Oscillation circuit and method for adjusting the bias feedback resistance thereof

Abstract

The application provides an oscillation circuit and a bias feedback resistance adjusting method thereof. The oscillation circuit comprises a resonator, a first capacitor, a second capacitor, a bias feedback resistance adjusting circuit, a current detection circuit and a processing unit. The first capacitor is coupled to a first end point of the resonator. The second capacitor is coupled to a second end point of the resonator. The bias feedback resistance adjusting circuit is coupled to the resonator and comprises an inverting amplifier and a first variable resistance array. The current detection circuit is coupled to the resonator and the bias feedback resistance adjusting circuit and detects a drain current value of the inverting amplifier. The processing unit comprises an operation unit and a storage unit, is coupled to the bias feedback resistance adjusting circuit and the current detection circuit, and adjusts a feedback resistance value of the first variable resistance array according to the drain current value.

Description

Technical Field

[0001] This application relates to an oscillation circuit and a method for adjusting the bias feedback resistor thereon, and more specifically, to an oscillation circuit that can improve the stability of crystal oscillation. Background Technology

[0002] Traditional Pierce crystal oscillator circuits, such as Figure 1 As shown, the circuit includes an inverter INV, a feedback resistor Rf, a current-limiting resistor REXT, and a resonator XTAL. The voltage at the receiving end of the inverter is V1, and the voltage at the output end is V2. The feedback resistor Rf is connected between V1 and V2 of the inverter INV. The current-limiting resistor REXT is connected between V2 and the second shunt capacitor C2. The resonator XTAL (e.g., a quartz crystal) is located between the first shunt capacitor C1 and the second shunt capacitor C2.

[0003] In traditional oscillator circuits, one way to improve oscillation stability is to use a crystal with a lower equivalent series resistance (ESR). However, with the miniaturization and power saving of wearable devices, choosing smaller crystals is becoming the mainstream, and smaller crystals have higher ESR values. Another method is to adjust the load capacitance, but this causes a shift in the resonant frequency. While this improves oscillation stability, it is unacceptable for applications requiring high precision (e.g., 1 ppm). In crystal oscillator circuits, since the feedback resistor is connected between the gate and drain terminals of the inverter, theoretically, a larger feedback resistor value results in a higher safety factor, provided the bias point is designed properly. However, a significant drawback is that at high temperatures and leakage current, a higher feedback resistor value leads to a smaller output voltage amplitude, making the oscillation unstable.

[0004] Therefore, there is an urgent need for an oscillation circuit that can effectively improve oscillation stability while maintaining frequency accuracy without changing the selected high-ESR crystal or the first and second capacitors. There is also an urgent need for a method that can effectively improve oscillation stability while maintaining frequency accuracy without changing the selected high-ESR crystal or the first and second capacitors. Summary of the Invention

[0005] One objective of this application is to provide an oscillation circuit, including a resonator, a first capacitor, a second capacitor, a bias feedback resistor adjustment circuit, a current detection circuit, and a processing unit. The first capacitor is coupled to a first terminal of the resonator. The second capacitor is coupled to a second terminal of the resonator. The bias feedback resistor adjustment circuit, coupled to the resonator, includes an inverting amplifier and a first variable resistor array. The current detection circuit, coupled to the resonator and the bias feedback resistor adjustment circuit, detects the leakage current value of the inverting amplifier. The processing unit, including an arithmetic unit and a storage unit, is coupled to the bias feedback resistor adjustment circuit and the current detection circuit, and adjusts the feedback resistor value of the first variable resistor array based on the leakage current value.

[0006] In one embodiment, the processing unit sets a first threshold, a second threshold, and a third threshold for the feedback resistor value. The first threshold is set to make the safety factor of the oscillation circuit reach 90% of the saturation value, the second threshold is set to make the safety factor 3, and the third threshold is set to make the safety factor 1.

[0007] In one embodiment, the processing unit controls the feedback resistor value of the bias feedback resistor adjustment circuit to the first threshold value, and adjusts and sets the bias point and amplitude of the inverting amplifier through the first variable resistor array, so that the oscillation circuit starts to oscillate.

