Abstract:
An EEPROM memory cell gate control signal generating circuit, which includes a high-voltage row decoding circuit and a plurality of word selection circuits; the output of the high-voltage row decoding circuit is divided into two routes, which output a first total wordline voltage used for providing the erasing positive voltage and a second total wordline voltage used for providing the erasing negative voltage, respectively; besides, the two-route voltages are inputted into the individual word selection circuits respectively, which avoids the influence of the erasing positive voltage on the grid oxide layer of an NMOS transistor and the influence of the erasing negative voltage on a PMOS transistor, and can save the MOS transistor used for isolating the grid oxide layer.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a semiconductor integrated circuit, particularly to an EEPROM memory cell gate control signal generating circuit. 
       BACKGROUND 
       [0002]    The EEPROM (Electrically Erasable Programmable Read-Only Memory) structure based on the SONOS (Silicon-Oxide-Nitride-Oxide-Silicon) transistor has the following requirements as shown in Table 1 for the gate voltage of the memory cell, i.e., the wordline voltage WLS, and for the substrate VBULK of the memory cell: 
         [0000]    
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Unselected word 
               
             
          
           
               
                   
                   
                 In the 
                 In the 
                 In the 
               
               
                   
                   
                 same col- 
                 same 
                 different 
               
               
                   
                   
                 umn but 
                 row but 
                 row and 
               
               
                   
                 Selected 
                 different 
                 different 
                 different 
               
               
                   
                 word 
                 row 
                 column 
                 column 
               
               
                   
                   
               
             
          
           
               
                 WLS 
                 Erasing 
                 VNEG 
                 VPOS 
                 VSS 
                 VSS 
               
               
                   
                 Programming 
                 VPOS 
                 VNEG 
                 VSS 
                 VSS 
               
               
                 VBULK 
                 Erasing 
                 VPOS 
                 VPOS 
                 VSS 
                 VSS 
               
               
                   
                 Programming 
                 VNEG 
                 VNEG 
                 VSS 
                 VSS 
               
               
                   
               
             
          
         
       
     
