CN117394791A - Real-time clock circuit, integrated circuit, electronic device and design method - Google Patents

Abstract

The invention discloses a real-time clock circuit and a chip, which adopt 3 independent LDOs to respectively supply power to a temperature sensor, an analog-to-digital conversion circuit and a nonvolatile memory of the real-time clock circuit and the chip so as to isolate noise interference among different circuit modules. Meanwhile, the mode that the creatively designed low-power-consumption copying voltage stabilizer is combined with a current source to respectively supply power to a digital logic control module and an oscillator of a real-time clock circuit and a gap start-stop temperature sensor controlled by digital logic is adopted, so that temperature compensation is realized, and meanwhile, ultra-low power consumption and ultra-high frequency stability are achieved. The ultra-low power consumption is 500nA, the average working current is achieved, the ultra-high frequency stability reaches +/-2 ppm within the range of-20-50 ℃, and the ultra-high frequency stability reaches +/-2.5 ppm within the range of-40-85 ℃. The real-time clock circuit and the chip provided by the invention meet the requirement of high standard and accurate time reference of an electronic system, and can be widely applied to various fields such as industry, civil use and the like.

Description

Real-time clock circuit, integrated circuit, electronic device and design method

Technical Field

The invention belongs to the technical field of semiconductors, and particularly relates to a real-time clock circuit, an integrated circuit, electronic equipment and a design method.

Background

Real-Time Clock (RTC) is an application specific Clock integrated circuit with high integration level, is an important part of most electronic equipment, provides an accurate Time reference for an electronic system, and is widely applied to various fields such as communication, electric power, internet of things, security, medical treatment, automobiles, industrial control, consumer electronics and the like.

The precision of the common real-time clock in the market is about +/-20 ppm (error of nearly one minute per month), and the clock is often applied to occasions with low precision requirements. In some fields with higher time precision requirements, the requirements cannot be met. The precision of the high-precision RTC with the temperature compensation function can reach about +/-5 ppm.

Because the frequency precision of the real-time clock chip is mainly realized by a built-in crystal oscillator, the improvement of the precision and stability of the crystal oscillator is a necessary condition for realizing a high-precision RTC. In consideration of the fact that the temperature sensor module, the analog-to-digital converter module, the clock timing module and the crystal oscillation circuit module are integrated inside the RTC chip, due to the existence of power supply noise and mutual interference of signal noise of different circuits, the crystal oscillator, and clock frequency precision and stability of the RTC are affected.

Disclosure of Invention

In one embodiment of the invention, a real-time clock integrated circuit comprises a temperature sensor, an analog-to-digital converter and a memory,

the real-time clock circuit comprises 3 voltage regulators which respectively supply power to the temperature sensor, the analog-to-digital conversion circuit and the memory, namely

The first voltage stabilizer is connected with the temperature sensor to provide power VCC1 for the temperature sensor,

the second voltage stabilizer is connected with the analog-to-digital converter to provide power VCC2 for the analog-to-digital converter,

the third voltage stabilizer is connected into the memory to provide power VCC3 for the memory,

the temperature sensor is connected with the analog-to-digital converter.

The real-time clock circuit also comprises a digital module and a crystal oscillator, wherein the digital module comprises timing, calendar, alarm clock, interrupt and clock output functions for the real-time clock circuit. One output of the digital module is connected to the memory and the other output of the digital module is connected to the oscillator circuit.

The memory is a non-volatile memory and the regulator is a low dropout linear regulator (low dropout regulator, LDO).

The embodiment of the invention has the beneficial effects that the noise among all circuit modules in the real-time clock integrated circuit is isolated by providing the independent low dropout linear voltage regulator LDO for the temperature sensor, the analog-to-digital converter and the nonvolatile memory, so that the frequency stability of the real-time clock chip is improved.

Drawings

The above, as well as additional purposes, features, and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description when read in conjunction with the accompanying drawings. Several embodiments of the present invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which:

fig. 1 is a schematic diagram of a real-time clock circuit according to one embodiment of the present invention.

Fig. 2 is a schematic diagram of a circuit configuration of a low power replica voltage regulator (Replica regulator) according to one embodiment of the present invention.

Fig. 3 is a schematic diagram of the operation of an oscillator circuit according to the prior art.

Detailed Description

RTC belongs to a device which needs to be turned on for a long time in electronic circuit applications, and therefore, the RTC has a severe requirement on power consumption. Thus, in general, crystal oscillators are low power designs, often down to the order of hundreds of nA. In the existing RTC circuit, an external power supply is used for supplying power to an RTC analog circuit part, and an internal integration LDO provides a digital circuit working voltage, but the circuit structure cannot meet the requirements of a high-performance RTC on time precision and stability.

