Abstract:
The invention provides a clock generator and a switch-capacitor circuit comprising the same, and pertains to the technical field of integrated circuit (IC) design. The clock generator comprises a non-overlapping clock signal generating module and a ring oscillator, a frequency detecting module, a comparator module and a programmable biasing signal generating module for forming a feedback circuit, wherein a biasing signal generated by the programmable biasing signal generating module is fed back and input to the ring oscillator so as to adjust the frequency of the third clock signal output by the ring oscillator, until the frequency of the third clock signal is compared as being substantially equal to the frequency of a standard clock signal in the comparator module. Moreover, the biasing signal can be fed back and input to the non-overlapping clock signal generating module so as to reduce the offset of the two phase clock time interval τ. The time interval τ between two phase clocks of the multiple phase non-overlapping clock signal output by the clock generator is stable and has a high accuracy, and the switch-capacitor circuit using the clock generator exhibits an excellent performance.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention pertains to the technical field of integrated circuit (IC) design, relates to a clock generator, and in particular to a clock generator which is less susceptible to PVT factor and can generate a multiple phase non-overlapping clock signal as well as a switch-capacitor circuit applied with the clock generator. 
       BACKGROUND 
       [0002]    In IC design, some circuit modules in the chip needs to use a multiple phase clock signal, especially a multiple phase non-overlapping clock signal simultaneously, wherein a time interval is set between any two clock signals so that for the clock signals in each phase, any two clock signals will not be in an “on” status simultaneously at any timing. Therefore, a time sequence relationship between the clock signals in individual phases has to be well controlled so as to ensure non-overlapping. 
         [0003]      FIG. 1  is a schematic view of a two-phase none-overlapping clock signal, wherein “clock  1 ” indicates of one clock signal and “clock  2 ” indicates of another clock signal. In the embodiment shown in  FIG. 1 , a phase difference between clock  1  and clock  2  is 180°, and the clock signals of the two phases must not be in an “on” status simultaneously at any timing. In order to ensure non-overlapping between clocks, a corresponding clock generator must ensure that a gap is kept between a trailing edge of any one of the clock signals and a rising edge of the other clock signal, which gap is referred to as a time interval between two phase clocks (i.e., the “τ” shown in  FIG. 1 ). 
         [0004]    The multiple-phase none-overlapping clock signal such as that shown in  FIG. 1  has been widely used in integrated circuits. Moreover, the higher the time sequence accuracy is, the better performance the integrated circuit exhibits. Taking the two-phase none-overlapping clock signal as an example, it has been widely used in a switch-capacitor circuit. For example, in a sample and hold circuit of a AD converter, in order to achieve a sampling and amplifying function of the switch-capacitor circuit, a clock signal control is required to be provided therefore; in order to avoid a so-called “charge sharing” phenomenon in the switch-capacitor circuit and to reduce the destruct to the accuracy of information caused by charge-sharing, the switch circuit thereof generally adopts the two-phase none-overlapping clock signal shown in  FIG. 1 . 
         [0005]      FIG. 2  is a schematic view of the circuit of a conventional clock generator for generating a two-phase none-overlapping clock signal shown in  FIG. 1 , wherein a phase inverter I 0  is used for inverting clocks; an input end of the NOT-AND gate N 1  is connected to a reference clock signal, the other input end is input with clock  2  signal, and the output end of the NOT-AND gate N 1  is output to a first set of phase inverters (I 11 /I 12 /I 13 ) connected in series sequentially; an input end of the NOT-AND gate N 2  is connected to an inverted clock signal (I 0  output), the other end of input with clock 1  signal, and the output end of the NOT-AND gate N 2  is output to a second set of phase inverters (I 21 /I 22 /I 23 ) connected in series sequentially. The closed-loop circuit composed of the NOT-AND gates (N 1 , N 2 ) and two sets of phase inverters (I 11 /I 12 /I 13  and I 21 /I 22 /I 23 ) can ensure a time interval τ between clock  1  and clock  2 ; the specific size of the time interval τ can be also determined by a delay (t) of the first set of phase inverters (I 11 /I 12 /I 13 ) or the second set of phase inverters (I 21 /I 22 /I 23 ). 