         [0003]    Wherein VPOS is the erasing positive voltage, a positive high voltage required for erasing and programming, and VNEG is the erasing negative voltage, a negative high voltage required for erasing and programming. While programming, the gate and the substrate of the selected memory cell are applied with VPOS and VNEG, respectively, and carry out the programming operation; both the gate and the substrate of the unselected memory cell in the same column with the selected memory cell are applied with VNEG, and the programming operation will not be carried out. While erasing, the gate and the substrate of the selected memory cell are applied with VNEG and VPOS, respectively, the erasing operation will be carried out; both the gate and the substrate of the unselected memory cell in the same column with the selected memory cell are applied with VPOS, the programming operation will not be carried out. VSS represents ground. 
         [0004]    As shown in  FIG. 1 , an existing EEPROM memory cell gate control signal generating circuit comprises: its generating circuit is divided into two parts: a high-voltage row decoding circuit  101  and a plurality of word selection circuits, such as a word selection circuit  1  and a word selection circuit n, which are marked with  1021  and  102   n , respectively, wherein  102   i  represents any word selection circuit i, with i being any digit from 1 to n. 
         [0005]    The total wordline voltage GWLS is generated by the high-voltage row decoding circuit  101 . The total wordline voltage GWLS needs the two values, VNEG and VPOS, wherein VPOS is generated by the PMOS transistors P 0  and P 1  under the control of the control signals X 2 SP, S 2 SPB, OE_SP and VDP, and VNEG is generated by the NMOS transistors N 0  and N 1  under the control of the control signals X 2 SN, S 2 SNB, OE_SN and VDN. However, the drains of the PMOS transistors P 0  and P 1  cannot be connected directly to the drains of the NMOS transistors N 0  and N 1 ; otherwise, when the drains of the PMOS transistors P 0  and P 1  output VPOS, VNEG will appear at the gates of the NMOS transistors N 0  and N 1 , which will make the voltage of the gate oxide layer of the NMOS transistors N 0  and N 1  too high; when the drains of the NMOS transistors N 0  and N 1  output VNEG, VPOS will appear at the gates of the PMOS transistors P 0  or P 1 , which will make the voltage of the gate oxide layer of the PMOS transistors P 0  or P 1  too high. Therefore, a PMOS transistor P 2  and an NMOS transistor N 2  need to be added to the existing technology to realize isolation, wherein the gate of the PMOS transistor P 2  is connected to the ground VSS, and the gate of the NMOS transistor N 2  is connected to the working voltage VDD, which make the voltage of the gate oxide layer of the PMOS transistors P 0  and P 1  and the NMOS transistors N 0  and N 1  reduced, thus protecting the gate oxide layer. 
         [0006]    The word selection circuit is the same in structure. Taking i of any digit from 1 to n as an example, the word selection circuit i includes the PMOS transistor  4   i , and the NMOS transistors N 4   i , N 6   i  and N 5   i , with the individual grids connected to the control signals BSPBi, BSNi, VDD and BDN, respectively; the word selection circuit i outputs the wordline voltage WSLi, which selects an output from the total wordline voltage GWLS and VSS, with the total wordline voltage GWLS including the two voltages, VPOS and VNEG. Likewise, the PMOS transistor P 3   i  is used for protection of the gate oxide layer of the PMOS transistor P 4   i , and the NMOS transistor N 3   i  is used for protection of the gate oxide layer of the NMOS transistor N 4   i , the gate of the PMOS transistor P 3   i  being connected to the ground VSS, the gate of the NMOS transistor N 4   i  being connected to the working voltage VDD. 
       SUMMARY 
       [0007]    A technical problem to be solved by the present invention is to provide an EEPROM memory cell gate control signal generating circuit, which can simplify the circuit and reduce cost. 
         [0008]    In order to solve the above technical problem, the EEPROM memory cell gate control signal generating circuit provided by the present invention comprises: a high-voltage row decoding circuit and a plurality of word selection circuits. 
         [0009]    The high-voltage row decoding circuit comprises a first-part row decoding circuit composed of a first PMOS transistor and a second PMOS transistor, and a second-part row decoding circuit composed of a first NMOS transistor and a second NMOS transistor. 
         [0010]    The drain of the first PMOS transistor is connected to the drain of the second PMOS transistor to output a first total wordline voltage the gate of the first PMOS transistor is connected to a first control signal, the gate of the second PMOS transistor is connected to a second control signal, the source of the first PMOS transistor is connected to a third control signal, and the source of the second PMOS transistor is connected to a fourth control signal; the first total wordline voltage outputted by the first-part row decoding circuit is made to be either the erasing positive voltage or levitation under the control of the first control signal, the second control signal, the third control signal and the fourth control signal. 
         [0011]    The drain of the first NMOS transistor is connected to the drain of the second NMOS transistor to output a second total wordline voltage, the gate of the first NMOS transistor is connected to a fifth control signal, the gate of the second NMOS transistor is connected to a sixth control signal, the source of the first NMOS transistor is connected to a seventh control signal, and the source of the second NMOS transistor is connected to an eighth control signal; the second total wordline voltage outputted by the second-part row decoding circuit is made to be either the erasing negative voltage or levitation under the control of the fifth control signal, the sixth control signal, the seventh control signal and the eighth control signal; the second total wordline voltage being levitated when the first total wordline voltage is the erasing positive voltage, the first total wordline voltage being levitated when the second total wordline voltage is the erasing negative voltage. 
         [0012]    A wordline of each memory cell of EEPROM is connected to one of the word selection circuits, which are the same in structure. Each of the word selection circuits including a third PMOS transistor, a third NMOS transistor, a fourth NMOS transistor and a fifth NMOS transistor. 