In accordance with one or more embodiments, a real time clock circuit, as shown in FIG. 1, includes a temperature sensor, an analog-to-digital conversion circuit (ADC), a low dropout linear regulator LDO, a non-volatile memory (OTP), a low power replica regulator, a current reference source, a digital module, and a crystal oscillation circuit.

The real-time clock circuit comprises 3 LDO voltage regulators which respectively supply power for the temperature sensor, the analog-to-digital conversion circuit and the memory. The first LDO voltage stabilizer is connected with a temperature sensor and provides a power supply VCC1 for the temperature sensor. The second LDO voltage stabilizer is connected to the analog-to-digital converter to provide power VCC2 for the analog-to-digital converter. The third LDO regulator is connected to the memory to provide power VCC3 for the memory. The memory adopts a nonvolatile memory OTP.

The real-time clock circuit also comprises a current source, a replica voltage stabilizer, a digital module and a crystal oscillator. The digital module includes timing, calendar, alarm clock, interrupt, and clock output functions for the real-time clock circuit. The digital module is a digital logic control module. The current source is connected to the first LDO voltage stabilizer, the second LDO voltage stabilizer, the third LDO voltage stabilizer and the replica voltage stabilizer. The replica voltage stabilizer is connected to the digital module and the oscillator circuit to respectively provide a power supply VREF1 for the digital module and a power supply VREF2 for the oscillator circuit.

One output of the digital module is connected to the memory, the other output of the digital module is connected to the oscillator circuit, and the third output of the digital module is connected to a replica voltage regulator (this output connection is not shown in fig. 1). The temperature sensor is connected with the analog-to-digital converter, and the output of the analog-to-digital converter is connected with the digital control module. Meanwhile, the output of the memory OTP can also be connected into a crystal oscillator circuit. The crystal oscillator circuit of the real-time clock circuit RTC may be connected in parallel to the terminals of the off-chip quartz crystals X1, X2.

Due to the low power consumption requirements of the RTC, the RTC average power consumption is typically less than 1uA. Whereas a typical linear regulator current is relatively large, on the order of about 10 uA. The oscillator circuit and the digital module in the RTC are required to be always started, the working mode is maintained, and the working mode of interval starting cannot be adopted. Therefore, if a normal linear regulator is also used for the oscillator circuit and the digital module, the power consumption of the RTC may not be satisfactory. The low-power-consumption replica voltage stabilizer can overcome the problem that the common linear voltage stabilizer cannot meet the requirement.

The oscillation frequency of the oscillator circuit may vary due to temperature drift. A temperature sensor is employed in the RTC circuit. Typically, temperature change is not a short time process and temperature can be detected by means of time intervals. Only when temperature detection is needed, the corresponding detection circuit is opened, so that the power consumption of the RTC is reduced. In general, the time interval for temperature compensation of the RTC circuit is about 2 seconds for the interval on time for temperature detection, i.e., the change of the ambient temperature can be satisfied. In the embodiment of the disclosure, an ultra-low power consumption replica voltage stabilizer is adopted for an oscillator circuit and a digital module, and an LDO is adopted for a temperature sensor and an analog-digital conversion circuit, so that even if 2ms is set for the starting time, the working current of the circuit in 2ms is about 10uA, and the current only accounts for one thousandth of the total working time. The overall average power consumption of the RTC circuit is small, and the power consumption of the overall RTC is not influenced, so that the embodiment of the disclosure can completely meet the design requirement of the RTC circuit by adopting an interval opening mode for the temperature detection and compensation circuit of the RTC circuit.

The digital module is herein a digital logic control module, or may also be referred to as a digital logic function module, comprising the timing, calendar, alarm clock, interrupt, clock output functions required in the RTC circuit. The digital module can realize digital logic control through a built-in programmable module. The digital module here can also be realized directly with a microcontroller.

In the RTC circuit, 3 independent LDOs are adopted for supplying power, and power sources VCC1, VCC2 and VCC3 are respectively provided for a temperature sensor, an analog-to-digital conversion circuit (ADC) and a nonvolatile memory (OTP). The LDO adopts a conventional structure, and the power consumption is about 10 uA. The noise of the real-time clock circuit is isolated, wherein the isolation design means that the power isolation is realized by providing independent power supply for each module, and the noise interference among each circuit module is further restrained through the power isolation.

