CN103259532A - Resistor-capacitor filter calibrating circuit - Google Patents

Abstract

The invention discloses a resistor-capacitor filter calibration circuit, which includes a tuning unit, a comparator and a digital controller; the tuning unit includes the tuning resistor, the tuning capacitor, the first switching tube and the second switching tube, the tuning resistor and the tuning capacitor In series, the tuning resistor is connected to the power supply through the first switch tube, the tuning capacitor is connected in parallel with the second switch tube, and are connected to the common ground; the forward terminal of the comparator is connected to the common terminal of the tuning resistor and the tuning capacitor; the reverse terminal of the comparator is connected to Input the preset reference voltage; the output terminal of the comparator is connected with the input terminal of the digital controller; the filter control terminal of the digital controller is connected with the resistor capacitor filter, the charging control terminal is connected with the first switch tube, and the discharge control terminal is connected with the first switching tube. The second switching tube is connected, and the tuning control terminal is connected to the tuning capacitor. The invention realizes the calibration of the filter, has simple structure and low power consumption, and solves the problems of the prior art. The invention discloses a method for calibrating a resistance-capacitance filter.

Description

A resistor capacitor filter calibration circuit

technical field

The present application relates to the technical field of integrated circuits, in particular to a calibration circuit for a resistor-capacitor filter.

Background technique

Resistor-capacitor (RC) filters are widely used in analog integrated circuits because of their good linearity and simple implementation. However, due to the limitations of the manufacturing process, the actual values of the resistors and capacitors deviate from the ideal values, resulting in the filter not working properly. Therefore, it is necessary to calibrate the time constant of the RC filter (that is, the product of the capacitance value of the filter and the resistance value) to realize the frequency correction of the filter.

The existing RC filter calibration methods include off-chip calibration and on-chip calibration. In order to reduce the occupied area of the circuit and meet the high integration requirements of the circuit, the on-chip calibration method is usually used. Commonly used on-chip calibration circuits mainly include a phase-locked loop (PLL) structure based on a voltage-controlled oscillator (VCO) and a calibration circuit based on a constant transconductance structure. Since the two types of on-chip calibration circuits respectively use a phase-locked loop and a constant transconductance structure, the structure of the calibration circuit is complicated and the power consumption is large, which increases the cost during use.

Contents of the invention

In view of this, the purpose of the present application is to provide a resistor-capacitor filter calibration circuit to solve the problems of complex structure and high power consumption of existing calibration circuits.

In order to achieve the above object, the application provides the following technical solutions:

A resistor-capacitor filter calibration circuit, including a tuning unit, a comparator and a digital controller;

The tuning unit includes the tuning resistor, the tuning capacitor, the first switching tube and the second switching tube, the tuning resistor and the tuning capacitor are connected in series, the tuning resistor is connected to the power supply through the first switching tube, and the tuning The capacitor is connected in parallel with the second switch tube, and is grounded together; wherein, the resistance value of the tuning resistor is the same as that of the resistor-capacitor filter;

The positive terminal of the comparator is connected to the common terminal of the tuning resistor and the tuning capacitor; the negative terminal of the comparator is connected to a preset reference voltage; the output terminal of the comparator is connected to the digital controller The input terminal connection;

The filter control terminal of the digital controller is connected to the resistor-capacitor filter; the charging control terminal of the digital controller is connected to the first switch tube; the discharge control terminal of the digital controller is connected to the first switching tube. The two switch tubes are connected; the tuning control terminal of the digital controller is connected to the tuning capacitor;

The digital controller is used to control the charging process of the tuning capacitor, record the actual number of clock cycles taken for the voltage across the tuning capacitor to rise from zero to the reference voltage; compare the actual number with the preset value, and generate a tuning control signal according to the comparison result; output the tuning control signal through the tuning control terminal to adjust the capacitance value of the tuning capacitor; generate according to the tuning control signal and output the filter through the filter control terminal The controller control signal to adjust the capacitance value of the resistor capacitor filter.

