High-precision low-temperature drift voltage-controlled oscillator without off-chip crystal oscillator and calibration method

Abstract

The application relates to a high-precision low-temperature drift Colpitts oscillator without an off-chip crystal oscillator and a calibration method, and belongs to the technical field of oscillators. The high-precision low-temperature drift Colpitts oscillator is characterized in that it comprises a zero-temperature drift current source, an adjustable reference voltage, a comparator, a latch, a PVT detection circuit and a temperature drift calibration circuit. The zero-temperature drift current source is generated by the current generated by the combination of a band-gap reference voltage and a zero-temperature drift resistor, and then the current is used for rough adjustment of the process angle deviation through more than one high-precision current mirror. The voltage of the zero-temperature drift current source and the adjustable reference voltage are sequentially input into the PVT detection circuit and the temperature drift calibration circuit, and then compared in the comparator, and finally output to the latch to generate an oscillation frequency. Finally, the high-precision low-temperature drift clock frequency is obtained by precisely adjusting the frequency through the current generated by the band-gap reference voltage and the high-precision resistor voltage dividing network. The application provides the high-precision low-temperature drift clock frequency which can replace the off-chip quartz crystal oscillator through rough adjustment and precise adjustment of the oscillator and further online correction.

Description

Technical Field

[0001] This invention relates to a relaxation oscillator, and more particularly to a high-precision, low-temperature drift relaxation oscillator that does not require an external crystal oscillator and a calibration method for the drift relaxation oscillator. Background Technology

[0002] Oscillators are key components providing synchronous reference clocks for communication chips, CPU / MCU chips, and memory chips. Traditionally, oscillators can be divided into off-chip high-precision quartz crystal oscillators and on-chip integrated low-cost oscillators. Although quartz crystal oscillators have a stable absolute oscillation frequency and extremely low temperature drift, they cannot be used for CMOS process integration in very large-scale integrated circuits (VLSI) and can only be used as off-chip discrete devices. This not only increases system costs but also adds additional electromagnetic interference pathways in complex environments such as automotive and industrial control.

[0003] Relaxation oscillators are widely used reference clocks in ultra-large-scale integrated systems (SoCs) such as MCUs, with operating frequencies ranging from several megahertz to tens of megahertz. The oscillation frequency of a relaxation oscillator varies significantly with process angle (P-process), supply voltage (V-Voltage), and temperature (T-Temperature) (e.g., 20%-30% in 55nm CMOS processes). Traditional relaxation oscillators use a superposition of currents with a positive temperature coefficient (PTAT) and a current with a negative temperature coefficient (CTAT) to generate a current with a "zero" temperature coefficient. The time constant of the charging and discharging of a capacitor is then controlled by a MOS switch to produce the desired clock oscillation frequency. However, in practice, since PTAT and CTAT cannot perfectly complement each other, the fine-tuning current mirror used for adding PTAT and CTAT has a large mismatch, which makes the superimposed current still have a certain temperature coefficient. The small current mirror used for fine-tuning the frequency also has a large mismatch. With multiple parameters intertwined, the frequency temperature drift of the relaxation oscillator is large. Moreover, the accuracy of the current mirror is severely affected by matching / size / load voltage. It is difficult to solve the batch consistency problem of mass production by using the current mirror for fine-tuning the frequency, which limits the application scenarios of the relaxation oscillator. Summary of the Invention

[0004] The purpose of this invention is to provide a high-precision, low-temperature drift relaxation oscillator and calibration method that eliminates the need for an external crystal oscillator. This method systematically corrects the influence of PVT variations on the output frequency of the relaxation oscillator, providing an on-chip high-precision, low-temperature drift clock for MCUs that can replace an external quartz crystal oscillator.

[0005] Technical solution:

[0006] A high-precision, low-temperature drift relaxation oscillator without an external crystal oscillator includes a zero-temperature drift current source, an adjustable reference voltage, a comparator, a latch, a PVT detection circuit, and a temperature drift calibration circuit. The zero-temperature drift current source is generated by the current produced by the combination of a bandgap reference voltage (VBG) and a zero-temperature drift resistor, which is then coarsely adjusted for process angle deviation by one or more high-precision current mirrors. The voltage of the zero-temperature drift current source and the adjustable reference voltage are sequentially passed through the PVT detection circuit and the temperature drift calibration circuit, and then compared by the comparator. The result is then output to the latch to generate the oscillation frequency. Finally, the frequency is finely adjusted by the current generated by the bandgap reference voltage and the high-precision resistor voltage divider network to obtain the high-precision, low-temperature drift clock frequency. At this point, the output frequency of the relaxation oscillator is inversely proportional to the comparator reference voltage (VREF_CMP) and directly proportional to the voltage of the zero-temperature drift current source (VREF_IGEN).

