CN114123974A - High-precision RC oscillating circuit - Google Patents

High-precision RC oscillating circuit Download PDF

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Publication number
CN114123974A
CN114123974A CN202111492840.0A CN202111492840A CN114123974A CN 114123974 A CN114123974 A CN 114123974A CN 202111492840 A CN202111492840 A CN 202111492840A CN 114123974 A CN114123974 A CN 114123974A
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switch
current source
capacitor
comparator
resistor
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张华磊
焦继业
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Xi'an Endi Integrated Circuit Co ltd
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Xi'an Endi Integrated Circuit Co ltd
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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
    • H03B5/02—Details
    • H03B5/04—Modifications of generator to compensate for variations in physical values, e.g. power supply, load, temperature
    • 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
    • H03B5/20—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element comprising resistance and either capacitance or inductance, e.g. phase-shift oscillator
    • H03B5/24—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element comprising resistance and either capacitance or inductance, e.g. phase-shift oscillator active element in amplifier being semiconductor device

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Abstract

The invention provides a high-precision RC oscillating circuit, comprising: the circuit comprises a first current source, a second current source, an amplifier, a comparator, a first capacitor, a second capacitor, a resistor, a latch and first to eighth switches; the second current source is a mirror image of the first current source; the first current source, the amplifier, the resistor, the seventh switch and the eighth switch are used for providing reference voltage for the comparator; the second current source, the first capacitor, the second capacitor and the first to sixth switches are used for controlling the charging and discharging processes of the first capacitor and the second capacitor and providing capacitor charging voltage for the comparator; the comparator is used for outputting a comparison result signal; the latch is used for controlling the first switch to the eighth switch to be opened or closed according to the signal output by the comparator; the second current source comprises a plurality of mirror circuits connected in parallel, wherein the current of the current source of the most significant bit adopts a temperature decoding mode, and the current of the current source of the least significant bit adopts a binary decoding mode.

