation of the analog input signal is performed; and the second SAR ADC converts the remaining voltage into a digital signal while a sampling operation of the remaining voltage is performed. 
     In some embodiments, the first and second SAR ADCs may generate a sub analog digital converting path supporting an analog digital converting operation while a sampling operation is performed and a main analog digital converting path supporting an analog digital converting operation after a sampling operation is performed, respectively. 
     In other embodiments, while a sampling operation is performed, the main analog digital converting path of the first and second SAR ADCs may be cut off 
     In still other embodiments, after a sampling operation is completed, the sub analog digital converting path of the first and second SAR ADCs may be cut off. 
     In even other embodiments, the first and second SAR ADCs may perform an analog digital converting operation using respective comparators while a sampling operation is performed. 
     In yet other embodiments, the first and second SAR ADCs may perform an analog digital converting operation using respective flash ADCs while a sampling operation is performed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain principles of the present invention. In the drawings: 
         FIG. 1  is a block diagram illustrating a multistage Successive Approximation Register (SAR) Analog Digital Converter (ADC) according to an embodiment of the present invention; 
         FIG. 2  is a timing diagram illustrating an operation of the multistage SAR ADC of  FIG. 1 ; 
         FIG. 3  is a block diagram illustrating a multistage SAR ADC according to another embodiment of the present invention; 
         FIG. 4  is a timing diagram illustrating an operation of the multistage SAR ADC of  FIG. 3 ; 
         FIG. 5  is a detailed view illustrating a structure of the multistage SAR ADC of  FIG. 3 ; and 
         FIG. 6  is a block diagram illustrating a multistage SAR ADC according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be constructed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. 
       FIG. 1  is a block diagram illustrating a multistage Successive Approximation Register (SAR) Analog Digital Converter (ADC) according to an embodiment of the present invention. Exemplarily, a 2 stage SAR ADC is shown in  FIG. 1 . Referring to  FIG. 1 , the multistage SAR ADC  100  includes a first SAR ADC  110 , a second SAR ADC  120 , and a remaining voltage amplifier  130 . 
     The first SAR ADC  110  includes a first capacitor array  111 , a first comparator  112 , and a first SAR logic circuit  113 . Similar to this, the second SAR ADC  120  includes a second capacitor array  121 , a second comparator  122 , and a second SAR ADC logic circuit  123 . 
     In the first and second SAR ADCs  110  and  120 , the first and second capacitor arrays  111  and  121  receive an analog input voltage Vin and an output voltage of the remaining voltage amplifier  130 , respectively. Each of the first and second capacitor arrays  111  and  121  includes a plurality of capacitors (not shown). The first and second capacitor arrays  111  and  121  stores the received analog input voltage Vin and output voltage of the remaining voltage amplifier  130  in the capacitors, respectively. An operation for storing an analog input voltage Vin and an output voltage of the remaining voltage amplifier  130  may be referred to as a sampling operation. 
     Additionally, each of the first and second capacitor arrays  111  and  121  generates a level voltage. Here, a level voltage is a value for determining a level of a received analog input voltage Vin and also is a value divided appropriately according to a digital resolution of the ADC. That is, the capacitors of the first and second capacitor arrays  111  and  121  may have respectively different capacitances and the first and second capacitor arrays  111  and  121  generate a level voltage using a charge redistribution method. 
     The first and second comparators  111  and  121  receive level voltages generated in the first and second capacitor arrays  112  and  122 . The first and second comparators  111  and  121  compare a level voltage with a predetermined voltage (e.g., a ground) to output a high or low signal. 
     The first and second SAR logic circuits  113  and  123  receive respective signals generated in the first and second comparators  112  and  122  and convert an analog input voltage Vin into a digital signal through the received signals. 
     The remaining voltage amplifier  130  is connected between the first SAR ADC  110  and the second SAR ADC  120  and amplifies a remaining voltage outputted from the first SAR ADC  110 . Hereinafter, an operation of the multistage SAR ADC  110  is described. 
