Abstract:
A boost circuit, such as might be used to generate a boosted voltage in an integrated circuit device (e.g., an EEPROM), includes a plurality of charge pump circuits having outputs connected in common and that generate current pulses responsive to respective phased periodic signals. The boost circuit further includes a multi-phase periodic signal generator circuit that generates the phased periodic signals such that they have respective different phases. For example, the multi-phase periodic signal generator circuit may include a control signal generator circuit that produces a control signal responsive to a voltage produced by the plurality of charge pump circuits, and an oscillator circuit that generates the plurality of phased periodic signals responsive to the control signal. Related operating methods are described.

Description:
RELATED APPLICATION 
     This application claims priority to Korean Application No. 2001-3889, filed Jan. 27, 2001, the disclosure of which is hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to integrated circuits and methods of operation thereof, and more particularly, to boost circuits and methods of operating thereof. 
     Many integrated circuit devices internally utilize higher voltages than are supplied by an external power source. For example, a memory device, such as an electrically erasable and programmable read-only memory (EEPROM) or flash EEPROM, may use a higher reading voltage than is supplied by the power supply voltage applied to the memory device. This high voltage is typically generated by a voltage boost circuit (or multiplier) integrated with the memory circuit. 
     Many conventional voltage boost circuits use a charge pump that charges a capacitor to develop a boosted voltage. The size of the capacitor is typically determined by the frequency of an available internal clock signal used to operate the charge pump. For example, if the frequency of the internal clock signal is relatively low, an off-chip capacitor having a large capacitance may be required to achieve the desired voltage boost. 
     If an off-chip capacitor is used for the voltage boost circuit, the potential at the chip pad that forms a junction between the chip and the capacitor may become higher than a source voltage supplied to the chip. This may necessitate use of an additional circuit attached to the chip pad. Also, if the voltage boost circuit operates in a frequency range lower or higher than the designed frequency, the boosted voltage value may be changed. 
     Some conventional voltage boost circuits include an oscillator circuit that receives an external control signal and generates an internal clock signal, and a charge pump circuit that receives the internal clock signal and generates a boosted voltage responsive thereto. Some conventional voltage boost circuits may not control the boosted output voltage particularly well, and may produce unacceptable voltage ripple. 
     SUMMARY OF THE INVENTION 
     According to some embodiments of the present invention, a boost circuit, such as might be used to generate a boosted voltage in an integrated circuit device, (e.g., an EEPROM) is provided. The boost circuit includes a plurality of charge pump circuits having outputs connected in common and that generate current pulses responsive to respective phased periodic signals. The boost circuit further includes a multi-phase periodic signal generator circuit that generates the phased periodic signals such that they have respective different phases. In particular, the multi-phase periodic signal generator circuit may generate the phased periodic signals such that current pulses produced by the plurality of charge pump circuits are distributed over a repeating cycle. 
     In some embodiments, the multi-phase input signal generator circuit comprises a control signal generator circuit that produces a control signal responsive to a voltage produced by the plurality of charge pump circuits, and an oscillator circuit that generates the plurality of phased periodic signals responsive to the control signal. For example, the control signal generator circuit may produce the control signal responsive to a comparison of the voltage to a desired value. In some embodiments, the control signal generator circuit produces a control voltage responsive to a comparison of the voltage produced by the plurality of charge pump circuits to a desired value, and the oscillator circuit comprises a voltage controlled oscillator circuit that varies a frequency of the phased periodic signals responsive to the control voltage. 
     Related operating methods are also described. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram illustrating a voltage boost circuit according to some embodiments of the present invention. 
     FIG. 2 is a schematic diagram illustrating a control signal generator circuit according to some embodiments of the present invention. 
     FIG. 3 is a schematic diagram illustrating a charge pump circuit according to some embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed 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 invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. Like numbers refer to like elements throughout. 
     Referring to FIG. 1, a voltage boost circuit  100  according to some embodiments of the present invention includes a control signal generator circuit  110 , an oscillator circuit  120 , and charge pump circuits  130 , 131 , . . . ,  132 . The control signal generator circuit  110  receives a boosted voltage VDD_HI and generates a control signal VCNT in response to a boost voltage select signal VDD_HI_SEL for controlling the value of the boosted voltage VDD_HI. The oscillator circuit  120  generates complementary pairs of internal clock signals ICK 1 , ICKB 1 , ICK 2 , ICKB 2 , . . . , ICKn, ICKBn in response to the control signal VCNT. The charge pump circuits  130 ,  131 , . . . ,  132  receive the pairs of internal clock signals ICK 1 , ICKBI, ICK 2 , ICKB 2 , . . . , ICKn, ICKBn and generate the boosted voltage VDD_HI responsively thereto. 
     The pairs of the internal clock signals ICK 1 , ICKB 1 , ICK 2 , ICKB 2 , . . . , ICKn, ICKBn have the same frequency but different phases. The oscillator circuit  120  controls frequency of the pairs of the internal clock signals ICK 1 , ICKB 1 , ICK 2 , ICKB 2 , . . . , ICKn, ICKBn responsive to the control signal VCNT generated by the control signal generator circuit  110 . For example, the control signal VCNT may be a voltage and the oscillator circuit  120  may be a conventional voltage controlled oscillator or ring oscillator. The pairs of internal clock signals ICK 1 , ICKB 1 , ICK 2 , ICKB 2 , . . . , ICKn, ICKBn are applied to the plurality of charge pump circuits  130 ,  131 , . . . ,  132 . Current pulses produced by the charge pump circuits  130 ,  131 , . . . ,  132  generate the boosted voltage VDD_HI by charging a capacitance (see FIG.  2 ). 
