CN113422578A - RC oscillator and temperature compensation method thereof - Google Patents
RC oscillator and temperature compensation method thereof Download PDFInfo
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- CN113422578A CN113422578A CN202110769406.6A CN202110769406A CN113422578A CN 113422578 A CN113422578 A CN 113422578A CN 202110769406 A CN202110769406 A CN 202110769406A CN 113422578 A CN113422578 A CN 113422578A
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
- H03B5/00—Generation of oscillations using amplifier with regenerative feedback from output to input
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- H03B5/04—Modifications of generator to compensate for variations in physical values, e.g. power supply, load, temperature
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Abstract
The invention relates to the field of integrated circuits, in particular to an RC oscillator and a temperature compensation method thereof; the RC oscillator comprises a charging circuit, and the charging and discharging capacitor is controlled by a charging switch to be charged; the discharge circuit is controlled by the discharge switch to discharge the charge and discharge capacitor; a charge-discharge capacitor for outputting voltage to the comparator; a comparator which compares the output voltage with a threshold voltage and outputs a high level voltage or a low level voltage; the high-level voltage controls the charging switch to be switched off, and the discharging switch is switched on; the low level voltage controls the charging switch to be turned on, and the discharging switch is turned off; the charge and discharge capacitor comprises a control capacitor and an MOS capacitor array with a selectable capacitance value; according to the invention, the MOS capacitor with the negative temperature coefficient is used for carrying out temperature drift compensation on the comparator with the positive temperature coefficient, so that the temperature drift of the RC oscillator is reduced; digital control words are designed to select a certain MOS capacitance value, so that the frequency change caused by the temperature drift of the time delay of the comparator can be quickly and accurately compensated.
Description
Technical Field
The invention relates to the field of integrated circuits, relates to a temperature compensation technology of a low-temperature-drift RC oscillator, and particularly relates to an RC oscillator and a temperature compensation method thereof.
Background
For communication and control chips, a clock with low temperature drift is needed in certain states, the traditional crystal oscillator needs an off-chip element although the temperature drift coefficient is low, the power consumption is high, the requirement cannot be met particularly under the design requirement of low power consumption, and the RC oscillator with low temperature drift is particularly suitable for the scenes. The RC oscillator is composed of a capacitor, a resistor, a comparator and a switch, and forms a delay loop. The power supply voltage charges the capacitor through the resistor and the switch, the voltage on the capacitor rises, when the voltage exceeds the threshold voltage of the comparator, the comparator outputs a high level voltage, the voltage is used for switching off the charging switch of the capacitor, the discharging switch of the capacitor is switched on, the voltage on the capacitor drops, and when the voltage is lower than the threshold voltage of the comparator, the comparator outputs a low level voltage, so that the charging switch of the capacitor is switched on, and the discharging switch is switched off. The above steps are repeated to generate an oscillation signal.
The capacitance, resistance and comparator in the oscillator are temperature dependent in addition to process corner dependent. The MOM capacitor and the POLY resistor are adopted, the temperature coefficients of the MOM capacitor and the POLY resistor are small, and therefore the temperature drift of the oscillator mainly comes from the comparator. If the oscillator frequency is high, the comparator delay accounts for a large proportion, so that the temperature drift of the comparator is large in proportion coefficient and is transferred to the temperature drift of the oscillator, and the actual use is affected.
Disclosure of Invention
In view of the fact that the temperature characteristic of the delay of the comparator is monotonous and is a positive temperature coefficient and the MOS capacitor is a negative temperature coefficient, the RC oscillator uses the MOS capacitor as a part of the charge and discharge capacitor so as to compensate the temperature drift of the delay of the comparator and realize low temperature drift.
In order to solve the technical problem, the invention provides the RC oscillator and the temperature compensation method thereof to realize the compensation of the RC oscillator, reduce the temperature drift of the RC oscillator and improve the accuracy of the RC oscillator.
In a first aspect of the present invention, an object of the present invention is to provide an RC oscillator with a small temperature drift, the RC oscillator comprising:
the charging circuit is used for controlling charging and discharging of the charging capacitor by the charging switch;
the discharge circuit is controlled by the discharge switch to discharge the charge and discharge capacitor;
a charge-discharge capacitor for outputting voltage to the comparator;
a comparator which compares the output voltage with a threshold voltage and outputs a high level voltage or a low level voltage;
the high-level voltage controls the charging switch to be switched off, and the discharging switch is switched on; the low level voltage controls the charging switch to be turned on, and the discharging switch is turned off;
the charging and discharging capacitor comprises a control capacitor and an MOS capacitor array with a selectable capacitance value, and the MOS capacitor array is connected with the control capacitor in parallel.