[0008] In one embodiment, the arithmetic unit calculates the bias point and the safety factor. If the safety factor is less than the second threshold safety factor, the current detection circuit determines a suitable shunt resistor value based on the leakage current value, adjusts the shunt resistor value through the second variable resistor array, measures the leakage current value through the amplified voltage value of the differential amplifier, and calculates the optimal feedback resistor value based on the leakage current value. The optimal feedback resistor value is stored in the storage unit, and the resistance value of the first variable resistor array is adjusted based on the optimal feedback resistor value. The bias point and amplitude are then recalculated.

[0009] In one embodiment, the arithmetic unit recalculates the safety factor. If the safety factor is greater than the third threshold but less than the second threshold, the processing unit substitutes the optimal feedback resistor value from the storage unit into the bias feedback resistor adjustment circuit, updates the bias point and the amplitude, and repeats the steps of substituting the first threshold and then the optimal feedback resistor value calculated by the processing unit, aiming to approach the second threshold, and oscillates using the newly calculated feedback resistor value, and records the first safety warning in the storage unit.

[0010] Another objective of this application is to provide a method for adjusting the bias feedback resistor of an oscillating circuit, applicable to oscillating circuits, comprising: setting a first threshold, a second threshold, and a third threshold for the feedback resistor value; controlling the bias feedback resistor adjustment circuit to update the feedback resistor value; adjusting the bias point and amplitude of the inverting amplifier through a first variable resistor array to start the oscillating circuit oscillation; calculating whether the bias point and the safety factor are greater than the safety factor of the second threshold; if so, maintaining the current setting value and storing this setting value to maintain the oscillation of the oscillating circuit; if not, adjusting the shunt resistor value for measuring the leakage current value through the second variable resistor array, and then measuring the leakage current value through the amplification voltage value of the differential amplifier; calculating the optimal feedback resistor value based on the leakage current value and the bias point threshold; substituting the optimal feedback resistor value into the first variable resistor array to update the bias point and the amplitude; and resetting the bias point to start the oscillating circuit oscillation. The process involves oscillating; recalculating the bias point and whether the safety factor is less than the third threshold safety factor; if the safety factor is greater than the second threshold safety factor, setting a new feedback resistor value for oscillation; if the safety factor is greater than the third threshold safety factor but less than the second threshold safety factor, the processing unit substitutes the optimal feedback resistor value from the storage unit into the bias feedback resistor adjustment circuit, updates the bias point and the amplitude, and repeats the steps of substituting the first threshold and then the optimal feedback resistor value calculated by the processing unit, aiming to approach the second threshold, oscillating with the newly calculated feedback resistor value, and recording the first safety warning in the storage unit; and if the safety factor is less than the third threshold safety factor, the processing unit uses the lowest feedback resistor value of the third threshold to oscillate the oscillation circuit, and records the second safety warning in the storage unit.

[0011] As can be seen from the above, the oscillation circuit provided in this application can effectively improve oscillation stability and maintain frequency accuracy without changing the selected high ESR crystal or the first and second capacitors. Attached Figure Description

[0012] The accompanying drawings are provided to enable those skilled in the art to further understand this application and are incorporated into and constitute a part of this application's specification. The drawings illustrate exemplary embodiments of this application and are used, together with the specification, to explain the principles of this application. The following is a brief description of the various figures:

[0013] Figure 1 This is the traditional Pierce crystal oscillator circuit.

[0014] Figure 2This is a circuit architecture diagram of an oscillation circuit according to an embodiment of this application.

[0015] Figure 3 This is a circuit architecture diagram of a bias feedback resistor adjustment circuit according to an embodiment of this application.

[0016] Figure 4 This is a circuit architecture diagram of a current detection circuit according to an embodiment of this application.

[0017] Figure 5A and Figure 5B This is a diagram showing the relationship between the oscillation safety factor and the feedback resistance of the oscillation circuit designed according to an embodiment of this application.

[0018] Figure 6A The graph shows the relationship between leakage current, feedback resistance, and voltage output amplitude.

[0019] Figure 6B The graph shows the relationship between leakage current, feedback resistance, and voltage output amplitude changes within the maximum voltage decay value of 600mV.

[0020] Figure 7 This is a flowchart illustrating the operation of a bias feedback resistor adjustment method for an oscillating circuit according to an embodiment of this application.