Preferably, the circuit further includes a first voltage dividing resistor and a second voltage dividing resistor: the first voltage dividing resistor and the second voltage dividing resistor are connected in series between the power supply and the ground potential, and the first voltage dividing resistor The common terminal of the piezoresistor and the second voltage dividing resistor is connected to the reverse terminal of the comparator; the voltage of the common terminal of the first voltage dividing resistor and the second voltage dividing resistor is used as the reference voltage.

Preferably, the tuning capacitor includes at least two shunt capacitors, each shunt capacitor is connected in parallel, and a capacitor switch is connected in series in at least one parallel branch;

The digital controller controls the on/off of the capacitor switch through the tuning control signal, so as to adjust the capacitance value of the tuning capacitor.

A resistor-capacitor filter calibration method, based on a resistor-capacitor filter calibration circuit;

The circuit includes a tuning unit, a comparator and a digital controller; the tuning unit includes a tuning resistor, a tuning capacitor, a first switch tube and a second switch tube, the tuning resistor and the tuning capacitor are connected in series, and the tuning resistor passes through the The first switching tube is connected to the power supply, the tuning capacitor is connected in parallel with the second switching tube, and are commonly grounded; the forward terminal of the comparator is connected to the common terminal of the tuning resistor and the tuning capacitor; the comparison The inverting end of the comparator is connected to a preset reference voltage; the output end of the comparator is connected to the input end of the digital controller; the filter control end of the digital controller is connected to the resistor-capacitor filter; The charge control terminal of the digital controller is connected to the first switch tube; the discharge control terminal of the digital controller is connected to the second switch tube; the tuning control terminal of the digital controller is connected to the tuning capacitor connect;

The methods include:

The digital controller generates and outputs a charging control signal to turn on the first switch tube and start charging the tuning capacitor;

In the process of charging the tuning capacitor, the digital controller counts clock cycles to obtain the actual number of clock cycles;

When the signal received by the input terminal of the digital controller changes from low level to high level, compare the actual number with the preset number, and generate a tuning control signal according to the comparison result;

Outputting the tuning control signal through the tuning control terminal to adjust the capacitance value of the tuning capacitor so that the time constant of the tuning unit is equal to the ideal time constant of the resistor-capacitor filter;

According to the tuning control signal when the actual number is equal to the preset number, a filter control signal is generated and output to adjust the capacitance value of the resistor-capacitor filter so that the actual time constant of the resistor-capacitor filter equal to the ideal time constant.

Preferably, the circuit further includes a first voltage dividing resistor and a second voltage dividing resistor: the first voltage dividing resistor and the second voltage dividing resistor are connected in series between the power supply and the ground potential, and the first voltage dividing resistor The common terminal of the piezoresistor and the second voltage dividing resistor is connected to the reverse terminal of the comparator; the voltage of the common terminal of the first voltage dividing resistor and the second voltage dividing resistor is used as the reference voltage;

The method further includes changing the reference voltage by adjusting a resistance ratio of the first voltage dividing resistor and the second voltage dividing resistor.

Preferably, the preset number of values is determined according to the clock period, ideal time constant and reference voltage.

As can be seen from the above-mentioned technical scheme, the application simulates the capacitor-resistance filter through the tuning unit, and adjusts the capacitance value of the tuning capacitor in conjunction with a comparator, a digital controller, etc., according to making the actual time constant of the tuning unit reach its ideal The tuning control signal of the time constant generates a corresponding filter control signal, and adjusts the capacitance value of the capacitor-resistance filter through the filter control signal, so that the actual time constant of the capacitor-resistance filter also reaches its ideal time constant. Calibration of the filter. Therefore, the present application not only realizes the calibration of the filter, but also has a simple structure, does not require large power consumption structures such as constant transconductance, and solves the problems of the prior art.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present application. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

FIG. 1 is a structural diagram of a resistor-capacitor filter calibration circuit provided in Embodiment 1 of the present application;

FIG. 2 is a timing diagram of each signal during the working process of the resistor-capacitor filter calibration circuit provided by the embodiment of the present application;

FIG. 3 is a structural diagram of a calibration circuit for a resistor-capacitor filter provided in Embodiment 2 of the present application;

FIG. 4 is a flowchart of a method for calibrating a resistor-capacitor filter provided in an embodiment of the present application.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the application with reference to the drawings in the embodiments of the application. Apparently, the described embodiments are only some of the embodiments of the application, not all of them. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of this application.

