Negative voltage generator

Abstract

A circuit capable of generating a negative voltage on a negative voltage supply node. The circuit comprises a negative voltage generation circuit, an oscillator and an oscillator control signal generator. The negative voltage generation circuit generates a negative voltage on a negative voltage supply node in response to receiving a signal from the oscillator. The negative voltage generated by the negative voltage generation circuit depends on the frequency of the signal from the oscillator. The oscillator controls the signal generator to control the frequency of the signal from the oscillator by sensing a negative voltage present on the negative voltage supply node and correspondingly increasing or decreasing the frequency of the signal from the oscillator. Thus, charge is supplemented to the negative voltage supply node to more closely match the draw of charge from the negative voltage supply node, thereby more accurately generating the negative voltage.

Description

Background Art

[0001] Electronic circuits are made up of various electronic components, such as resistors, capacitors, inductors, diodes, transistors, operational amplifiers, and / or other types of analog or digital electronic components. These components are selected and connected together so that the circuit performs a specific function. For example, circuits are often used to perform amplification, calculation, power transmission, communication, etc.

[0002] Although circuits can be composed of discrete components connected together via wires, some circuits have recently been constructed in an integrated manner using semiconductor materials and semiconductor processing techniques. Specifically, integrated circuits can be manufactured by performing semiconductor processing steps to epitaxially grow various semiconductor layers on a substrate (e.g., via chemical vapor deposition, physical vapor deposition, or other epitaxial growth processes). As these layers are deposited, the layers are also patterned, for example, via photolithography, etching, and other processes. By applying a variety of semiconductor processing techniques, integrated circuits are effectively grown on a substrate and are typically solid-state electronic devices. Therefore, the circuits so manufactured are called "integrated circuits."

[0003] Typically, power is supplied to an integrated circuit via a conductive terminal (e.g., a pad or pin, etc.). For example, an integrated circuit typically includes a ground terminal that makes a common ground (also referred to as Vss) available throughout the integrated circuit. In addition, a common power supply voltage (also referred to as Vdd) is available throughout the integrated circuit by applying a designed power supply voltage to the power supply terminal of the integrated circuit.

[0004] However, in some cases, the integrated circuit may include electronic components that operate using negative voltages. Thus, the integrated circuit may be designed to be able to receive a negative voltage from an external negative voltage source via one or more external pins. For example, an inductor-based inverting voltage converter (e.g., an inverting buck converter, an inverting boost converter, an inverting buck-boost converter, or an inverting A negative voltage supply external to the integrated circuit can be generated by using a transformer (e.g., using an isolation topology or an auxiliary winding).

[0005] The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in the above-described environment. Rather, this background is merely provided to illustrate one exemplary technology area where some embodiments described herein may be practiced. Summary of the invention

[0006] This Summary is provided to introduce some concepts in a simplified form that are further described in the Detailed Description below. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0007] Embodiments described herein relate to a circuit capable of internally generating a negative voltage on a negative voltage supply node. As a specific example, a negative voltage may be applied to a gate terminal of a field effect transistor to ensure that the field effect transistor remains off even if the supply voltage drops below ground.

[0008] The circuit includes a negative voltage generating circuit, an oscillator, and an oscillator control signal generator. The negative voltage generating circuit generates a negative voltage on a negative voltage power supply node in response to receiving an oscillation signal from the oscillator. The negative voltage generated by the negative voltage generating circuit depends on the frequency of the oscillation signal from the oscillator and on the load driven by the negative voltage. The oscillator control signal generator controls the frequency of the oscillation signal from the oscillator by sensing the negative voltage present on the negative voltage power supply node and setting the frequency of the oscillation signal accordingly.

[0009] For example, if the negative value of the negative voltage is greater than the negative value it should be, and the oscillation signal is at a higher frequency, the frequency can be adjusted to a lower frequency, thereby also reducing the operating frequency of the negative voltage generating circuit. This lower operating frequency allows the negative value of the negative voltage to be smaller. On the other hand, if the negative value of the negative voltage is less than the negative value it should be, and the oscillation signal is at a lower frequency, the frequency can be adjusted to a higher frequency, thereby also increasing the operating frequency of the negative voltage generating circuit. This higher operating frequency causes the negative value of the negative voltage to be larger.

[0010] Therefore, when the charge is quickly drawn from the negative voltage power supply node, the oscillator control signal generator can increase the frequency of the oscillator, so that the negative voltage generating circuit replenishes the charge more quickly. On the other hand, when the charge is slowly drawn from the negative voltage power supply node, the oscillator control signal generator circuit can reduce the frequency of the oscillator, so that the negative voltage generating circuit replenishes the charge more slowly. In any case, the oscillator frequency is more closely matched to the charge on the negative voltage power supply node, thereby more accurately controlling the negative voltage on the negative voltage power supply node.

[0011] Additional features and advantages will be set forth in the following description, and some features and advantages will be apparent from the description, or may be learned by practicing the teachings herein. The features and advantages of the present invention may be realized and obtained by the instruments and combinations particularly pointed out in the appended claims. The features of the present invention will become more apparent from the following description and the appended claims, or may be learned by practicing the present invention as described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to describe the manner in which the advantages and features of the principles described herein may be obtained, a more particular description will be given by reference to specific embodiments, which are illustrated in the accompanying drawings. Understanding that these drawings depict only typical embodiments of the principles described herein and are therefore not to be considered limiting of their scope, certain embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:

[0013] Figure 1 A circuit that can implement the principles described herein is shown, which is only one example of a circuit consistent with the principles described herein;

[0014] Figure 2 shows a charge pump, which is Figure 1 An example of a negative voltage generating circuit;

[0015] Figure 3 An oscillator control signal generator is shown. Figure 1 An example of an oscillator control signal generator;

[0016] Figure 4 shows a circuit which is Figure 1 An example of a circuit of; and

[0017] Figure 5 shows a signal diagram showing the Figure 4 An example of a signal generated by the operation of the circuit. DETAILED DESCRIPTION

[0018] Embodiments described herein relate to a circuit capable of internally generating a negative voltage on a negative voltage supply node. As a specific example, a negative voltage may be applied to a gate terminal of a field effect transistor to ensure that the field effect transistor remains off even if the supply voltage drops below ground.