         [0013]    The drain of the third PMOS transistor, the drain of the third NMOS transistor and the drain of the fourth NMOS transistor are connected together to output a wordline voltage, which is inputted into a wordline of the corresponding memory cell. 
         [0014]    The source of the third PMOS transistor is connected to the first total wordline voltage, the source of the third NMOS transistor is connected to the second total wordline voltage, the source of the fourth NMOS transistor is connected to the drain of the fifth NMOS transistor, and the source of the fifth NMOS transistor is grounded. 
         [0015]    The gate of the third PMOS transistor is connected to a ninth control signal, the gate of the third NMOS transistor is connected to a tenth control signal, the gate of the fourth NMOS transistor is connected to the working voltage, and the gate of the fifth NMOS transistor is connected to an eleventh control signal; the wordline voltage is made to output one of the erasing negative voltage, erasing positive voltage and ground under the control of the ninth control signal, the tenth control signal and the eleventh control signal. 
         [0016]    As a further improvement, the first control signal, the second control signal, the third control signal and the fourth control signal are all switched between ground and the erasing positive voltage. 
         [0017]    As a further improvement, the first control signal and the second control signal are just mutually inverting in logic. 
         [0018]    As a further improvement, the fifth control signal, the sixth control signal, the seventh control signal and the eighth control signal are all switched between the working voltage and the erasing negative voltage. 
         [0019]    As a further improvement, the fifth control signal and the sixth control signal are just mutually inverting in logic. 
         [0020]    As a further improvement, the ninth control signal is switched between ground and the erasing positive voltage, the tenth control signal is switched between the working voltage and the erasing negative voltage, and the eleventh control signal is switched between the working voltage and the erasing negative voltage. 
         [0021]    As a further improvement, when one of the memory cells of EEPROM is selected, the ninth control signal of the word selection circuit to which this memory cell corresponds is grounded, the tenth control signal is connected to the working voltage, the eleventh control signal is connected to the erasing negative voltage, and the wordline voltage is one of the erasing negative voltage and the erasing positive voltage. 
         [0022]    As a further improvement, when one of the memory cells of EEPROM is not selected, the ninth control signal of the word selection circuit to which this memory cell corresponds is connected to the erasing positive voltage, the tenth control signal is connected to the erasing negative voltage, the eleventh control signal is connected to the working voltage, and the wordline voltage is ground. 
         [0023]    As a further improvement, the erasing positive voltage is used during programming for being applied to the gate of the selected memory cell and programming this selected memory cell, and also used during erasing for being applied to the gate of the unselected memory cell in the same column with the selected memory cell and preventing the unselected memory cell in the same column with the selected memory cell from being erased; the erasing negative voltage is used during erasing for being applied to the gate of the selected memory cell and erasing the selected memory cell, and also used during programming for being applied to the gate of the unselected memory cell in the same column with the selected memory cell and preventing the unselected memory cell in the same column with the selected memory cell from being programmed. 
         [0024]    As a further improvement, the memory cell of EEPROM is an SONOS transistor. 
         [0025]    The present invention, by which the total wordline voltage of the high-voltage row decoding circuit are outputted into two routes which are the erasing positive voltage transferred by PMOS and the erasing negative voltage transferred by NMOS, can thus eliminate the influence of the positive high voltage on the gate oxide layer of the negative high-voltage output terminal, and the influence of the negative high voltage on the gate oxide layer of the positive high-voltage output terminal, and therefore two MOS transistors used for isolating the gate oxide layer in the high-voltage row decoding circuit are saved; besides, the two routes of the total wordline voltage outputted by the high-voltage row decoding circuit of the present invention are inputted into the individual word selection circuits, which can likewise save two MOS transistors used for isolating the gate oxide layer in each of the word selection circuits, and therefore the present invention can simplify the circuit and reduce the cost. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The present invention will be further described below in detail with reference to drawings and specific embodiments: 
           [0027]      FIG. 1  is a diagram of an existing EEPROM memory cell gate control signal generating circuit; and 
           [0028]      FIG. 2  is a diagram of the EEPROM memory cell gate control signal generating circuit of the example of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    As shown in  FIG. 2 , it is a diagram of the EEPROM memory cell gate control signal generating circuit of the example of the present invention. The EEPROM memory cell gate control signal generating circuit of the example of the present invention includes: a high-voltage row decoding circuit  1  and a plurality of word selection circuits; for example, the word selection circuit  1  to n are marked with  21  to  2   n , respectively, wherein  2   i  marks the word selection circuit, with i being any digit from 1 to n. 
         [0030]    The high-voltage row decoding circuit  1  includes a first-part row decoding circuit composed of a first PMOS transistor P 0  and a second PMOS transistor P 1 , and a second-part row decoding circuit composed of a first NMOS transistor N 0  and a second NMOS transistor N 1 . 
         [0031]    The drain of the first PMOS transistor P 0  is connected to the drain of the second PMOS transistor P 1  to output a first total wordline voltage GWLS_P, the gate of the first PMOS transistor P 0  is connected to a first control signal X 2 SP, the gate of the second PMOS transistor P 1  is connected to a second control signal X 2 SPB, the source of the first PMOS transistor P 0  is connected to a third control signal OE-SP and the source of the second PMOS transistor P 1  is connected to a fourth control signal VDP the first total wordline voltage GWLS_P outputted by the first-part row decoding circuit is made to be one of the erasing positive voltage, i.e. VPOS, and levitation under the control of the first control signal X 2 SP, the second control signal X 2 SPB, the third control signal OE-SP and the fourth control signal VDP. 