The embodiment of the present application discloses a resistor-capacitor filter calibration circuit to solve the problems of complex structure and high power consumption of the existing calibration circuit.

Referring to FIG. 1 , the resistor-capacitor filter calibration circuit provided by Embodiment 1 of the present application includes a tuning unit 101 , a comparator 102 and a digital controller 103 .

The tuning unit 101 includes a tuning resistor R ₀ , a tuning capacitor C ₀ , a first switch M1 and a second switch M2, the tuning resistor R ₀ and the tuning capacitor C ₀ are connected in series, and the tuning resistor R ₀ is connected to the power supply Vdd through the first switch M1 The tuning capacitor C ₀ is connected in parallel with the second switching tube M2, and they are also grounded together. The tuning unit 101 is used to simulate a capacitor-resistor filter.

The positive terminal of the comparator 102 is connected to the common terminal of the tuning resistor R ₀ and the tuning capacitor C ₀ ; the negative terminal of the comparator 102 is connected to the preset reference voltage V _ref ; the output terminal of the comparator 102 is connected to the digital controller 103 The first input terminal connection. The second input end of digital controller 103 accesses clock signal; The third input end of digital controller 103 accesses preset numerical value _NS ; The filter control terminal Out1 of digital controller 103 is connected with resistor-capacitor filter 100; The charging control terminal Out2 of the controller 103 is connected to the first switch tube M1; the discharge control terminal Out3 of the digital controller is connected to the second switch tube M2; the tuning control terminal Out4 of the digital controller 103 is connected to the tuning capacitor _C0 .

The working process and principle of the above-mentioned calibration circuit are introduced as follows.

Referring to the timing diagram shown in FIG. 2 , when the calibration starts, the digital controller 103 generates a charging control signal CT _c , and outputs the charging control signal CT _c through the charging control terminal Out2, so that the first switch tube M1 is turned on, and the power supply Vdd is tuned The resistor R ₀ charges the tuning capacitor C ₀ ; while outputting CT _c , the digital controller 103 starts counting its own clock signal, that is, records the number N of clock cycles t _CK occupied by the charging process.

The voltage V _cap across the tuning capacitor C0 (that is, the common terminal voltage of the tuning resistor R0 and the tuning capacitor C0) is input to the positive terminal of the comparator 102; the comparator 102 compares V _cap and V _ref , and outputs a digital value of the comparison result controller. In the initial stage of charging, since V _cap < V _ref , the output signal Vout of the comparator 102 is at a low level. When V _cap =V _ref , the output level of the comparator 102 is reversed, Vout becomes high level, and the digital controller 103 records the number of clock cycles at this time as the actual value N ₀ . Since the charging time T=N ₀ *t _CK , and the voltage across the tuning capacitor C ₀ when charging is completed $V_{\mathrm{cap}}=V_{\mathrm{ref}}=\mathrm{Vdd}\&Center\; Dot;(1-e^{-\frac{T}{R_0{C}_0}}),$ Right now:

T=R ₀ C ₀ ·ln(Vdd/(Vdd-V _ref ))=N ₀ ·t _CK (Formula 1).