[0021] Symbol explanation:

[0022] R f Feedback resistor; INV inverting amplifier; R EXT Current limiting resistor; XTAL resonator; C1 first shunt capacitor; C2 second shunt capacitor; V1, V2 voltages; 200 oscillation circuit; 202 bias feedback resistor adjustment circuit; 204 current detection circuit; 206 processing unit; 208 variable resistor array; V3 voltage; 302 variable resistor array; MP PMOS; MN NMOS; R f [0]、R f [1]、…、R f

[31] Resistance; V dd Reference voltage; 402 variable resistor array; R E1 R E2 ..., R E15 Shunt resistor; R1 (first resistor); R2 (second resistor); R3 (third resistor); R4 (fourth resistor); C d Capacitor; OP operational amplifier; V IN+ V IN- V OUT Voltage; S702~S718 steps. Detailed Implementation

[0023] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without making any inventive contributions are within the scope of protection of this application.

[0024] In view of the above problems, embodiments of this application have developed an oscillation circuit that can effectively improve oscillation stability and maintain frequency accuracy without changing the selected high ESR crystal or the first and second capacitors.

[0025] Please see Figure 2 One embodiment of this application provides an oscillation circuit 200, including a resonator XTAL, a first capacitor C1, a second capacitor C2, a bias feedback resistor adjustment circuit 202, a current detection circuit 204, and a processing unit 206. The bias feedback resistor adjustment circuit 202 includes a variable resistor array 208 and an inverting amplifier INV. In one embodiment, the resonator XTAL is a quartz crystal, but this application is not limited thereto. In the oscillation circuit 200, the first node of the first capacitor C1 is coupled to the input terminal of the inverting amplifier INV, and the output terminal of the inverting amplifier INV is coupled to the first input node of the current detection circuit 204. The second node of the first capacitor C1 is coupled to ground. The first node of the second capacitor C2 is coupled to the second input node of the current detection circuit 204, and the second node of the resonator XTAL is coupled to the input terminal of the inverting amplifier INV. The second node of the resonator XTAL is coupled to the second input node of the current detection circuit 204. The output node of the current detection circuit 204 is coupled to the first node of the processing unit 206. The second node of processing unit 206 is coupled to the input terminal of inverting amplifier INV, and the third node of processing unit 206 is coupled to the output terminal of inverting amplifier INV. The first node of variable resistor array 208 is coupled to the input terminal of inverting amplifier INV, and the second node of variable resistor array 208 is coupled to the output terminal of inverting amplifier INV, and variable resistor array 208 is controlled by processing unit 206. At this time, the input voltage of inverting amplifier INV is V1, the output voltage of inverting amplifier INV (i.e., the first input node of current detection circuit 204) is V2, and the second input node voltage of current detection circuit 204 is V3.

[0026] Figure 2 The oscillator circuit 200 is a modified version of the previous Pierce oscillator circuit (see...). Figure 1 The current-limiting resistor R in ) EXT Replace with current detection circuit 204, and change the feedback resistor R. fAlong with the inverter INV, a bias feedback resistor adjustment circuit 202 is replaced. The leakage current value detected by the current detection circuit 204 is input to the processing unit 206, which then adjusts the variable resistance value of the bias feedback resistor adjustment circuit 202 based on the leakage current value. Compared to the previous Pierce oscillator circuit, Figure 2 The oscillation circuit 200 can precisely adjust the feedback resistor value based on the detected leakage current value to prevent the leakage current from causing distortion or cessation of the oscillation waveform, thereby improving oscillation stability and maintaining frequency accuracy. The following will describe in detail the circuit structure and operation of the bias feedback resistor adjustment circuit 202, the current detection circuit 204, and the processing unit 206.

[0027] Please see Figure 3 The bias feedback resistor adjustment circuit 202 includes a PMOS MP, an NMOS MN, and a variable resistor array 302. In one embodiment, the variable resistor array 302 includes 32 groups that can be processed by the processing unit 206 ( Figure 3 (Not shown) Switching resistor R f [0]、R f [1], R f

[31] . PMOS MP and NMOS MN form a CMOS inverter, which is... Figure 2 The inverter INV is located within the bias feedback resistor adjustment circuit 202. This embodiment uses a CMOS inverter to implement the inverter INV, but this application is not limited to this. In this embodiment, the source terminal of the PMOS MP of the CMOS inverter formed by PMOS MP and NMOS MN is coupled to the reference voltage V. dd The NMOS MN source terminal is coupled to ground.