Description

High-precision RC oscillating circuit
Technical Field
The invention belongs to the technical field of electronic circuits, and particularly relates to a high-precision RC oscillating circuit.
Background
The RC oscillator is simple to implement and low in cost, and is widely applied to analog circuits and pulse digital circuits. However, in practical application, the oscillation frequency of the RC oscillator is often affected by factors such as offset voltage and temperature and humidity, and then the use effect is affected.
In the prior art, in one oscillation period of an RC oscillator, a timing signal output by a comparator is controlled to be inverted twice, so that offset voltages of the comparator in one oscillation period are mutually offset, thereby reducing the influence of the offset voltages on oscillation frequency; but this scheme does not take into account the effects of temperature on the reference voltage and the charging current.
When the RC oscillation circuit is calibrated, in the prior art, a series-parallel switch is usually adopted to directly adjust a resistance value of a resistor or a capacitance value of a capacitor in the oscillation circuit, and this method may introduce additional errors, which affects the accuracy of the oscillation frequency.
Therefore, it is necessary to provide a high-precision RC oscillation circuit capable of reducing the influence of offset voltage and temperature on the oscillation frequency and improving the calibration precision.
Disclosure of Invention
In order to solve the above technical problem, the present invention discloses a high-precision RC oscillation circuit, including:
the circuit comprises a first current source, a second current source, an amplifier, a comparator, a first capacitor, a second capacitor, a resistor, a latch and first to eighth switches;
the second current source is a mirror image of the first current source;
the first current source, the amplifier, the resistor, the seventh switch and the eighth switch are used for providing reference voltage for the comparator;
the second current source, the first capacitor, the second capacitor and the first to sixth switches are used for controlling the charging and discharging processes of the first capacitor and the second capacitor and providing capacitor charging voltage for the comparator;
the comparator is used for comparing the reference voltage with the capacitor charging voltage and outputting a comparison result signal;
the latch is used for controlling the first switch to the eighth switch to be switched on or switched off according to the signal output by the comparator and outputting a clock signal to a downstream module;
the second current source comprises a plurality of mirror circuits connected in parallel; in the second current source, the current of the current source of the most significant bit adopts a temperature decoding mode, and the current of the current source of the least significant bit adopts a binary decoding mode.
Furthermore, in the second current source, the difference multiple between the current of the current source of the most significant bit and the current of the current source of the least significant bit can be adjusted according to actual needs, and the adjustment step error caused by mismatch of the current mirrors can be effectively reduced.
Preferably, in the second current source, a current of a current source of the most significant bit differs from a current of a current source of the least significant bit by a multiple of 32 or less.
Furthermore, the resistors are formed by connecting resistors with opposite temperature coefficients in series or in parallel in the chip, so that the influence of the temperature change of the resistors on the oscillation frequency of the oscillation circuit is reduced.
Furthermore, the resistor is an off-chip high-precision resistor, and the temperature change of the off-chip high-precision resistor does not influence the oscillation frequency of the oscillation circuit.
Further, the specific way of providing the reference voltage to the comparator by the first current source and the amplifier and the resistor is as follows:
the first current source is connected with the output end of the amplifier and is grounded through the resistor;
the positive input end of the amplifier provides an initial reference voltage, and the negative input end of the amplifier, the output end of the amplifier and the resistor are connected in series and used for amplifying signals and providing an amplified reference voltage for the oscillating circuit;
the opposite ends of the resistor connected with the negative input end of the amplifier are respectively connected with a seventh switch and an eighth switch which are connected in parallel; the positive electrode of the seventh switch is connected with the resistor, and the negative electrode of the seventh switch is connected with the positive input end of the comparator; the positive pole of the eighth switch is connected with the resistor, and the negative pole of the eighth switch is connected with the negative input end of the comparator.
Further, the second current source, the first capacitor, the second capacitor, and the first to sixth switches control the charging and discharging processes of the first capacitor and the second capacitor, and the specific way of providing the capacitor charging voltage to the comparator is as follows:
the positive electrode of the first switch is connected with the output end of the second current source; the negative electrode of the first switch is respectively connected with the positive electrode of the third switch, the positive electrode of the fifth switch and the first capacitor; the negative electrode of the third switch is grounded; the opposite end of the first capacitor connected with the first switch is grounded; the negative electrode of the fifth switch is connected with the positive input end of the comparator;
the first switch is connected with the second switch in parallel;