         [0032]    The drain of the first NMOS transistor NO is connected to the drain of the second NMOS transistor N 1  to output a second total wordline voltage GWLS_N, the gate of the first NMOS transistor N 0  is connected to a fifth control signal X 2 SN, the gate of the second NMOS transistor N 1  is connected to a sixth control signal X 2 SNB, the source of the first NMOS transistor N 0  is connected to a seventh control signal OE_SN, and the source of the second NMOS transistor N 1  is connected to an eighth control signal VDN; the second total wordline voltage GWLS_N outputted by the second-part row decoding circuit is made to be one of the erasing negative voltage, i.e. VNEG, and levitation under the control of the fifth control signal X 2 SN, the sixth control signal X 2 SNB, the seventh control signal OE_SN and the eighth control signal VDN; the second total wordline voltage GWLS_N is levitated when the first total wordline voltage GWLS_P is the erasing positive voltage, the first total wordline voltage GWLS_P is levitated when the second total wordline voltage GWLS_N is the erasing negative voltage. 
         [0033]    A wordline of each memory cell of EEPROM is connected to one of the word selection circuits, which are the same in structure; taking the word selection circuit i marked with  2   i  as an example, each of the word selection circuits includes a third PMOS transistor P 4   i , a third NMOS transistor N 4   i , a fourth NMOS transistor N 6   i  and a fifth NMOS transistor N 5   i.    
         [0034]    The drain of the third PMOS transistor P 4   i , the drain of the third NMOS transistor N 4   i  and the drain of the fourth NMOS transistor N 6   i  are connected together to output the wordline voltage WLSi, which is inputted into a wordline of the corresponding memory cell. 
         [0035]    The source of the third PMOS transistor P 4   i  is connected to the first total wordline voltage GWLS_P, the source of the third NMOS transistor N 4   i  is connected to the second total wordline voltage GWLS_N, the source of the fourth NMOS transistor N 6   i  is connected to the drain of the fifth NMOS transistor N 5   i , and the source of the fifth NMOS transistor N 5   i  is connected to the ground VSS. 
         [0036]    The gate of the third PMOS transistor P 4   i  is connected to a ninth control signal BSPBi, the gate of the third NMOS transistor N 4   i  is connected to a tenth control signal BSNi, the gate of the fourth NMOS transistor N 6   i  is connected to the working voltage VDD, and the gate of the fifth NMOS transistor N 5   i  is connected to an eleventh control signal BDN; the wordline voltage WLSi is made to output one of the erasing negative voltage, erasing positive voltage and ground VSS under the control of the ninth control signal BSPBi, the tenth control signal BSNi and the eleventh control signal BDN. 
         [0037]    Preferably, the first control signal X 2 SP, the second control signal X 2 SPB, the third control signal OE_SP and the fourth control signal VDP are all switched between the ground VSS and the erasing positive voltage. The first control signal X 2 SP and the second control signal X 2 SPB are just mutually inverting. 
         [0038]    The fifth control signal X 2 SN, the sixth control signal X 2 SNB, the seventh control signal OE_SN and the eighth control signal VDN are all switched between the working voltage VDD and the erasing negative voltage. The fifth control signal X 2 SP and the sixth control signal X 2 SPB are just mutually inverting. 
         [0039]    The ninth control signal BSPBi is switched between the ground VSS and the erasing positive voltage, the tenth control signal BSNi is switched between the working voltage VDD and the erasing negative voltage, and the eleventh control signal BDN is switched between the working voltage VDD and the erasing negative voltage. 
         [0040]    When one of the memory cells of EEPROM is selected, the ninth control signal BSPBi of the word selection circuit to which this memory cell corresponds is connected to the ground VSS, the tenth control signal BSNi is connected to the working voltage VDD, the eleventh control signal BDN is connected to the erasing negative voltage, and the wordline voltage WLSi is either the erasing negative voltage or the erasing positive voltage. 
         [0041]    When one of the memory cells of EEPROM is not selected, the ninth control signal BSPBi of the word selection circuit to which this memory cell corresponds is connected to the erasing positive voltage, the tenth control signal BSNi is connected to the erasing negative voltage, the eleventh control signal BDN is connected to the working voltage VDD, and the wordline voltage WLSi is the ground VSS. 
         [0042]    The erasing positive voltage, i.e. VPOS, is used during programming for being applied to the gate of the selected memory cell and programming this selected memory cell, and also used during erasing for being applied to the gate of the unselected memory cell in the same column with the selected memory cell and preventing the unselected memory cell in the same column with the selected memory cell from being erased; the erasing negative voltage, i.e. VNEG, is used during erasing for being applied to the gate of the selected memory cell and erasing the selected memory cell, and also used during programming for being applied to the gate of the unselected memory cell in the same column with the selected memory cell and preventing the unselected memory cell in the same column with the selected memory cell from being programmed. The erasing positive voltage is greater than the working voltage VDD. 
         [0043]    In a preferred example, the individual control signals of the high-voltage row decoding circuit  1  can take the values shown in Table 2: 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 X2SP 
                 X2SPB 
                 X2SN 
                 X2SNB 
                 OE_SP 
                 OE_SN 
                 VDP 
                 VDN 
                 GWLS_P 
                 GWLS_N 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Erasing 
                 VSS 
                 VPOS 
                 VDD 
                 VNEG 
                 VSS 
                 VNEG 
                 VPOS 
                 VDD 
                 Levitation 
                 VNEG 
               