Here, the RTC circuit may detect the temperature in an operation mode of intermittent start-stop, and the intermittent start-up time is divided by a digital module with reference to a crystal oscillator clock, so as to obtain a desired temperature supplement time interval, and the interval signal is the control signal EN in fig. 1. The smaller the compensation interval, the more temperature real-time capture capability. The larger the compensation interval, the smaller the average power consumption. With respect to the specific time interval setting, a programmable module can be built in the digital module, and adjustment can be performed by writing in a register. Typically, there are several gear positions of 0.5S, 2S, 10S, 30S, which are adjustable in seconds. For example, 2S is set, which means that a frequency calibration is performed for each 2S. If 30S is set, it means that 30S does not perform frequency calibration once, and if the temperature of the RTC circuit in 30S is greatly changed, the RTC frequency deviation is increased.

The real time clock circuit also includes a current source (current bias), a low power replica voltage regulator (replica regulator), a crystal oscillator (oscillator), and an off-chip quartz crystal. This part of the module needs to work continuously and stably. Because the traditional LDO is used as a power supply for supplying power, the power consumption is relatively large, and a low-power-consumption replica voltage stabilizer is adopted, and independent power supplies VREF1 and VREF2 are provided for the digital functional module and the crystal oscillator.

The output of the analog-to-digital converter ADC is connected to a digital function module digital block, the digital function module digital block controls the OTP through the acquired temperature ADC value, reads the temperature compensation data prestored by the OTP, and then controls a capacitor array included in a crystal oscillator oscillascor, so that the output frequency of the real-time clock is regulated according to the temperature.

In the embodiment of the disclosure, the crystal oscillator adjusts the frequency circuit of the crystal oscillator by adopting real-time interpolation through the capacitor array, and the specific principle is shown in fig. 3. Analog-to-digital converter ADC acquires temperature data digital signal ADC [ n:1 ]]Input to digital block (n represents the number of ADC data bits). The digital function module is used for acquiring ADC [ n:1 ]]The value, the capacitor array control signal stored in advance in the nonvolatile memory OTP is read. The digital functional module comprises a linear interpolation module, and the compensation precision is improved through an interpolation algorithm. Due to the adoption of the linear interpolation algorithm, the byte capacity required by the OTP of the nonvolatile memory is only 2 ^n-2 . Digital blocks receive capacitance signal CAPi[n-2,1]Linearly interpolating to CAPj [ n ]; 1]The capacitor array control signal directly controls a capacitor array included in the crystal oscillator, and the oscillation frequency of the crystal oscillation circuit is adjusted by changing the capacitance of the capacitor array, so that the output frequency of the real-time clock is adjusted according to the temperature. The principle of the oscillator circuit shown in fig. 3 is also disclosed in the patent document with publication number CN 112422085A. In this document, a temperature sensor is provided to detect a temperature change, and an oscillator capacitor array is subjected to interpolation compensation according to the temperature change. If the oscillator circuit is also powered with a normal linear regulator, the RTC power consumption becomes unacceptable and unusable in many low power applications.

Accordingly, the beneficial effects of the embodiments of the present disclosure include:

1. in order to reduce the mutual interference of noise among different functional modules in the chip, the embodiment provides a multi-module independent power supply architecture which can obviously reduce the mutual noise interference and improve the precision and the stability of the real-time clock chip. Through independent power supply architecture, built-in linear voltage stabilizer not only plays the effect of isolating noise, but also can improve the power supply rejection ratio of real-time clock, reduces the sensitivity of real-time clock to power supply.

2. The copy voltage stabilizer with ultra-low power consumption is used for supplying power to the oscillator circuit and the digital logic control module which need to work continuously, so that the power consumption of the RTC circuit is greatly reduced.

And 3. The RTC circuit adopts a mode of starting work at intervals for the temperature detection and compensation circuit, so that the average power consumption of the RTC circuit is further reduced.

In accordance with one or more embodiments, a low power replica voltage regulator (Replica regulator) circuit is used for a real time clock circuit. As shown in FIG. 2, the power supply voltages VREF1, VREF2 and the like can be provided according to the use requirement, and the parallel outputs are multiplexed to isolate noise interference. Wherein, I1 is a current source provided by "current bias", MN3, MN4, MN31, MN41 form a current mirror structure, where MN31, MN41 may be connected in parallel in multiple columns, and the parallel number is n+1. The digital module controls the current flowing through MP1 through outputting the high and low level of CTRL [ N:0] signal. MP1 and MP2 constitute a replica current mirror, and MN5 and MN6 constitute a replica current mirror. The drain end of MP1 is connected to the gate end of MP3 to form a negative feedback loop. Ensuring that the current flowing through MP1, MP2 and MP3 is changed in equal proportion. Therefore, the current flowing through the MP3 is controlled, the MN0 and the MN6 are connected by adopting diodes to be used as resistors, the current flowing through the MP3 to the ground flows through the MN0 and the MN6 to generate X point voltage, and the adjustable voltage V (X) is obtained. In the embodiments of the present disclosure, MP1, MP2, MP3, MN0, MN1, MN2, MN5, MN6, MN3, MN4, MN31, MN41, etc., NMOS transistors or PMOS transistors may be employed.

