CN114006615A - Crystal oscillator circuit capable of starting oscillation rapidly and control method - Google Patents

Abstract

The invention discloses a crystal oscillator circuit for quick oscillation starting and a control method thereof, the crystal oscillator circuit comprises a capacitor C1, a capacitor C2, a crystal oscillator, a feedback resistor and an inverter INV1, the inverter INV1 and the crystal oscillator form a loop, the two ends of the crystal oscillator are provided with the capacitor C1 and the capacitor C2, the other ends of the capacitor C1 and the capacitor C2 are both provided with grounding ends, the crystal oscillator circuit comprises a switch A1, a switch A2, a switch A3 and a power supply end, the input end of the inverter INV1 is connected with the power supply end through the switch A1, the output end of the inverter INV1 is connected with the power supply end through the switch A3 and the switch A2, the switch A3 is connected with the inverter INV1 in series, the switch A3 is connected with a series circuit of the inverter INV1 in parallel with the feedback resistor, and the switch A1, the switch A2 and the switch A3 work in combination to realize the quick oscillation starting of the crystal oscillator circuit.

Description

Crystal oscillator circuit capable of starting oscillation rapidly and control method

Technical Field

The invention relates to the technical field of electronic integrated circuits, in particular to a crystal oscillator circuit capable of starting oscillation rapidly and a control method.

Background

The conventional crystal oscillator realizes oscillation by continuously amplifying noise, but the process is very slow, and the oscillation starting is slow. Some existing improvements are to increase the gm value of the inverter by controlling to realize accelerated start-up, other improvements are to accelerate start-up in the start-up stage and reduce power consumption in the working stage by dynamically adjusting the feedback resistor, the two ways need to additionally increase a digital control circuit, the start-up time is only slightly reduced, and the fast start-up aspect needs to be improved.

Disclosure of Invention

In order to solve the problems, the invention discloses a crystal oscillator circuit capable of starting oscillation quickly and a control method. The specific technical scheme is as follows:

a crystal oscillator circuit capable of starting oscillation rapidly comprises a capacitor C1, a capacitor C2, a crystal oscillator, a feedback resistor and an inverter INV1, wherein the crystal oscillator is arranged between the capacitor C1 and the capacitor C2, the other end of the capacitor C1 and the other end of the capacitor C2 are both provided with grounding ends, the crystal oscillator circuit comprises a switch A1, a switch A2, a switch A3 and a power supply end, the input end of the inverter INV1 is connected with the power supply end through a switch A1, the output end of the inverter INV1 is connected with the power supply end through a switch A3 and a switch A2, a series circuit formed by the switch A3 and the inverter INV1 is connected with the crystal oscillator and the feedback resistor in parallel respectively, and the switch A1, the switch A2 and the switch A3 work in a combined mode to achieve rapid oscillation starting of the crystal oscillator circuit.

Further, the switch a1 includes a PMOS transistor, a gate of the PMOS transistor of the switch a1 is configured to receive the switch control signal EN, a source of the PMOS transistor is connected to a power source, and a drain of the PMOS transistor is connected to an input terminal of the inverter INV 1.

Further, the switch a2 includes a PMOS transistor, a gate of the PMOS transistor of the switch a2 is used for receiving an enable signal, a source is connected to a power supply terminal, and a drain is connected to the switch A3.

Further, the gate of the PMOS transistor of the switch a1 and the gate of the PMOS transistor of the switch a2 are connected to receive the same switch control signal EN.

Further, the switch A3 includes an NMOS transistor, the gate of the NMOS transistor of the switch A3 and the gate of the PMOS transistor of the switch a1 and the gate of the PMOS transistor of the switch a2 receive the same switch control signal EN, the source is connected to the output terminal of the inverter INV1, and the drain is connected to the switch a 2.

Further, the switch A3 includes an inverter and a PMOS transistor, the gate of the PMOS transistor of the switch A3 receives the same switch control signal EN with the gate of the PMOS transistor of the switch a1 and the gate of the PMOS transistor of the switch a2 through the inverter, the source is connected to the output terminal of the inverter INV1, and the drain is connected to the switch a 2.

Further, the inverter INV1 includes two field effect transistors, the two field effect transistors include a PMOS transistor and an NMOS transistor, gates of the two field effect transistors are connected to serve as an input end of the inverter INV1, drains of the two field effect transistors are connected to the switch A3, and an output signal and an output end of the inverter INV1 are obtained through the switch A3, in the two field effect transistors of the inverter INV1, a source of the PMOS field effect transistor is connected to a power supply end, and a source of the NMOS field effect transistor is connected to a ground end.

