A filter bandwidth automatic calibration circuit and method

Abstract

The present invention discloses a filter bandwidth automatic calibration circuit and method. The present invention calculates the preset number of clock cycles that an RC relaxation oscillator should generate according to the tuning resistance and tuning capacitance of the RC relaxation oscillator, records the actual number of clock cycles generated by the RC relaxation oscillator, determines the preset tuning control signal corresponding to the preset number of clock cycles, calculates the actual tuning control signal corresponding to the actual number of clock cycles according to the preset number of clock cycles, the preset tuning control signal and the actual number of clock cycles, adjusts the capacitance of the tuning capacitor to the capacitance corresponding to the actual tuning control signal, controls the capacitance error of the bandwidth adjustment capacitor and the tuning capacitor in the filter to be within an allowable range, can automatically calibrate the bandwidth of the filter, and compared with the traditional phase-locked loop structure of the voltage-controlled oscillator, the circuit structure is simple and the power consumption is low.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to a filter bandwidth automatic calibration circuit and method. Background Art

[0002] The filter composed of capacitors and resistors is widely used in CMOS integrated circuit design because of its simple structure and good linearity. The capacitors and resistors in the filter are affected by the manufacturing process, power supply voltage and ambient temperature, which will cause their resistance and capacitance values ​​to deviate from the ideal values, affecting the value of the filter bandwidth and making the filter unable to work properly. Therefore, it is necessary to calibrate the resistance and capacitance values ​​to correct the filter bandwidth.

[0003] Existing filter bandwidth calibration methods include off-chip calibration and on-chip calibration. In order to save circuit area and meet the requirements of high integration, on-chip calibration is usually used. Common on-chip calibration methods mainly include a phase-locked loop structure based on a voltage-controlled oscillator, which has a complex structure, high power consumption, and increases the chip area. Summary of the invention

[0004] The present invention solves the technical problem of how to calibrate the bandwidth of a filter composed of capacitors and resistors by providing a filter bandwidth automatic calibration circuit and method.

[0005] On the one hand, the present invention provides the following technical solutions:

[0006] A filter bandwidth automatic calibration circuit includes an RC relaxation oscillator and a controller, wherein the RC relaxation oscillator includes a first voltage-dividing resistor, a second voltage-dividing resistor, a feedback resistor, a tuning resistor, a tuning capacitor, and an operational amplifier;

[0007] The power supply is connected to the ground via the first voltage-dividing resistor and the second voltage-dividing resistor in sequence, the common end of the first voltage-dividing resistor and the second voltage-dividing resistor is connected to the non-inverting input end of the operational amplifier, the non-inverting input end of the operational amplifier is also connected to the output end of the operational amplifier via the feedback resistor, the output end of the operational amplifier is also connected to the inverting input end of the operational amplifier via the tuning resistor, the inverting input end of the operational amplifier is also connected to the ground via the tuning capacitor, the resistance error of the first voltage-dividing resistor, the second voltage-dividing resistor and the feedback resistor is within the allowable range, and the unit resistance error of the first voltage-dividing resistor, the second voltage-dividing resistor, the feedback resistor, the tuning resistor and the bandwidth adjustment resistor in the filter is within the allowable range;

[0008] The output end of the operational amplifier is also connected to the input end of the controller, the first output end of the controller is connected to the tuning capacitor, and the second output end of the controller is connected to the filter. The controller is used to calculate the preset number of clock cycles that the RC relaxation oscillator should generate based on the tuning resistance and the tuning capacitor, record the actual number of clock cycles generated by the RC relaxation oscillator, determine the preset tuning control signal corresponding to the preset number of clock cycles, calculate the actual tuning control signal corresponding to the actual number of clock cycles based on the preset number of clock cycles, the preset tuning control signal and the actual number of clock cycles, adjust the capacitance of the tuning capacitor to the capacitance corresponding to the actual tuning control signal, and control the capacitance error of the bandwidth adjustment capacitor in the filter and the tuning capacitor to be within an allowable range.

[0009] Preferably, the first voltage-dividing resistor, the second voltage-dividing resistor, and the feedback resistor have the same resistance value.

[0010] Preferably, the first voltage-dividing resistor, the second voltage-dividing resistor, the feedback resistor, the tuning resistor, and the bandwidth adjustment resistor in the filter have the same unit resistance.

[0011] Preferably, the controller is also used to control the capacitance of the bandwidth adjustment capacitor in the filter to be the same as the capacitance of the tuning capacitor.