[0028] In the previous Pierce oscillator circuit (see...) Figure 1 In the figure, the feedback resistance value R f This is a bias point in the linear region of the transistor that provides the INV of the inverting amplifier. To obtain the maximum oscillation amplitude and avoid the input signal from approaching the saturation or cutoff regions, the bias point is usually taken close to half of the reference voltage, i.e., V. dd / 2. In conventional Pierce oscillator circuits, the typical Rf value is fixed at 1MΩ. In another embodiment, with a reference voltage V... dd The input voltage of the inverting amplifier INV is used as the supply voltage, and a variable current source is used as the input of the inverting amplifier to change the transconductance gain g. m At this point, the bias point will depend on the length, size, and transconductance gain g of the PMOS and NMOS. m The combination determines this. The inverting amplifier INV (e.g.) Figure 3The gate voltage of the CMOS inverter is V1, and the drain voltage is V2. The difference between V1 and V2 is less than the CMOS threshold voltage V. th Since this is the saturation region, the amplifier's operating region is the linear amplification region, effectively amplifying the signal at input terminal V1. In this embodiment, the safety factor value and the feedback resistor value R... f The relationship is as follows:

[0029] C3 = C0 + C s

[0030]

[0031] a=Z1Z3+Z2Z3+g m Z1Z2Z3

[0032] b = Z1 + Z2 + Z3 + g m Z1Z2

[0033]

[0034] Where C0 is the static capacitance, which is a capacitance formed by two electrodes using a quartz crystal as the dielectric. s Z1 represents the stray capacitance in the circuit. Z2 represents the total gate-to-source impedance, Z3 represents the total drain-to-source impedance, and Z4 represents the total drain-to-gate impedance. From the above formula, it can be seen that the safety factor SF is proportional to the feedback resistance value R. f Therefore, the feedback resistance value R f The larger the value, the higher the safety factor and the more stable the circuit.

[0035] In previous Pierce oscillator circuits, the feedback resistance value R f The resistance value is fixed and cannot be changed. This application designs a circuit that allows the resistance value to be changed, altering the original fixed feedback resistance value R. f Modify it to a variable resistor array. Figure 3 In the embodiment shown, there are 32 groups that can be processed by the processing unit 206 ( Figure 3(Not shown) A variable resistor array 302 is switched, wherein the first node of the variable resistor array 302 is coupled to the gate terminal of the CMOS inverting amplifier, and the second node of the variable resistor array 302 is coupled to the drain terminal of the CMOS inverting amplifier. The input terminal of the amplifier is usually set with a fixed bias voltage, but at high temperatures, the transistor has significant leakage current, which may cause the input terminal of the amplifier to deviate from the originally set bias voltage value, causing the positive or negative period of the output signal to enter the saturation or cutoff region, resulting in waveform distortion, and in severe cases, causing oscillation to stop. To improve this problem, this application uses a current detection circuit 204 (see below) to measure the accurate leakage current value, which is then used by the processing unit 206 to calculate the optimal bias feedback resistor, and then adjust the resistance value of the variable resistor array 302 accordingly.

[0036] Please see Figure 4 The current detection circuit 204 includes a variable resistor array 402, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, and a capacitor C. d And operational amplifier OP. The first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4, and operational amplifier OP form a differential amplifier. Figure 4 In the illustrated embodiment, the variable resistor array 402 includes 15 sets of shunt resistors R for measuring current. E1 R E2 ..., R E15 Different shunt resistors are selected based on the magnitude of the current to be detected. The first terminal of the variable resistor array 402 is the first input node V2 of the current detection circuit 204, and its voltage value is V. IN+ The second terminal of the variable resistor array 402 is the second input node V3 of the current detection circuit 204, and its voltage value is V. IN- The first terminal of the first resistor R1 is coupled to the second terminal V3 of the variable resistor array 402, and the second terminal of the first resistor R1 is coupled to the negative input terminal of the operational amplifier OP. The first terminal of the second resistor R2 is coupled to the second terminal of the first resistor R1, and the second terminal of the second resistor R2 is coupled to the output terminal V of the operational amplifier OP. OUT The first terminal of the third resistor R3 is coupled to the first terminal V2 of the variable resistor array 402, and the second terminal of the third resistor R3 is coupled to the positive input terminal of the operational amplifier OP. The first terminal of the fourth resistor R4 is coupled to the second terminal of the third resistor R3, and the second terminal of the fourth resistor R4 is coupled to ground. Capacitor C d The first terminal is coupled to the reference voltage +5V of the operational amplifier OP, and the capacitor C dThe second terminal is coupled to ground. In one embodiment, the resistance of the first resistor R1 is 1KΩ, the resistance of the second resistor R2 is 20KΩ, the resistance of the third resistor R3 is 1KΩ, the resistance of the fourth resistor R4 is 20KΩ, and the capacitor C... d The capacitance value is 0.1μF, but this application is not limited to this.

