Oscillator circuit and integrated circuit

Abstract

The present application provides an oscillator circuit (20) comprising: a parallel circuit formed by connecting a resistor element (1) and a flip-flop (3) in parallel; and a capacitor element (2) connected in series with the parallel circuit and having a PMOS transistor (4), wherein a gate terminal (10) in the PMOS transistor (4) is connected to a power supply side, and a source terminal (8), a drain terminal (9) and a substrate (5) in the PMOS transistor (4) are connected to a ground side. Thus, the capacitor element (2) with a negative temperature coefficient is realized, so that the temperature drift of the oscillator circuit (20) is extremely low, or even the temperature drift of the oscillator circuit (20) is completely eliminated. In this case, since no additional device needs to be added, the chip using the oscillator circuit (20) can have high integration, the design difficulty of the chip is simplified, the power consumption of the chip is reduced, and the cost is reduced.

Description

Technical Field

[0001] This invention relates to an oscillator circuit composed of an RC clock, and more particularly to an oscillator circuit capable of achieving low temperature drift, and an integrated circuit including the oscillator circuit. Background Technology

[0002] In modern electronic systems, clock signals are like the beating of a heart, providing a precise time reference for digital circuits. From microcontrollers and communication modules to consumer electronics, almost all electronic devices require a stable and reliable clock source. Among the many clocking solutions, the resistor-capacitor (RC) oscillator is widely used in embedded systems and low-to-medium precision applications due to its advantages such as low cost, easy integration, and rapid startup.

[0003] The basic principle of an RC oscillator circuit is to generate periodic oscillations by utilizing the time constant of charging and discharging a capacitor with a resistor. The relationship between its output frequency f and the resistor R and capacitor C can be simplified to f∝1 / (RC). This circuit structure is simple, requires no external crystal, and is particularly suitable for cost-sensitive large-scale applications. However, this simplicity also brings inherent limitations: the frequency stability of the RC oscillator circuit is highly dependent on the temperature characteristics of the resistor and capacitor.

[0004] However, in typical RC oscillator circuits, conventional resistors and capacitors usually have positive temperature coefficients, meaning that both resistance and capacitance increase with temperature. With both having positive temperature coefficients, their effects on frequency are additive, causing a significant drift in the output frequency of the RC oscillator circuit with temperature changes. This makes it difficult for RC oscillator circuits to meet accuracy requirements in wide temperature range applications.

[0005] To address the aforementioned temperature drift, the main solutions currently available on the market are as follows: The first solution is to use external high-precision components, such as quartz crystals or MEMS oscillators. While this can achieve extremely low temperature drift of ±10-50ppm / °C, it increases the number of external components, substrate area, and overall cost, sacrificing the high integration advantage of the RC oscillator circuit itself. The second solution is a digital dynamic compensation scheme. This involves integrating a temperature sensor and digital logic circuits such as lookup tables or algorithm units within the chip to detect the temperature in real time and dynamically adjust the parameters of the programmable capacitor array or clock divider. Although this solution can achieve extremely low temperature drift, it significantly increases circuit complexity, chip area, design difficulty, and power consumption, making it particularly unsuitable for applications that are extremely sensitive to power consumption and cost. Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] As mentioned above, in existing RC oscillator circuits, temperature has a significant impact on the output frequency of the RC oscillator circuit, and the temperature coefficients of each component constituting the RC oscillator circuit are different. Therefore, it is necessary to rationally select different components based on the temperature coefficients of each component in the RC oscillator circuit to construct an RC oscillator circuit with a stable output frequency.

[0008] Technical means for solving technical problems

[0009] To address the aforementioned technical problems, this application proposes an oscillator circuit that employs a capacitor element with a negative temperature coefficient, complementing a resistor element with a positive temperature coefficient. According to the oscillator circuit with this structure, when the temperature rises, the resistance of the resistor element increases, leading to a decrease in the output frequency. However, the capacitance of the capacitor element decreases, increasing the output frequency. These two effects cancel each other out, thereby maintaining a stable output frequency for the oscillator circuit.