[0012] Preferably, the controller is also used for:

[0013] Calculate the ideal charge and discharge frequency of the RC relaxation oscillator based on the tuning resistance and tuning capacitance;

[0014] The preset number of clock cycles is calculated according to the ideal charge and discharge frequency.

[0015] Preferably, the ideal charge and discharge frequency satisfies: f0 is the ideal charge and discharge frequency, R is the resistance of the tuning resistor, and C is the capacitance of the tuning capacitor.

[0016] Preferably, the preset number of clock cycles satisfies: N0 is the number of the preset clock cycles, f ox is the clock signal, and b is the number of binary bits of the counter used by the controller.

[0017] Preferably, the actual tuning control signal satisfies: F c is the actual tuning control signal, F0 is the preset tuning control signal, and N is the number of actual clock cycles.

[0018] Preferably, the tuning capacitor includes a normally-open capacitor and a plurality of capacitor branches connected in parallel with the normally-open capacitor, and each of the capacitor branches is formed by a capacitor and a switch connected in series.

[0019] On the other hand, the present invention also provides the following technical solutions:

[0020] A filter bandwidth automatic calibration method, applied to any of the controllers described above, comprising:

[0021] Calculating the number of preset clock cycles that the RC relaxation oscillator should generate based on the tuning resistance and the tuning capacitance of the RC relaxation oscillator;

[0022] Recording the actual number of clock cycles generated by the RC relaxation oscillator, and determining a preset tuning control signal corresponding to the preset number of clock cycles;

[0023] Calculating an actual tuning control signal corresponding to the actual number of clock cycles according to the preset number of clock cycles, the preset tuning control signal and the actual number of clock cycles;

[0024] The capacitance of the tuning capacitor is adjusted to the capacitance corresponding to the actual tuning control signal, and the capacitance of the bandwidth adjustment capacitor in the control filter is controlled to be the same as the capacitance of the tuning capacitor.

[0025] One or more technical solutions provided by the present invention have at least the following technical effects or advantages:

[0026] The preset number of clock cycles that the RC relaxation oscillator should generate is calculated based on the tuning resistance and tuning capacitance of the RC relaxation oscillator, the actual number of clock cycles generated by the RC relaxation oscillator is recorded, the preset tuning control signal corresponding to the preset number of clock cycles is determined, the actual tuning control signal corresponding to the actual number of clock cycles is calculated based on the preset number of clock cycles, the preset tuning control signal and the actual number of clock cycles, the capacitance of the tuning capacitor is adjusted to the capacitance corresponding to the actual tuning control signal, the capacitance error of the bandwidth adjustment capacitor in the control filter and the capacitance of the tuning capacitor are controlled within an allowable range, the broadband of the filter can be automatically calibrated, and compared with the traditional phase-locked loop structure of the voltage-controlled oscillator, the circuit structure is simple and the power consumption is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 is a circuit diagram of a filter bandwidth automatic calibration circuit in an embodiment of the present invention;

[0029] Figure 2 is a circuit diagram of a tuning capacitor in an embodiment of the present invention;

[0030] Figure 3 Flow chart of the automatic filter bandwidth calibration method in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The embodiment of the present invention solves the technical problem of how to calibrate the bandwidth of a filter composed of capacitors and resistors by providing a filter bandwidth automatic calibration circuit and method.

[0032] In order to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0033] First of all, the term "and / or" in this article is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0034] like Figure 1 As shown, the filter bandwidth automatic calibration circuit of this embodiment includes an RC relaxation oscillator and a controller. The RC relaxation oscillator includes a first voltage-dividing resistor, a second voltage-dividing resistor, a feedback resistor, a tuning resistor, a tuning capacitor, and an operational amplifier.

[0035] The power supply is connected to the ground via the first voltage-dividing resistor and the second voltage-dividing resistor in sequence, the common end of the first voltage-dividing resistor and the second voltage-dividing resistor is connected to the non-inverting input end of the operational amplifier, the non-inverting input end of the operational amplifier is also connected to the output end of the operational amplifier via the feedback resistor, the output end of the operational amplifier is also connected to the inverting input end of the operational amplifier via the tuning resistor, the inverting input end of the operational amplifier is also connected to the ground via the tuning capacitor, the resistance error of the first voltage-dividing resistor, the second voltage-dividing resistor and the feedback resistor is within the allowable range, and the unit resistance error of the first voltage-dividing resistor, the second voltage-dividing resistor, the feedback resistor, the tuning resistor and the bandwidth adjustment resistor in the filter is within the allowable range.