         [0006]    However, in an actual integrated circuit, the clock generator generating a multiple-phase none-overlapping clock signal are easily affected by many factors such as process, voltage and/or temperature (abbreviated as PVT in the industry), and the time interval τ between the clocks of two phases will also be prone to offset with the variation of PVT. For example, when the batches of water are different, the time intervals τ may be different; when the environment temperatures are different, the time intervals τ may be different; and when the voltages of power source are different, the time intervals τ may be different. Therefore, in an existing clock generator, the time interval τ between any two phase clock signals generated thereby is not stable, and a large offset may easily occur. The larger the offset of the time interval τ is, the more easily the performance of the circuit system using the clock signal is affected. For example, in a switch-capacitor circuit, when the value of τ is shortened to a certain degree (due to a larger offset of τ), a “charge sharing” phenomenon might occur in the switch-capacitor circuit because of a delay mismatch of a buffer behind the clock generator, thus greatly reducing the performance of the switch-capacitor circuit. 
       SUMMARY OF THE INVENTION 
       [0007]    The object of the invention is to reduce the offset of the time interval τ between two phase clocks of a multiple phase non-overlapping clock signal and to improve the stability of the time interval τ between two phase clocks. 
         [0008]    In order to achieve the above object or other objects, the invention provides the following technical solutions. 
         [0009]    According to an aspect of the invention, a clock generator is provided, comprising a non-overlapping clock signal generating module ( 31 ) for generating a multiple phase non-overlapping clock signal, and further comprising: 
         [0010]    a ring oscillator ( 32 ) for generating a third clock signal (clock 3 ) which reflects the offset of the time interval (τ) between two phase clocks of the multiple phase non-overlapping clock signal; 
         [0011]    a frequency detecting module ( 33 ) for detecting the frequency of a standard clock signal (clock 4 ) input by the frequency detecting module ( 33 ) and the frequency of the third clock signal (clock 3 ); 
         [0012]    a comparator module ( 34 ) for comparing the frequency of the standard clock signal (clock 4 ) and the frequency of the third clock signal (clock 3 ); 
         [0013]    a programmable biasing signal generating module ( 35 ) for adjustably outputting a biasing signal according to the comparison result output by the comparator module ( 34 ); 
         [0014]    wherein the biasing signal is fed back and input to the ring oscillator ( 32 ) so as to adjust the frequency of the third clock signal (clock 3 ) until the frequency of the third clock signal (clock 3 ) is compared as be substantially equal to the frequency of the standard clock signal (clock 4 ) in the comparator module ( 34 ); and 
         [0015]    wherein, the biasing signal is fed back and input to the non-overlapping clock signal generating module ( 31 ) so as to reduce the offset of the time interval (τ) between two phase clocks. 
         [0016]    In the clock generator according to an embodiment of the invention, the non-overlapping clock signal generating module ( 31 ) is disposed adjacent to the ring oscillator ( 32 ) in the chip and is manufactured in synchronization with the ring oscillator ( 32 ) in the same process. 
         [0017]    Further, optionally, the phase inverter for generating delay used in the non-overlapping clock signal generating module ( 31 ) is the same as the phase inverter for generating delay used in the ring oscillator ( 32 ), and the layouts and structures of them are also the same. 
         [0018]    In the clock generator according to any of the above embodiments, the delay (τ 1 ) generated by the phase inverter used in the ring oscillator ( 32 ) is n times larger than the time interval (τ) between two phase clocks generated by the phase inverter used in non-overlapping clock signal generating module ( 31 ), wherein n is an integer larger than or equal to 1. 
         [0019]    In the clock generator according to any of the above embodiments, a plurality of phase inverters used in the non-overlapping clock signal generating module ( 31 ) can be the same, or be different. 
         [0020]    In the clock generator according to another embodiment of the invention, the offset of the time interval (τ) between two phase clocks is caused by the fact that the multiple phase non-overlapping clock signal is influenced by the factors of process, voltage and/or temperature. 
         [0021]    In the clock generator according to any of the above embodiments, the influence on the third clock signal (clock 3 ) by the factors of process, voltage and/or temperature is substantially equal to the influence on the multiple phase non-overlapping clock signal by the factors of process, voltage and/or temperature. 