     The control signal generator circuit  110  raises the value of the control signal VCNT when the boosted voltage VDD_HI is lower than desired, thus increasing the frequency of the pairs of the internal clock signals ICK 1 , ICKB 1 , ICK 2 , ICKB 2 , . . . , ICKn, ICKBn. As the frequency of the pairs of the internal clock signals ICK 1 , ICKB 1 , ICK 2 , ICKB 2 , . . . , ICKn, ICKBn increases, the outputs of the charge pump circuits  130 ,  131 , . . . ,  132  increase, and the boosted voltage VDD_HI becomes higher. In contrast, if the boosted voltage (VDD_HI) is higher than desired, the value of the control signal (VCNT) is lowered, and the frequency of the pairs of the internal clock signals ICK 1 , ICKB 1 , ICK 2 , ICKB 2 , . . . , ICKn, ICKBn is decreased. If the frequency of the pairs of the internal clock signals ICK 1 , ICKB 1 , ICK 2 , ICKB 2 , . . . , ICKn, ICKBn is lowered, the outputs of the charge pump circuits  130 ,  131 , . . . ,  132  decrease, and the boosted voltage VDD_HI is lowered. The boosted voltage select signal VDD_HI_SEL represents the desired boosted voltage. 
     According to embodiments of the present invention illustrated in FIG. 2, the control signal generator circuit  110  includes a first variable resistor R 1 , a second resistor R 2 , a feedback network CF, RF, and a voltage divider circuit  220  that includes resistors RA, RB. One end of the first resistor R 1  is connected to the boosted voltage VDD_HI, and the other end is connected to an inverting terminal of a differential amplifier  210 . The resistance of the first resistor R 1  varies in response to the boosted voltage select signal VDD_HI_SEL. One end of the second resistor R 2  is connected to the inverting terminal of the differential amplifier  210 , and the other end is connected to ground VSS. The feedback network CF, RF is connected between the inverting terminal of the differential amplifier  210  and an output terminal of the differential amplifier  210 . The voltage divider circuit  220  includes resistors RA, RB connected in series between the source voltage VDD and the ground VSS, and applies a voltage derived from the source voltage VDD to a non-inverting terminal of the differential amplifier  210 . The control signal generator circuit  110  acts as a filter, in particular, as a low pass filter. 
     The voltage divider circuit  220  applies a voltage to the differential amplifier  210  that is dependent on the relative values of the resistors RA, RB. For example, if the source voltage is 5 volts and the ratio of the resistors RA, RB is 1:1, 2.5 volts is applied to the non-inverting terminal of the differential amplifier  210 . The first resistor R 1  is a variable resistor that is responsive to the boosted voltage select signal VDD_HI_SEL. For example, if the boosted voltage select signal VDD_HI_SEL is a digital signal, the resistance of the first resistor R 1  may be selected from one of several discrete resistance values. 
     According to embodiments of the present invention illustrated in FIG. 3, a charge pump circuit  130  includes inverters I 1 , I 2  for receiving and inverting a pair of internal clock signals ICK, ICKB having a complementary phase. Capacitors CP 1 , CP 2  are respectively connected to the inverters I 1 , I 2 . First and second NMOS transistors MN 1 , MN 2  are connected to the source voltage VDD and to capacitors CP 1 , CP 2  at nodes N 1 , N 2 . First and second PMOS transistors MP 1 , MP 2  are connected between the first and second nodes N 1 , N 2  and an output terminal  139  at which the boosted voltage VDD_HI is produced. A capacitor CWB is connected to the bulk regions of the first and second PMOS transistors MP 1 , MP 2 , and to the ground VSS, and a capacitor CS connected between the output terminal  139  and the ground VSS. Gates of the first NMOS transistor MN 1  and the first PMOS transistor MP 1  are connected to the second node N 2 . Gates of the second NMOS transistor MN 2  and the second PMOS transistor MP 2  are connected to the first node N 1 . 
     The inverters  11 ,  12  invert clock signals ICK, ICKB and apply the resultant signals to the capacitors CP 1 , CP 2 . The capacitor CWB prevents latch-up when the first and second PMOS transistors MP 1 , MP 2  operate. The capacitors CP 1 , CP 2  charge and discharge responsive to the clock signals ICK, ICKB. 
     The first and second NMOS transistors MN 1 , MN 2  and the first and second PMOS transistors MP 1 , MP 2  turn on or turn off according to voltage levels of the first and second nodes N 1 , N 2 . When the voltage level of the first node N 1  is high and the voltage level of the second node N 2  is low, the second NMOS transistor MN 2  and the first PMOS transistor MP 1  turn on, and the first NMOS transistor MN 1  and the second PMOS transistor MP 2  turn off. When the voltage level of the first node N 1  is low and the voltage level of the second node N 2  is high, the second NMOS transistor MN 2  and the first PMOS transistor MP 1  turn off and the first NMOS transistor MN 1  and the second PMOS transistor MP 2  turn on. Accordingly, the boosted voltage VDD_HI of the source voltage VDD level charged in the second node N 2  is applied to the capacitor CS. Here, the capacitor CS continuously charges and applies the boosted voltage VDD_HI to the output terminal. 
     The charge pump circuit  130  delivers current through the transistors MP 1 , MP 2  during half periods of the pair of the internal clock signals ICK, ICKB. Since the plurality of charge pump circuits  130 ,  131 , . . . ,  132  are connected in parallel and phased in their operation, the amount of charge pumped by each charge pump circuit  130 ,  131 , . . . ,  132  can be reduced and the amount of ripple of the boosted voltage VDD_HI can be reduced. 
     In the drawings and specification, there have been disclosed typical embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.