[0037] This application embodiment replaces the current-limiting resistor R in the traditional Pierce circuit. EXT Replacing it with current sensing circuit 204 has the major advantage of not requiring additional changes to the external configuration of the oscillation circuit, including the current-limiting resistor R. EXT The shunt resistor is replaced with one used for current measurement. Different types of shunt resistors are selected based on the magnitude of the current to be measured. When using a shunt resistor, a smaller resistance value is needed for measuring large currents, and a larger resistance value is needed for measuring small currents. In this embodiment, a large resistance is used for measuring small currents. Since the leakage current is in the nanoampere (nA) range, the voltage drop is relatively small, which may cause the processing unit 206 to have difficulty detecting accurate voltage. Therefore, this embodiment is designed to use the shunt resistors of the variable resistor array 402 in conjunction with a differential amplifier for current measurement. Figure 4 As shown, this embodiment uses a differential amplifier circuit to detect the current. The amplifier converts the low voltage generated between the shunt resistors in the variable resistor array 402 into a higher voltage for the processing unit to detect. In this embodiment, the differential amplifier circuit uses a 20x amplification factor as an example (but is not limited to this). Through experimental measurement of minute currents in the nA range, the amplification factor in some embodiments is 20 to 100x. The amplification factor formula is as follows:

[0038]

[0039] When R1 = R3 and R2 = R4, the above equation can be simplified to:

[0040]

[0041] Therefore, V IN+ and V IN- The difference is magnified by a factor of (R2 / R1). In one embodiment, the magnification factor is 20 times, but this application is not limited thereto.

[0042] The processing unit 206 includes an arithmetic unit and a storage unit. In one embodiment, the processing unit 206 first sets a maximum feedback resistance value for the oscillation circuit. Ideally, the feedback resistance value is designed to be infinitely large, but in reality, an infinitely large resistance does not exist. Therefore, a relatively large resistance value is designed first to approximate the ideal state. Figure 5A and Figure 5B This is a diagram showing the relationship between the oscillation safety factor and the feedback resistance of the oscillation circuit designed according to the embodiments of this application. Figure 5A and Figure 5B It is known that when the feedback resistance value is 100MΩ, it is close to 90% of the safety factor saturation value. Further increasing the safety factor will not significantly improve its effectiveness. Therefore, this embodiment sets three thresholds (but not limited to these): the first threshold is 90% of the safety factor saturation value, the second threshold is 3 times the safety factor, and the third threshold is 1 times the safety factor. In the oscillation circuit, oscillation can start when the safety factor is 1, and a safety factor greater than or equal to 3 is a safer design. Therefore, in this embodiment, the first (highest) threshold for the feedback resistance is set to 100MΩ, the second (3 times) threshold is 8MΩ, and the third (lowest) threshold is 2MΩ.

[0043] Subsequently, in one embodiment, the processing unit 206 controls the bias feedback resistor adjustment circuit 202 to update the feedback resistor value. The first time, a preset first threshold is substituted, and then the optimal feedback resistor value calculated by the processing unit 206 is substituted. The bias point and amplitude of the inverting amplifier INV are adjusted by the variable resistor array 208, so that the oscillation circuit 200 starts to oscillate.

[0044] Subsequently, in one embodiment, the arithmetic unit in the processing unit 206 calculates the current bias point and whether the safety factor is greater than the second threshold safety factor. When the safety factor is greater than the second threshold safety factor, the current setting value is maintained and stored in the storage unit to maintain the oscillation of the oscillation circuit 200.