[0019] The circuit includes a negative voltage generating circuit, an oscillator, and an oscillator control signal generator. The negative voltage generating circuit generates a negative voltage on a negative voltage power supply node in response to receiving an oscillation signal from the oscillator. The negative voltage generated by the negative voltage generating circuit depends on the frequency of the oscillation signal from the oscillator and on the load driven by the negative voltage. The oscillator control signal generator controls the frequency of the oscillation signal from the oscillator by sensing the negative voltage present on the negative voltage power supply node and setting the frequency of the oscillation signal accordingly.

[0020] For example, if the negative value of the negative voltage is greater than the negative value it should be, and the oscillation signal is at a higher frequency, the frequency can be adjusted to a lower frequency, thereby also reducing the operating frequency of the negative voltage generating circuit. This lower operating frequency allows the negative value of the negative voltage to be smaller. On the other hand, if the negative value of the negative voltage is less than the negative value it should be, and the oscillation signal is at a lower frequency, the frequency can be adjusted to a higher frequency, thereby also increasing the operating frequency of the negative voltage generating circuit. This higher operating frequency causes the negative value of the negative voltage to be larger.

[0021] Therefore, when the charge is quickly drawn from the negative voltage power supply node, the oscillator control signal generator can increase the frequency of the oscillator, so that the negative voltage generating circuit replenishes the charge more quickly. On the other hand, when the charge is slowly drawn from the negative voltage power supply node, the oscillator control signal generator circuit can reduce the frequency of the oscillator, so that the negative voltage generating circuit replenishes the charge more slowly. In any case, the oscillator frequency is more closely matched to the charge on the negative voltage power supply node, thereby more accurately controlling the negative voltage on the negative voltage power supply node.

[0022] Figure 1 A circuit 100 is shown that can implement the principles described herein, which is only one example of a circuit consistent with the principles described herein. The circuit 100 is configured to provide a negative voltage to a negative voltage supply node 101. The negative voltage on the negative voltage supply node 101 can be used to power components such as field effect transistors (not shown). However, the principles described herein are not limited to the type of components that receive power from the negative voltage supply node 101 or the reason for generating a negative voltage on the negative voltage supply node 101.

[0023] The circuit 100 includes a negative voltage generating circuit 110, an oscillator 120, and an oscillator control signal generator 130. The negative voltage generating circuit 110 generates a negative voltage on a negative voltage power supply node 101 in response to receiving an oscillation signal from the oscillator 120. The oscillation signal may be a sinusoidal signal having a specific frequency. Alternatively, the oscillation signal may be another AC signal (e.g., a square wave) having a fundamental frequency. In either case, the signal will be referred to as an "oscillation signal," and the "frequency" of the oscillation signal refers to the fundamental frequency of the oscillation signal.

[0024] The negative voltage generated by the negative voltage generating circuit 110 depends on the frequency of the oscillation signal from the oscillator 120 (although the negative voltage may also depend on other factors, such as the charge usage rate on the negative voltage power supply node 101). The oscillator control signal generator 130 controls the frequency of the oscillation signal from the oscillator 120 by sensing the negative voltage present on the negative voltage power supply node 101 and setting the frequency of the oscillation signal accordingly. This process of controlling the frequency of the oscillation signal based on the negative voltage present on the negative voltage power supply node 101 can occur continuously, so that the oscillator control signal generator 130 continuously senses the negative voltage and continuously sets the frequency of the oscillation signal accordingly. Alternatively, the process can occur less continuously, so that the oscillator control signal generator 130 only periodically samples the negative voltage power supply node 101 and then periodically sets the frequency of the oscillation signal accordingly.

[0025] exist Figure 1 , arrow line 141 indicates that the negative voltage generating circuit 110 generates a negative voltage on the negative voltage power supply node 101, and indicates that the oscillator control signal generator 130 senses the negative voltage on the negative voltage power supply node 101. In addition, arrow line 142 indicates that the oscillator control signal generator 130 outputs an oscillator control signal to the oscillator 120, thereby setting the frequency of the oscillation signal from the oscillator 120. Finally, arrow line 143 indicates that the oscillator 120 outputs an oscillation signal having a specific frequency to the negative voltage generating circuit 110, thereby causing the negative voltage generating circuit 110 to output a negative voltage to the negative voltage power supply node 101.

[0026] As an example, assume that the function of the circuit 100 is to ideally generate a specific negative voltage (also referred to herein as a "specified negative voltage") on the negative voltage power supply node 101. It is also assumed that the presence of a voltage with a negative value less than the specified negative voltage will indicate a higher frequency of the oscillation signal is guaranteed, and the presence of a voltage with a negative value greater than the specified negative voltage will indicate a lower frequency of the oscillation signal is guaranteed. In this case, if the oscillator control signal generator 130 senses that the negative value of the negative voltage on the negative voltage power supply node 101 is less than the specified negative voltage, the oscillator control signal generator 130 can ensure that the oscillation signal from the oscillator 120 is at a higher frequency. Therefore, the operating frequency of the negative voltage generating circuit 110 is also high, which causes the negative value of the negative voltage on the negative voltage power supply node 101 to be larger (because negative charge is provided on the negative voltage power supply node 101 faster than the load draws negative charge). In the case where the negative voltage generating circuit 110 is a charge pump, this can be achieved by increasing the rate at which negative charge is pumped to the negative voltage power supply node 101.