[0036] The output end of the operational amplifier is also connected to the input end of the controller, the first output end of the controller is connected to the tuning capacitor, and the second output end of the controller is connected to the filter. The controller is used to calculate the preset number of clock cycles that the RC relaxation oscillator should generate based on the tuning resistance and the tuning capacitor, record the actual number of clock cycles generated by the RC relaxation oscillator, determine the preset tuning control signal corresponding to the preset number of clock cycles, calculate the actual tuning control signal corresponding to the actual number of clock cycles based on the preset number of clock cycles, the preset tuning control signal and the actual number of clock cycles, adjust the capacitance of the tuning capacitor to the capacitance corresponding to the actual tuning control signal, and control the capacitance error of the bandwidth adjustment capacitor in the filter and the tuning capacitor to be within an allowable range.

[0037] Among them, the resistance values ​​of the first voltage-dividing resistor, the second voltage-dividing resistor, and the feedback resistor should be the same, the unit resistance of the first voltage-dividing resistor, the second voltage-dividing resistor, the feedback resistor, the tuning resistor, and the bandwidth adjustment resistor in the filter should be the same, and the capacitance of the bandwidth adjustment capacitor in the filter should be the same as the capacitance of the tuning capacitor. However, considering that the manufacturing process of resistors and capacitors may cause the characteristics of the two devices to not be exactly the same, it is allowed to be within the error range, but preferably the same.

[0038] The first voltage-dividing resistor, the second voltage-dividing resistor, the feedback resistor, the tuning resistor and the bandwidth adjustment resistor in the filter can all be composed of multiple unit resistors connected in series or in parallel. For example, if the tuning resistor includes 4 2k resistors, two 2k resistors are connected in parallel and then in series with two 2k resistors to obtain a 5K tuning resistor, and the unit resistance of the tuning resistor is 2k. The first voltage-dividing resistor, the second voltage-dividing resistor, the feedback resistor, the tuning resistor and the bandwidth adjustment resistor in the filter have the same unit resistance, which can be understood as: if the unit resistance of the bandwidth adjustment resistor in the filter is 2k, then the first voltage-dividing resistor, the second voltage-dividing resistor, the feedback resistor, the tuning resistor and the bandwidth adjustment resistor in the filter are all obtained by connecting 2k resistors in series and in parallel, which can ensure that the manufacturing process, power supply voltage and ambient temperature have the same influence on the RC relaxation oscillator and the resistors in the filter, thereby ensuring the calibration of the filter bandwidth.

[0039] The structure of the tuning capacitor is the same as that of the bandwidth adjustment capacitor in the filter. Figure 2 As shown, the tuning capacitor or the bandwidth adjustment capacitor of the filter may include a normally open capacitor and a plurality of capacitor branches connected in parallel with the normally open capacitor, each capacitor branch being composed of a capacitor and a switch connected in series. The controller controls the opening and closing of the switch in the tuning capacitor by outputting an actual tuning control signal to adjust the capacitance of the tuning capacitor, and controls the opening and closing of the switch in the bandwidth adjustment capacitor by outputting a bandwidth control signal to adjust the capacitance of the bandwidth adjustment capacitor, which is equivalent to each actual tuning control signal corresponding to the capacitance of a tuning capacitor, and each bandwidth control signal corresponding to the capacitance of a bandwidth adjustment capacitor. When the actual tuning control signal is the same as the bandwidth control signal, the capacitance of the tuning capacitor is the same as the capacitance of the bandwidth adjustment capacitor.

[0040] In this embodiment, the controller is used to calculate the ideal charge and discharge frequency of the RC relaxation oscillator according to the tuning resistance and the tuning capacitance, and calculate the preset number of clock cycles according to the ideal charge and discharge frequency. The ideal charge and discharge frequency is the charge and discharge frequency of the RC relaxation oscillator when it is not affected by process parameters, power supply voltage and ambient temperature, and satisfies: f0 is the ideal charge and discharge frequency, R is the resistance of the tuning resistor, and C is the capacitance of the tuning capacitor. The preset number of clock cycles is the number of clock cycles generated by the RC relaxation oscillator when the RC relaxation oscillator is not affected by process parameters, power supply voltage, and ambient temperature, and satisfies: N0 is the number of preset clock cycles, f ox is the clock signal, and b is the number of binary bits of the counter used by the controller.