[0045] In one embodiment, when the safety factor is less than the second threshold safety factor, the current detection circuit 204 determines an appropriate shunt resistor value based on the magnitude of the leakage current, adjusts the shunt resistor value for measuring the leakage current through the variable resistor array 402, and then measures the accurate leakage current value through the amplified voltage value of the differential amplifier.

[0046] In one embodiment, when the safety factor calculated by the arithmetic unit in processing unit 206 is less than the safety factor of the second threshold but greater than the safety factor of the third threshold, it indicates that the leakage current value at this time affects the bias point and output amplitude value of the inverter INV. In this case, the leakage current value is measured by the current detection circuit 204, and the optimal feedback resistance value is calculated by processing unit 206.

[0047] Figure 6A This is a graph showing the relationship between leakage current, feedback resistance, and changes in voltage output amplitude. Figure 6AIt can be seen that at low leakage current (e.g., I = 1nA), if the maximum feedback resistance is 100MΩ, the voltage attenuation is approximately 0.1V. However, at high leakage current (e.g., I = 100nA), if the maximum feedback resistance is 100MΩ, the voltage attenuation is approximately 10V. Therefore, the original maximum feedback resistance of 100MΩ would result in a 10V voltage attenuation. Since the typical bias point of a general inverting amplifier is approximately 300mV to 600mV, and this embodiment uses the maximum design value of 600mV, meaning that at high temperature leakage current, the voltage attenuation cannot exceed 600mV. Therefore, a 100MΩ resistance value is unusable.

[0048] Figure 6B This graph shows the relationship between leakage current, feedback resistance, and voltage output amplitude changes within a maximum voltage decay value of 600mV. Figure 6B It can be seen that at low leakage current (e.g., I = 1nA), if the maximum feedback resistance is 100MΩ, the attenuation voltage is approximately 0.1V, which is within the usable range. However, at high leakage current (e.g., I = 100nA), to meet the condition that the attenuation voltage is less than or equal to 0.6V, the maximum feedback resistance is 6MΩ. In this way, the arithmetic unit in processing unit 206 calculates the relationship between leakage current and feedback resistance, finds the optimal feedback resistance, and stores it in the storage unit.

[0049] Subsequently, in one embodiment, the processing unit 206 substitutes the optimal feedback resistor value stored in the storage unit into the bias feedback resistor adjustment circuit 202. Through the variable resistor array 208 designed in this application, the corresponding resistance value can be directly changed without replacing the physical resistor. After substituting the optimal feedback resistor value, the processing unit 206 recalculates the amplifier bias point and amplitude, and the circuit begins to oscillate.

[0050] Subsequently, in one embodiment, the arithmetic unit in the processing unit 206 calculates the current bias point and whether the safety factor is less than the third threshold. When the safety factor is less than the third threshold, the lowest feedback resistance value of the aforementioned third threshold is used to ensure that the oscillation circuit 200 can oscillate normally, and a second safety warning is recorded in the storage unit. When the safety factor is greater than the third threshold but less than the second threshold, the processing unit 206 substitutes the optimal feedback resistance value in the storage unit into the bias feedback resistance adjustment circuit 202, updates the bias point and amplitude, and repeats the steps of substituting the preset first threshold and then the optimal feedback resistance value calculated by the processing unit 206, aiming to approach the second threshold. Subsequently, oscillation is performed using the newly calculated feedback resistance value, and a first safety warning is recorded in the storage unit. If the safety factor is greater than the second threshold, a new feedback resistance value is set for oscillation. If none of the feedback resistance values ​​adjusted by the variable resistor array 208 can exceed the second threshold, the processing unit will automatically reduce the multiplier to rematch the resistance values ​​until they are less than the third threshold. Then, the processing unit 206 will use the lowest feedback resistance value to oscillate the oscillation circuit 200 and record this value in the storage unit.

[0051] This application also provides a method for adjusting the bias feedback resistor of an oscillator circuit, which can effectively improve oscillation stability and maintain frequency accuracy without changing the high ESR crystal selected for the oscillator circuit or the first and second capacitors. Please refer to [link to relevant documentation]. Figure 7 To gain a more detailed understanding of the operation of the bias feedback resistor adjustment method for the oscillation circuit provided in this application.