Further, the switch A3 is disposed in the inverter INV1, the switch A3 includes two fets, the two fets include a PMOS transistor and an NMOS transistor, wherein the gate of the NMOS transistor and the control signal receiving terminals of the switch a1 and the switch a2 are commonly connected to the switch control signal EN; the switch A3 further includes an inverter INV2, gates of two field effect transistors of the switch A3 are connected through the inverter INV2, that is, while a gate of an NMOS transistor in the switch A3 receives the switch control signal EN, an input end of the inverter INV2 is connected, a gate of a PMOS transistor in the switch A3 is connected to an output end of the inverter INV2, a signal received by a gate of a PMOS transistor in the switch A3 is an inverted signal ENB obtained by the signal EN passing through the inverter INV2, sources of two field effect transistors of the switch A3 are respectively connected to drains of two field effect transistors of the inverter INV1, that is, a source of the PMOS transistor in the switch A3 is connected to a drain of a PMOS transistor in the inverter INV1, a source of the NMOS transistor in the switch A3 is connected to a drain of an NMOS transistor in the inverter INV1, and drains of two field effect transistors of the switch A3 are connected to serve as an output end of the inverter INV 1.

A control method of a crystal oscillator circuit, the control method is used for controlling the crystal oscillator circuit with rapid oscillation starting, the control method comprises the following steps:

s1: the switch A1 and the switch A2 are closed, the switch A3 is opened, and the crystal oscillator circuit enters a preparation stage;

s2: after the crystal oscillator circuit is in the preparation phase and continues for the set time, the switch A1 and the switch A2 are opened, and the switch A3 is closed, so that the crystal oscillator circuit enters the working phase.

Further, the set time is the time from the occurrence of the voltage change of the capacitors C1 and C2 to the stabilization of the voltage after the switches a1 and a2 are closed, and is generally within 10 ns.

Compared with the prior art, the technical scheme of the application realizes quick start by only adding the switch and the corresponding control signal on the crystal oscillator circuit and constructing the mode that the electric potential difference which changes at the two ends of the crystal oscillator instantly adds the initial deformation potential energy to the crystal oscillator, has simple structure, does not increase the power consumption and effectively reduces the oscillation starting time of the crystal oscillator; through flow sheet simulation verification, the oscillation starting time can be reduced by about 50%.

Drawings

Fig. 1 is a schematic structural diagram 1 of a fast-start crystal oscillator circuit according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of an inverter and switch A3 according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a fast-start crystal oscillator circuit according to an embodiment of the present invention, shown in FIG. 2;

fig. 4 is a schematic structural diagram 3 of a fast-start crystal oscillator circuit according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the present application. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments provided in the present application without any inventive step are within the scope of protection of the present application.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The terms "comprises," "comprising," and the like, as used herein, specify the presence of stated features, operations, and/or components, but do not preclude the presence or addition of one or more other features, operations, or components. All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It is noted that the terms used herein should be interpreted as having a meaning that is consistent with the context of this specification and should not be interpreted in an idealized or overly formal sense.