It can be known from Formula 1 that N ₀ is proportional to the actual time constant R ₀ C ₀ of the tuning unit 101 . Based on formula 1, for the determined reference voltage V _ref , the actual number corresponding to the ideal time constant of the tuning unit 101 can be calculated and used as the preset number N _S ; and then the digital controller 103 judges whether N ₀ is equal to N _S , if no, it means that the actual time constant of the tuning unit 101 is not equal to its ideal time constant, then generate a corresponding tuning control signal _MT to adjust the capacitance of the tuning capacitor C ₀ . The adjustment principle is: if N ₀ < _NS , then increase C ₀ , and if N ₀ > _NS , then decrease C ₀ , so that the actual time constant of the tuning unit 101 is closer to its ideal time constant. In order to verify the adjustment effect, while generating _MT , the digital controller 103 generates a discharge control signal CT _d to turn on the second switching tube M2 to rapidly discharge the tuning capacitor C ₀ . After the discharge is completed (V _cap quickly drops to zero), CT _d disappears, and under the action of CT _c , the tuning capacitor C ₀ starts charging again, and at the same time, the digital controller 103 counts the clock cycle again, and obtains by judging the current charging process Whether the actual value N ₀ is equal to N _S , if it is not equal, then generate the corresponding again, adjust the capacitance value of the tuning capacitor C ₀ again, and so on, until N ₀ = _NS (the actual time constant of the tuning unit 101 is equal to its ideal time constant).

Further, the digital controller generates a filter control signal _MF according to the last tuning control signal _MT , and adjusts the capacitance value of the capacitor-resistor filter 100 through _MF , so that the actual time constant of the capacitor-resistor filter 100 reaches its ideal time constant.

It can be seen from the above structure and working principle that the embodiment of the present application simulates the capacitor-resistor filter through the tuning unit, and adjusts the capacitance value of the tuning capacitor in combination with a comparator, a digital controller, etc., according to making the actual time constant of the tuning unit reach its The tuning control signal of the ideal time constant generates a corresponding filter control signal, and adjusts the capacitance value of the capacitor resistance filter through the filter control signal, so that the actual time constant of the capacitor resistance filter also reaches its ideal time constant, realizing Calibration of the filter. Therefore, the embodiment of the present application not only realizes the calibration of the filter, but also has a simple structure, does not require a large power consumption structure such as a constant transconductance, and solves the problems of the prior art.

In addition, according to Formula 1, under the premise of a fixed clock period t _CK , the embodiment of the present application can prolong the charging time T by increasing the magnitude of the reference voltage, thereby reducing the calibration error.

It should be noted that, in order to ensure calibration accuracy, the tuning unit 101 and the resistor-capacitor filter 100 in the above embodiment are completely matched, that is, both have the same layout form, circuit structure and resistor-capacitor value. Correspondingly, the digital controller can directly use the last tuning control signal _MT as _MF to adjust the capacitor-resistor filter 100 . Further, in order not to affect the normal operation of the resistor-capacitor _filter , the filter control signal _MF is updated to the tuning control signal _MT only when the change of the tuning control signal MT exceeds a preset range.

Referring to FIG. 3 , the resistor-capacitor filter calibration circuit provided by Embodiment 2 of the present application includes a tuning unit 301 , a comparator 302 , a digital controller 303 , a first voltage-dividing resistor R1 and a second voltage-dividing resistor R2 .

The tuning unit 301 includes a tuning resistor R ₀ , a tuning capacitor C ₀ , a first switching tube M1 and a second switching tube M2, the tuning resistor R ₀ and the tuning capacitor C ₀ are connected in series, and the tuning resistor R ₀ is connected to the power supply Vdd through the first switching tube M1 The tuning capacitor C ₀ is connected in parallel with the second switching tube M2, and they are also grounded together. The tuning unit 301 is used to simulate a capacitor-resistor filter. Wherein, the tuning capacitor C ₀ includes at _least two shunt capacitors, such as capacitors C _b , C ₁ , C ₂ . , capacitive switches S ₁ , S ₂ . . . S _n shown in FIG. 3 .

The first voltage dividing resistor R1 and the second voltage dividing resistor R2 are connected in series between the power supply Vdd and the ground potential, the common end of the first voltage dividing resistor R1 and the second voltage dividing resistor R2 is connected to the reverse end of the comparator 302, That is, the voltage at the common terminal of the first voltage dividing resistor R1 and the second voltage dividing resistor R2 is input to the inverting terminal of the comparator 302 as the reference voltage V _ref . The positive terminal of the comparator 302 is connected to the common terminal of the tuning resistor R ₀ and the tuning capacitor C ₀ , that is, the voltage across the tuning capacitor C ₀ is input to the positive terminal of the comparator 302 . The output terminal of the comparator 302 is connected to the first input terminal of the digital controller 303 . The second input end of digital controller 303 accesses clock signal; The third input end of digital controller 303 accesses preset numerical value _NS ; The filter control terminal Out1 of digital controller 303 is connected with resistor-capacitor filter 300; Digital The charging control terminal Out2 of the controller 303 is connected to the first switch tube M1; the discharge control terminal Out3 of the digital controller 303 is connected to the second switch tube M2; the tuning control terminal Out4 of the digital controller 303 is connected to the tuning capacitor _C0 .