[0052] First, in step S702, the processing unit 206 sets a first, second, and third threshold value for the feedback resistor. In one embodiment, the first threshold is 90% of the safety factor saturation value, the second threshold is 3 times the safety factor, and the third threshold is 1 times the safety factor.

[0053] Next, in step S704, the processing unit 206 controls the bias feedback resistor adjustment circuit 202 to update the feedback resistor value, and adjusts the bias point and amplitude of the inverting amplifier INV through the variable resistor array 208, so that the oscillation circuit 200 starts to oscillate.

[0054] Subsequently, in step S706, the arithmetic unit of processing unit 206 calculates the current bias point and whether the safety factor is greater than the second threshold safety factor. Based on whether the safety factor is greater than the second threshold safety factor, the process is divided into two paths. If yes, the process proceeds to step S708. If no, the process proceeds to step S710.

[0055] In step S708, the current setting value is maintained and stored in the storage unit, the oscillation of the oscillation circuit 200 is maintained, and the process ends.

[0056] In step S710, the current detection circuit 204 adjusts the shunt resistor value for measuring leakage current through the variable resistor array 402, and then measures the accurate leakage current value by amplifying the voltage value through the differential amplifier.

[0057] Subsequently, in step S712, the processing unit 206 calculates the optimal feedback resistance value based on the leakage current value and the set bias point threshold. In one embodiment, the bias point threshold is 600mV.

[0058] Subsequently, in step S714, the bias feedback resistor adjustment circuit 202 updates the bias point and output amplitude by substituting the optimal feedback resistor value into the variable resistor array 208.

[0059] Subsequently, in step S716, the processing unit 206 resets the amplifier bias point, causing the oscillation circuit 200 to start oscillating.

[0060] Subsequently, in step S718, the arithmetic unit in processing unit 206 calculates the current bias point and whether the safety factor is less than the third threshold safety factor. Based on the current safety factor, the process is divided into three paths.

[0061] If, in step S718, the safety factor is greater than the second threshold safety factor, the process proceeds to step S720, a new feedback resistor value is set for oscillation, and the process ends.

[0062] If, in step S718, the safety factor is greater than the third threshold but less than the second threshold, the process proceeds to step S722. Processing unit 206 substitutes the optimal feedback resistor value from the storage unit into the bias feedback resistor adjustment circuit 202, updating the bias point and amplitude. The process then repeats the steps of substituting the preset first threshold and then the optimal feedback resistor value calculated by processing unit 206, aiming to approach the second threshold. Subsequently, the process proceeds to step S724, where the newly calculated feedback resistor value is used for oscillation, and a first safety warning is recorded in the storage unit, ending the process.

[0063] If the safety factor is less than the third threshold safety factor in step S718, the process proceeds to step S726, where the processing unit 206 uses the lowest feedback resistance value of the third threshold to oscillate the oscillation circuit 200, records a second safety warning in the storage unit, and the process ends.

[0064] As can be seen from the above, the oscillation circuit provided in this application can effectively improve oscillation stability and maintain frequency accuracy without changing the selected high ESR crystal or the first and second capacitors.

[0065] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An oscillation circuit, characterized in that, include: A resonator; A first capacitor is coupled to a first terminal of the resonator; A second capacitor is coupled to a second terminal of the resonator; A bias feedback resistor adjustment circuit is coupled to the resonator, and the bias feedback resistor adjustment circuit includes an inverting amplifier and a first variable resistor array. A current detection circuit, coupled to the resonator and the bias feedback resistor adjustment circuit, detects a leakage current value of the inverting amplifier. as well as A processing unit, including an arithmetic unit and a storage unit, is coupled to the bias feedback resistor adjustment circuit and the current detection circuit, and adjusts a feedback resistor value of the first variable resistor array according to the leakage current value.

2. The oscillation circuit as described in claim 1, characterized in that, The current detection circuit includes a second variable resistor array and a differential amplifier. The second variable resistor array is a shunt resistor. The second variable resistor array detects the leakage current value, and the differential amplifier amplifies the leakage current value for use by the processing unit.