[0010] Specifically, according to one aspect of the present invention, an oscillator circuit is provided, comprising: A parallel circuit consisting of a resistor and a flip-flop connected in parallel; and A capacitor element having a PMOS transistor connected in series with the parallel circuit. The gate terminal of the PMOS transistor is connected to the power supply side, while the source terminal, drain terminal, and substrate of the PMOS transistor are connected to the ground side.

[0011] Preferably, in the oscillator circuit of the present invention, the temperature coefficient of the capacitor element is a negative temperature coefficient.

[0012] Preferably, in the oscillator circuit of the present invention, the gate-source capacitance generated between the gate terminal and the source terminal in the PMOS transistor has a negative temperature coefficient.

[0013] Preferably, in the oscillator circuit of the present invention, the gate-drain capacitance generated between the gate terminal and the drain terminal in the PMOS transistor has a negative temperature coefficient.

[0014] Preferably, in the oscillator circuit of the present invention, the temperature coefficient of the resistive element is a positive temperature coefficient.

[0015] Preferably, in the oscillator circuit of the present invention, the absolute value of the negative temperature coefficient of the capacitor element is equal to the absolute value of the positive temperature coefficient of the resistor element.

[0016] As described above, the oscillator circuit proposed in this application utilizes a PMOS transistor whose gate terminal is connected to the power supply side, and whose source terminal, drain terminal, and substrate are connected to the ground side, to form a capacitor element. This achieves a capacitor element with a negative temperature coefficient, resulting in extremely low or even completely eliminated temperature drift of the oscillator circuit. In this case, since no additional components are required, the chip employing this oscillator circuit can achieve high integration, simplifying chip design, reducing power consumption, and lowering costs.

[0017] Preferably, in the oscillator circuit of the present invention, the capacitor element further comprises a metal-oxide-metal capacitor connected in parallel with the PMOS transistor.

[0018] Preferably, in the oscillator circuit of the present invention, the temperature coefficient of the capacitor element is adjusted by adjusting the ratio of the capacitance values ​​of the metal-oxide-metal capacitor and the PMOS transistor.

[0019] Preferably, in the oscillator circuit of the present invention, the capacitance value of the metal-oxide-metal capacitor is adjusted by adjusting at least one of the following: the number of metal stack layers, the size of the interdigitated structure, the metal linewidth, and the metal spacing.

[0020] As described above, the oscillator circuit proposed in this application constructs a capacitor element by connecting a metal-oxide-metal capacitor in parallel with a PMOS transistor, thereby enabling precise control of the temperature coefficient of the capacitor element and completely eliminating temperature drift of the oscillator circuit.

[0021] Additionally, according to another aspect of the present invention, an integrated circuit is provided, comprising: any one of the oscillator circuits described above.

[0022] Other features and aspects of the invention will become clearer from the following detailed description taken in conjunction with the accompanying drawings. Attached Figure Description

[0023] The invention can be better understood by describing exemplary embodiments of the invention in conjunction with the accompanying drawings, in which: Figure 1 This is a schematic diagram showing the overall structure of the oscillator circuit according to an embodiment of the present invention; Figure 2 This is a cross-sectional view showing a specific structure of a capacitor element in an oscillator circuit according to an embodiment of the present invention; Figure 3This is a circuit diagram illustrating another specific structure of the capacitor element in the oscillator circuit according to an embodiment of the present invention; Figure 4 This is a graph showing the relationship between output frequency and temperature obtained from a simulation of the oscillator circuit involved in an embodiment of the present invention. Detailed Implementation

[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this application. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0025] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not specifically singular and may include plural forms. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0026] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application. In addition, although the terminology used in this application is selected from commonly known and used terms, some terms mentioned in this application's specification may have been chosen by the applicant according to his or her judgment, and their detailed meanings are explained in the relevant sections of this description. Moreover, this application should be understood not only through the actual terms used, but also through the meaning implied by each term.

[0027] <Overall Structure of Oscillator Circuit 20>

[0028] Below, refer to Figure 1 The overall structure of the oscillator circuit 20 involved in the embodiments of the present invention will be described in detail.

[0029] in, Figure 1 This is a schematic diagram showing the overall structure of the oscillator circuit according to an embodiment of the present invention.