The crystal oscillator is a quartz crystal resonator, which is a quartz crystal or a crystal oscillator for short, wherein a slice (wafer for short) is cut from a quartz crystal according to a certain azimuth angle; and a crystal element in which an IC is added inside a package to constitute an oscillation circuit is called a crystal oscillator. The product is generally packaged by a metal shell, and also packaged by a glass shell, ceramics or plastics. The single chip microcomputer crystal oscillator circuit is a crystal oscillator for short, and can be electrically equivalent to a two-end network formed by connecting a capacitor and a resistor in parallel and then connecting the capacitor in series. The network has two resonance points in the electrical engineering, with the higher and lower frequency being the series resonance; the higher frequency is the parallel resonance. Since the distance between the two frequencies is quite close due to the characteristics of the crystal, the crystal oscillator is equivalent to an inductor in an extremely narrow frequency range, and therefore, a parallel resonant circuit can be formed as long as two ends of the crystal oscillator are connected with proper capacitors in parallel. The parallel resonant circuit is added to a negative feedback circuit to form a sine wave oscillating circuit, and the frequency range of the oscillator equivalent to inductance is narrow, so that the frequency of the oscillator does not change greatly even if the parameters of other elements change greatly. The crystal oscillator has an important parameter, namely a load capacitance value, and the nominal resonant frequency of the crystal oscillator can be obtained by selecting a parallel capacitor equal to the load capacitance value. In a general crystal oscillator oscillation circuit, a crystal oscillator is connected to two ends of an inverting amplifier (note that the amplifier is not an inverter), two capacitors are connected to two ends of the crystal oscillator respectively, the other end of each capacitor is connected to ground, and the capacitance value of the series connection of the two capacitors should be equal to the load capacitance. Note that the pins of a typical IC all have equivalent input capacitance, which cannot be ignored. The load capacitance of general crystal oscillator is 15pF or 12.5pF, if the equivalent input capacitance of component pin is considered again, then it is better selection that two 22 pF's electric capacity constitute crystal oscillator's oscillating circuit, and load capacitance's resistance also can set up according to actual demand, and load capacitance's resistance can also be other resistances, as long as make the function of circuit normally realize, do not limit.

The crystal oscillator circuit of the present inverter structure is a structure commonly used in pierce oscillators, and the working principle thereof is that an inverter INV1 is connected at two ends of the crystal oscillator to provide negative resistance for the crystal oscillator, capacitors C1 and C2 are respectively connected between two ends of the crystal oscillator and ground, and C1= C2, a feedback resistor R is connected with an input end and an output end of the inverter INV1, and has the functions of providing direct-current working voltage for the operation of the inverter INV1 to enable the inverter to work in an amplification mode and reduce gain, etc., the oscillation principle is that the equivalent resistance value of the crystal oscillator is counteracted through the negative resistance provided by the inverter INV1 to enable a loop to be in positive feedback, and the normally provided negative resistance needs to be 3-5 times of the equivalent resistance of the crystal oscillator, when in operation, some noises in the circuit are positively fed back and amplified through a continuous loop formed by the inverter INV1 and the crystal oscillator, thereby generating oscillation, and when the oscillation amplitude is close to the power supply voltage, thereby outputting a stable clock.

As shown in fig. 1, it is a schematic diagram of a crystal oscillator circuit with fast oscillation starting proposed herein, the crystal oscillator circuit includes a capacitor C1, a capacitor C2, a crystal oscillator, a feedback resistor R and an inverter INV1, the inverter INV1 and the crystal oscillator form a loop, two ends of the crystal oscillator are respectively provided with a capacitor C1 and a capacitor C2, the other end of the capacitor C1 and the other end of the capacitor C2 are both provided with grounding ends, meanwhile, the crystal oscillator circuit also comprises a switch A1, a switch A2, a switch A3 and a power supply end, wherein the input end of the inverter INV1 is connected with the power supply end through the switch A1, the output terminal of the inverter INV1 is connected to a power supply terminal through the switch A3 and the switch a2, the switch A3 is connected in series with the inverter INV1, and the series circuit of the switch A3 and the inverter INV1 is respectively connected in parallel with the crystal oscillator and the feedback resistor R, the switch A1, the switch A2 and the switch A3 work in combination to realize the quick start of the crystal oscillation circuit.