For the working process and principle of the calibration circuit described in Embodiment 2 of the present application, reference may be made to Embodiment 1 above. The tuning control signal M _T changes the number of parallel branches forming the tuning capacitor C ₀ by adjusting the on/off of the capacitor switches S ₁ , S ₂ . . . S _n , thereby achieving the purpose of adjusting its capacitance value.

In addition, by changing the resistance ratio of the first voltage dividing resistor R1 and the second voltage dividing resistor R2, the magnitude of the reference voltage can be changed, thereby changing the charging time T. Specifically, according to the conversion formula T=R ₀ C ₀ ·ln(1+R2/R1)=N ₀ ·t _CK (Formula 2) of formula 1, it can be known that as long as the ratio R2/R1 is increased, the charging time can be increased T, thereby reducing the calibration error.

Based on the circuit described in Embodiment 1 above, Embodiment 3 of the present application further provides a method for calibrating a resistor-capacitor filter. With reference to Fig. 4, this method comprises the steps:

S401: Generate and output a charging control signal through a digital controller to turn on the first switch and start charging the tuning capacitor;

S402: During the process of charging the tuning capacitor, the digital controller counts the clock cycle t _CK to obtain the actual value N ₀ of the clock cycle;

S403: When the signal received by the input terminal of the digital controller changes from low level to high level, compare the actual number N ₀ with the preset number N _S , and generate a tuning control signal according to the comparison result;

That is, when the voltage value V _cap of the tuning capacitor reaches the reference voltage V _ref , charging ends.

S404: Output the tuning control signal through the tuning control terminal to adjust the capacitance value of the tuning capacitor, so that the time constant of the tuning unit is equal to the ideal time constant of the resistor-capacitor filter;

S405: According to the tuning control signal when the actual number _N0 is equal to the preset number _NS , generate and output a filter control signal to adjust the capacitance value of the resistor-capacitor filter, so that the actual value of the resistor-capacitor filter The time constant is equal to the ideal time constant.

Wherein, in the above method embodiment, based on the above formula 1, the preset number N _S is determined according to the clock cycle t _CK , the ideal time constant and the reference voltage V _ref . By adjusting and increasing the reference voltage V _ref , the charging time T can be extended, thereby reducing the calibration error. Specifically, for the circuit structure in which the reference voltage is provided by the first voltage dividing resistor R1 and the second voltage dividing resistor R2 described in the second embodiment above, the charging time T can be extended by increasing the resistance value ratio R2/R1, To achieve the purpose of reducing the calibration error.

Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be implemented through computer programs to instruct related hardware, and the programs can be stored in a computer-readable storage medium. When the program is executed, it may include the processes of the embodiments of the above-mentioned methods. Wherein, the storage medium may be a magnetic disk, an optical disk, a read-only memory (Read-Only Memory, ROM) or a random access memory (Random Access Memory, RAM), etc.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the application. Therefore, the present application will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (6)

