Patent Publication Number: US-10770153-B2

Title: Charge pump drive circuit with two switch signals

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of Chinese patent application number 201810327023.1, filed on Apr. 12, 2018, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to the field of semiconductor technology and, in particular, to a charge pump drive circuit. 
     BACKGROUND 
     A charge pump circuit is a basic block of a flash memory and greatly affects the flash memory&#39;s program/erase speed. The continuous advancement of integrated circuit (IC) fabrication technology and our relentless pursuit for lower power consumption lead to the development of ICs powered by increasingly lower supply voltages. 
     On the other hand, in flash memories, program/erase operations of a cell still require relatively high voltages. In such a context, more and more importance is being attached to charge pump circuits in the continuously-developing IC domain. Currently, charge pumps have become a focus of research efforts in the field of flash memory design. 
     A charge pump, also known as a switched-capacitor voltage converter, is a kind of DC to DC converter that uses so-called “flying” or “pumping” capacitors (rather than inductors or transformers) for energetic charge storage to raise, lower an input voltage or to produce a negative voltage. An internal field effect transistors (FET) switch array of the charge pump controls transfer of electric charges among the capacitors in a certain manner (usually, uses clock signals to control the charge/discharge of the capacitors) so that the input voltage is raised (or reduced) in a certain way to a desired output level. 
     When a memory is reading data, a charge pump therein provides the memory with a read current and a read voltage of about 5.5 V. Therefore, before the read operation begins, the charge pump needs to raise the voltage to 5.5 V to place the memory into a standby state. After the read operation commences, the memory switches to an active reading state. In the standby state, as the output voltage of the charge pump may experience drops due to leakage currents, a detection circuit is required to monitor the output voltage of the charge pump in real time so as to increase the output voltage when it drops below the read voltage. If the detection circuit is powered by a supply voltage of 5.5 V, it will require a relatively large current and thus consume a significant power. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a charge pump drive circuit which does not require a great current during a read standby state of a memory in which it is employed. 
     To this end, the present invention proposes a charge pump drive circuit for providing a charge pump with a switch signal, the charge pump providing a memory with a read voltage and a read current, the charge pump drive circuit comprising a read drive circuit and a standby drive circuit, wherein: 
     the read drive circuit is powered by a first power supply and provides the charge pump with a first switch signal when the memory is in a read active state; 
     the standby drive circuit is powered by a second power supply and provides the charge pump with a second switch signal when the memory is in a read standby state; and 
     the first power supply provides a voltage level ranging from 1.6 V to 3.8 V and the second power supply provides a voltage level of 1.5 V. 
     Optionally, the charge pump drive circuit may further comprise an OR gate having two inputs connected respectively to an output of the read drive circuit and an output of the standby drive circuit and an output connected to the charge pump. 
     Optionally, in the charge pump drive circuit, when the memory is in a writing, erasing or programming state, the read drive circuit may provide the charge pump with the first switch signal. 
     Optionally, the charge pump drive circuit may further comprise a first signal selection circuit and a second signal selection circuit, wherein: 
     the first signal selection circuit is provided with a first reference signal, a second reference signal and a selection signal; 
     the second signal selection circuit is provided with a first feedback voltage, a second feedback voltage and the selection signal; 
     the selection signal is dependent on the state of the memory; 
     when the memory is in the active reading state or the read standby state, the selection signal causes the first signal selection circuit to output the first reference signal and causes the second signal selection circuit to output the first feedback voltage; and 
     when the memory is in the writing, erasing or programming state, the selection signal causes the first signal selection circuit to output the second reference signal and causes the second signal selection circuit to output the second feedback voltage. 
     Optionally, the charge pump drive circuit may further comprise a first resistor network and a second resistor network, wherein: 
     each of the first resistor network and the second resistor network is connected between an output of the charge pump and a ground; and 
     the first feedback voltage is coupled to the first resistor network and the second feedback voltage is coupled to the second resistor network. 
     Optionally, in the charge pump drive circuit, the read drive circuit may comprise a first comparator and a first voltage controlled oscillator (VCO), wherein: 
     the first comparator has a non-inverting input connected to an output of the first signal selection circuit, an inverting input connected to an output of the second signal selection circuit and an output connected to an input of the first VCO; and the first VCO has an output serving as the output of the read drive circuit. 
     Optionally, in the charge pump drive circuit, the read drive circuit may further comprise two first switches, wherein: 
     the first power supply respectively powers the first comparator and the first VCO via the two first switches, and 
     the first switches are opened or closed under the control of a first switch signal. 