[0041] Assuming that there is no influence of manufacturing process, power supply voltage and ambient temperature, the actual charge and discharge frequency of the RC relaxation oscillator obtained by the controller should be the same as the ideal charge and discharge frequency, and the actual number of clock cycles generated by the RC relaxation oscillator should be the same as the preset number of clock cycles. Since resistance and capacitance are affected by process parameters, power supply voltage and ambient temperature, the charge and discharge frequency generated by the RC relaxation oscillator also changes. If the tuning capacitor C is affected by process parameters, power supply voltage and ambient temperature and its capacitance becomes C1, and the tuning resistor R remains unchanged, then the charge and discharge frequency f1 generated by C1 through the RC relaxation oscillator satisfies This shows that the change of the tuning capacitor C can be reflected by the difference in the charge and discharge frequency of the RC relaxation oscillator. The change of the resistance of the tuning resistor R with the process parameters, power supply voltage and ambient temperature can be attributed to the change of the capacitance of the tuning capacitor C.

[0042] When the bandwidth of the filter is affected by process parameters, power supply voltage and ambient temperature, the RC relaxation oscillator is also affected in the same way and has the same effect. The bandwidth of the filter can be calibrated by calculating the capacitance of the tuning capacitor corresponding to the actual tuning control signal. c is the actual tuning control signal, F0 is the preset tuning control signal, and N is the actual number of clock cycles. Therefore, after obtaining the preset number of clock cycles, the preset tuning control signal, and the actual number of clock cycles, The actual tuning control signal corresponding to the capacitance of the bandwidth adjustment capacitor for calibrating the filter bandwidth is calculated, and then the capacitance of the tuning capacitor corresponding to the actual tuning control signal can be obtained, that is, the capacitance of the bandwidth adjustment capacitor for calibrating the filter bandwidth.

[0043] As can be seen from the above, the filter bandwidth automatic calibration circuit of this embodiment calculates the preset number of clock cycles that the RC relaxation oscillator should generate based on the tuning resistance and tuning capacitance of the RC relaxation oscillator, records the actual number of clock cycles generated by the RC relaxation oscillator, determines the preset tuning control signal corresponding to the preset number of clock cycles, calculates the actual tuning control signal corresponding to the actual number of clock cycles based on the preset number of clock cycles, the preset tuning control signal and the actual number of clock cycles, adjusts the capacitance of the tuning capacitor to the capacitance corresponding to the actual tuning control signal, controls the capacitance error of the bandwidth adjustment capacitor in the filter and the capacitance error of the tuning capacitor to be within the allowable range, and can automatically calibrate the broadband of the filter. Compared with the traditional phase-locked loop structure of the voltage-controlled oscillator, the circuit structure is simple and the power consumption is low.

[0044] It should be noted that calibrating the bandwidth of the filter will affect the normal operation of the filter. In this embodiment, the filter is calibrated through the filter bandwidth automatic calibration circuit only when the change of the bandwidth control signal exceeds the set range.

[0045] like Figure 3 As shown, this embodiment also provides a filter bandwidth automatic calibration method, which is applied to the above controller, including:

[0046] Step S1, calculating the number of preset clock cycles that the RC relaxation oscillator should generate according to the tuning resistance and the tuning capacitance of the RC relaxation oscillator;

[0047] Step S2, recording the actual number of clock cycles generated by the RC relaxation oscillator, and determining a preset tuning control signal corresponding to the preset number of clock cycles;

[0048] Step S3, calculating an actual tuning control signal corresponding to the actual number of clock cycles according to the preset number of clock cycles, the preset tuning control signal and the actual number of clock cycles;

[0049] Step S4, adjusting the capacitance of the tuning capacitor to the capacitance corresponding to the actual tuning control signal, and controlling the capacitance error between the capacitance of the bandwidth adjustment capacitor in the filter and the capacitance of the tuning capacitor to be within an allowable range.

[0050] The filter bandwidth automatic calibration circuit of the present embodiment calculates the preset number of clock cycles that the RC relaxation oscillator should generate based on the tuning resistance and tuning capacitance of the RC relaxation oscillator, records the actual number of clock cycles generated by the RC relaxation oscillator, determines the preset tuning control signal corresponding to the preset number of clock cycles, calculates the actual tuning control signal corresponding to the actual number of clock cycles based on the preset number of clock cycles, the preset tuning control signal and the actual number of clock cycles, adjusts the capacitance of the tuning capacitor to the capacitance corresponding to the actual tuning control signal, controls the capacitance error of the bandwidth adjustment capacitor and the tuning capacitor in the filter to be within the allowable range, and can automatically calibrate the broadband of the filter. Compared with the traditional phase-locked loop structure of the voltage-controlled oscillator, the circuit structure is simple and the power consumption is low.