According to fig. 2, a part of a low-power replica voltage regulator (Replica regulator) circuit, a current source I1 is connected in series with a series circuit of transistors MN3, MN4, a series circuit of transistors MN31, MN41 is connected in parallel with the series circuit of transistors MN3, MN4, a gate of MN31 is connected to a gate of MN3, and a gate of MN4 is connected to a power supply VCC. Further, transistors MN32 and MN42 are also provided, the series circuit of the transistors MN32 and MN42 is connected in parallel with the series circuit of the transistors MN31 and MN41, and the gate of MN32 is connected to the gate of MN 31. For further precise control, and so on, a series circuit of transistors MN33, MN43 is provided in parallel with a series circuit of transistors MN31, MN41, a gate of MN33 is connected to a gate of MN31, a series circuit of … … transistors MN3N, MN N is in parallel with a series circuit of transistors MN31, MN41, and a gate of MN3N is connected to a gate of MN 31. The gates of MN41, MN42, MN43, … … MN4N are connected to the control CTRL [ N:0] signal pin, respectively. The sources of the transistors MN4 and MN41, MN42, MN43, … … MN4N are connected in parallel and then grounded.

In one embodiment, a portion of the low power replica voltage regulator (Replica regulator) circuit, the gate of transistor MP1 is connected to the gate of MP2, and the gate of transistor MP3 is connected to the drain of MP 1. The transistor MP3 is connected in series with the series circuit of the transistors MN0 and MN6, the transistor MP2 is connected in series with the transistor MN5, and the gate of the transistor MN5 is connected with the transistor MN6. The sources of the transistors MN5, MN6 are connected in parallel and then grounded.

In one embodiment, a portion of the low power replica voltage regulator (Replica regulator) circuit, the gate of transistor MN1 is connected to the drain of transistor MP3, the connection point is set to point X, and the gate of transistor MN2 is connected to the gate of transistor MN1, i.e., connection point X. Voltage VREF1 is drawn from the drain of MN1 and voltage VREF2 is drawn from the drain of MN 2. Voltage VREF2 and voltage VREF1 correspond to the meaning of "replica".

In one embodiment, the gate of transistor MN1 is connected to the drain of transistor MP3 through resistor R1, and the gate of transistor MN2 is connected to the gate of transistor MN1 through resistor R2. The gate of the transistor MN1 is grounded through the capacitor C1, and the gate of the transistor MN2 is grounded through the capacitor C2. The drain of the transistor MN1 is grounded through a capacitor C3, and the drain of the transistor MN2 is grounded through a capacitor C4.

In the circuit configuration in fig. 2, a voltage V (X) =vth (MN 0) +vth (MN 6) is generated at the connection point X. Here, vth is a threshold voltage of the transistor. Thus, the voltage value of V (X) can be adjusted in 3 ways:

1) The diode connected mn0+mn6 is a 2-stage series. The voltage V (X) can be adjusted by increasing or decreasing the number of series steps.

V (X) =m×vth (NMOS), where M represents the series number of diode connections.

2) Trimming V (X) is performed by changing the width and length dimensions of NMOS transistor MN 0.

3) The current through MN0, MN6 is regulated by the CTRL [ N:0] control signal, regulating V (X).

The connection point X is connected to the gate terminals of MN1, MN2, at which point,

VREF1＝VREF2＝V(X)-Vth(MN1)＝V(X)-Vth(MN2)。

here, MN1, MN2 are selected from active NMOS (vth≡0v), VREF 1=vref 2≡v (X). Conventional NMOS (Vth. Apprxeq. 0.7V) may also be used.

According to the working current of the digital functional module and the crystal oscillator circuit, the sizes of MN1 and MN2 are properly adjusted to obtain proper voltages VREF1 and VREF2. The VREF1 and VREF2 are independent of each other, and noise on VREF1 and VREF2 is isolated from each other.