               
                   
                 VSS 
                 VPOS 
                 VDD 
                 VNEG 
                 VPOS 
                 VDD 
                 VPOS 
                 VDD 
                 VPOS 
                 Levitation 
               
               
                   
                 VPOS 
                 VSS 
                 VNEG 
                 VDD 
                 VPOS 
                 VDD 
                 VPOS 
                 VDD 
                 VPOS 
                 Levitation 
               
               
                   
                 VPOS 
                 VSS 
                 VNEG 
                 VDD 
                 VSS 
                 VNEG 
                 VPOS 
                 VDD 
                 VPOS 
                 Levitation 
               
               
                 Programming 
                 VSS 
                 VPOS 
                 VDD 
                 VNEG 
                 VPOS 
                 VDD 
                 VSS 
                 VNEG 
                 VPOS 
                 Levitation 
               
               
                   
                 VSS 
                 VPOS 
                 VDD 
                 VNEG 
                 VSS 
                 VNEG 
                 VSS 
                 VNEG 
                 Levitation 
                 VNEG 
               
               
                   
                 VPOS 
                 VSS 
                 VNEG 
                 VDD 
                 VSS 
                 VNEG 
                 VSS 
                 VNEG 
                 Levitation 
                 VNEG 
               
               
                   
                 VPOS 
                 VSS 
                 VNEG 
                 VDD 
                 VPOS 
                 VDD 
                 VSS 
                 VNEG 
                 Levitation 
                 VNEG 
               
               
                   
               
             
          
         
       
     
         [0044]    In a preferred example, the individual control signals of the individual word selection circuits can take the values shown in Table 3: 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 BSPB 
                 BSN 
                 BDN 
                 WLS 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 A word selection circuit 
                 VSS 
                 VDD 
                 VNEG 
                 VPOS or VNEG 
               
               
                 in the same column with 
               
               
                 the selected word 
               
               
                 A word selection circuit 
                 VPOS 
                 VNEG 
                 VDD 
                 VSS 
               
               
                 in a column not the same 
               
               
                 with the selected word 
               
               
                   
               
             
          
         
       
     
         [0045]    The memory cell of EEPROM in the example of the present invention is an SONOS transistor. 
         [0046]    It can be known from  FIG. 2  that, the present invention connects the first total wordline voltage GWLS_P and the second total wordline voltage GWLS_N separately; because the first total wordline voltage GWLS_P is used for outputting VPOS, VPOS will not influence the gate oxide layer of the first NMOS transistor NO, the second NMOS transistor N 1  and the third NMOS transistor N 4   i ; likewise, because the second total wordline voltage GWLS_N is used for outputting VNEG, VNEG will not influence the gate oxide layer of the first PMOS transistor P 0 , the second PMOS transistor P 1  and the third PMOS transistor P 4   i ; therefore, compared with the existing circuit in  FIG. 1 , the example of the present invention can save the MOS transistor used for isolating the gate oxide layer, thus simplifying the circuit and reducing the cost. 
         [0047]    The present invention is described above in detail through specific examples, which, however, do not restrict the present invention. Without departing from the principle of the present invention, those skilled in the art may also make many variations and improvements, which should also be considered to be within the scope of protection of the present invention.