[0051] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0052] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A filter bandwidth automatic calibration circuit, characterized in that: It includes an RC relaxation oscillator and a controller, wherein the RC relaxation oscillator includes a first voltage-dividing resistor, a second voltage-dividing resistor, a feedback resistor, a tuning resistor, a tuning capacitor, and an operational amplifier; The power supply is connected to the ground via the first voltage-dividing resistor and the second voltage-dividing resistor in sequence, the common end of the first voltage-dividing resistor and the second voltage-dividing resistor is connected to the non-inverting input end of the operational amplifier, the non-inverting input end of the operational amplifier is also connected to the output end of the operational amplifier via the feedback resistor, the output end of the operational amplifier is also connected to the inverting input end of the operational amplifier via the tuning resistor, the inverting input end of the operational amplifier is also connected to the ground via the tuning capacitor, the resistance error of the first voltage-dividing resistor, the second voltage-dividing resistor and the feedback resistor is within the allowable range, and the unit resistance error of the first voltage-dividing resistor, the second voltage-dividing resistor, the feedback resistor, the tuning resistor and the bandwidth adjustment resistor in the filter is within the allowable range; The output end of the operational amplifier is also connected to the input end of the controller, the first output end of the controller is connected to the tuning capacitor, and the second output end of the controller is connected to the filter. The controller is used to calculate the preset number of clock cycles that the RC relaxation oscillator should generate according to the tuning resistance and the tuning capacitor, record the actual number of clock cycles generated by the RC relaxation oscillator, determine the preset tuning control signal corresponding to the preset number of clock cycles, calculate the actual tuning control signal corresponding to the actual number of clock cycles according to the preset number of clock cycles, the preset tuning control signal and the actual number of clock cycles, adjust the capacitance of the tuning capacitor to the capacitance corresponding to the actual tuning control signal, and control the capacitance error of the bandwidth adjustment capacitor in the filter and the tuning capacitor to be within an allowable range; The actual tuning control signal satisfies: = , is the actual tuning control signal, is the preset tuning control signal, is the actual number of clock cycles, is the preset number of clock cycles.

2. The filter bandwidth automatic calibration circuit according to claim 1, characterized in that: The first voltage-dividing resistor, the second voltage-dividing resistor, and the feedback resistor have the same resistance value.

3. The filter bandwidth automatic calibration circuit according to claim 1, characterized in that: The first voltage-dividing resistor, the second voltage-dividing resistor, the feedback resistor, the tuning resistor, and the bandwidth adjusting resistor in the filter have the same unit resistance.

4. The filter bandwidth automatic calibration circuit according to claim 1, characterized in that: The controller is also used to control the capacitance of the bandwidth adjustment capacitor in the filter to be the same as the capacitance of the tuning capacitor.

5. The filter bandwidth automatic calibration circuit according to claim 1, characterized in that: The controller is also used to: Calculate the ideal charge and discharge frequency of the RC relaxation oscillator based on the tuning resistance and tuning capacitance; The preset number of clock cycles is calculated according to the ideal charge and discharge frequency.

6. The filter bandwidth automatic calibration circuit according to claim 5, characterized in that: The ideal charge and discharge frequency satisfies: , is the ideal charge and discharge frequency, R is the resistance of the tuning resistor, and C is the capacitance of the tuning capacitor.

7. The filter bandwidth automatic calibration circuit according to claim 6, characterized in that: The preset number of clock cycles satisfies: = , is the clock signal, The number of binary bits of the counter used by the controller.

8. The filter bandwidth automatic calibration circuit according to claim 1, characterized in that: The tuning capacitor includes a normally-open capacitor and a plurality of capacitor branches connected in parallel with the normally-open capacitor, and each of the capacitor branches is formed by a capacitor and a switch connected in series.

9. A filter bandwidth automatic calibration method, applied to the controller according to any one of claims 1 to 8, characterized in that: include: Calculating the number of preset clock cycles that the RC relaxation oscillator should generate based on the tuning resistance and the tuning capacitance of the RC relaxation oscillator; Recording the actual number of clock cycles generated by the RC relaxation oscillator, and determining a preset tuning control signal corresponding to the preset number of clock cycles; Calculating an actual tuning control signal corresponding to the actual number of clock cycles according to the preset number of clock cycles, the preset tuning control signal and the actual number of clock cycles; The capacitance of the tuning capacitor is adjusted to the capacitance corresponding to the actual tuning control signal, and the capacitance error between the bandwidth adjustment capacitor and the tuning capacitor in the control filter is within an allowable range.

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