[0027] As a specific example, if the specified negative voltage is negative 3 volts, and the oscillator control signal generator 130 senses that the negative voltage on the negative voltage power supply node 101 is only negative 2.6 volts, the oscillator control signal generator 130 will ensure that the frequency of the oscillation signal from the oscillator 120 is at a higher frequency. Therefore, the operating frequency of the negative voltage generating circuit 110 will also be at a higher frequency, thereby causing the negative voltage on the negative voltage power supply node 101 to be closer to negative 3 volts.

[0028] For example, if the circuit 100 has just been powered on, and the negative voltage generating circuit 110 has not had time to completely reduce the negative voltage on the negative voltage supply node 101 to approximately the specified negative voltage, the negative value of the negative voltage sensed on the negative voltage supply node 101 may be less than the specified negative voltage. Alternatively, this may occur, for example, if the load coupled to the negative voltage supply node 101 draws a large amount of negative charge from the negative voltage supply node 101, thereby quickly depleting the negative charge from the negative voltage supply node 101.

[0029] If the oscillator control signal generator 130 senses that the negative value of the negative voltage on the negative voltage supply node 101 is greater than the specified negative voltage, the oscillator control signal generator 130 can ensure that the oscillation signal from the oscillator 120 is at a lower frequency. Therefore, the operating frequency of the negative voltage generating circuit 110 is also low, which therefore allows the negative value of the negative voltage on the negative voltage supply node 101 to be smaller (because providing negative charge on the negative voltage supply node 101 is slower than the load draws negative charge). In the case where the negative voltage generating circuit 110 is a charge pump, this can be achieved by reducing the rate at which negative charge is pumped to the negative voltage supply node 101.

[0030] For example, if the negative voltage generating circuit 110 has had time to previously reduce the negative voltage on the negative voltage supply node 101 to a more negative value than the specified negative voltage, and the load coupled to the negative voltage supply node 101 does not draw a large amount of negative charge from the negative voltage supply node 101, the negative voltage sensed on the negative voltage supply node 101 may be lower than the specified negative voltage. For context, when acceptable, reducing the operating frequency of the negative voltage generating circuit 110 allows the negative voltage generating circuit 110 to reduce power consumption and heat dissipation.

[0031] Therefore, in embodiments where the function of circuit 100 is to ideally generate a specified negative voltage, circuit 100 is able to accurately generate a negative voltage on negative voltage supply node 101 by automatically adjusting the operating frequency of negative voltage generating circuit 110. However, in other embodiments, the specified negative voltage to be generated by circuit 100 may vary dynamically over time. For example, perhaps circuit 100 is to generate a square wave that alternates between negative 2 volts and negative 1 volt. In this case, circuit 100 may still operate to target the dynamically changing specified negative voltage by comparing the actual negative voltage on negative voltage supply node 101 with any specified negative voltage that should be present on negative voltage supply node 101 at any given time.

[0032] Further, frequent automatic operating frequency adjustment allows the circuit 100 to: 1) quickly reduce the negative voltage on the negative voltage supply node 101 to approximately a specified negative voltage when the circuit 100 is first powered on, 2) quickly reduce the negative voltage on the negative voltage supply node 101 to approximately a specified negative voltage when the load draws a large amount of charge from the negative voltage supply node 101, and 3) reduce power loss by reducing the frequency of the signal from the oscillator 120 when the negative voltage generating circuit 110 has sufficiently reduced the negative voltage on the negative voltage supply node 101.

[0033] Generating a negative voltage internally at negative voltage supply node 101 (e.g., on an integrated circuit chip, such as, on circuit 100) may avoid providing an external negative voltage supply. Thus, because no external negative voltage supply needs to be provided or generated, the construction of any device incorporating circuit 100 may be more compact and less expensive. This is because generating a negative supply voltage externally may require relatively large and expensive components, such as a transformer or an isolated power converter.

[0034] As previously mentioned, the principles described herein are not limited to the type of components that receive power from the negative voltage supply node 101 or the reason for generating a negative voltage on the negative voltage supply node 101. However, in one embodiment, a negative voltage is provided to the gate terminal of the field effect transistor in order to ensure that the field effect transistor remains turned off. To explain why this may be helpful, a brief description of a field effect transistor will now be described.

[0035] A control voltage may be applied to the gate terminal of the field effect transistor (e.g., via a gate driver) to control whether current flows between the drain terminal and the source terminal of the field effect transistor. In order to turn on the field effect transistor, a sufficiently high control voltage may be applied to the gate terminal so that the gate-source voltage of the field effect transistor is higher than the threshold voltage. In order to turn off the field effect transistor, a sufficiently low control voltage may be applied to the gate terminal so that the gate-source voltage of the field effect transistor is lower than the threshold voltage. As an example, in many cases, the field effect transistor may be turned off by applying zero volts to the gate terminal of the field effect transistor, while the power supply voltage is grounded. Therefore, in this case, the gate-source voltage is zero.

[0036] The gate driver can be used to control the control voltage on the gate terminal of the field effect transistor. Phenomena such as Miller coupling, parasitic inductance between the field effect transistor and the gate driver, or any other trace inductance that may be present in a device including the circuit 100 may cause a short residual peak in the gate-source voltage after the field effect transistor has been turned off (e.g., by applying zero volts to the gate terminal of the field effect transistor). This peak is referred to as a "residual" peak because it is not expected to occur after the field effect transistor is turned off. The short residual peak of the gate-source voltage may be higher than the aforementioned threshold voltage of the field effect transistor and may therefore cause the field effect transistor to be turned on unexpectedly. This may cause serious damage to the field effect transistor and / or any circuit including or coupled to the field effect transistor.

[0037] Therefore, in order to ensure that any brief residual peak in the gate-source voltage of the field effect transistor does not exceed the threshold voltage of the field effect transistor after the field effect transistor is turned off, the field effect transistor can be turned off by applying a negative voltage to the gate terminal of the field effect transistor instead. Although there is still a residual peak in this case, the negative voltage applied to the gate terminal ensures that the gate-source voltage does not increase above the threshold voltage. Therefore, the field effect transistor remains turned off even during the residual peak. By way of example only, one can use Figure 1 The circuit 100 is used to generate a negative voltage applied to the gate terminal.