Preferably, the MOS capacitor array comprises array-arranged control switches and array-arranged MOS capacitors; each control switch is connected with one MOS capacitor; and all the control switches are controlled by digital control words to be connected with the array MOS capacitors, namely, each control switch is at least associated with one MOS capacitor, and whether the control switch is connected with the MOS capacitor or not is judged by the digital control words.
Preferably, an inverter is further included between the charging switch and the output end of the comparator; through setting up the inverter, guarantee the charging switch can open under low level voltage, can break under high level voltage.
Preferably, the RC oscillator further comprises a buffer, connected to the output end of the comparator, for outputting the output result of the RC oscillator; the buffer may isolate or isolate the RC oscillator from external circuitry; the load effect problem can be easily solved.
In a second aspect of the invention, it is an object of the invention to select a suitable MOS capacitance value such that the RC oscillator frequency varies minimally with temperature; the invention provides a temperature compensation method of an RC oscillator, wherein the RC oscillator is the RC oscillator in the first aspect of the invention, and the temperature compensation method comprises the following steps:
s1, determining the minimum value (the control word is all 0 at the beginning), the middle value (the highest bit of the control word is 1 at the beginning and the rest bits are 0 at the beginning) and the maximum value (the control word is all 1 at the beginning) of the digital control word, respectively controlling and connecting the MOS capacitor array as the input of the control switch, and counting the output result of the RC oscillator in the same time window;
s2, determining the difference value of the count values of the RC oscillator under different temperature conditions, and determining the temperature drift percentage and the temperature drift symbol under the current digital control value;
s3, if the signs of the three temperature drift signs are completely the same, comparing the absolute values of the three temperature drift percentages continuously, and taking the control word with the minimum absolute value of the temperature drift percentages as the optimal MOS capacitance value control word to compensate the temperature drift of the RC oscillator;
s4, if the signs of the three temperature drift signs are not identical, determining an optimal MOS capacitance value interval according to two temperature drift percentages with different signs, if the temperature drift percentage of the maximum value of the control word is a positive number, and the temperature drift percentages of the middle value and the minimum value are negative numbers, the optimal MOS capacitance value control word is in the interval of the maximum value and the middle value, and if the temperature drift percentages of the maximum value and the middle value of the control word are positive numbers and the temperature drift percentages of the minimum value are negative numbers, the optimal MOS capacitance value control word is in the interval of the minimum value and the middle value;
and S5, taking the two endpoint values and the middle value of the interval as the minimum value, the maximum value and the middle value of the updated digital control word, returning to the step S1 until the signs of the three temperature drift percentages are completely the same or only three control words exist in the interval, and selecting the control word with the minimum absolute value of the temperature drift percentage as the control word with the optimal MOS capacitance value to compensate the temperature drift of the RC oscillator.
Preferably, the different temperature conditions include any temperature interval between the maximum temperature and the minimum temperature allowed by the RC oscillator.
Preferably, when only three values exist in the interval, the two endpoint values and the middle value of the interval are respectively used as the input of the control switches arranged in the array to control and connect the corresponding MOS capacitor array; counting the output result of the RC oscillator in the same time window; determining the difference value of the count values of the RC oscillator under different temperature conditions, and determining the temperature drift percentage and the temperature drift symbol under the current digital control value; and comparing the absolute values of the three temperature drift percentages, and taking the current digital control value corresponding to the minimum absolute value as the optimal MOS capacitance value.
The invention has the beneficial effects that:
according to the invention, the MOS capacitor with the negative temperature coefficient is used for carrying out temperature drift compensation on the comparator with the positive temperature coefficient, so that the temperature drift of the RC oscillator is reduced; the invention also designs a digital control word to select a certain MOS capacitance value, and the digital control word of the optimal MOS capacitance value is found out by adopting the principle of a binary method, so that the frequency change caused by the temperature drift of the time delay of the comparator can be quickly and accurately compensated; thereby achieving a minimum variation of the oscillator frequency with temperature.