the positive electrode of the second switch is connected with the output end of the second current source; the negative electrode of the second switch is respectively connected with the positive electrode of the fourth switch, the positive electrode of the sixth switch and the second capacitor; the negative electrode of the fourth switch is grounded; the opposite end of the second capacitor connected with the second switch is grounded; and the negative electrode of the sixth switch is connected with the negative input end of the comparator.
Further, the first switch, the fourth switch, the fifth switch and the eighth switch are synchronously opened or closed; the second switch, the third switch, the sixth switch and the seventh switch are synchronously opened or closed.
Specifically, when the circuit is powered on, the first switch, the fourth switch, the fifth switch and the eighth switch are turned off, the second switch, the third switch, the sixth switch and the seventh switch are turned on, and the reference voltage amplified by the amplifier is input to the positive input end of the comparator;
the second current source charges the second capacitor through the second switch, and the negative input end of the comparator inputs second capacitor charging voltage; the reference voltage is greater than the second capacitor charging voltage;
when the second capacitor is charged until the charging voltage of the second capacitor is greater than the reference voltage, the first switch, the fourth switch, the fifth switch and the eighth switch are closed, and the second switch, the third switch, the sixth switch and the seventh switch are opened;
the negative input end of the comparator inputs the reference voltage amplified by the amplifier; the second current source charges the first capacitor through the first switch, and the positive input end of the comparator inputs a first capacitor charging voltage;
when the first capacitor is charged until the charging voltage of the first capacitor is greater than the reference voltage, the circuit is turned over, the first switch, the fourth switch, the fifth switch and the eighth switch are switched off, the second switch, the third switch, the sixth switch and the seventh switch are switched on, and the reference voltage amplified by the amplifier is input to the positive input end of the comparator. The first capacitor and the second capacitor are alternately charged along with circuit turnover, and offset voltage of the comparator introduced during circuit working can be effectively offset.
According to the oscillator circuit, the output frequency is adjusted by adopting the current source, linear adjustment is realized, the high-order current source and the low-order current source are respectively controlled by the thermometer code and the binary code, the mismatch of the current mirror is reduced, and the adjustment step error is further reduced; the resistor with the opposite temperature coefficient in the chip or the high-precision resistor outside the chip is adopted, so that the influence of temperature on oscillation frequency is reduced, and meanwhile, the high-precision RC oscillator circuit is realized by combining an offset voltage elimination technology.
Drawings
Fig. 1 is a circuit diagram of a high-precision RC oscillation circuit according to an embodiment.
Fig. 2 is a schematic diagram of a high-precision RC oscillating circuit for eliminating offset of a comparator according to an embodiment.
Detailed Description
The invention will be further explained and illustrated with reference to specific examples.
In one embodiment, as shown in fig. 1, the high-precision RC oscillation circuit includes a first current source, a second current source, an amplifier BUF, a comparator CMP, a first capacitor C1, a second capacitor C2, a resistor R, a latch SR, first to eighth switches S1 to S8; the second current source is a mirror image of the first current source, the current of the current source MSB of the most significant bit of the second current source adopts a temperature decoding mode, and the current of the current source LSB of the least significant bit adopts a binary decoding mode; the resistor R is a resistor string formed by serially connecting resistors with opposite temperature coefficients in the chip. Note that the first current source and the second current source in the embodiments are merely used for illustrating the present invention, and should not be construed as limiting the specific forms of the first current source and the second current source in the present invention.
The specific connection mode of the high-precision RC oscillating circuit is as follows:
the first current source is connected with the output end of the amplifier BUF and is grounded through a resistor R;
the positive input terminal of the amplifier BUF provides an initial reference voltageV ref The negative input end of the amplifier BUF, the output end of the amplifier BUF and the resistor R are connected in series and used for amplifying signals and providing amplified reference voltage for the oscillating circuitV ref0 ；
The opposite ends of the resistor R connected with the negative input end of the amplifier BUF are respectively connected with a seventh switch S7 and an eighth switch S8 which are connected in parallel; the positive electrode of the seventh switch S7 is connected with the resistor R, and the negative electrode S7 of the seventh switch is connected with the positive input end of the comparator CMP; the positive electrode of the eighth switch S8 is connected with the resistor R, and the negative electrode of the eighth switch S8 is connected with the negative input end of the comparator CMP;
the anode of the first switch S1 is connected with the output end of the second current source; the negative electrode of the first switch S1 is respectively connected with the positive electrode of the third switch S3, the positive electrode of the fifth switch S5 and the first capacitor C1; the negative electrode of the third switch S3 is grounded; the opposite end of the first capacitor C1 connected to the first switch S1 is grounded; the negative electrode of the fifth switch S5 is connected to the positive input terminal of the comparator CMP;