[0038] Figure 2 A charge pump 200 is shown. Figure 1The charge pump 200 includes a charging capacitor 210, four switches 220A to 220D, and three input voltage sources 230, 240, and 250. The charging capacitor 210 has a first capacitor terminal 211 and a second capacitor terminal 212. The first switch 220A is connected between the first capacitor terminal 211 and the first input voltage source 230. The second switch 220B is connected between the second capacitor terminal 212 and the second input voltage source 240. The third switch 220C is connected between the first capacitor terminal 211 and the third input voltage source 250. Finally, the fourth switch 220D is connected between the second capacitor terminal 212 and, for example, Figure 1 The first input voltage supply 230 provides a positive voltage (eg, positive 3 volts), while the second input voltage supply 240 and the third input voltage supply 250 both provide a ground voltage.

[0039] In operation, the charge pump 200 pumps charge to the negative voltage supply node 101 during each repetition of the charge pump cycle. In the first phase of the charge pump cycle, the first switch 220A and the second switch 220B are closed, while the third switch 220C and the fourth switch 220D are open. In this first phase, the charging capacitor 210 is charged to the voltage difference between the first input voltage supply 230 and the second input voltage supply 240. As an example, when the first input voltage supply 230 provides positive 3 volts and the second input voltage supply 240 provides ground voltage, the charging capacitor 210 will be charged so that there is a voltage difference of 3 volts between its first capacitor terminal 211 and its second capacitor terminal 212. In this case, the voltage at the first capacitor terminal 211 will be positive 3 volts, and the voltage at the second capacitor terminal 212 will be ground voltage.

[0040] In the second phase of the charge pump cycle, the third switch 220C and the fourth switch 220D are closed, while the first switch 220A and the second switch 220B are open. In this second phase, the charging capacitor 210 maintains the voltage difference between the first capacitor terminal 211 and the second capacitor terminal 212. However, assuming that the third input voltage supply 250 provides a ground voltage, the voltage at the first capacitor terminal 211 will be the ground voltage, and the voltage at the second capacitor terminal 212 is now negative 3 volts. Therefore, since the negative voltage supply node 101 is coupled to the second capacitor terminal 212 via the switch 220D in the second phase of the charge pump cycle, negative charge is provided from the charging capacitor 210 to the negative voltage supply node 101. Because the negative charge will then flow out of the second capacitor terminal 212, the voltage at the second capacitor terminal 212 will then rise. However, the negative charge has indeed been pumped to the negative voltage supply node 101.

[0041] In one embodiment, the charging capacitor 210 is a relatively small capacitor (e.g., 100 picofarads) so as to be easily mounted on an integrated circuit. However, the charge on the negative voltage supply node 101 may be stored on an external capacitor that is many times the size of the charging capacitor 210. For example, while the charging capacitor 210 may have a capacitance of 100 picofarads, the external capacitor may have a capacitance of 50 nanofarads (500 times greater than the charging capacitor 210). Therefore, in order for the charge pump 200 to sufficiently provide negative charge to the negative voltage supply node 101, the charge pump 200 will repeat the charge pump cycle at a high frequency. Therefore, when the charge pump 200 repeats the charge pump cycle at a high frequency, the negative voltage supply node 101 has sufficient negative charge, and the negative voltage is reduced to approximately negative 3 volts. The charge pump 200 includes a transistor and a small capacitor, and uses a voltage supply that is widely available in integrated circuits (e.g., by applying it externally). Therefore, the negative voltage generating circuit 110 (if embodied as a charge pump 200) can be more easily implemented within an integrated circuit.

[0042] Figure 3 An oscillator control signal generator 300 is shown. Figure 1 The oscillator control signal generator 300 includes a comparator 310, a level shifter 320, and a reference voltage source 330. The comparator 310 has a positive comparator input node 311 connected to the level shifter 320, a negative comparator input node 312 connected to the reference voltage source 330, and a positive comparator input node 313 connected to the reference voltage source 330. Figure 1 The comparator output node 313 of the oscillator 120 .

[0043] The positive comparator input node 311 is coupled to, for example, the negative voltage power supply node 101 via the level shifter 320. The level shifter 320 takes the negative voltage from the negative voltage power supply node 101 as an input, and outputs a shifted voltage depending on the negative voltage to the positive comparator input node 311. The comparator 310 compares the shifted voltage on the positive comparator input node 311 with a reference voltage on a negative comparator input node 312 provided by a reference voltage power supply 330, and outputs an oscillator control signal to a comparator output node 313.

[0044] The use of level shifter 320 allows comparator 310 to compare two different positive voltages, rather than directly comparing the negative voltage on negative voltage supply node 101 with another negative voltage provided by a negative reference voltage supply. This makes oscillator control signal generator 300 (or any circuit including oscillator control signal generator 300) more compact, without the need for additional components necessary to provide a negative reference voltage to negative comparator input node 312.

[0045] In the case where the specified negative voltage is a fixed negative voltage, the reference voltage power supply 330 can provide a fixed voltage. For example, the fixed reference voltage can be programmable through an internal memory or via a manual instruction of a user. Similarly, the specified negative voltage can be programmable, for example, through an internal memory or via a manual instruction of a user. However, as previously described, the specified negative voltage may change dynamically over time. To facilitate this, the reference voltage power supply 330 can provide a variable reference voltage that tracks the expected change of the specified negative voltage. Therefore, the reference voltage can be a dynamic voltage that changes according to, for example, a dynamic change of the specified negative voltage. Alternatively, the level shifter 320 can be a variable level shifter that changes the shift amount of the shift voltage so as to track the expected change of the specified negative voltage.