[0030] like Figure 1As shown, the oscillator circuit 20 involved in the embodiment of the present invention includes a resistor element 1, a capacitor element 2 and a trigger 3. Specifically, the resistor element 1 and the trigger 3 are connected in parallel to obtain a parallel circuit, and the parallel circuit is connected in series with the capacitor element 2 to obtain an oscillator circuit 20 with an RC differentiating circuit structure.

[0031] in, Figure 1 In the diagram, a Schmitt trigger is shown as trigger 3, but trigger 3 is not limited to a Schmitt trigger; this is just an example.

[0032] Furthermore, the embodiments of the present invention are described using an RC differentiating circuit structure as an example, but the RC oscillator is not limited to the RC differentiating circuit; this is just an example.

[0033] Furthermore, in the oscillator circuit 20 according to the embodiments of the present invention, the capacitor element 2 has a PMOS transistor 4, which will be described in detail below.

[0034]

[0035] Below, refer to Figure 2 The present invention will describe in detail a specific structure of the capacitor element 2 in the oscillator circuit 20 according to the embodiments of the present invention.

[0036] in, Figure 2 This is a cross-sectional view showing a specific structure of a capacitor element in an oscillator circuit according to an embodiment of the present invention.

[0037] In the oscillator circuit 20 according to the embodiments of the present invention, the capacitor element 2 has a PMOS transistor 4. Specifically, the structure of the PMOS transistor 4 is as follows: Figure 2 As shown in the cross-sectional view. First, a silicon oxide layer 6 and a polysilicon layer 7 are sequentially formed on an N-type semiconductor substrate 5. Then, a p+ type channel is formed on both sides of the silicon oxide layer 6 and the polysilicon layer 7 on the N-type semiconductor substrate 5, thereby forming the source terminal 8 and the drain terminal 9 of the PMOS transistor 4 on the N-type semiconductor substrate 5. Finally, the gate terminal 10 is formed on the N-type semiconductor substrate 5 by the silicon oxide layer 6 and the polysilicon layer 7. Thus, the following is obtained: Figure 2 The PMOS transistor 4 is shown.

[0038] In addition, under normal circumstances, the temperature coefficient of the resistive element 1 is positive. Therefore, in order to significantly reduce the temperature drift of the oscillator circuit 20, it is necessary to implement the capacitor element 2 with a negative temperature coefficient.

[0039] Specifically, such as Figure 2 As shown, in the oscillator circuit 20 according to the embodiment of the present invention, a capacitor element 2 is formed by using a PMOS transistor 4. In order to obtain a capacitor element 2 with a negative temperature coefficient, the gate terminal 10 of the PMOS transistor 4 is connected to the power supply side, and the source terminal 8, the drain terminal 9 and the N-type semiconductor substrate 5 of the PMOS transistor 4 are all connected to the ground side.

[0040] More specifically, such as Figure 2 As shown, in the PMOS transistor 4, when the N-type semiconductor substrate 5 is grounded, by connecting the gate terminal 10 to the power supply side and the source terminal 8 to the ground side, the gate-source capacitance generated between the gate terminal 10 and the source terminal 8 (i.e., the ground side) has a negative temperature coefficient.

[0041] Furthermore, such as Figure 2 As shown, in the PMOS transistor 4, when the N-type semiconductor substrate 5 is grounded, by connecting the gate terminal 10 to the power supply side and the drain terminal 9 to the ground side, the gate-drain capacitance generated between the gate terminal 10 and the drain terminal 9 (i.e., the ground side) has a negative temperature coefficient.

[0042] Therefore, as described above, by adjusting the connection of the gate terminal 10, source terminal 8, drain terminal 9 and N-type semiconductor substrate 5 in the PMOS transistor 4 relative to the power supply side and the ground side, the temperature coefficient of the capacitor element 2 can be made to exhibit a negative temperature coefficient.