     Once an analog input voltage Vin is inputted, the first SAR ADC  110  performs an n-bit analog digital converting operation. Then, the remaining voltage amplifier  130  amplifies a remaining voltage after the n-bit analog digital converting operation. The second SAR ADC  120  receives the amplified remaining voltage and performs an m-bit analog digital converting operation through the received voltage. As a result, the analog input voltage Vin is converted into an n+m bit digital signal using the first and second SAR ADCs  110  and  120 . 
     In this case, a consumed time that the multistage SAR ADC  100  converts one analog input voltage Vin into an n+m bit digital signal may be similar to a time consumed in a typical SAR ADC. However, if several analog input voltages are continuously inputted, a time consumed for digital conversion in the multistate SAR ADC  100  becomes shorter than a time consumed in a typical SAR ADC. This is because while the first SAR ADC  110  performs a digital converting operation on an n analog input voltage, the second SAR ADC  120  performs a digital converting operation on an n−1 analog input voltage. This will be described in more detail with reference to  FIG. 2 . 
       FIG. 2  is a timing diagram illustrating an operation of the multistage SAR ADC  100  of  FIG. 1 . Referring to  FIG. 2 , the SAR ADC  100  operates in response to a clock signal CK. In  FIG. 2 , exemplarily, it is assumed that the multistage SAR ADC  100  operates in response to four clocks Q 1  to Q 4 . 
     Referring to  FIGS. 1 and 2 , the first SAR ADC  110  samples an nth analog signal (n is an integer greater than 1) during the clock Q 1  and performs an analog digital converting operation during the clocks Q 2  and Q 3 . The remaining voltage amplifier  130  amplifies a remaining voltage outputted from the first SAR ADC  110 . The second SAR ADC  120  performs a digital converting operation on an n−1th analog signal during the clocks Q 1 , Q 2 , and Q 3  and samples a remaining voltage outputted from the remaining voltage amplifier  130  during the clock Q 4 . 
     This operation repeats by a period of four clocks. Accordingly, when analog input signals are continuously inputted, while the second SAR ADC  120  performs a digital converting operation on an n−1th analog input signal, the first SAR ADC  110  may perform a digital converting operation on an nth analog input signal. As a result, a time consumed for performing a digital converting operation in the multistage SAR ADC  100  becomes shorter than a time consumed for performing a digital converting operation in a typical SAR ADC. 
     Moreover, a digital converting time in the multistage SAR ADC  100  of  FIG. 1  is determined by a resolution of the multistage SAR ADC and one bit converting time. In this case, a 1 bit converting time is determined by manufacturing processes of an SAR ADC. As a result, a digital converting time of the multistage SAR ADC  100  is increased as its resolution is increased. Hereinafter, another embodiment of the present invention for reducing a digital converting time of a multistage SAR ADC with the same resolution will be described in more detail. 
       FIG. 3  is a block diagram illustrating a multistage SAR ADC  200  according to another embodiment of the present invention. A configuration of the multistage SAR ADC  200  of  FIG. 3  is similar to that of the multistage SAR ADC  100  of  FIG. 1 . Accordingly, difference with respect to the multistage SAR ADC  100  of  FIG. 1  will be mainly described. Referring to  FIG. 3 , the multistage SAR ADC  200  includes a first SAR ADC  210 , a second SAR ADC  220 , and a remaining voltage amplifier  230 . 
     In the first and second SAR ADCs  210  and  220 , the first and second comparators  212  and  222  receive an analog input voltage Vin and an output voltage, respectively. While the first and second capacitor arrays  211  and  221  perform a sampling operation, each of the first and second comparators  212  and  222  outputs a compare signal with respect to an analog input voltage Vin and an output voltage of the remaining voltage amplifier  230 . The first and second SAR logic circuits  213  and  223  receive a comparison result and determine a digital bit through the received comparison result. 