Drawings
FIG. 1 is a schematic diagram of an RC oscillator according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an RC oscillator in a preferred embodiment of the present invention;
FIG. 3 is a schematic diagram of a MOS capacitor array structure according to an embodiment of the invention;
fig. 4 is a flowchart of a method for compensating temperature of an RC oscillator according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
Fig. 1 is a schematic structural diagram of an RC oscillator in an embodiment of the present invention, and as shown in fig. 1, the RC oscillator includes:
100. a charging circuit, which is controlled by a charging switch to charge the charging/discharging capacitor 300;
200. a discharge circuit for discharging the charge/discharge capacitor 300 under the control of a discharge switch;
300. a charge and discharge capacitor for outputting a voltage to the comparator 400;
400. a comparator which compares the output voltage with a threshold voltage and outputs a high level voltage or a low level voltage;
in the embodiment, a first loop is formed by the charging circuit 100, the charging and discharging capacitor 300 and the comparator 400, and a second loop is formed by the discharging circuit 200, the charging and discharging capacitor 300 and the comparator 400; the first loop is used for charging the charge-discharge circuit 300 and outputting a counting result through the comparator 400; the second loop is used for discharging the charge and discharge capacitor 300 and outputting a counting result through the comparator 400.
Wherein the comparator 400 includes a positive phase input + and a negative phase input-, and an output; the charge and discharge capacitor 300 outputs a capacitor voltage at the current moment, the capacitor voltage is input to a non-inverting input terminal of the comparator 400, a threshold voltage is additionally connected to an inverting input terminal of the comparator 400, the comparator 400 compares the output voltage input by the charge and discharge capacitor 300 with the threshold voltage, if the output voltage is higher than the threshold voltage, the comparator 400 outputs a high level voltage, and if the output voltage is lower than the threshold voltage, the comparator 400 outputs a low level voltage.
The high-level voltage returns to the charging circuit 100 and the discharging circuit 200 from the first loop and the second loop, and the charging switch is controlled to be switched off and the discharging switch is controlled to be switched on; the low-level voltage returns to the charging circuit 100 and the discharging circuit 200 from the first loop and the second loop, and controls the charging switch to be opened and the discharging switch to be disconnected.
The charge and discharge capacitor 300 comprises a control capacitor and an MOS capacitor array with a selectable capacitance value, and the MOS capacitor array is connected with the control capacitor in parallel; since the comparator 400 has a positive temperature coefficient and the MOS capacitor has a negative temperature coefficient, the present invention can effectively compensate the temperature drift of the comparator 400 by using the MOS capacitor as a part of the charge and discharge capacitor 300.
It is understood that some components are omitted in this embodiment, and those skilled in the art can make corresponding additions according to actual situations.
Fig. 2 is a schematic structural diagram of an RC oscillator in a preferred embodiment of the present invention, and as shown in fig. 2, the RC oscillator includes:
a positive phase input end + of the comparator is used for inputting a Vp voltage signal, and an inverted phase input end-of the comparator is used for inputting a Vref voltage signal;
in some preferred embodiments, a buffer is connected to an output terminal of the comparator, and the clock count result CLK OUT is output through the buffer.
The charging circuit is composed of a charging switch and a resistor, wherein two ends of the charging switch are respectively connected with one end of the resistor and power supply voltage; the signal control end of the charging switch is connected with an inverter, and the input end of the inverter is connected with the output end of the comparator; the other end of the resistor is connected to one end of the charge and discharge capacitor.
The discharge circuit is composed of a discharge switch, two ends of the discharge switch are respectively connected with two ends of a charge-discharge capacitor, and one end of the discharge switch is grounded; and the signal control end of the discharge switch is connected with the output end of the comparator.
The charging and discharging capacitor is composed of a control capacitor and an MOS array capacitor, and the control capacitor is connected with the MOS array capacitor in parallel; the MOS array capacitor realizes selectable MOS capacitance values through a digital control word Csel < x:0 >.
Fig. 3 is a schematic structural diagram of a MOS capacitor array according to an embodiment of the present invention, and as shown in fig. 3, the MOS capacitor array is composed of array-arranged control switches and array-arranged MOS capacitors; each control switch is connected with one MOS capacitor; and all control switches are controlled by digital control words Csel < x:0> to be connected with the array MOS capacitors, and the capacitance values of all the MOS capacitors can be the same or different, thereby realizing the capacitance values with different sizes; assuming that the MOS capacitor array comprises 8 MOS capacitors, when the signal Csel <7:0> of the digital control word is 00001110, it indicates that the 2 nd to 4 th control switches are turned on, and the remaining five control switches are kept turned off.