[0043] For example, in a typical oscillator circuit 20, on the one hand, the temperature coefficient of a conventional resistive element 1, such as a poly resistor, is approximately 220 ppm / ℃, and the temperature coefficient deviation can reach ±1.75% when the operating temperature is in the range of -40℃ to +120℃. On the other hand, the temperature coefficient deviation of a conventional capacitor element 2, such as a mom capacitor, can reach ±0.4% when the operating temperature is in the range of -40℃ to +120℃. If the oscillator circuit 20 is obtained by combining the resistive element 1 and the capacitor element 2 as described above, the total temperature drift of the resulting oscillator circuit 20 can easily reach several percentage points, which cannot meet the accuracy requirements in applications with a wide temperature range.

[0044] In contrast, this application proposes a clever compensation scheme: using a capacitor element 2 with a negative temperature coefficient to complement the resistor element 1 with a positive temperature coefficient. When the temperature rises, the resistance of the resistor element 1 increases, causing the output frequency of the oscillator circuit 20 to decrease. However, the capacitance of the capacitor element 2 with a negative temperature coefficient decreases with rising temperature, causing the output frequency of the oscillator circuit 20 to increase. This allows the temperature drift effects of the resistor element 1 with a positive temperature coefficient and the capacitor element 2 with a negative temperature coefficient to cancel each other out, thus maintaining a stable output frequency of the oscillator circuit 20.

[0045] Regarding the principle of the above compensation scheme, as a premise, the output frequency f of the oscillator circuit 20 satisfies f = k / (R·C), where k represents the circuit structure constant, R is the resistance value of resistor element 1, and C is the capacitance value of capacitor element 2. In this case, differentiating with respect to temperature T, the temperature coefficient of the output frequency f satisfies α_f = α_R + α_C, where α_f represents the temperature coefficient of the oscillator circuit 20, α_R represents the temperature coefficient of resistor element 1, and α_C represents the temperature coefficient of capacitor element 2. By selecting the PMOS transistor 4 as described above to construct capacitor element 2, satisfying α_C ≈ -α_R, theoretically, the output frequency α_f of the oscillator circuit 20 can be made close to zero.

[0046] For example, in the oscillator circuit 20 according to an embodiment of the present invention, when a resistive element 1 with a positive temperature coefficient of approximately 220 ppm / ℃ is used, such as Figure 2 As shown, by adjusting the connection of the gate terminal 10, source terminal 8, drain terminal 9, and N-type semiconductor substrate 5 of the PMOS transistor 4 relative to the power supply side and ground side, a capacitor element 2 with a negative temperature coefficient is obtained, with a temperature coefficient of -294ppm / ℃. Furthermore, the absolute value of the negative temperature coefficient of the capacitor element 2 is made equal to the absolute value of the positive temperature coefficient of the resistor element 1. This results in extremely low temperature drift of the oscillator circuit 20, or even complete elimination of temperature drift. In this case, since no additional components are required, the chip using this oscillator circuit 20 can achieve high integration, simplifying chip design, reducing power consumption, and lowering costs.

[0047] Furthermore, in order to completely eliminate the temperature drift of the oscillator circuit 20, in the oscillator circuit 20 according to the embodiment of the present invention, when the output frequency f of the oscillator circuit 20 is fixed at 32kHz, according to the formula f = k / (R·C), while keeping R·C constant, by adjusting the ratio between the positive temperature coefficient of the resistor element 1 and the negative temperature coefficient of the capacitor element 2, it is possible to achieve α_C = -α_R, thereby making the positive temperature coefficient of the resistor element 1 and the negative temperature coefficient of the capacitor element 2 completely cancel each other out, thereby realizing an oscillator circuit 20 that is completely free of temperature drift.

[0048] As described above, the oscillator circuit 20 according to an embodiment of the present invention utilizes a PMOS transistor 4 whose gate terminal 10 is connected to the power supply side, and whose source terminal 8, drain terminal 9, and N-type semiconductor substrate 5 are connected to the ground side to form a capacitor element 2. This achieves a capacitor element 2 with a negative temperature coefficient, resulting in extremely low or even completely eliminated temperature drift of the oscillator circuit 20. In this case, since no additional components are required, the chip employing this oscillator circuit 20 can achieve high integration, simplifying chip design, reducing chip power consumption, and lowering costs.