     While a sampling operation is performed, since a part of a digital converting operation is performed using the first and second comparators  212  and  222 , the multistage SAR ADC  200  has a less consumed time for a digital converting operation than the multistage SAR ADC  100  of  FIG. 1 . 
     To be more specific, first, an analog input voltage Vin is provided to the first capacitor array  211  and the first comparator  212 . The first capacitor array  211  performs a sampling operation using the analog input voltage Vin. Since an operation of the first capacitor  211  is similar to that  111  of  FIG. 1 , its detailed description will be omitted. 
     While the first capacitor array  211  performs a sampling operation, the first comparator  212  receives an analog input signal Vin and outputs a compare signal. The first SAR logic circuit  213  receives a comparison result from the first comparator  212  and performs a digital converting operation of more than 1 bit. That is, while a sampling operation is performed, since the analog input voltage Vin maintains a predetermined level, an operation for converting the analog input voltage Vin into a digital bit is partially performed using the first comparator  212 . 
     A digital converting operation performed using the first comparator  212  while the first capacitor array  211  performs a sampling operation may be referred to as a sub analog digital converting operation (i.e., a sub ADC operation). Additionally, a path through which an analog input voltage Vin is provided to the first comparator  212  may be referred to as a sub ADC path. 
     Once a sampling operation is completed in the first capacitor array  211 , the sub ADC path is cut off and a main ADC path is formed. Then, a main analog digital converting operation (hereinafter, a main ADC operation) is performed. Here, the main ADC operation means an operation determining a bit other than a digital bit determined in the sub ADC operation. Additionally, the main ADC path means a path formed between the first capacitor array  211  and the first comparator  212  to perform the main ADC operation. 
     For convenience of description, it is assumed that the first SAR ADC  210  converts an analog input signal Vin into an n-bit digital signal. Additionally, it is assumed that the first comparator  212  performs a 1-bit digital converting operation during a sampling operation. 
     In this case, since a 1-bit digital converting operation is performed during a sub ADC operation, the main ADC operation performs an n−1 bit digital converting operation. As a result, a time consumed for performing a digital converting operation in the first SAR ADC  210  of  FIG. 3  becomes shorter than a time consumed for performing a digital converting operation in the first SAR ADC  110 . 
     Moreover, since the main ADC operation is similar to the digital converting operation described with reference to  FIGS. 1 and 2 , its detailed description will be omitted. Additionally, since an operation of the second SAR ADC  220  is similar to that of the first SAR ADC  210 , its detailed description will be omitted. 
       FIG. 4  is a timing diagram illustrating an operation of the multistage SAR ADC  200  of  FIG. 3 . Referring to  FIG. 4 , the multistage SAR ADC  200  operates in response to a clock signal CK. For convenience of description, like  FIG. 2 , it is assumed that the multistage SAR ADC  200  operates in response to four clocks Q 1  to Q 4  in  FIG. 4 . 
     Referring to  FIGS. 3 and 4 , the first SAR ADC  210  samples an nth analog signal (n is an integer greater than 1) during clock Q 1 . While a sampling operation is performed, the first comparator  212  of the first SAR ADAC  210  performs a sub ADC operation of more than 1 bit. That is, a sub ADC operation is performed during the clock Q 1 . Then, the first SAR ADC  210  performs a main ADC operation during the clocks Q 2  and Q 3 . 
     Since a part of a digital converting operation for an analog input voltage Vin is performed in the sub ADC operation, a time consumed for performing a main ADC operation becomes shorter according to a digital bit converted during the sub ADC operation. Accordingly, a duration time of the clocks Q 2  and Q 3  necessary for performing a main ADC operation may be set less than that of the SAR ADC  110  of  FIG. 1 . 