1. A resistor-capacitor filter calibration circuit, characterized in that, includes a tuning unit, a comparator and a digital controller; The tuning unit includes the tuning resistor, the tuning capacitor, the first switching tube and the second switching tube, the tuning resistor and the tuning capacitor are connected in series, the tuning resistor is connected to the power supply through the first switching tube, and the tuning The capacitor is connected in parallel with the second switch tube, and is grounded together; wherein, the resistance value of the tuning resistor is the same as that of the resistor-capacitor filter; The positive terminal of the comparator is connected to the common terminal of the tuning resistor and the tuning capacitor; the negative terminal of the comparator is connected to a preset reference voltage; the output terminal of the comparator is connected to the digital controller The input terminal connection; The filter control terminal of the digital controller is connected to the resistor-capacitor filter; the charging control terminal of the digital controller is connected to the first switch tube; the discharge control terminal of the digital controller is connected to the first switching tube. The two switch tubes are connected; the tuning control terminal of the digital controller is connected to the tuning capacitor; The digital controller is used to control the charging process of the tuning capacitor, record the actual number of clock cycles taken for the voltage across the tuning capacitor to rise from zero to the reference voltage; compare the actual number with the preset value, and generate a tuning control signal according to the comparison result; output the tuning control signal through the tuning control terminal to adjust the capacitance value of the tuning capacitor; generate according to the tuning control signal and output the filter through the filter control terminal The controller control signal to adjust the capacitance value of the resistor capacitor filter. 2. The circuit according to claim 1, further comprising a first voltage dividing resistor and a second voltage dividing resistor: the first voltage dividing resistor and the second voltage dividing resistor are connected in series to the power supply and ground Between potentials, the common terminal of the first voltage dividing resistor and the second voltage dividing resistor is connected to the reverse terminal of the comparator; the voltage of the common terminal of the first voltage dividing resistor and the second voltage dividing resistor is used as the the reference voltage. 3. The circuit according to claim 1 or 2, wherein the tuning capacitor comprises at least two shunt capacitors, each shunt capacitor is connected in parallel, and at least one parallel branch is connected in series with a capacitor switch; The digital controller controls the on/off of the capacitor switch through the tuning control signal, so as to adjust the capacitance value of the tuning capacitor. 4. A method for calibrating a resistor-capacitor filter, characterized in that, based on a calibration circuit for a resistor-capacitor filter; The circuit includes a tuning unit, a comparator and a digital controller; the tuning unit includes a tuning resistor, a tuning capacitor, a first switch tube and a second switch tube, the tuning resistor and the tuning capacitor are connected in series, and the tuning resistor passes through the The first switching tube is connected to the power supply, the tuning capacitor is connected in parallel with the second switching tube, and are commonly grounded; the forward terminal of the comparator is connected to the common terminal of the tuning resistor and the tuning capacitor; the comparison The inverting end of the comparator is connected to a preset reference voltage; the output end of the comparator is connected to the input end of the digital controller; the filter control end of the digital controller is connected to the resistor-capacitor filter; The charge control terminal of the digital controller is connected to the first switch tube; the discharge control terminal of the digital controller is connected to the second switch tube; the tuning control terminal of the digital controller is connected to the tuning capacitor connect; The methods include: The digital controller generates and outputs a charging control signal to turn on the first switch tube and start charging the tuning capacitor; In the process of charging the tuning capacitor, the digital controller counts clock cycles to obtain the actual number of clock cycles; When the signal received by the input terminal of the digital controller changes from low level to high level, compare the actual number with the preset number, and generate a tuning control signal according to the comparison result; Outputting the tuning control signal through the tuning control terminal to adjust the capacitance value of the tuning capacitor so that the time constant of the tuning unit is equal to the ideal time constant of the resistor-capacitor filter; According to the tuning control signal when the actual number is equal to the preset number, a filter control signal is generated and output to adjust the capacitance value of the resistor-capacitor filter so that the actual time constant of the resistor-capacitor filter equal to the ideal time constant. 5. The method according to claim 4, wherein the circuit further comprises a first voltage dividing resistor and a second voltage dividing resistor: the first voltage dividing resistor and the second voltage dividing resistor are connected in series to the Between the power supply and the ground potential, the common end of the first voltage dividing resistor and the second voltage dividing resistor is connected to the reverse end of the comparator; the common end of the first voltage dividing resistor and the second voltage dividing resistor voltage as the reference voltage; The method further includes changing the reference voltage by adjusting a resistance ratio of the first voltage dividing resistor and the second voltage dividing resistor. 6. The method according to claim 4 or 5, wherein the preset number of values is determined according to the clock period, ideal time constant and reference voltage.

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