[0049] <Another specific structure for capacitor element 2>

[0050] Below, refer to Figure 3 This paper describes in detail another specific structure of the capacitor element 2 in the oscillator circuit 20 according to the embodiments of the present invention.

[0051] in, Figure 3 This is a circuit diagram illustrating another specific structure of the capacitor element in the oscillator circuit according to an embodiment of the present invention.

[0052] like Figure 3 As shown, in the oscillator circuit 20 of the embodiment of the present invention, for the capacitor element 2, a MOM capacitor 11, i.e. a metal-oxide-metal capacitor, is added to the PMOS transistor 4 as described above, and a switching element 12 is provided in the parallel circuit of the PMOS transistor 4 and the MOM capacitor 11 to control the charging and discharging of the capacitor element 2.

[0053] As a premise, as mentioned above, as the core temperature compensation part of capacitor element 2, since the gate-source capacitance generated between the gate terminal 10 and the ground side in PMOS transistor 4, and the gate-drain capacitance generated between the gate terminal 10 and the ground side have a natural negative temperature coefficient, a basic negative temperature coefficient can be provided for PMOS transistor 4, thereby effectively offsetting the temperature drift caused by other parts of PMOS transistor 4 with positive temperature coefficients, such as the resistance of polysilicon layer 7, bandgap reference source, etc., and optimizing the overall operating characteristics of oscillator circuit 20 in the full temperature range.

[0054] Based on this, such as Figure 3 As shown, in the composite structure composed of PMOS transistor 4 and MOM capacitor 11, MOM capacitor 11 is a high-precision on-chip capacitor with an extremely low temperature coefficient. The capacitance value of MOM capacitor 11 can be adjusted by adjusting at least one of the following: the number of metal stack layers, the size of the interdigitated structure, the metal line width, and the metal spacing. Therefore, by connecting MOM capacitor 11 and PMOS transistor 4 in parallel, the negative temperature coefficient of PMOS transistor 4 can be calibrated and finely adjusted more precisely. Moreover, by adjusting the ratio of MOM capacitor 11 to PMOS transistor 4 in capacitor element 2, the temperature coefficient of capacitor element 2 can be adjusted more precisely.

[0055] As described above, the oscillator circuit 20 according to the embodiment of the present invention forms a capacitor element 2 by connecting a metal-oxide-metal capacitor 11 in parallel with a PMOS transistor 4, which enables more precise control of the temperature coefficient of the capacitor element 2, thereby completely eliminating the temperature drift of the oscillator circuit 20.

[0056] <Technical Effects of Oscillator Circuit 20>

[0057] Below, refer to Figure 4 The technical effects of the oscillator circuit 20 involved in the embodiments of the present invention will be explained in detail.

[0058] in, Figure 4 This is a graph showing the relationship between output frequency and temperature obtained from a simulation of the oscillator circuit involved in an embodiment of the present invention.

[0059] like Figure 4 As shown, the horizontal axis represents temperature T (°C), and the vertical axis represents the output frequency f (kHz) of the oscillator circuit 20. Figure 4 The solid line at the top center represents the simulation result obtained after simulating the oscillator circuit 20 according to the embodiment of the present invention. Figure 4The dashed line at the bottom center represents the simulation results obtained after simulating an oscillator composed of a traditional metal capacitor, i.e., a metal-insulator-metal capacitor. From Figure 4 It can be observed that, with the temperature coefficient of the conventional metal capacitor used being -254 ppm / ℃ and the temperature coefficient of the capacitor element 2 with PMOS transistor 4 being -13 ppm / ℃, without introducing other modules, the temperature drift of the oscillator circuit 20 involved in the embodiment of the present invention can be reduced to 1 / 19 of that of the oscillator circuit using a conventional metal capacitor.

[0060] In summary, the oscillator circuit 20 according to the embodiments of the present invention has the following technical effects: (1) The oscillator circuit 20 involved in the embodiments of the present invention has a simple structure and extremely low cost. It completely retains the circuit topology of the traditional oscillator circuit and does not require the introduction of complex modules such as temperature sensors, ADCs, digital processing units or programmable capacitor arrays, and does not increase the additional chip area and design complexity.