[0046] To illustrate the operation of the oscillator control signal generator 300, it is assumed that the reference voltage supply 330 provides a constant reference voltage of positive 1 volt, the shifted voltage output by the level shifter 320 is 4 volts higher than the negative voltage on the negative voltage supply node 101, and the specified negative voltage to be generated on the negative voltage supply node 101 is negative 3 volts. It is further assumed that if the negative voltage is more negative than the specified negative voltage, the frequency of the oscillation signal and the operating frequency of the negative voltage generating circuit 100 should be high frequencies. On the other hand, it is further assumed that if the negative voltage is less negative than the specified negative voltage, the frequency of the oscillation signal and the operating frequency of the negative voltage generating circuit 100 should be low frequencies.

[0047] In this case, if the negative voltage on the negative voltage power supply node 101 is not reduced to the specified negative voltage, the comparator 310 will output a high signal as an oscillator control signal, indicating that the oscillator should ensure that the frequency of the oscillation signal is a high frequency. Therefore, as an example, if the negative voltage on the negative voltage power supply node 101 is only reduced to negative 2 volts, the level shifter 320 will output a shift voltage of positive 2 volts. Since the 2 volt positive shift voltage on the positive comparator input node 311 is higher than the 1 volt reference voltage on the negative comparator input node 312, the comparator 310 will output a high signal as an oscillator control signal, indicating that the oscillator should ensure that the frequency of the oscillation signal is a high frequency.

[0048] On the other hand, when the negative voltage on the negative voltage power supply node 101 has been reduced to a negative value greater than the specified negative voltage, the comparator 310 will output a low signal as an oscillator control signal, indicating that the oscillator should ensure that the frequency of the oscillation signal is a low frequency. Therefore, in this example, once the negative voltage on the negative voltage power supply node 101 has been reduced to a negative value greater than negative 3 volts, the level shifter 320 will output a shift voltage less than positive 1 volt. When the shift voltage on the positive comparator input node 311 is less than the 1 volt reference voltage on the negative comparator input node 312, the comparator 310 will output a low signal as an oscillator control signal, indicating that the oscillator should ensure that the frequency of the oscillation signal is a low frequency.

[0049] In some embodiments, other components may be added or modifications may be made to the oscillator control signal generator 300 to add additional levels of control over the output oscillator control signal. For example, in one embodiment, the oscillator control signal generator may include an operational amplifier used as an analog comparator, instead of a digital comparator (e.g., Figure 3 This can be accomplished, for example, by configuring the operational amplifier to operate in an open loop mode, or by configuring the operational amplifier to operate using positive feedback or negative feedback.

[0050] The operational amplifier may have an operational amplifier positive input node coupled to, for example, a negative voltage supply node. In one embodiment, the operational amplifier positive input node may be coupled to the negative voltage supply node via a level shifter that outputs a shifted voltage that depends on the negative voltage on the negative voltage supply node. The operational amplifier may also include an operational amplifier negative input node connected to a reference voltage supply (possibly provided by negative feedback) and an operational amplifier output node connected to, for example, an oscillator 120. As an example, in operation, when the shift voltage is higher than the reference voltage, the operational amplifier causes the frequency of the oscillating signal generated by the oscillator 120 to be higher than when the shift voltage is lower than the reference voltage.

[0051] Although a digital comparator (e.g., comparator 310) has the advantage of quickly reacting to changes in the negative voltage on the negative voltage supply node due to the characteristics of the digital comparator, some digital comparators may also have only two output options (e.g., a high signal or a low signal). On the other hand, an operational amplifier used as an analog comparator will have the advantage of being able to continuously change the output signal based on the negative voltage on the negative voltage supply node. However, an operational amplifier used as an analog comparator may not have as fast a reaction time as a digital comparator. In order to achieve a balance between fast reaction time and variability of output signal options, a digital multi-level comparator may be used in the oscillator control signal generator, such as Figure 5 However, the oscillator control signal generator 300 is only Figure 1300 is an example of an oscillator control signal generator 130 , and thus the principles described herein are not limited to any particular structure of the oscillator control signal generator 300 .

[0052] Figure 4 shows a circuit 400 which is Figure 1 Specifically, the circuit 400 includes Figure 2 An example of a charge pump 200 of Figure 1 The oscillator 120 and Figure 3 An example of an oscillator control signal generator 300 is as follows: Figure 1 The circuit 400 also includes an external capacitor 410 and a non-overlapping element 420.

[0053] and Figure 1 Similarly, arrow line 141 indicates that the charge pump 200 generates a negative voltage on the negative voltage supply node 101, and indicates that the oscillator control signal generator 300 senses the negative voltage on the negative voltage supply node 101 (via the level shifter 320). Further, arrow line 142 indicates that the oscillator control signal generator 300 outputs an oscillator control signal to the oscillator 120, thereby increasing or decreasing the frequency of the oscillation signal from the oscillator 120. Finally, arrow lines 143A and 143B indicate that the oscillator 120 outputs an oscillation signal having a specific frequency (via the non-overlapping element 420) to the switches 220A to 220D of the charge pump 200, thereby causing the charge pump 200 to output a negative voltage (depending on the frequency of the oscillation signal from the oscillator 120) to the negative voltage supply node 101. The non-overlapping element 420 ensures that not all four switches 220A, 220B, 220C, and 220D are closed at the same time, thereby preventing current surges.

[0054] Again, for purposes of explanation, assume that the specified negative voltage to be generated on the negative voltage supply node 101 is negative 3 volts, the reference voltage supply 330 provides a reference voltage of positive 1 volt, and the shifted voltage output by the level shifter 320 is 4 volts higher than the negative voltage on the negative voltage supply node 101.