3. The oscillation circuit as described in claim 2, characterized in that, The processing unit sets a first threshold, a second threshold, and a third threshold for the feedback resistor value. The first threshold is set to make a safety factor of the oscillation circuit reach 90% of the saturation value. The second threshold is set to make the safety factor 3. The third threshold is set to make the safety factor 1.

4. The oscillation circuit as described in claim 3, characterized in that, The processing unit controls the feedback resistor value of the bias feedback resistor adjustment circuit to the first threshold value, and adjusts and sets a bias point and an amplitude of the inverting amplifier through the first variable resistor array, so that the oscillation circuit starts to oscillate.

5. The oscillation circuit as described in claim 4, characterized in that, The arithmetic unit calculates the bias point and the safety factor. If the safety factor is greater than the second threshold safety factor, the current setting value is maintained and stored in the storage unit to maintain the oscillation of the oscillation circuit.

6. The oscillation circuit as described in claim 4, characterized in that, The arithmetic unit calculates the bias point and the safety factor. If the safety factor is less than the second threshold safety factor, the current detection circuit determines a suitable shunt resistor value based on the leakage current value, adjusts the shunt resistor value through the second variable resistor array, measures the leakage current value through the amplified voltage value of the differential amplifier, and calculates an optimal feedback resistor value based on the leakage current value. The optimal feedback resistor value is stored in the storage unit, and the resistance value of the first variable resistor array is adjusted based on the optimal feedback resistor value. The bias point and amplitude are then recalculated.

7. The oscillation circuit as described in claim 6, characterized in that, The optimal feedback resistor value is related to the bias point of the inverting amplifier.

8. The oscillation circuit as described in claim 6, characterized in that, The arithmetic unit recalculates the safety factor. If the safety factor is less than the third threshold safety factor, the feedback resistor value of the third threshold is used to ensure that the oscillation circuit can oscillate normally, and a second safety warning is recorded in the storage unit.

9. The oscillation circuit as described in claim 6, characterized in that, The arithmetic unit recalculates the safety factor. If the safety factor is greater than the third threshold but less than the second threshold, the processing unit substitutes the optimal feedback resistor value in the storage unit into the bias feedback resistor adjustment circuit, updates the bias point and the amplitude, and repeats the steps of substituting the first threshold and then the optimal feedback resistor value calculated by the processing unit, aiming to approach the second threshold, and oscillates using the newly calculated feedback resistor value, and records a first safety warning in the storage unit.

10. A method for adjusting the bias feedback resistor of an oscillating circuit, applicable to an oscillating circuit, characterized in that, The method for adjusting the bias feedback resistor of the oscillation circuit includes: Set a first threshold, a second threshold, and a third threshold for a feedback resistor value; A bias feedback resistor adjustment circuit is controlled to update the feedback resistor value. A bias point and an amplitude of an inverting amplifier are adjusted and set through a first variable resistor array, so that the oscillation circuit starts to oscillate. Calculate the bias point and whether a safety factor is greater than the second threshold safety factor. If yes, maintain the current setting value and store this setting value to maintain the oscillation of the oscillation circuit. If no, adjust the value of a shunt resistor for measuring a leakage current value through a second variable resistor array, and then measure the leakage current value through the amplified voltage value of a differential amplifier. Based on the leakage current value and a bias point threshold, calculate an optimal feedback resistance value; By substituting the optimal feedback resistance value into the first variable resistor array, the bias point and the amplitude are updated. The bias point is reset to make the oscillation circuit start oscillating; Recalculate the bias point and whether the safety factor is less than the third threshold safety factor; If the security factor is greater than the security factor of the second threshold, then a new feedback resistor value is set to oscillate. If the safety factor is greater than the third threshold but less than the second threshold, the processing unit substitutes the optimal feedback resistor value from a storage unit into the bias feedback resistor adjustment circuit, updates the bias point and the amplitude, and repeats the steps of substituting the first threshold and then the optimal feedback resistor value calculated by the processing unit, aiming to approach the second threshold, oscillating with the newly calculated feedback resistor value, and recording a first safety warning in the storage unit; and If the safety factor is less than the third threshold safety factor, the processing unit uses the lowest feedback resistance value of the third threshold to perform oscillation of the oscillation circuit and records a second safety warning in the storage unit.

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