         [0022]    In the clock generator according to any of the above embodiments, the non-overlapping clock signal generating module ( 31 ) is a current controllable non-overlapping clock signal generating module ( 31 ), the ring oscillator ( 32 ) is a current controllable ring oscillator ( 32 ), and the biasing signal is a biasing current signal. 
         [0023]    In the clock generator according to any of the above embodiments, the biasing current signal adjusts the magnitude of current according to the comparison result of the comparator module ( 34 ) so as to correct the frequency of the third clock signal (clock 3 ) and the time interval (τ) between two phase clocks. 
         [0024]    In the clock generator according to any of the above embodiments, the biasing signal is biased onto all the gate circuits of the ring oscillator ( 32 ), and the biasing signal is also biased onto all the gate circuits of the non-overlapping clock signal generating module ( 31 ). 
         [0025]    In the clock generator according to any of the above embodiments, the multiple phase non-overlapping clock signal can be a multiple phase non-overlapping clock signal of two or more than two phases. 
         [0026]    In the clock generator according to any of the above embodiments, a reference clock signal generated by crystal oscillator is input to the non-overlapping clock signal generating module ( 31 ). 
         [0027]    In the clock generator according to any of the above embodiments, the standard clock signal (clock 4 ) is not influenced by the factors of process, voltage and/or temperature. 
         [0028]    In the clock generator according to any of the above embodiments, the time interval between two phase clocks of the multiple phase non-overlapping clock signal is controlled by the standard clock signal (clock 4 ). 
         [0029]    According to another aspect of the invention, a switch-capacitor circuit is provided, comprising any of the above described clock generators, wherein the multiple phase non-overlapping clock signal output by the clock generator is applied in the switch-capacitor circuit. 
         [0030]    In the clock generator and switch-capacitor circuit provided by the invention, a feedback circuit (i.e., a compensation circuit or compensation system) is formed by the ring oscillator, the frequency detecting module, the comparator module and the programmable biasing signal generating module; the biasing signal is fed back and the frequency of the clock signal output by the ring oscillator is adjusted to be equal to the frequency of the standard clock signal, and meanwhile, the time interval between two phase clocks of the multiple phase non-overlapping clock signal can be also corrected in real time or in a one-time manner. Therefore, the offset of the time interval τ between two phase clocks is reduced so that it is substantially immune to the influence by the factors of PVT, etc. The time interval τ between two phase clocks of the multiple phase non-overlapping clock signal output by the clock generator is stable and has a high accuracy, and the switch-capacitor circuit using the clock generator exhibits an excellent performance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The above and other objects and advantages of the invention will become completely apparent from the following detailed description with reference to the accompanying drawings, wherein identical or similar elements are denoted by identical reference signs. 
           [0032]      FIG. 1  is a schematic view of a two-phase none-overlapping clock signal. 
           [0033]      FIG. 2  is a schematic view of the circuit of a conventional clock generator for generating the two-phase none-overlapping clock signal shown in  FIG. 1 . 
           [0034]      FIG. 3  is a schematic structure view of the clock generator according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    Some of the many possible embodiments of the invention will be described below in order to provide a basic understanding of the invention, and it is not intended to identify the crucial or decisive elements of the invention or limit the scope of protection. It is easily understood that according to the technical solutions of the invention, those skilled in the art can propose other alternative implementations without departing from the true spirit of the invention. Therefore, the following specific embodiments and drawings are merely exemplary description of the technical solutions of the invention, and should not be taken as the whole invention or as defining or limiting the technical solutions of the invention. 
         [0036]    In the following description, in order to the make the description clear and concise, not all the many component shown in the drawings are described. Many components that enable those skilled in the art to completely carry out the invention are shown in the Drawings. For those skilled in the art, the operation of many components is familiar and obvious. 