[0007] Furthermore, the zero-temperature-drift resistor combination consists of at least one set of positive temperature coefficient resistors and at least one set of negative temperature coefficient resistors.

[0008] Furthermore, the adjustable reference voltage is generated by voltage division using a combination of an adjustable resistor and a zero-temperature-drift resistor.

[0009] Furthermore, the high-precision resistor divider network consists of a series combination of one or more resistors with the same or different resistance values, and the connection points between adjacent resistors are all connected to the lead wires with switches.

[0010] Furthermore, the PVT detection circuit includes a process corner detection circuit, a voltage detection circuit, and a temperature detection circuit.

[0011] Furthermore, the temperature drift calibration circuit includes an initialization register and a calibration register. The initialization register stores the initialization switching current source control word and the initialization reference voltage control word calibrated by the relaxation oscillator before leaving the factory. The calibration register stores the calibration reference voltage control word adjusted according to different temperatures.

[0012] A method for calibrating a high-precision, low-temperature drift relaxation oscillator without an external crystal oscillator is disclosed. The method employs the aforementioned high-precision, low-temperature drift relaxation oscillator without an external crystal oscillator. Before leaving the factory, the frequency of the process angle is coarsely and finely calibrated twice. The calibrated initialization switch current source control word, initialization adjustable reference voltage control word, and control words for each temperature are written into the temperature drift calibration circuit. Before operation, the initialization switch current source control word and initialization adjustable reference voltage control word are imported. During operation, the calibration adjustable reference voltage is imported based on the temperature detected by the PVT detection circuit, thereby achieving real-time, high-precision calibration of the relaxation oscillator's output frequency.

[0013] The calibration steps before leaving the factory are as follows:

[0014] Step S101: Check the process corners, power supply voltages, and transistor junction temperatures of each component in the factory-released relaxation oscillator;

[0015] Step S102: Compare the output frequency of the relaxation oscillator with the frequency of the quartz crystal used for factory calibration;

[0016] Step S103: Use a switching current source to coarsely adjust the output frequency of the relaxation oscillator to be close to the quartz crystal frequency, and calibrate it to initialize the switching current source control word;

[0017] Step S104: Fine-tune the output frequency of the relaxation oscillator to match the frequency of the quartz crystal using the adjustable reference voltage, and calibrate it to initialize the adjustable reference voltage control word;

[0018] Step S105: Write the initialization switch current source control word and the initialization adjustable reference voltage control word into the initialization register;

[0019] Step S106: Gradually change the temperature within the operating temperature range of the relaxation oscillator and adjust the adjustable reference voltage accordingly to make the output frequency of the relaxation oscillator consistent with the frequency of the quartz crystal oscillator. The calibration is set as the calibration adjustable reference voltage control word at each temperature.

[0020] Step S107: Write the calibration adjustable reference voltage control word into the calibration register;

[0021] The calibration steps for use are as follows:

[0022] Step S201: Import the initialization switch current source control word and the initialization adjustable reference voltage control word from the initialization register;

[0023] Step S202: In non-dormant state, detect the temperature of the relaxation oscillator at regular intervals, compare the temperature difference between adjacent time periods, if the temperature difference is greater than a specified threshold, proceed to step S203, if the difference is less than or equal to the specified threshold, proceed to step S204.

[0024] Step S203: After importing the calibration adjustable reference voltage control word for the corresponding temperature from the calibration register, proceed to step S204;

[0025] Step S204: The oscillator is working normally.

[0026] Beneficial effects:

[0027] 1) This invention utilizes resistors with low positive temperature coefficients and low negative temperature coefficients to create a resistor with a "zero temperature coefficient". Combined with a bandgap reference voltage with a "zero temperature coefficient", it provides a charging current with a "zero temperature coefficient" for the relaxation oscillator. This establishes a strong correlation between the bandgap reference voltage, the comparator reference voltage, and the zero temperature drift voltage, thus solving the problem of additional temperature drift caused by the decoupling of the three.

[0028] 2) The frequency of the process corner is coarsely adjusted (error <10%) by using a high-precision current mirror with a large area, and then the oscillation frequency is finely adjusted (error <0.1%) by using a high-precision resistor voltage divider network. The method of decoupling coarse and fine adjustment avoids the adaptation and inter-chip inconsistency problems caused by small current mirrors, and further reduces temperature drift.