As one example, switch a1 and switch a2 may be operated to open or close simultaneously. The operation of the switch A3 is opposite to the operation state of the switch A1 and the switch A2, namely when the switch A1 and the switch A2 are closed, the switch A3 is opened; switch A3 is closed when switch a1 and switch a2 are open. The PMOS transistor is conducted at a low grid level (VGS < Vthp), and is disconnected at a high level, so that the PMOS transistor can be controlled to be conducted with a power supply. The switch A1 comprises a PMOS tube, the grid electrode of the PMOS tube of the switch A1 is used for receiving a switch control signal EN, the source electrode is connected with the power supply end, and the drain electrode is connected with the input end of the inverter INV 1. The switch A2 comprises a PMOS tube, the grid electrode of the PMOS tube of the switch A2 is used for receiving a switch control signal EN, the source electrode is connected with a power supply end, and the drain electrode is connected with the switch A3. The grid electrode of the PMOS tube of the switch A1 is connected with the grid electrode of the PMOS tube of the switch A2 and receives the same switch control signal EN. The switch A3 comprises an NMOS tube, the grid electrode of the NMOS tube of the switch A3, the grid electrode of the PMOS tube of the switch A1 and the grid electrode of the PMOS tube of the switch A2 receive the same switch control signal EN, the source electrode is connected with the output end of the inverter INV1, and the drain electrode is connected with the switch A2. The switch A3 comprises an NOT gate and a PMOS tube, the grid electrode of the PMOS of the switch A3 receives the same switch control signal EN with the grid electrode of the PMOS of the switch A1 and the grid electrode of the PMOS of the switch A2 through the NOT gate, the source electrode is connected with the output end of the inverter INV1, and the drain electrode is connected with the switch A2. The NMOS transistor is switched on at a high grid level (VGS > Vthn), and is switched off at a low grid level, and can be used for controlling the conduction between the NMOS transistor and the ground. The switch a1 and the switch a2 may also be NMOS transistors, and when the gates of the NMOS transistors of the switch a1 and the switch a2 receive the same switch control signal EN, if the switch A3 is an NMOS transistor, the gate of the NMOS transistor of the switch A3 receives the same switch control signal EN through the not gate and the gates of the NMOS transistors of the switch a1 and the switch a 2; if the switch A3 is a PMOS transistor, the gate of the NMOS transistor of the switch A3 directly receives the same switch control signal EN as the gates of the NMOS transistors of the switch a1 and the switch a 2. The switch a1, the switch a2, and the switch A3 may be other suitable switches, such as MOS switches, transmission gates, or other suitable switches.

As shown in fig. 2, the inverter INV1 includes two field effect transistors, each of which includes a PMOS transistor and an NMOS transistor, gates of the two field effect transistors are connected to serve as an input terminal of the inverter INV1, drains of the two field effect transistors are connected to the switch A3, an output is obtained through the switch A3 and serves as an output terminal of the inverter INV1, and in the two field effect transistors, a source of the PMOS field effect transistor is connected to a power supply terminal, and a source of the NMOS field effect transistor is connected to a ground terminal. The switch A3 is arranged in the inverter INV1, the inverter INV2 is arranged in the switch A3, the switch A3 includes two field effect transistors, which are a PMOS transistor and an NMOS transistor respectively, gates of the two field effect transistors of the switch A3 are connected through the inverter INV2, that is, a gate of an NMOS transistor in the switch A3 is connected to an input terminal of the inverter INV2 while receiving a switch control signal EN, an output terminal of the inverter INV2 is connected to a gate of a PMOS transistor in the switch A3 for obtaining a control signal ENB opposite to the EN signal, sources of the two field effect transistors of the switch A3 are connected to drains of the two field effect transistors of the PMOS inverter INV1, that is, a source of the transistor in the switch A3 is connected to a drain of the PMOS transistor in the inverter INV1, a source of the NMOS transistor in the switch A3 is connected to a drain of the NMOS transistor in the inverter 1, and drains of the two field effect transistors of the switch A3 are connected to drains of the drain, as the output of inverter INV 1.

A control method of a crystal oscillator circuit, the control method is used for controlling the crystal oscillator circuit with rapid oscillation starting, the control method comprises the following steps: s1: the switch control signal EN is low, so that the switch A1 and the switch A2 are closed, the switch A3 is opened, and the crystal oscillator circuit enters a preparation stage; s2: after the crystal oscillator circuit continues to be set for a set time in the preparation stage, the set time is 10ns, the switch control signal EN is changed to be high, the switch A1 and the switch A2 are switched off, the switch A3 is switched on, and the crystal oscillator circuit enters the working stage. The specific working process is as follows:

according to the equivalent model of the crystal oscillator and the specific circuit structure of the switches a1, a2 and A3, the working circuit is equivalent as shown in fig. 3, in the preparation stage, the switch control signal EN is set to low level to make the gates of the PMOS transistors in the switches a1 and a2 low, the PMOS transistors are turned on, i.e. the switches a1 and a2 are closed, the upper plates of the capacitor C1 and the capacitor C2 are connected to the power supply terminal, the power supply terminal charges the capacitor C1 and the capacitor C2 through the switch a1 and the switch a2, meanwhile, when EN is set to low level, the EN signal obtains a high level signal ENB opposite to the EN signal through the inverter INV2 in the switch A3, EN is connected to the gate of the NMOS transistor in the A3, ENB is connected to the gate of the PMOS transistor in the A3, so that the NMOS gate in the switch A3 is low state, the PMOS gate in the switch A3 is high INV state, so that the switch A5 is opened, i.e. the connection between the output of the inverter a 5857324 and the capacitor b is disconnected, at this stage, the voltages of the upper plates of the capacitor C1 and the capacitor C2 are raised to the power supply voltage, i.e., the voltages at the two ends of the crystal oscillator are raised to the power supply voltage, so that the node voltages X1 and X2 at the two ends of the capacitor in the equivalent model of the crystal oscillator are raised to the power supply voltage; at this time, the voltage at the input end of the inverter INV1 is a high voltage, and the voltage at the output end is a low voltage, but because the switch A3 is turned off, the voltage at the upper plate of the capacitor C2 is not affected by the output of the inverter INV1, and power consumption is not consumed.