         [0037]      FIG. 3  is a schematic structure view of the clock generator according to an embodiment of the invention. In this embodiment, the clock generator  30  is used for generating a two-phase none-overlapping clock signal, i.e., clock signals clock 1  and clock 2 . Therefore, the clock generator  30  necessarily comprises a non-overlapping clock signal generating module  31  which can output an input reference clock signal to generate two none-overlapping clock signals, i.e., clock signals clock 1  and clock 2 . The reference clock signal can be generated by crystal oscillator, but not limited thereto. Specifically, as shown in  FIG. 1 , the non-overlapping clock signal generating module  31  uses several phase inverters and NOT-AND gates, wherein the phase inverter  311  is used for inverting the reference clock signal and further inputting the inverted reference clock signal to an end of the NOT-AND gate  316 ; an input end of the NOT-AND gate  312  is connected with the reference clock signal, and the other input end is feedback input by the clock signal clock 2 . The reference clock signal and the clock signal clock 2  are processed in a NOT-AND logic by the NOT-AND gate  312  and then output to the phase inverter  311 . Further, the phase inverters  313 ,  314  and  315  that are connected in series sequentially are used for generating delay, which is substantially equal to the time interval τ. Further, the phase inverter  315  outputs the clock signal clock 1 ; the clock signal clock 1  is input to another input end of the NOT-AND gate  316  in feedback, and the inverted reference clock signal and clock signal clock 1  are processed in a NOT-AND logic by the NOT-AND gate  316  and then output to the phase invert  317 . Further, the phase inverters  317 ,  318  and  319  that are connected in series sequentially are used for generating delay, which is substantially equal to the time interval τ. Further, the phase inverter  319  outputs the clock signal clock 2 ; the clock signal clock 1  is feedback input to the NOT-AND gate  312 , and the clock signal clock 2  is feedback input to the NOT-AND gate  316 , thus ensuring a two phase clock time interval τ (referred to as “time interval τ” for short hereinafter) exists between clock 1  and clock 2 . Not considering the influences of such factors as PVT, the offset of the time interval τ is substantially zero, i.e., the time interval τ is a certain predetermined constant value. However, under the influence of such factors as PVT, the variation of the frequencies of clock 1  and clock 2  enables the time interval τ to change and offset relative to the predetermined constant value, i.e., an offset of the two phase clock time interval τ is generated. 
         [0038]    In order to reduce the offset generated by the time interval τ due to an influence by the PVT, preferably, the phase inverters  313 ,  314 ,  315 ,  317 ,  318  and  319  are the same phase inverters. Not only the structures and parameters of them are identical, but also the layout and arrangement are identical, and they are disposed adjacent to each other; therefore, the delay generated by the phase inverters  313 ,  314  and  315  are the same as the delay generated by the phase inverters  317 ,  318  and  319  to the greatest extent possible. 
         [0039]    With continued reference to  FIG. 3  the clock generator  30  further comprises a ring oscillator  32 . Specifically, the ring oscillator  32  can be also mainly composed of NOT-AND gates and a plurality of phase inverters. The delay τ 1  generated by the plurality of phase inverters determines the frequency of the clock signal clock 3  output by the ring oscillator  32 . In this embodiment, the ring oscillator  32  is disposed adjacent to the non-overlapping clock signal generating module  31  in the chip and is manufactured in synchronization with the non-overlapping clock signal generating module  31  in the same process. The NOT-AND gates used in the ring oscillator  32  are the same as the NOT-AND gates used in the non-overlapping clock signal generating module  31 , the phase inverters used in the ring oscillator  32  are the same as the phase inverters used in the non-overlapping clock signal generating module  31 , and the structure and layout of the phase inverters in the ring oscillator  32  are also the same as those of the phase inverters in the non-overlapping clock signal generating module  31 . Therefore, the ring oscillator  32  and the non-overlapping clock signal generating module  31  can be easily made to have the same process (i.e., the same manufacture process), the same voltage (i.e., the same power source voltage) and the same temperature (i.e., the same environment temperature). The influence on the output clock signal clock 3  of the ring oscillator  32  by the PVT is substantially equal to the influence on the output clock signals clock 1  and clock 2  of the non-overlapping clock signal generating module  31  by the PVT. Therefore, the variation in the frequency caused by the influence on the clock signal clock 3  by PVT can reflect the offset of the two phase clock time interval τ between clock 1  and clock 2 . In this embodiment, the frequency of clock 3  is determined by the delay τ 1  of the plurality of phase inverters connected in series used by clock 3 . When τ 1  is equal to τ, the frequency of the clock signal clock 3  is equal to the frequencies of the clock signal clock 1  and clock 2 . Moreover, the ratio of ON/OFF of the clock signal clock 3  is also the same as the ratio of ON/OFF of the clock signal clock 1  or clock 2 . The larger the difference between the frequency of the clock signal clock 3  and the frequency of the standard signal clock 4  is, the larger the offset of the two phase clock time interval τ in the non-overlapping clock signal generating module  31  is (the t becomes larger or smaller), and vice-versa. 