     Optionally, in the charge pump drive circuit, the standby drive circuit may comprise a second comparator and a second VCO, wherein: 
     the second comparator has a non-inverting input connected to an output of the first signal selection circuit, an inverting input connected to an output of the second signal selection circuit and an output connected to an input of the second VCO; and the second VCO has an output connected to the output of the standby drive circuit. 
     Optionally, in the charge pump drive circuit, the standby drive circuit may further comprise two second switches, wherein: 
     the second power supply respectively powers the second comparator and the second VCO via the two second switches; and 
     the second switches are opened or closed under control of a second switch signal. 
     Optionally, the charge pump drive circuit may further comprise an electrical level shifting circuit connected between the output of the second VCO and one of the inputs of the OR gate. 
     The present invention proposes a charge pump drive circuit for providing a charge pump with a switch signal, the charge pump configured to provide a memory with a read voltage and a read current, the charge pump drive circuit comprising a read drive circuit, a standby drive circuit and an OR gate, wherein: 
     the read drive circuit is powered by a first power supply and provides a first switch signal for the charge pump when the memory is in a read active state; 
     the standby drive circuit is powered by a second power supply and provides a second switch signal for the charge pump when the memory is in a read standby state; 
     the OR gate has two inputs connected respectively to an output of the read drive circuit and an output of the standby drive circuit and an output connected to the charge pump; and 
     the first power supply provides a voltage level ranging from 1.6 V to 3.8 V and the second power supply provides a constant voltage lower than the first power supply. 
     Optionally, in the charge pump drive circuit, when the memory is in a writing, erasing or programming state, the read drive circuit may provide the first switch signal for the charge pump. 
     Optionally, the charge pump may further comprise a first signal selection circuit and a second signal selection circuit, wherein: 
     the first signal selection circuit is provided with a first reference signal, a second reference signal and a selection signal; 
     the second signal selection circuit is provided with a first feedback voltage, a second feedback voltage and the selection signal; 
     the selection signal is dependent on the state of the memory; 
     when the memory is in the read active state or the read standby state, the selection signal causes the first signal selection circuit to output the first reference signal and causes the second signal selection circuit to output the first feedback voltage; and 
     when the memory is in the writing, erasing or programming state, the selection signal causes the first signal selection circuit to output the second reference signal and causes the second signal selection circuit to output the second feedback voltage. 
     Optionally, the charge pump drive circuit may comprise a first resistor network and a second resistor network, wherein: 
     each of the first resistor network and the second resistor network is connected between an output of the charge pump and a ground; and 
     the first feedback voltage is coupled to the first resistor network and the second feedback voltage is coupled to the second resistor network. 
     Optionally, in the charge pump drive circuit, the read drive circuit comprises a first comparator and a first voltage controlled oscillator (VCO), 
     the first comparator having a non-inverting input connected to an output of the first signal selection circuit, 
     the first comparator having an inverting input connected to an output of the second signal selection circuit, 
     the first comparator having an output connected to an input of the first VCO, the first VCO having an output serving as the output of the read drive circuit. 
     Optionally, in the charge pump drive circuit, the read drive circuit further comprises two first switches, 
     wherein the first power supply respectively powers the first comparator and the first VCO via the two first switches, 
     and wherein the first switches are opened or closed under control of a first switch signal. 
     Optionally, in the charge pump drive circuit, the standby drive circuit comprises a second comparator and a second VCO, 
     the second comparator having a non-inverting input connected to an output of the first signal selection circuit, 
     the second comparator having an inverting input connected to an output of the second signal selection circuit, 
     the second comparator having an output connected to an input of the second VCO, the second VCO having an output serving as the output of the standby drive circuit. 
     Optionally, in the charge pump drive circuit, the standby drive circuit further comprises two second switches, 
     wherein the second power supply respectively powers the second comparator and the second VCO via the two second switches, 
     and wherein the second switches are opened or closed under control of a second switch signal. 
     Optionally, the charge pump drive circuit may further comprise an electrical level shifting circuit connected between the output of the second VCO and one of the inputs of the OR gate. 
     In the charge pump drive circuit of the present invention, when the memory is in the read standby state, the standby drive circuit is powered by the second power supply and provides the charge pump with a switch signal. Additionally, the first power supply provides a voltage level ranging from 1.6 V to 3.8 V, and the second power supply provides a voltage level of 1.5 V. Powering the standby drive circuit with the constant lower level (1.5 V) provided by the second power supply in the read standby state enables the operation in the standby state at a current maintained at a minimized level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a charge pump drive circuit according to an embodiment of the present invention. 
         FIG. 2  schematically illustrates waveforms of various signals in a charge pump drive circuit according to another embodiment of the present invention. 