Fig. 4 is a flowchart of a method for compensating the temperature of an RC oscillator according to an embodiment of the present invention, as shown in fig. 4, the method includes:
s1, determining the minimum value, the middle value and the maximum value of the digital control word, respectively controlling the minimum value, the middle value and the maximum value as the input of a control switch to be connected with the MOS capacitor array, and counting the output result of the RC oscillator in the same time window;
the minimum value of the digital control word is the minimum value in the binary signal, the maximum value of the digital control word is the maximum value in the binary signal, and the middle value of the digital control word is the middle value in the binary signal, for example, if an 8-bit binary signal is provided, the minimum value is 00000000, the maximum value is 11111111, and the middle value is 10000000.
And inputting the binary signal to a control switch, controlling and connecting the corresponding MOS capacitor, and jointly driving a comparator to output a comparison result by the three different MOS capacitor values and the control capacitor.
In this embodiment, the output results of the comparators corresponding to the three different capacitance values are counted under different temperature conditions in the same time window, where the temperature condition may be any temperature interval between the highest temperature and the lowest temperature required by the design, and certainly, in order to take the temperature drift property of the RC oscillator into consideration in the whole and obtain the optimal result, the embodiment may select the optimal temperature interval from the highest temperature to the lowest temperature.
S2, determining the difference value of the count values of the RC oscillator under different temperature conditions, and determining the temperature drift percentage and the temperature drift symbol under the current digital control value;
the temperature drift value of the RC oscillator under the current digital control value is reflected by the percentage of change of the counting value, namely the percentage of change of the frequency of the RC oscillator along with the temperature, the positive and negative of the difference value of the counting value represent the positive and negative characteristics of the temperature drift, if the value is A0 at the temperature T0 and the value is A1 at the temperature T1, the percentage of change of the counting value is 100 (A1-A0)/A0, the percentage of the temperature drift is 100 (A1-A0)/(A0 (T1-T0)), and the unit of the temperature drift is percent per degree centigrade (%/° C).
S3, if the signs of the three temperature drift signs are completely the same, comparing the absolute values of the three temperature drift percentages continuously, and taking the control word with the minimum absolute value of the temperature drift percentages as the optimal MOS capacitance value control word to compensate the temperature drift of the RC oscillator;
s4, if the signs of the three temperature drift signs are not identical, determining an optimal MOS capacitance value interval according to two temperature drift percentages with different signs;
specifically, the determining manner of the interval specifically includes: if the signs of the three temperature drift signs are not completely the same, determining an optimal MOS capacitance value interval according to two temperature drift percentages with different signs, if the temperature drift percentage of the maximum value of the control word is a positive number, and the temperature drift percentages of the middle value and the minimum value are negative numbers, the optimal MOS capacitance value control word is in the interval of the maximum value and the middle value, and if the temperature drift percentages of the maximum value and the middle value of the control word are positive numbers and the temperature drift percentages of the minimum value are negative numbers, the optimal MOS capacitance value control word is in the interval of the minimum value and the middle value.
And S5, taking the two endpoint values and the middle value of the interval as the minimum value, the maximum value and the middle value of the updated digital control word, returning to the step S1 until the signs of the three temperature drift signs are completely the same or only three control words exist in the interval, selecting the control word with the minimum absolute value of the temperature drift percentage as the control word of the optimal MOS capacitance value to compensate the temperature drift of the RC oscillator, and stopping searching continuously.
Specifically, when only three values exist in the interval, the two end point values and the middle value of the interval are respectively used as the input of the control switches arranged in the array to control and connect the corresponding MOS capacitor array; counting the output result of the RC oscillator in the same time window; determining the difference value of the count values of the RC oscillator under different temperature conditions, and determining the temperature drift percentage and the temperature drift symbol under the current digital control value; the absolute values of the three temperature drift percentages are compared, and the current digital control value corresponding to the minimum absolute value is taken as the optimal MOS capacitance value in the present embodiment.
In the description of the present invention, it is to be understood that the terms "coaxial", "bottom", "one end", "top", "middle", "other end", "upper", "one side", "top", "inner", "outer", "front", "center", "both ends", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "disposed," "connected," "fixed," "rotated," and the like are to be construed broadly, e.g., as meaning fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; the terms may be directly connected or indirectly connected through an intermediate, and may be communication between two elements or interaction relationship between two elements, unless otherwise specifically limited, and the specific meaning of the terms in the present invention will be understood by those skilled in the art according to specific situations.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (9)
1. An RC oscillator comprising:
the charging circuit is used for controlling charging and discharging of the charging capacitor by the charging switch;
the discharge circuit is controlled by the discharge switch to discharge the charge and discharge capacitor;
a charge-discharge capacitor for outputting voltage to the comparator;
a comparator which compares the output voltage with a threshold voltage and outputs a high level voltage or a low level voltage;
the high-level voltage controls the charging switch to be switched off, and the discharging switch is switched on; the low level voltage controls the charging switch to be turned on, and the discharging switch is turned off;
the charging and discharging capacitor comprises a control capacitor and an MOS capacitor array with a selectable capacitance value, and the MOS capacitor array is connected with the control capacitor in parallel.