         [0040]    In other embodiments, when the clock generator  30  is applied to a high speed situation, in order to avoid a too short period of clock 3  (or to avoid a too high frequency), a multiple relationship can be formed between τ 1  and τ. That is, the number of the phase inverters used in the ring oscillator  32  is n times of the number of the phase inverters for generating the time interval τ used in the non-overlapping clock signal generating module  31  (n is an integer larger than or equal to 2, e.g., n=10). In this way, the frequency f 3  of the clock signal clock 3  is one n th  of the frequency of the clock signal clock 1  or clock 2 . At this time, the influence on the ring oscillator  32  by the PVT is also consistent with the influence on the non-overlapping clock signal generating module  31  by the PVT. 
         [0041]    With continued reference to  FIG. 3 , the clock generator  30  further comprises a frequency detecting module  33 , to which the clock signal clock 3  output from the ring oscillator  32  and the standard clock signal clock 4  provided externally are input simultaneously. The frequency detecting module  33  can detect the frequency f 3  of the clock signal clock 3 , and can also detect the frequency f 4  of the standard clock signal clock 4 . The standard clock signal clock 4  has a very high accuracy, and is substantially immune to the influence from PVT. The standard clock signal clock 4  has the same frequency as the clock signal clock 1  or clock 2  generated by the non-overlapping clock signal generating module  31  when the offset of the two phase clock time interval τ is zero. Therefore, the two phase clock time interval between the two phase non-overlapping clock signals (clock 1  and clock 2 ) can be controlled by the standard clock signal clock 4 . 
         [0042]    With continued reference to  FIG. 3 , the clock generator  30  further comprises a comparator module  34  and a programmable biasing signal generating module  35 . The comparator module  34  can compare the frequency f 3  of the clock signal clock 3  with the frequency f 4  of the clock signal clock 4 . If the frequencies f 3  and f 4  are not the same, it means that the ring oscillator  32  is influenced by the PVT, and an offset of the two phase clock time interval τ between the two phase non-overlapping clock signals has occurred. The comparator module  34  can output a control signal to the programmable biasing signal generating module  35  so that the programmable biasing signal generating module  35  can adjust the height of an output biasing signal. If the frequencies f 3  and f 4  are the same, it means that the ring oscillator  32  is substantially not influenced by the PVT, and an offset of the two phase clock time interval τ between the two phase non-overlapping clock signals has not occurred. The comparator module  34  outputs another control signal to the programmable biasing signal generating module  35  so that the programmable biasing signal generating module  35  still outputs a biasing signal of the same height. 
         [0043]    In this embodiment, the output end  351  of the programmable biasing signal generating module  35  outputs a biasing signal p 1  to the ring oscillator  32 , and the output end  352  outputs a biasing signal p 2  to the non-overlapping clock signal generating module  31 , wherein the biasing signals p 1  and p 2  are the same. In case where the non-overlapping clock signal generating module  31  is a current controllable non-overlapping clock signal generating module and the ring oscillator  32  is a current controllable ring oscillator, the biasing signals p 1  and p 2  are the same biasing current signals, and the magnitude of the current of the biasing signals p 1  and p 2  can be adjustably output according to a comparison result of the frequencies f 3  and f 4  in the comparator module  34 . Therefore, the variation in the magnitude of the output biasing current signals can further cause a change of the frequency of the ring oscillator  32 , until the frequencies f 3  and f 4  are substantially the same. Meanwhile, the biasing current signal (p 2 ) is also adjusted synchronously, and the frequencies of clock 1  and clock 2  can thus be adjusted, thus further reducing an offset of the two phase clock time interval τ. When the frequencies f 3  and f 4  are substantially the same, which means that an offset of the two phase clock time interval τ has been substantially eliminated, the accuracy of the output two phase non-overlapping clock signals (clock 1  and clock 2 ) is high, making it easier to ensure no overlapping will occur between the two clock signals (clock 1  and clock 2 ). When it is applied to a CMOS switch-capacitor circuit, a “charge sharing” phenomenon will not occur, which is highly advantageous for an accurate linearization process of an analogue signal in an AD converter. 