     
    
    
     In these figures:  10 , denotes a charge pump;  20 , a read drive circuit;  21 , a first VCO;  30 , a standby drive circuit;  31 , a second VCO;  40 , a first signal selection circuit;  50 , a second signal selection circuit;  60 , a first resistor network;  70 , a second resistor network; and  80 , a level shifting circuit. 
     DETAILED DESCRIPTION 
     The charge pump drive circuit constructed in accordance with this invention will be described below in further detail with reference to the accompanying drawings and specific embodiments. Features and advantages of the invention will be more apparent from the following detailed description, and from the appended claims. It is noted that the figures are provided in a very simplified form not necessarily presented to scale, with the only intention to facilitate convenience and clarity in explaining the embodiments of the invention. 
     The core concept of the present invention is to provide a charge pump drive circuit which does not require a great current during a read standby state of a memory in which it is employed. 
     To this end, the present invention provides a charge pump drive circuit for providing a switch signal to a charge pump which provides a memory with a read voltage and a read current. The charge pump drive circuit comprises a read drive circuit and a standby drive circuit. The read drive circuit is powered by a first power supply and provides the charge pump with the switch signal when the memory is in an active reading state. The standby drive circuit is powered by a second power supply and provides the charge pump with the switch signal when the memory is in a read standby state. The first power supply provides a voltage level ranging from 1.6 V to 3.8 V and the second power supply provides a voltage level of 1.5 V. 
       FIG. 1  is a schematic illustration of a charge pump drive circuit according to an embodiment of the present invention, for providing a charge pump  10  with a switch signal. The charge pump  10  provides a memory with a read voltage and a read current. The charge pump drive circuit comprises a read drive circuit  20  and a standby drive circuit  30 . The read drive circuit  20  is powered by a first power supply VCC and provides the charge pump  10  with the switch signal when the memory is in the read active state. The standby drive circuit  30  is powered by a second power supply VDD and provides the charge pump  10  with the switch signal when the memory is in the read standby state. The first power supply VCC provides a voltage level ranging from 1.6 V to 3.8 V and the second power supply VDD provides a voltage level of 1.5 V. 
     As shown in  FIG. 1 , the charge pump drive circuit may further comprise an OR gate U 3  having two inputs connected respectively to an output of the read drive circuit  20  and an output of the standby drive circuit  30  and an output connected to the charge pump  10 . 
     Specifically, the charge pump drive circuit may further comprise a first signal selection circuit  40  and a second signal selection circuit  50 . The first signal selection circuit  40  is provided with a first reference signal ref 1 , a second reference signal ref 2  and a selection signal READ, and the second signal selection circuit  50  is provided with a first feedback voltage fb 1 , a second feedback voltage fb 2  and the selection signal READ. The charge pump drive circuit may further comprise a first resistor network  60  and a second resistor network  70 . Each of the first resistor network  60  and the second resistor network  70  is connected between an output of the charge pump  10  which outputs a voltage of Vppi and the ground. The first feedback voltage fb 1  is coupled to the first resistor network  60 , and the second feedback voltage fb 2  is coupled to the second resistor network  70 . 
     In the read active state or the read standby state of the memory (with the selection signal READ at a high level), the selection signal READ may cause the first signal selection circuit  40  to output the first reference signal ref 1  and cause the second signal selection circuit  50  to output the first feedback voltage fb 1 . The first reference signal ref 1  may be a constant-value signal provided by a band-gap reference circuit. In case of the first resistor network  60  consisting of five resistors R, with the first feedback voltage fb 1  being coupled to a node preceding the last resistor R and with Vppi being exactly of 5.5 V, the first feedback voltage should be 1.1 V, i.e., first reference signal ref 1  should be provided by the band-gap reference circuit with an output voltage of 1.1 V. When the memory is in the writing, erasing or programming state (with the selection signal READ at a low voltage level and inverted with respect to a mode signal), the selection signal READ may cause the first signal selection circuit  40  to output the second reference signal ref 2  and cause the second signal selection circuit  50  to output the second feedback voltage fb 2 . The second reference signal ref 2  may be generated by dividing the first reference signal ref 1  and therefore its level is usually lower than that of the first reference signal ref 1 . The division may depend on practical needs. For example, it may be determined by a required level of the output voltage Vppi and the number of resistors in the second resistor network  70 . In case of the second feedback voltage fb 2  being coupled to a node preceding the last resistor R in the second resistor network  70 , the second feedback voltage will be equal to Vppi divided by the number of the resistors in the second resistor network  70 . 