[0029] 3) The relaxation oscillator is calibrated by using a time-to-digital converter in combination with an external high-precision reference clock, and the calibration result is stored in a lookup table register. The output frequency of the relaxation oscillator is further calibrated online by an on-chip temperature sensor, providing the MCU with a high-precision low-temperature drift clock solution that can replace the external quartz crystal oscillator. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of the oscillator;

[0031] Figure 2 This is a flowchart of the oscillator calibration process before it leaves the factory.

[0032] Figure 3 A calibration flowchart for oscillator use;

[0033] Wherein: 1 is the PVT detection circuit, and 2 is the temperature drift calibration circuit. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0035] like Figure 1 As shown, a high-precision low-temperature drift relaxation oscillator without an external crystal oscillator includes a zero-temperature drift current source, an adjustable reference voltage, a comparator, a latch, a PVT detection circuit 1, and a temperature drift calibration circuit 2. The zero-temperature drift current source is generated by the current produced by the combination of a bandgap reference voltage and a zero-temperature drift resistor, which is then coarsely adjusted for process angle deviation by one or more high-precision current mirrors. The voltage of the zero-temperature drift current source and the adjustable reference voltage are sequentially passed through the PVT detection circuit and the temperature drift calibration circuit and then connected to the comparator for comparison. The result is then output to the latch to generate the oscillation frequency. Finally, the frequency is finely adjusted by the current generated by the bandgap reference voltage and the high-precision resistor voltage divider network to obtain the high-precision low-temperature drift clock frequency.

[0036] A zero-temperature-drift resistor combination consists of at least one set of positive temperature coefficient resistors and at least one set of negative temperature coefficient resistors.

[0037] The adjustable reference voltage is generated by voltage division using a combination of an adjustable resistor and a zero-temperature-drift resistor.

[0038] A high-precision resistor divider network consists of a series combination of one or more resistors with the same or different resistance values, and the connection points between adjacent resistors are all connected to leads with switches.

[0039] The PVT detection circuit includes a process corner detection circuit, a voltage detection circuit, and a temperature detection circuit.

[0040] The temperature drift calibration circuit includes an initialization register and a calibration register. The initialization register stores the initialization switching current source control word and the initialization reference voltage control word that were calibrated before the relaxation oscillator left the factory. The calibration register stores the calibration reference voltage control word that is adjusted according to different temperatures.

[0041] A method for calibrating a high-precision, low-temperature drift relaxation oscillator without an external crystal oscillator is disclosed. The method employs the aforementioned high-precision, low-temperature drift relaxation oscillator without an external crystal oscillator. Before leaving the factory, the frequency of the process angle is coarsely and finely calibrated twice. The calibrated initialization switch current source control word, initialization adjustable reference voltage control word, and control words for each temperature are written into the temperature drift calibration circuit. Before operation, the initialization switch current source control word and initialization adjustable reference voltage control word are imported. During operation, the calibration adjustable reference voltage is imported based on the temperature detected by the PVT detection circuit, thereby achieving real-time, high-precision calibration of the relaxation oscillator's output frequency.

[0042] The calibration steps before leaving the factory are as follows:

[0043] Step S101: Check the process corners, power supply voltages, and transistor junction temperatures of each component in the factory-released relaxation oscillator;

[0044] Step S102: Compare the output frequency of the relaxation oscillator with the frequency of the quartz crystal used for factory calibration;

[0045] Step S103: Use a switching current source to coarsely adjust the output frequency of the relaxation oscillator to be close to the quartz crystal frequency, and calibrate it to initialize the switching current source control word;

[0046] Step S104: Fine-tune the output frequency of the relaxation oscillator to match the frequency of the quartz crystal using the adjustable reference voltage, and calibrate it to initialize the adjustable reference voltage control word;

[0047] Step S105: Write the initialization switch current source control word and the initialization adjustable reference voltage control word into the initialization register;

[0048] Step S106: Gradually change the temperature within the operating temperature range of the relaxation oscillator and adjust the adjustable reference voltage accordingly to make the output frequency of the relaxation oscillator consistent with the frequency of the quartz crystal oscillator. The calibration is set as the calibration adjustable reference voltage control word at each temperature.

[0049] Step S107: Write the calibration adjustable reference voltage control word into the calibration register;

[0050] The calibration steps for use are as follows:

[0051] Step S201: Import the initialization switch current source control word and the initialization adjustable reference voltage control word from the initialization register;

[0052] Step S202: In non-dormant state, detect the temperature of the relaxation oscillator at regular intervals, compare the temperature difference between adjacent time periods, if the temperature difference is greater than a specified threshold, proceed to step S203, if the difference is less than or equal to the specified threshold, proceed to step S204.