the first switch S1 is connected in parallel with the second switch S2;
the anode of the second switch S2 is connected with the output end of the second current source; the negative electrode of the second switch S2 is respectively connected with the positive electrode of the fourth switch S4, the positive electrode of the sixth switch S6 and the second capacitor C2; the negative electrode of the fourth switch S4 is grounded; the opposite end of the second capacitor C2 connected to the second switch S2 is grounded; the negative electrode of the sixth switch S6 is connected with the negative input end of the comparator CMP;
the first switch S1, the fourth switch S4, the fifth switch S5 and the eighth switch S8 are synchronously opened or closed; the second switch S2, the third switch S3, the sixth switch S6 and the seventh switch S7 are synchronously opened or closed.
When the circuit is powered on, the first switch S1, the fourth switch S4, the fifth switch S5 and the eighth switch S8 are turned off, the second switch S2, the third switch S3, the sixth switch S6 and the seventh switch S7 are turned on, and the reference voltage amplified by the amplifier BUF is input to the positive input end of the comparator CMPV ref0 ；
The second current source charges the second capacitor C2 through the second switch S2, and the negative input terminal of the comparator CMP inputs the second capacitor charging voltageV chg2 (ii) a Reference voltage at this timeV ref0 Is greater than the charging voltage of the second capacitorV chg2 ；
When the second capacitor C2 is charged to the second capacitor charging voltageV chg2 Greater than a reference voltageV ref0 When the latch SR is turned off according to the signal output by the comparator, the circuit is turned overA second switch S2, a third switch S3, a sixth switch S6, a seventh switch S7, a first switch S1, a fourth switch S4, a fifth switch S5, an eighth switch S8;
at this time, the negative input terminal of the comparator CMP inputs the reference voltage amplified by the amplifier BUFV ref0 (ii) a The second current source charges the first capacitor C1 through the first switch S1, and the positive input terminal of the comparator CMP inputs the first capacitor charging voltageV chg1 ；
When the first capacitor C1 is charged to the first capacitor charging voltageV chg1 Greater than a reference voltageV ref0 At this time, the latch SR inverts the circuit according to the signal output from the comparator to open the first switch S1, the fourth switch S4, the fifth switch S5, and the eighth switch S8, close the second switch S2, the third switch S3, the sixth switch S6, and the seventh switch S7, and input the reference voltage amplified by the amplifier to the positive input terminal of the comparator CMPV ref0 The second current source charges the second capacitor C2 through the second switch S2.
When the oscillating circuit works, it will generate offset voltage of comparatorV os The positive and negative input terminals of the comparator CMP are alternately connected by alternately charging and discharging the first capacitor C1 and the second capacitor C2V ref0 AndV chg1 /V chg2 the offset of the comparator can be eliminated. As shown in FIG. 2, the first capacitor C1 is charged to a first capacitor charging voltageV chg1 Greater than a reference voltageV ref0 Time of t1The second capacitor C2 is charged to the second capacitor charging voltageV chg2 Greater than a reference voltageV ref0 Time of t2The offset voltage can be described according to the following formulaV os During the alternating charging and discharging of the first capacitor C1 and the second capacitor C2, the offset is eliminated.
Figure 364219DEST_PATH_IMAGE002
Reference voltage of oscillating circuitV ref0 In the embodiment, the resistor R is a resistor string with zero temperature coefficient, which is formed by paired resistors with opposite temperature coefficients in a chip, so that the temperature change of the resistor R in the circuit operation process is reduced, the output frequency of the oscillation circuit has smaller temperature coefficient, and the output is stable.
In the working process of the oscillator, a process of charging the capacitor by fixed current exists, and the output frequency of the oscillator is obtained by deducing from the working principle
Figure 81640DEST_PATH_IMAGE004
From the formula, the output frequency is linear with the current.
If the current source is designed to be linearly adjustable, the output frequency also varies linearly, and the step of the adjustment is determined by Δ I/I. In order to achieve a relatively wide regulation range and a relatively small regulation step, Δ I needs to be sufficiently small, I needs to be sufficiently large, i.e. the multiple between the current of the current source MSB of the most significant bit and the current of the current source LSB of the least significant bit is very different, which results in a large Mismatch of the mirror current.
In this embodiment, in order to reduce the mismatch between the current of the current source MSB of the most significant bit and the current of the current source LSB of the least significant bit, the LSB current is decoded in a binary manner, the MSB current is decoded in a thermometer code manner, and the difference between the MSB and the LSB is multiplied by 32 times, which can effectively reduce the adjustment step error introduced by the mismatch of the current mirrors.
In another embodiment, the resistor R of the high-precision RC oscillating circuit is an off-chip high-precision resistor, and does not affect the oscillation frequency due to temperature variation generated during the operation of the oscillating circuit; the other structures and configurations are the same as those of the above-described embodiment.
The above examples are only two of the specific embodiments of the present invention, and should not be used to limit other embodiments of the present invention; any improvements, substitutions and modifications made on the basis of the present invention without any creative effort are included in the protection scope of the present invention.