     For example, it is assumed that the first SAR ADC  110  of  FIG. 1  performs a digital converting operation during the clocks Q 2  and Q 3  and each of the clocks Q 2  and Q 3  lasts for T 1 . In this case, as shown in  FIG. 4 , duration times of the clocks Q 2  and Q 3  for performing a main ADC operation in the first SAR ADC  210  of  FIG. 3  may be wet with T 1  and T 2 , respectively. That is, the duration time of the clock Q 3  may be reduced by T 3 . As a result, a timed consumed for performing an n-bit digital converting operation on an analog input voltage Vin in the first SAR ADC  210  may be reduced by T 3  compared to the first SAR ADC  110  of  FIG. 1 . 
     Moreover, the remaining voltage amplifier  230  amplifies a remaining voltage outputted from the first SAR ADC  210  during the clock Q 4 . The second SAR ADC  220  performs a digital converting operation on an n−1th analog signal during the clocks Q 1 , Q 2 , and Q 3  and samples a remaining voltage outputted from the remaining voltage amplifier  130  during the clock Q 4 . This operation repeats by a period of four clocks. 
     As mentioned above, the multistage SAR ADC  200  of  FIG. 3  supports a sub ADC operation. Accordingly, the multistage SAR ADC  200  of  FIG. 3  performs a fast digital converting operation with the same resolution compared to the multistage SAR ADC  100  of  FIG. 1 . 
       FIG. 5  is a detailed view illustrating a structure of the multistage SAR ADC  200  of  FIG. 3 . In  FIG. 5 , a structure of the first SAR ADC  210  and a connection relationship between the first SAR ADC  210  and the remaining current amplifier  230  are described in detail. 
     Referring to  FIG. 5 , the first SAR ADC  210  includes a first capacitor  211 , a first comparator  212 , a first SAR logic circuit  213 , a decoding circuit  214 , a sub ADC connection circuit  215 , and a main ADC connection circuit  216 . 
     The first capacitor array  211  receives an analog input voltage Vin and samples it. The first capacitor array  211  includes a plurality of capacitors and a plurality of switches. In  FIG. 5 , exemplarily, the first capacitor array  211  includes sixteen capacitors C 1  to C 16  and thus supports a 4-bit digital converting operation. The capacitors C 1  to C 16  have respectively different capacitances. For example, the capacitances of the capacitors C 1  to C 16  may be increased by 2 n . 
     The capacitors C 1  to C 16  are connected to an analog input voltage Vin through the respective switches S 1  to S 16 . While a sampling operation is performed, the switches S 1  to S 16  are turned on and the analog input voltage Vin is accumulated in the capacitors C 1  to C 16 . 
     Additionally, the capacitors C 1  to C 16  are connected to a first reference voltage Vrefn, a second reference voltage Vrefp, and a ground voltage through the switches S 22  to S 37 . That is, while the main ADC is performed, the switches S 22  to S 37  are connected to one of the first reference voltage Vrefn, the second reference voltage Vrefp, and the ground voltage through the switches S 22  to S 37 . In this case, a level voltage is generated through a charge redistribution method. 
     The first comparator  212  is connected to an analog input voltage Vin through the sub ADC connection circuit  215 . Additionally, the first comparator  212  is connected to the first capacitor array  211  through the main ADC connection circuit  216 . The first comparator  212  outputs a compare signal of the received signal and delivers it to the first SAR logic circuit  213 . The first SAR logic circuit  213  receives a compare signal and determines a digital bit by a 1 bit unit. 
     In  FIG. 5 , it is shown that the sub ADC connection circuit  215  and the main ADC connection circuit  216  are realized with the switches S 17  and S 21 , respectively. However, this is just exemplary and thus the sub ADC connection circuit  215  and the main ADC connection circuit  216  may be realized with a multiplexer. 