[0053] Step S203: After importing the calibration adjustable reference voltage control word for the corresponding temperature from the calibration register, proceed to step S204;

[0054] Step S204: The oscillator is working normally.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the principles and spirit of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-precision low-temperature drift RC oscillator calibration method without an off-chip crystal oscillator, characterized by: The zero temperature drift current source, the adjustable reference voltage, the comparator, the latch, the PVT detection circuit (1), and the temperature drift calibration circuit (2); wherein the zero temperature drift current source is generated by the current combined by the band gap reference voltage and the zero temperature drift resistance, and then is adjusted by more than one high-precision current mirror to rough adjust the deviation of the process angle, the voltage of the zero temperature drift current source and the adjustable reference voltage are sequentially passed through the PVT detection circuit and the temperature drift calibration circuit, and then are compared by the comparator, and are output to the latch to generate the oscillation frequency, finally the high-precision low-temperature drift crystal oscillator is obtained by the high-precision low-temperature drift crystal oscillator which is generated by the band gap reference voltage and the high-precision resistance voltage dividing network, the frequency of the process angle is calibrated twice before the factory, the initialization switch current source control word, the initialization adjustable reference voltage control word and the control word at each temperature are written into the temperature drift calibration circuit, the initialization switch current source control word and the initialization adjustable reference voltage control word are introduced before the operation, and the calibration adjustable reference voltage is introduced according to the temperature detected by the PVT detection circuit during the operation, so as to realize the real-time high-precision calibration of the output frequency of the running relaxation oscillator.

2. The high precision low temperature drift motional oscillator calibration method of claim 1, wherein: The zero temperature drift resistance combination is combined by at least one group of positive temperature coefficient resistors and at least one group of negative temperature coefficient resistors.

3. The high precision low temperature drift motional oscillator calibration method of claim 1, wherein: The adjustable reference voltage is generated by the adjustable resistance and the zero temperature drift resistance combination voltage dividing.

4. The high precision low temperature drift zener oscillator calibration method of claim 1, wherein: The PVT detection circuit includes the process angle detection circuit, the voltage detection circuit and the temperature detection circuit.

5. The high precision low temperature drift zener oscillator calibration method of claim 1, wherein: The high-precision resistance voltage dividing network is more than one resistance combination with the same or different resistance values, and the connection points between adjacent resistances are connected with the lead-out lines with switches.

6. The high precision low temperature drift zener oscillator calibration method of claim 1, wherein: The temperature drift calibration circuit includes the initialization register and the calibration register, the initialization switch current source control word and the initialization reference voltage control word calibrated by the relaxation oscillator before the factory are stored in the initialization register, and the calibration reference voltage control word adjusted according to different temperatures is stored in the calibration register.

7. The high precision low temperature drift zener oscillator calibration method of claim 1, wherein: The steps of the factory calibration are: Step S101: detecting the process angle, the power supply voltage and the transistor junction temperature of each device of the factory relaxation oscillator; Step S102: comparing the output frequency of the relaxation oscillator with the quartz crystal frequency used for factory calibration; Step S103: roughly adjusting the output frequency of the relaxation oscillator to be close to the quartz crystal frequency by the switch current source, and marking the initialization switch current source control word; Step S104: finely adjusting the output frequency of the relaxation oscillator to be consistent with the quartz crystal frequency by the adjustable reference voltage, and marking the initialization adjustable reference voltage control word; Step S105: writing the initialization switch current source control word and the initialization adjustable reference voltage control word into the initialization register; Step S106: gradually changing the temperature within the working temperature range of the relaxation oscillator, and adjusting the adjustable reference voltage to make the output frequency of the relaxation oscillator consistent with the quartz crystal frequency, and marking the calibration adjustable reference voltage control word at each temperature; Step S107: writing the calibration adjustable reference voltage control word into the calibration register.

8. The method of claim 1, wherein: The steps of the calibration during use are: Step S201: importing initialization switch current source control word and initialization adjustable reference voltage control word from initialization register; Step S202: detecting the temperature of the relaxation oscillator every certain time in non-sleep state, comparing the temperature difference between adjacent time periods, if the temperature difference is greater than a specified threshold, entering step S203, if the difference is less than or equal to the specified threshold, entering step S204; Step S203: importing the calibration adjustable reference voltage control word of the corresponding temperature from the calibration register, and then entering step S204; Step S204: the oscillator works normally.

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