Claims (8)

1. A high-precision RC oscillation circuit, comprising:
the circuit comprises a first current source, a second current source, an amplifier, a comparator, a first capacitor, a second capacitor, a resistor, a latch and first to eighth switches;
the second current source is a mirror image of the first current source;
the first current source, the amplifier, the resistor, the seventh switch and the eighth switch are used for providing reference voltage for the comparator;
the second current source, the first capacitor, the second capacitor and the first to sixth switches are used for controlling the charging and discharging processes of the first capacitor and the second capacitor and providing capacitor charging voltage for the comparator;
the comparator is used for comparing the reference voltage with the capacitor charging voltage and outputting a comparison result signal;
the latch is used for controlling the first switch to the eighth switch to be switched on or switched off according to the signal output by the comparator and outputting a clock signal to a downstream module;
the second current source comprises a plurality of mirror circuits connected in parallel; in the second current source, the current of the current source of the most significant bit adopts a temperature decoding mode, and the current of the current source of the least significant bit adopts a binary decoding mode.
2. A high precision RC oscillator circuit as claimed in claim 1, wherein the current of the most significant current source and the current of the least significant current source in said second current source are adjusted by a multiple according to actual needs.
3. A high accuracy RC oscillator circuit as claimed in claim 2, wherein the current of the most significant current source and the current of the least significant current source in said second current source are controlled within a multiple of 32.
4. A high accuracy RC oscillator circuit as claimed in claim 1, wherein said resistors are series or parallel resistors with opposite temperature coefficients in the chip.
5. A high accuracy RC oscillator circuit as claimed in claim 1 in which the resistor is an off-chip high accuracy resistor.
6. A high accuracy RC oscillator circuit as claimed in claim 1, wherein said first current source and said amplifier and said resistor provide reference voltages to the comparator by:
the first current source is connected with the output end of the amplifier and is grounded through the resistor;
the positive input end of the amplifier provides an initial reference voltage, and the negative input end of the amplifier, the output end of the amplifier and the resistor are connected in series and used for amplifying signals and providing an amplified reference voltage for the oscillating circuit;
the opposite ends of the resistor connected with the negative input end of the amplifier are respectively connected with a seventh switch and an eighth switch which are connected in parallel; the positive electrode of the seventh switch is connected with the resistor, and the negative electrode of the seventh switch is connected with the positive input end of the comparator; the positive pole of the eighth switch is connected with the resistor, and the negative pole of the eighth switch is connected with the negative input end of the comparator.
7. A high precision RC oscillator circuit according to claim 1,
the second current source, the first capacitor, the second capacitor and the first to sixth switches control the charging and discharging processes of the first capacitor and the second capacitor, and the specific mode of providing capacitor charging voltage for the comparator is as follows:
the positive electrode of the first switch is connected with the output end of the second current source; the negative electrode of the first switch is respectively connected with the positive electrode of the third switch, the positive electrode of the fifth switch and the first capacitor; the negative electrode of the third switch is grounded; the opposite end of the first capacitor connected with the first switch is grounded; the negative electrode of the fifth switch is connected with the positive input end of the comparator;
the first switch is connected with the second switch in parallel;
the positive electrode of the second switch is connected with the output end of the second current source; the negative electrode of the second switch is respectively connected with the positive electrode of the fourth switch, the positive electrode of the sixth switch and the second capacitor; the negative electrode of the fourth switch is grounded; the opposite end of the second capacitor connected with the second switch is grounded; and the negative electrode of the sixth switch is connected with the negative input end of the comparator.
8. A high precision RC oscillation circuit according to any one of claims 1 to 7,
the first switch, the fourth switch, the fifth switch and the eighth switch are synchronously opened or closed; the second switch, the third switch, the sixth switch and the seventh switch are synchronously opened or closed.
CN202111492840.0A 2021-12-08 2021-12-08 High-precision RC oscillating circuit Pending CN114123974A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
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Application Number Priority Date Filing Date Title
CN202111492840.0A CN114123974A (en) 2021-12-08 2021-12-08 High-precision RC oscillating circuit

Publications (1)

Publication Number Publication Date
CN114123974A true CN114123974A (en) 2022-03-01

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