     Additionally, in the charge pump drive circuit, the read drive circuit  20  may include a first comparator U 1  and a voltage controlled oscillator (VCO)  21 . The first comparator has a non-inverting input connected to an output of the first signal selection circuit  40 , an inverting input connected to an output of the second signal selection circuit  50  and an output connected to an input of the first VCO  21 . The first VCO  21  has an output serving as the output of the read drive circuit  20 . The read drive circuit  20  may further include two first switches EN 1  through which the first power supply VCC respectively powers the first comparator U 1  and the first VCO  21 . As shown in  FIG. 2 , the first switches EN 1  may be opened or closed under the control of a first switch signal EN 1 . A waveform of the first switch signal EN 1  is shown in  FIG. 2 . The first switches may be closed at a high level of the first switch signal EN 1  and opened at a low level thereof. The standby drive circuit  30  may include a second comparator U 2  and a second VCO  31 . The second comparator U 2  has a non-inverting input connected to the output of the first signal selection circuit  40 , an inverting input connected to the output of the second signal selection circuit  50  and an output connected to an input of the second VCO  31 . The second VCO  31  has an output serving as the output of the standby drive circuit  30 . The standby drive circuit  30  may further include two second switches EN 2  through which the second power supply VDD respectively powers the second comparator U 2  and the second VCO  31 . The second switches EN 2  may be opened or closed under the control of a second switch signal EN 2 . A waveform of the second switch signal EN 2  is shown in  FIG. 2 . The second switches may be closed at a high level of the second switch signal EN 2  and opened at a low level thereof. The first switch signal EN 1  and second switch signal EN 2  do not overlap in time. That is, the read drive circuit and standby drive circuit do not provide the switch signals to the charge pump at the same time. 
     When the memory is in the writing, erasing or programming state, the read drive circuit  20  provides the charge pump  10  with the switch signal. As shown in  FIG. 2 , when the mode signal is at a high level, the memory is in the writing, erasing or programming state. At this point, the signal EN 1  is at the high level, causing the first switches EN 1  to be closed. As a result, the first power supply VCC powers the first comparator U 1  and the first VCO  21 . At the same time, the signal EN 2  is at the low voltage level, causing the second switches EN 2  to be opened. Consequently, the second power supply VDD cannot power the second comparator U 2  and the second VCO  31 . The charge pump drive circuit may further include an electrical level shifting circuit  80  connected between the output of the second VCO  31  and the input of the OR gate U 3 . The electrical level shifting circuit  80  is configured to shift the second power supply VDD at its input to the first power supply VCC and provide it to the OR gate, in order to ensure a full response of the OR gate U 3 . 
     When the first switch signal EN 1  is at the high level concurrently with the second switch signal EN 2  at the low level, VCC is activated while VDD is not. When in the read active state, the first comparator U 1  outputs an analog voltage signal based on the first reference signal ref 1  and the first feedback voltage fb 1 . When in the writing, erasing, programming or another state, the first comparator U 1  outputs the analog voltage signal based on the second reference signal ref 2  and the second feedback voltage fb 2 . The analog voltage signal controls a pulse frequency which is output by the first VCO  21  and the pulse frequency, in turn, controls the amplitude of the output voltage of the charge pump. At this point, the charge pump will require an additional drive current which may, when large in magnitude, cause a decrease in the output voltage. So, it is necessary to prevent this from happening. 
     When the first switch signal EN 1  is at the low level concurrently with the second switch signal EN 2  at the high level, VDD is activated while VCC is not. As a result, the memory will be certainly in the read standby state, in which the second comparator U 2  outputs, based on the first reference signal and the first feedback voltage, a single-pulse signal which controls the second VCO  31  to output another single-pulse signal and slightly increases the amplitude of the output voltage of the charge pump with the aid of the OR gate U 3 . At this point, the only thing needed is to boost the output voltage. 
     In the charge pump drive circuit of the present invention, when the memory is in the read standby state, the standby drive circuit  30  is powered by the second power supply VDD and provides the charge pump  10  with the switch signal. Additionally, the first power supply VCC provides a voltage level ranging from 1.6 V to 3.8 V, and the second power supply provides a voltage level of 1.5 V. Powering the standby drive circuit  30  with the constant lower voltage level (1.5 V) provided by the second power supply VDD in the read standby state enables the operation in the standby state at a current maintained at a minimized level. 
     In summary, various configurations of the charge pump drive circuit have been detailed in the above embodiments. Of course, the present invention includes, but not limited to, the configurations disclosed above, and any and all modifications made to these configurations are considered to fall within the scope of the invention. Those skilled in the art can extend the inventive ideas in many ways. 
     The description presented above is merely that of a few preferred embodiments of the present invention and does not limit the scope thereof in any sense. Any and all changes and modifications made by those of ordinary skill in the art based on the above teachings fall within the scope as defined in the appended claims.