After the preparation phase lasts for a certain time (which may be 10ns, or other values, but is not limited), the enable phase is entered, in the enable phase, the switch control signal EN is set to high level, so that the gates of the PMOS transistors in the switch a1 and the switch a2 are high level, the PMOS transistors are turned off, that is, the switch a1 and the switch a2 are opened, the connection between the capacitor C1 and the upper plate of the capacitor C2 and the power supply is disconnected, meanwhile, when EN is set to high level, in the switch A3, the EN signal obtains a low level signal ENB opposite to the EN signal through the inverter INV2, EN is connected to the gate of the NMOS transistor in the A3, ENB is connected to the gate of the PMOS transistor in the A3, so that the NMOS gate in the switch A3 is in a high conducting state, the PMOS gate in the switch A3 is in a low conducting state, so that the switch A3 is closed, the output of the inverter INV 37 is connected to the upper plate INV of the capacitor C2, the crystal oscillator starts to enter a normal operation mode, and the voltage at this time, because the upper plate of the capacitor C3985 is still connected to the power supply input terminal 1, therefore, the voltage of the upper plate of the capacitor C2 is quickly pulled down to the voltage of the ground end by the low voltage output by the inverter INV1, but because the current of the equivalent inductor of the crystal oscillator equivalent model does not suddenly change, the voltage of the node X2 on the other side of the equivalent inductor is still the power voltage, and a voltage difference between two ends of the equivalent inductor is formed, so as to achieve the effect of providing potential energy for the equivalent inductor of the crystal oscillator model, the potential difference between two ends of the equivalent inductor can make the inductor generate a current flowing from X2 to N2, thereby gradually pulling down X2 and pulling up N2, meanwhile, the voltage X1 on the other end of the equivalent capacitor of the crystal oscillator equivalent model is also pulled down, and the node voltage of N1 is also pulled down by the equivalent resistor in the crystal oscillator equivalent model, the inductor current is the largest when X2 and N2 are equal, at this time, the electrical potential energy at two ends of the inductor is all converted into the current flowing from X2 to N2, and because of the inductor maintains the current, the voltage of N2 starts to be pushed up, the voltage of X2 continues to be reduced, and the voltage difference between X2 and N2 gradually reaches the maximum value; when the voltage difference between two ends of the inductor changes to the maximum value, the inductor current is zero, the equivalent inductor obtains the maximum potential energy again, the potential difference between two ends of the equivalent inductor can enable the inductor to generate current flowing from N2 to X2, so that N2 is gradually pulled down, X2 is pulled up, meanwhile, the voltage X1 at the other end of the equivalent capacitor of the crystal oscillator equivalent model is also pulled up, N1 is influenced by the equivalent resistor in the crystal oscillator equivalent model, the voltage of an N1 node is also pulled up, the equivalent inductor current is maximum when X2 and N2 are equal, at the moment, the potential energy at two ends of the inductor is completely converted into the current flowing from N2 to X2 through the equivalent inductor, due to the maintaining characteristic of the inductor to the current, the voltage of X2 starts to be pushed up, the voltage of N2 continues to be reduced, the voltage difference between X2 and N2 gradually reaches the maximum value, the voltage of each node finishes the change of one period, and the next period can be carried out according to the same change trend; meanwhile, due to the negative resistance provided by the inverter INV1, the equivalent resistance of the crystal oscillator equivalent model is offset, and the provided negative resistance value is greater than the equivalent resistance of the crystal oscillator, so that the specific working effect is as follows: when the voltage of the node N1 is reduced, the voltage of the node N2 is increased, the voltage of the node N1 is reduced and is reversely amplified through the inverter INV1, the increasing effect of the voltage of the node N2 is enhanced, when the voltage of the node N1 is increased, the voltage of the node N2 is reduced, the voltage of the node N1 is reversely amplified through the inverter INV1, the reducing effect of the voltage of the node N2 is enhanced, in the periodic change process, the waveform of the node N1 is amplified and transmitted to the node N2 through the inverter INV1, then the amplitude of the node N1 is affected, the periodically changed voltage of each node is continuously amplified, and finally, the clock output is achieved.