[0055] In operation, when the circuit 400 is first powered on, the voltage on the negative voltage supply node 101 is approximately zero volts. As the charge pump 200 begins to provide negative charge to the negative voltage supply node 101, the negative charge is stored on the external capacitor 410. Figure 4 The external capacitor 410 is shown in FIG. 1 , but the external capacitor 410 may actually be present in Figure 44 is outside the circuit 400 and is therefore referred to as an “external capacitor.” Recall that the external capacitor 410 can be many times larger (e.g., 500 times larger) than the charging capacitor 210, so the charge pump 200 can operate at a high frequency to provide sufficient negative charge to the negative voltage supply node 101 and sufficiently reduce the negative voltage on the negative voltage supply node 101 to approximately the specified negative voltage.

[0056] As the charge pump 200 begins to reduce the negative voltage to a level closer to the specified negative voltage (i.e., the negative voltage is higher than negative 3 volts), the shifted voltage output by the level shifter 320 is higher than the 1 volt reference voltage. In this case, the comparator 310 will output a high signal, indicating that the oscillation signal provided by the oscillator 120 is ensured to be at a high frequency, thereby ensuring that the charge pump 200 quickly provides negative charge to the negative voltage power supply node 101. Therefore, the circuit 400 is able to increase the frequency at which the charge pump 200 provides negative charge to the negative voltage power supply node 101, thereby allowing the negative voltage on the negative voltage power supply node 101 to quickly decrease to the specified negative voltage when the circuit 400 is first powered on.

[0057] Once the charge pump 200 successfully reduces the negative voltage to below the specified negative voltage (e.g., negative 3 volts), the shifted voltage output by the level shifter 320 will be less than the 1 volt reference voltage. In this case, the comparator 310 will output a low signal, indicating that the oscillation signal provided by the oscillator 120 is ensured to be at a low frequency, thereby ensuring that the charge pump 200 provides negative charge to the negative voltage power supply node 101 more slowly. Therefore, when the charge pump 200 has sufficiently reduced the negative voltage on the negative voltage power supply node 101 to approximately the specified negative voltage, the circuit 400 is able to reduce the power loss in the charge pump 200 by reducing the frequency at which the charge pump 200 provides negative charge to the negative voltage power supply node 101.

[0058] When a load (e.g., a gate terminal of a field effect transistor) coupled to the negative voltage power supply node 101 draws a large amount of charge from the negative voltage power supply node 101, the negative voltage on the negative voltage power supply node 101 may begin to be pulled away from the specified negative voltage. Therefore, the shifted voltage output by the level shifter 320 will be higher than the 1 volt reference voltage. In this case, the comparator 310 will output a high signal again to ensure that the charge pump 200 quickly replenishes negative charge to the negative voltage power supply node 101. Therefore, when the load draws a large amount of charge from the negative voltage power supply node 101, the circuit 400 can increase the frequency at which the charge pump 200 replenishes charge to the negative voltage power supply node 101.

[0059] Figure 5 A signal diagram 500 is shown, which shows the signal generated by Figure 44. An example of signals generated by operation of the circuit 400 of FIG. 4. Three signals 501, 502, and 503 are shown, which are provided only as examples. The horizontal axis represents the time elapsed from left to right, wherein the same horizontal position in each of the three signals 501, 502, and 503 represents the same time. The vertical axis of each respective signal 501, 502, and 503 represents the amplitude of the respective signal. The time is divided into three general time periods 511, 512, and 513.

[0060] Signal 501 represents a negative voltage (in volts) generated on negative voltage power supply node 101. Signal 502 represents an oscillating signal from oscillator 120, wherein the oscillating signal from oscillator 120 oscillates between a high voltage (e.g., positive 6 volts) and a low voltage (e.g., zero volts). For example, at a rising edge of the oscillating signal from oscillator 120, charge pump 200 may begin to operate in a first phase of a charge pump cycle, and at a falling edge of the oscillating signal from oscillator 120, charge pump 200 may begin to operate in a second phase of a charge pump cycle, and vice versa. Further, at a rising edge of the oscillating signal from oscillator 120, charge pump 200 may begin to operate in a second phase of a charge pump cycle, and vice versa. Figure 5 , the signal from the oscillator 120 is shown as oscillating at three different frequencies. As previously described, this may be the case using a digital multi-level comparator with, for example, three different output options to enable three different oscillation frequencies of the oscillating signal generated by the oscillator 120. Finally, signal 503 represents the current (in milliamperes) drawn by the load coupled to the negative voltage supply node 101.

[0061] During time period 511, circuit 400 may be in a startup phase. For example, at the beginning of time period 511, circuit 400 may have just been powered on. During this time period 511, the load does not draw (or at least draws only a minimal amount of) negative charge from negative voltage supply node 101 (see signal 503 in time period 511). At the very beginning of time period 511, the negative voltage on negative voltage supply node 101 (signal 501) is shown to be at (or above) approximately zero volts. In this case, oscillator control signal generator 300 will cause the oscillating signal from oscillator 120 to operate at a high frequency, as shown in sub-portion 502A of signal 502. In fact, due to the resolution of the figure, oscillating signal 502 in sub-portion 502A oscillates so fast that signal 502 is at Figure 5 Shown as a solid line.

[0062] Once the charge pump 200 has reduced the negative voltage on the negative voltage supply node 101 to some intermediate negative voltage (e.g., approximately negative 1.8 volts in signal 501), the oscillator control signal generator 300 may cause the oscillation signal from the oscillator 120 to operate at an intermediate frequency, as shown in sub-portion 502B of signal 502. When the charge pump 200 has successfully reduced the negative voltage on the negative voltage supply node 101 to approximately a specified negative voltage (e.g., negative 3 volts), the oscillator control signal generator 300 may cause the oscillation signal from the oscillator 120 to be at a low frequency, as shown in sub-portion 502C of signal 502.