In the embodiment of the disclosure, the low-power-consumption copy voltage stabilizer has the following structural advantages: the power consumption is extremely low, and meanwhile, through reasonable design, the power consumption is less than 100nA. Compared with the traditional LDO, the LDO has no extra voltage dividing resistor power consumption. In practice, due to manufacturing process problems, the replica voltage stabilizer cannot guarantee the consistency of current sources, and the problem of different current output values may occur for devices in different batches. In the embodiment of the disclosure, according to different values of the actually measured output values of the current values of different batches, the digital module is programmed to set the signal level of the control CTRL [ N:0] of the digital module connected to the replica voltage stabilizer, so that the accurate adjustment and control of parallel mirror currents of multiple columns of serial circuits and the like of the transistors MN31 and MN41 are realized, the current source output in the replica voltage stabilizer accords with expected values, and finally accurate and stable voltages VREF1 and VREF2 are obtained.

Due to the adoption of the low-power-consumption copying voltage stabilizer, the real-time clock circuit realizes the temperature compensation function and simultaneously realizes ultra-low power consumption and ultra-high frequency stability. According to actual measurement, the integrated circuit of the real-time clock circuit achieves ultra-low power consumption and is 500nA of average working current; the ultra-high frequency stability reaches +/-2 ppm at the temperature ranging from minus 20 ℃ to 50 ℃ and +/-2.5 ppm at the temperature ranging from minus 40 ℃ to 85 ℃.

It should be understood that, in the embodiment of the present invention, the term "and/or" is merely an association relationship describing the association object, which means that three relationships may exist. For example, a and/or B may represent: a exists alone, A and B exist together, and B exists alone. In addition, the character "/" herein generally indicates that the front and rear associated objects are an "or" relationship.

While the invention has been described with reference to certain preferred embodiments, it will be understood by those skilled in the art that various changes and substitutions of equivalents may be made and equivalents will be apparent to those skilled in the art without departing from the scope of the invention. Therefore, the protection scope of the invention is subject to the protection scope of the claims.

Claims (10)

1. A real-time clock circuit comprises a temperature sensor, an analog-to-digital converter and a memory, and is characterized in that,

the real-time clock circuit comprises 3 voltage regulators which respectively supply power to the temperature sensor, the analog-to-digital conversion circuit and the memory, namely

The first voltage stabilizer is connected with the temperature sensor to provide power VCC1 for the temperature sensor,

the second voltage stabilizer is connected with the analog-to-digital converter to provide power VCC2 for the analog-to-digital converter,

the third voltage stabilizer is connected into the memory to provide power VCC3 for the memory,

the temperature sensor is connected with the analog-to-digital converter.

2. The real time clock circuit of claim 1, wherein the memory is a non-volatile memory.

3. The real time clock circuit of claim 1, wherein the voltage regulator is a low dropout linear voltage regulator.

4. The real time clock circuit of claim 1, further comprising a current source, a replica voltage regulator, a digital module, and a crystal oscillator,

the digital module comprises timing, calendar, alarm clock, interrupt and clock output functions for the real-time clock circuit,

the current source is connected with the first voltage stabilizer, the second voltage stabilizer, the third voltage stabilizer and the copying voltage stabilizer,

the replica voltage stabilizer is connected to the digital module and the oscillator circuit to respectively provide a power supply VREF1 for the digital module and a power supply VREF2 for the oscillator circuit.

5. The real time clock circuit of claim 4, wherein the real time clock circuit comprises,

one output of the digital module is connected to the memory, the other output of the digital module is connected to an oscillator circuit,

the output of the analog-to-digital converter is connected to the digital module.

6. The real time clock circuit of claim 5, wherein a third output of the digital module is coupled to the replica voltage regulator.

7. The real time clock circuit of claim 5, wherein the oscillator circuit is bonded to an external quartz crystal.

8. An integrated circuit comprising a real time clock circuit as claimed in any one of claims 1 to 6.

9. An electronic device comprising the integrated circuit of claim 8.

10. A real-time clock circuit design method is characterized in that,

the real-time clock circuit comprises a temperature sensor, an analog-to-digital converter and a memory,

3 voltage regulators are arranged for the real-time clock circuit to respectively supply power for the temperature sensor, the analog-digital conversion circuit and the memory, namely

The first voltage stabilizer is connected with the temperature sensor to provide power VCC1 for the temperature sensor,

the second voltage stabilizer is connected with the analog-to-digital converter to provide power VCC2 for the analog-to-digital converter,

the third voltage stabilizer is connected into the memory to provide power VCC3 for the memory,

the temperature sensor is connected with the analog-to-digital converter.