[0061] (2) The compensation process of the oscillator circuit 20 involved in the embodiments of the present invention is based entirely on the physical characteristics of passive components, without any active calibration or dynamic power consumption, and is particularly suitable for low power consumption scenarios.

[0062] (3) The performance of the oscillator circuit 20 involved in the embodiments of the present invention is significantly improved. The temperature drift index of the oscillator circuit 20 can be optimized from -254ppm / °C to a practical range of -13ppm / °C, making it suitable for most low-power applications such as UART communication, watchdog timing, and low-frequency real-time clock, which have basic requirements for timing stability.

[0063] (4) The oscillator circuit 20 involved in the embodiments of the present invention has very high reliability. The fully passive compensation mechanism has no timeliness problem and is not affected by the loss of digital logic state or calibration data. The system is stable from startup.

[0064] Integrated Circuits

[0065] Although not illustrated, the oscillator circuit 20 involved in the embodiments of the present invention can be applied to various integrated circuits as a clock module in the integrated circuit.

[0066] Therefore, embodiments of the present invention should also include integrated circuits having the oscillator circuit 20 as described above.

[0067] The various aspects of the present invention have been described above through exemplary embodiments. However, it should be understood that various modifications can be made to the above exemplary embodiments without departing from the spirit and scope of the invention. For example, if suitable results can be achieved if the described techniques are performed in a different order and / or if components in the described system, architecture, device, or circuit are combined in different ways and / or replaced or supplemented by other components or their equivalents, then correspondingly, these modified other embodiments also fall within the scope of protection of the claims.

[0068] Industrial practicality

[0069] This invention is particularly applicable to an oscillator circuit with extremely low temperature drift that can be used in applications with a wide temperature range, and to an integrated circuit that includes the oscillator circuit.

[0070] Label Explanation

[0071] 1 Resistor, 2 Capacitor, 3 Schmitt trigger, 4 PMOS transistor, 5 N-type semiconductor substrate, 6 Silicon oxide layer, 7 Polysilicon layer, 8 Source terminal, 9 Drain terminal, 10 Gate terminal, 11 Metal-oxide-metal capacitor, 12 Switching element, 20 Oscillator circuit.

Claims

1. An oscillator circuit, characterized in that, include: A parallel circuit consisting of a resistive element and a flip-flop connected in parallel; as well as A capacitor element having a PMOS transistor connected in series with the parallel circuit. The gate terminal of the PMOS transistor is connected to the power supply side, while the source terminal, drain terminal, and substrate of the PMOS transistor are connected to the ground side.

2. The oscillator circuit as described in claim 1, characterized in that, The temperature coefficient of the capacitor element is a negative temperature coefficient.

3. The oscillator circuit as described in claim 2, characterized in that, In the PMOS transistor, the gate-source capacitance generated between the gate terminal and the source terminal has a negative temperature coefficient.

4. The oscillator circuit as described in claim 2, characterized in that, In the PMOS transistor, the gate-drain capacitance generated between the gate terminal and the drain terminal has a negative temperature coefficient.

5. The oscillator circuit as described in claim 1, characterized in that, The temperature coefficient of the resistive element is a positive temperature coefficient.

6. The oscillator circuit as described in any one of claims 1 to 5, characterized in that, The absolute value of the negative temperature coefficient of the capacitor element is equal to the absolute value of the positive temperature coefficient of the resistor element.

7. The oscillator circuit as described in any one of claims 1 to 5, characterized in that, The capacitor element also has a metal-oxide-metal capacitor connected in parallel with the PMOS transistor.

8. The oscillator circuit as described in claim 7, characterized in that, The temperature coefficient of the capacitor element is adjusted by changing the ratio of the capacitance value of the metal-oxide-metal capacitor to that of the PMOS transistor.

9. The oscillator circuit as described in claim 7, characterized in that, For the metal-oxide-metal capacitor, the capacitance value of the metal-oxide-metal capacitor can be adjusted by adjusting at least one of the following: the number of metal stacking layers, the size of the interdigitated structure, the metal linewidth, and the metal spacing.

10. An integrated circuit, characterized in that, include: The oscillator circuit as described in any one of claims 1 to 9.

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