[0063] In time period 512, the load begins to draw a large amount of negative charge from the negative voltage supply node 101. During this period, as the charge pump 200 attempts to replenish the charge drawn by the load, the oscillator control signal generator 300 alternates between operating the signal from the oscillator 120 at a high frequency and operating at a medium frequency. Although timeline 501 shows that the negative voltage on the negative voltage supply node 101 may not be completely reduced to the specified negative voltage (e.g., negative 3 volts) during time period 512, reducing the negative voltage on the negative voltage supply node 101 even partially has the benefit of reducing the chance of unintentionally turning on the field effect transistor.

[0064] In time period 513, the load returns and does not draw a large amount of negative charge from negative voltage supply node 101. During this period, when charge pump 200 is able to sufficiently replenish charge to negative voltage supply node 101, oscillator control signal generator 300 causes the signal from oscillator 120 to operate at a medium frequency and then at a low frequency.

[0065] Therefore, by automatically adjusting the operating frequency of the charge pump 200, the circuit 400 is able to accurately generate a negative voltage on the negative voltage supply node 101. Further, the frequent automatic operating frequency adjustment allows the circuit 100 to: 1) quickly reduce the negative voltage on the negative voltage supply node 101 to approximately a specified negative voltage when the circuit 100 is first powered on, 2) quickly reduce the negative voltage on the negative voltage supply node 101 to approximately a specified negative voltage when the load draws a large amount of charge from the negative voltage supply node 101, and 3) reduce power loss by reducing the frequency of the signal from the oscillator 120 when the charge pump 200 has sufficiently reduced the negative voltage on the negative voltage supply node 101.

[0066] Written support section

[0067] Item 1. A circuit configured to generate a negative voltage on a negative voltage supply node, the circuit comprising: an oscillator; a negative voltage generating circuit configured to respond to receiving a signal from the oscillator by generating a negative voltage on the negative voltage supply node, wherein the negative voltage is a function of the frequency of the signal received from the oscillator; and an oscillator control signal generator configured to sense the negative voltage present on the negative voltage supply node and, in response to the sensing, control the frequency of the signal generated by the oscillator.

[0068] Clause 2. The circuit of clause 1, wherein the negative voltage generating circuit operates at an operating frequency that depends at least on a frequency of the signal generated by the oscillator.

[0069] Item 3. According to the circuit described in Item 2, the negative voltage generating circuit includes a charge pump, which includes: a charging capacitor, the charging capacitor having a first capacitor terminal and a second capacitor terminal; a first switch, the first switch is connected between a first input voltage power supply and the first capacitor terminal; a second switch, the second switch is connected between a second input voltage power supply and the second capacitor terminal; a third switch, the third switch is connected between the first capacitor terminal and a third input voltage power supply; and a fourth switch, the fourth switch is connected between the second capacitor terminal and the negative voltage power supply node.

[0070] Clause 4. The circuit of clause 3, wherein the first input voltage supply provides a positive voltage, the second input voltage supply provides a ground voltage, and the third input voltage supply provides a ground voltage.

[0071] Item 5. A circuit according to Item 3, wherein, in a first phase of a charge pump cycle, the first switch and the second switch are closed and the third switch and the fourth switch are opened, thereby providing charge to the charging capacitor, and in a second phase of the charge pump cycle, the third switch and the fourth switch are closed and the first switch and the second switch are opened, thereby providing charge from the charging capacitor to the negative voltage supply node.

[0072] Item 6. The circuit of Item 5, further comprising a non-overlapping element configured to prevent the first switch and the second switch from closing when the third switch and the fourth switch are closed, and configured to prevent the third switch and the fourth switch from closing when the first switch and the second switch are closed.

[0073] Clause 7. The circuit of clause 5, wherein the charge on the negative voltage supply node is stored on an external capacitor.

[0074] Item 8. The circuit of Item 2, wherein the oscillator control signal generator includes a comparator having a positive comparator input node coupled to the negative voltage supply node, a negative comparator input node connected to a reference voltage supply providing a reference voltage, and a comparator output node connected to the oscillator.

[0075] Item 9. The circuit of Item 8, wherein the oscillator control signal generator further comprises a level shifter connected between the negative voltage supply node and the positive comparator input node, the level shifter being configured to output a shifted voltage dependent on the negative voltage on the negative voltage supply node.

[0076] Clause 10. The circuit of Clause 9, wherein when the shift voltage is higher than the reference voltage, the comparator increases the frequency of the signal generated by the oscillator and the negative voltage generating circuit decreases the negative voltage.

[0077] Clause 11. The circuit of clause 9, wherein the comparator causes the frequency of the signal generated by the oscillator to be higher when the shift voltage is above the reference voltage than when the shift voltage is below the reference voltage.

[0078] Clause 12. The circuit of clause 10, wherein increasing the frequency of the signal generated by the oscillator causes the operating frequency of the negative voltage generating circuit to also increase, and decreasing the frequency of the signal generated by the oscillator causes the operating frequency of the negative voltage generating circuit to also decrease.

[0079] Clause 13. The circuit of clause 12, wherein the comparator is a multi-level comparator that causes the frequency of the signal generated by the oscillator to operate at three or more different frequency levels.

[0080] Clause 14. The circuit of clause 2, wherein the negative voltage supply node is coupled to a gate terminal of the field effect transistor.

[0081] Item 15. The circuit of Item 2, wherein the oscillator control signal generator comprises an operational amplifier having an operational amplifier positive input node coupled to the negative voltage power supply node, an operational amplifier negative input node connected to a reference voltage power supply providing a reference voltage, and an operational amplifier output node connected to the oscillator.

[0082] Item 16. According to the circuit described in Item 15, the oscillator control signal generator also includes a level shifter connected between the negative voltage supply node and the positive input node of the operational amplifier, and the level shifter is configured to output a shifted voltage depending on the negative voltage on the negative voltage supply node.

[0083] Clause 17. The circuit of Clause 16, wherein when the shift voltage is higher than the reference voltage, the operational amplifier increases the frequency of the signal generator through the oscillator, and the negative voltage generating circuit decreases the negative voltage.