2. An RC oscillator as claimed in claim 1, wherein said MOS capacitor array comprises an array of control switches and an array of MOS capacitors; each control switch is connected with one MOS capacitor; and all control switches are controlled by digital control words to connect with the array MOS capacitors.
3. An RC oscillator as claimed in claim 1, further comprising an inverter between the charge switch and the output of the comparator.
4. An RC oscillator as claimed in claim 1, further comprising a buffer connected to the output of the comparator for outputting the output of the RC oscillator.
5. A method of temperature compensation of an RC oscillator, the method comprising:
s1, determining the minimum value, the middle value and the maximum value of the digital control word, respectively controlling the minimum value, the middle value and the maximum value as the input of a control switch to be connected with the MOS capacitor array, and counting the output result of the RC oscillator in the same time window;
s2, determining the difference value of the count values of the RC oscillator under different temperature conditions, and determining the temperature drift percentage and the temperature drift symbol under the current digital control value;
s3, if the signs of the three temperature drift signs are completely the same, comparing the absolute values of the three temperature drift percentages continuously, and taking the control word with the minimum absolute value of the temperature drift percentages as the optimal MOS capacitance value control word to compensate the temperature drift of the RC oscillator;
s4, if the signs of the three temperature drift signs are not identical, determining an optimal MOS capacitance value interval according to two temperature drift percentages with different signs;
and S5, taking the two endpoint values and the middle value of the interval as the minimum value, the maximum value and the middle value of the updated digital control word, returning to the step S1 until the signs of the three temperature drift percentages are completely the same or only three control words exist in the interval, and selecting the control word with the minimum absolute value of the temperature drift percentage as the control word with the optimal MOS capacitance value to compensate the temperature drift of the RC oscillator.
6. The method as claimed in claim 5, wherein in step S1, the minimum value of the digital control word is that the control word is all 0; the highest bit of the middle value is 1, and the rest bits are 0; the maximum value is all 1's for the control word.
7. A method as claimed in claim 5, wherein said different temperature conditions include any temperature range from the maximum temperature to the minimum temperature allowed by the RC oscillator.
8. A method of temperature compensation of an RC oscillator as claimed in claim 5, wherein said optimum MOS capacitance range is determined by determining that the optimum MOS capacitance control word is within a range formed by the maximum value and the mean value if the temperature drift percentage of the maximum value of the control word is positive and the temperature drift percentages of the mean value and the minimum value are negative, and by determining that the optimum MOS capacitance control word is within a range formed by the minimum value and the mean value if the temperature drift percentages of the maximum value and the mean value of the control word are positive and the temperature drift percentages of the minimum value are negative.
9. The temperature compensation method of an RC oscillator according to claim 5 or 8, wherein when there are only three values in the interval, the two end points and the middle value in the interval are respectively used as the input of the control switch arranged in an array to control and connect the corresponding MOS capacitor array; counting the output result of the RC oscillator in the same time window; determining the difference value of the count values of the RC oscillator under different temperature conditions, and determining the temperature drift percentage and the temperature drift symbol under the current digital control value; and comparing the absolute values of the three temperature drift percentages, and taking the current digital control value corresponding to the minimum absolute value as the optimal MOS capacitance value.
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| CN202110769406.6A CN113422578A (en) | 2021-07-07 | 2021-07-07 | RC oscillator and temperature compensation method thereof |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114726315A (en) * | 2022-06-01 | 2022-07-08 | 苏州聚元微电子股份有限公司 | RC relaxation oscillation circuit and RC relaxation oscillator |
| CN114978134A (en) * | 2022-05-06 | 2022-08-30 | 上海韬润半导体有限公司 | Switch buffer circuit, temperature compensation control circuit and voltage-controlled oscillator |
-
2021
- 2021-07-07 CN CN202110769406.6A patent/CN113422578A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114978134A (en) * | 2022-05-06 | 2022-08-30 | 上海韬润半导体有限公司 | Switch buffer circuit, temperature compensation control circuit and voltage-controlled oscillator |
| CN114726315A (en) * | 2022-06-01 | 2022-07-08 | 苏州聚元微电子股份有限公司 | RC relaxation oscillation circuit and RC relaxation oscillator |
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