         [0044]    In other embodiments where the non-overlapping clock signal generating module  31  is a voltage controllable non-overlapping clock signal generating module and the ring oscillator  32  is a voltage controllable ring oscillator, the biasing signals p 1  and p 2  can be correspondingly set as biasing voltage signals, and the magnitude of the voltage of the biasing signals p 1  and p 2  can be adjustably changed according to a comparison result, thus further correcting the frequency of the third clock signal clock 3  and the two phase clock time interval τ. Therefore, in the above embodiments, the two phase clock time interval τ can be corrected in real time (in case where the PVT changes at any time) or be corrected in a one-time manner (in case where the PVT no longer changes) so as to reduce the offset of the two phase clock time interval τ. 
         [0045]    In an embodiment, the biasing current signal p 1  can be biased to all the gate circuits (e.g., NOT-AND gates and phase inverters) of the ring oscillator  32 , i.e., the output end  351  is coupled to all the gate circuits of the ring oscillator  32 ; the biasing current signal p 2  can be also biased to all the gate circuits (e.g., NOT-AND gates and phase inverters) of the non-overlapping clock signal generating module  31 , and output end  352  is coupled to all the gate circuits of the non-overlapping clock signal generating module  31 . The biasing current signal p 2  can be generated in a way of being the mirror of the biasing current signal p 1 . For example, if the frequency f 3  is larger than f 4 , the comparator module  34  will output a signal so that the current of the biasing current signal p 1  output by the programmable biasing signal generating module  35  will be reduced, and the current of p 2  will also be reduced. In this way, the frequency f 3  of the clock signal clock 3  will be reduced, the offset of the two phase clock time interval τ will also be reduced, and the influence by such factors as PVT will be corrected. 
         [0046]    It will be understood that the expression “programmable” in the programmable biasing signal generating module  35  indicates a characteristic that the magnitude of the biasing signal output by the programmable biasing signal generating module  35  is adjustable. 
         [0047]    The clock generator  30  in the embodiment shown in  FIG. 3  can be applied to a switch-capacitor circuit of an AD converter and an analogue filter, for example, and the two phase non-overlapping clock signal provided by the clock generator  30  in not easily influenced by PCT conditions. The offset of the two phase clock time interval is small, and the two phase clock time interval is stable and accurate. Therefore, when a switch-capacitor circuit uses the clock generator  30  of the embodiment, a “charge sharing” phenomenon can be avoided, thus greatly improving the performance of the switch-capacitor circuit. 
         [0048]    Although the above example have been described based on a clock generator  30  which generates a two phase non-overlapping clock signal, it is understood that on the basis of the above teaching or enlightenment, those skilled in the art can configure a clock generator which generates a multiple phase non-overlapping clock signal in which the offset of the two phase clock time interval is small. For example, if it is required to generate a multiple phase non-overlapping clock signal having three or more than three phases, the non-overlapping clock signal generating module  31  can be reconfigured equivalently so that it has the function of generating a non-overlapping clock signal having three or more than three phases. The structures and arrangements of other modules (e.g., the frequency detecting module  33 , the comparator module  34  and the programmable biasing signal generating module  35 ) do not have to be changed substantively, except for the adaptive changes made to them. 
         [0049]    It will be understood that when a component is referred to as “connected” or “coupled” to another component, it can be connected or coupled directly to the other component, or there can be an intermediate component. Rather, when a component is referred to as “directly connected” or “directly coupled” to another component, there is no intermediate component. Moreover, the expressions “connect” or “couple” used herein can comprise wireless connecting or coupling. As used herein, the term “and/or” comprises any and all combinations of one or more relevant listed items, and can be abbreviated as “/”. 
         [0050]    The above embodiments mainly describe the clock generator of the invention and a switch-capacitor circuit using the clock generator. While only some of the embodiments of the invention are described, those skilled in the art will understand that the invention can be carried out in many other ways without departing from the spirit and scope of the invention. Therefore, the illustrated examples and embodiments should be considered as illustrative rather than limiting. The invention may cover various modifications and substitutes without departing from the spirit and scope of the invention defined by the appended claims.