[0084] Clause 18. The circuit of clause 16, wherein the operational amplifier causes the frequency of the signal generated by the oscillator to be higher when the shift voltage is above the reference voltage than when the shift voltage is below the reference voltage.

[0085] Clause 19. The circuit of clause 18, wherein increasing the frequency of the signal generated by the oscillator causes the operating frequency of the negative voltage generating circuit to also increase, and decreasing the frequency of the signal generated by the oscillator causes the operating frequency of the negative voltage generating circuit to also decrease.

[0086] Although the subject matter is described in language specific to structural features and / or methodological acts, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the above-described features or acts or the order of the above-described acts. Instead, the described features and acts are disclosed as example forms of implementing the claims.

[0087] The present disclosure may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects as illustrative and non-restrictive. All changes within the meaning and range of equivalents of the claims are included within the scope of the claims.

[0088] When introducing elements in the appended claims, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

Claims

1. A circuit configured to generate a negative voltage on a negative voltage supply node, the circuit comprising: Oscillator; a negative voltage generating circuit configured to respond to receiving a signal from the oscillator by generating a negative voltage on the negative voltage supply node, wherein the negative voltage is a function of a frequency of the signal received from the oscillator; as well as An oscillator control signal generator is configured to sense the negative voltage present on the negative voltage supply node and, in response to the sensing, control the frequency of the signal generated by the oscillator.

2. The circuit according to claim 1, wherein The negative voltage generating circuit operates at an operating frequency that depends at least on the frequency of the signal generated by the oscillator.

3. The circuit according to claim 2, wherein the negative voltage generating circuit comprises a charge pump, wherein the charge pump comprises: a charging capacitor having a first capacitor terminal and a second capacitor terminal; a first switch connected between a first input voltage supply and the first capacitor terminal; a second switch connected between a second input voltage supply and the second capacitor terminal; a third switch connected between the first capacitor terminal and a third input voltage supply; as well as A fourth switch is connected between the second capacitor terminal and the negative voltage supply node.

4. The circuit according to claim 3, wherein: The first input voltage supply provides a positive voltage, the second input voltage supply provides a ground voltage, and the third input voltage supply provides a ground voltage.

5. The circuit according to claim 3, wherein: In a first phase of a charge pump cycle, the first switch and the second switch are closed, while the third switch and the fourth switch are opened, thereby providing charge to the charging capacitor, and In a second phase of the charge pump cycle, the third switch and the fourth switch are closed, while the first switch and the second switch are opened, thereby providing charge from the charging capacitor to the negative voltage supply node.

6. The circuit of claim 5 , further comprising a non-overlapping element configured to prevent the first switch and the second switch from being turned off when the third switch and the fourth switch are turned off, and configured to prevent the third switch and the fourth switch from being turned off when the first switch and the second switch are turned off.

7. The circuit according to claim 5, wherein: The charge on the negative voltage supply node is stored on an external capacitor.

8. The circuit of claim 2 , wherein the oscillator control signal generator comprises a comparator having a positive comparator input node coupled to the negative voltage supply node, a negative comparator input node connected to a reference voltage supply providing a reference voltage, and a comparator output node connected to the oscillator.

9. The circuit of claim 8, the oscillator control signal generator further comprising a level shifter connected between the negative voltage supply node and the positive comparator input node, the level shifter being configured to output a shifted voltage depending on the negative voltage on the negative voltage supply node.

10. The circuit according to claim 9, wherein: The comparator causes the frequency of the signal generated by the oscillator to be higher when the shift voltage is higher than the reference voltage than when the shift voltage is lower than the reference voltage.

11. The circuit according to claim 9, wherein: The reference voltage provided by the reference voltage power supply is a programmable voltage.

12. The circuit according to claim 9, wherein: The reference voltage provided by the reference voltage power supply changes dynamically.

13. The circuit according to claim 9, wherein: When the shift voltage is higher than the reference voltage, the comparator increases the frequency of the signal generated by the oscillator, and the negative voltage generating circuit decreases the negative voltage.

14. The circuit of claim 13, wherein: Increasing the frequency of the signal generated by the oscillator causes the operating frequency of the negative voltage generating circuit to also increase, and decreasing the frequency of the signal generated by the oscillator causes the operating frequency of the negative voltage generating circuit to also decrease.

15. The circuit of claim 14, wherein: The comparator is a multi-level comparator that causes the frequency of the signal generated by the oscillator to operate at three or more different frequency levels.

16. The circuit of claim 2, wherein: The negative voltage supply node is coupled to a gate terminal of a field effect transistor via a gate driver configured to provide a control voltage to the gate terminal of the field effect transistor.

17. The circuit of claim 2, wherein the oscillator control signal generator comprises an operational amplifier having an operational amplifier positive input node coupled to the negative voltage supply node, an operational amplifier negative input node connected to a reference voltage supply providing a reference voltage, and an operational amplifier output node connected to the oscillator.

18. The circuit of claim 17, the oscillator control signal generator further comprising a level shifter connected between the negative voltage supply node and the operational amplifier positive input node, the level shifter being configured to output a shifted voltage depending on the negative voltage on the negative voltage supply node.

19. The circuit of claim 18, wherein: When the shift voltage is higher than the reference voltage, the operational amplifier increases the frequency of the signal generator through the oscillator, and the negative voltage generating circuit decreases the negative voltage.

20. The circuit of claim 18, wherein: The operational amplifier causes the frequency of the signal generated by the oscillator to be higher when the shift voltage is higher than the reference voltage than when the shift voltage is lower than the reference voltage.

21. The circuit of claim 20, wherein: Increasing the frequency of the signal generated by the oscillator causes the operating frequency of the negative voltage generating circuit to also increase, and decreasing the frequency of the signal generated by the oscillator causes the operating frequency of the negative voltage generating circuit to also decrease.

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