     When a sampling operation is performed, the sub ADC connection circuit  215  is turned on and the main ADC connection circuit  216  is turned off Accordingly, the first comparator  212  receives an analog input voltage Vin through a sub ADC path. While the sampling operation is performed, the first comparator  212  compares the analog input voltage Vin with a predetermined voltage (e.g., a ground voltage) and then outputs a compare signal. The first SAR logic circuit  213  receives the compare signal and determined a part of a digital bit (e.g., a digital bit of more than 1) of the analog input voltage Vin. That is, the sub ADC operation is performed while the sampling operation is performed. 
     Once the sampling operation is completed, the sub ADC connection circuit  215  is turned on and the main ADC connection circuit  216  is turned on. Accordingly, the first compactor  212  receives a level voltage through a main ADC path and outputs a comparison result. The first SAR logic circuit  213  receives the comparison result and determines a digital bit of the analog input voltage Vin. That is, the main ADC operation is performed. 
     In the main ADC operation, the first comparator  212  an the first SAR logic circuit  213  determine digital bits other than a digital bit determined during the sub ADC operation. For example, when the most significant bit (MSB) is determined during the sampling operation, the first comparator  212  an the first SAR logic circuit  213  may determine digital bits from the next bit of the MSB to the least significant bit (LSB). 
     Moreover, the decoding circuit  214  receives an output signal of the first SAR logic circuit  213 . The decoding circuit  214  controls the switches S 22  to S 37  based on the received result of the first SAR logic circuit  213 . Then, an operation for determining each bit value from the next bit to the LSB is repeatedly performed. 
     Once the main ADC operation is completed, the switches S 18  and S 19  are turned on and the switches S 17 , S 21 , and S 20  are turned off. Accordingly, the first capacitor array  211  is connected to the remaining voltage amplifier  230  and the remaining voltage amplifier  230  amplifies the remaining voltage and provides it to the second SAR ADC  220  of  FIG. 3 . 
     As mentioned above, the multistage SAR ADC  200  determines a digital bit of more than 1 using a comparator while the sampling operation is performed. Accordingly, a time consumed for converting an analog input voltage 
     Vin into a digital signal may be reduced. However,  FIGS. 3 through 5  are understood as exemplary ones and the technical scopes of the present invention are not limited thereto. Hereinafter, an embodiment of a multistage SAR ADC using a sub ADC circuit instead of a comparator will be described with reference to  FIG. 6 . 
       FIG. 6  is a block diagram illustrating a multistage SAR ADC  300  according to another embodiment of the present invention. A configuration of the multistage SAR ADC  300  of  FIG. 3  is similar to that of the multistage SAR ADC  300  of  FIG. 3 . Accordingly, differences with respect to the multistage SAR ADC  300  of  FIG. 3  will be mainly described. Referring to  FIG. 6 , the multistage SAR ADC  300  includes a first SAR ADC  310 , a second SAR ADC  320 , and a remaining current amplifier  330 . 
     Unlike the multistage SAR ADC  200  of  FIG. 3 , the SAR ADC  300  of  FIG. 5  performs a sub ADC operation while the sub ADC circuits  314  and  324  perform a sampling operation. That is, the first and second SAR ADCs  310  and  320  include the first and second sub ADC circuits  314  and  324 , respectively, and the first and second sub ADC circuits  314  and  324  receives an analog input voltage Vin and an output voltage of the remaining voltage amplifier  330 , respectively. 
     While the first and second capacitor arrays  313  and  323  perform a sampling operation, the first and second sub ADC circuits  314  and  324  perform a digital converting operation of more than 1 bit. Accordingly, similar to the multistate SAR ADC  200  of  FIG. 3 , a time consumed for a digital converting operation may be reduced in the multistate SAR ADC  300  of  FIG. 5 . 
     In this case, the first and second ADC circuits  314  and  324  may be realized with various forms. For example, the first and second ADC circuits  314  and  324  may be realized with a flash ADC or a pipeline ADC. 
     An ADC according to an embodiment of the present invention performs an analog digital converting operation during a sampling operation, so that a time consumed for digital conversion may be reduced. 
     The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.