The above-mentioned pulling down, pulling up, pushing up, reducing, etc. are relative to the original voltage of the node, since the capacitance value of the equivalent capacitance of the crystal oscillator equivalent model is smaller relative to the capacitance C1 and the capacitance C2, such as the capacitance C1 and the capacitance C2 used in this embodiment are 18pF, and the equivalent capacitance of the 12MHz crystal oscillator equivalent model is only 20fF, and the capacitance value is about 1000 times different, the voltage change of the capacitor C1, the upper plate voltage N1 and N2 of the capacitor C2 and the voltage change of the node X1 inside the crystal oscillator equivalent model connected with the upper plate of the capacitor C1 through the equivalent resistance is approximately 1000 times different from the voltage change of the node X2, such as the voltage change of the node X2 from the supply voltage to the ground voltage, the voltage change of the node N2 is only one thousand times of the supply voltage, and when the N1 and N2 exhibit the amplitude change of the supply voltage, the voltage change of the node X2 is already large, which is caused by the very large characteristic of the crystal oscillator model.

The output end and the input end of the inverter INV1 are connected through the feedback resistor R, so that the crystal oscillator circuit can conduct current through the feedback resistor R after being enabled, so that two ends of the crystal oscillator obtain a direct current working voltage, and the N1 and N2 and the internal nodes X1 and X2 at the two ends of the crystal oscillator oscillate around the direct current voltage.

The traditional crystal oscillator circuit and some novel crystal oscillator circuits for rapid oscillation starting are quite long in process from the stage that the voltage of a crystal oscillator equivalent model node X2 is stable and unchanged when the circuit starts to work, the voltage starts to fluctuate under the influence of noise until the peak-to-peak amplitude of power supply voltage is reached, the circuit directly skips the process, the node X2 starts to oscillate when the circuit starts to work, the peak-to-peak value of an oscillation waveform is a power supply voltage value, and only the waveform needs to be continuously amplified until the voltage of upper polar plates of capacitors at two ends of the crystal oscillator also reaches the maximum amplitude, so that the structure has obvious effect of shortening the oscillation starting time; according to simulation examples and flow sheet verification, the starting time of the structure can be effectively reduced by about 50% compared with that of the traditional structure.

According to the equivalent model of the crystal oscillator and the specific circuit structure of the switches a1, a2 and A3, the circuit is also applicable when the crystal oscillator model connected with the node N2 is on the R side, and as shown in fig. 4, similarly, in the preparation stage, the switch control signal EN is set to low level, the gates of the PMOS transistors in the switches a1 and a2 are low, the PMOS transistors are turned on, that is, the switches a1 and a2 are closed, the upper plates of the capacitors C1 and C2 are connected to the power supply voltage, the power supply charges the capacitors C1 and C2 through the switches a1 and a2, and when EN is set to low level, the EN signal obtains a high level signal ENB opposite to the EN signal through the inverter INV2 in the switch A3, the EN is connected to the NMOS gate in the A3, the ENB is connected to the PMOS transistor gate in the A3, so that the NMOS gate in the switch A3 is low state, and the PMOS gate in the switch A3 is in the high state, therefore, the switch a3 is turned off, that is, the output of the inverter INV1 and the upper plate of the capacitor C2 are disconnected, and at this stage, the voltages of the upper plates of the capacitor C1 and the capacitor C2 are raised to the power supply voltage, that is, the voltages of the two ends of the crystal oscillator are raised to the power supply voltage, so that the node voltages X1 and X2 of the equivalent capacitor in the equivalent model of the crystal oscillator are raised to the power supply voltage; at this time, the voltage at the input terminal of the inverter INV1 is a high voltage, and the output voltage is a low voltage, but because the switch A3 is turned off, the output of the inverter INV1 does not affect the voltage at the top plate of the capacitor C2 and does not consume power.

When the preparation phase lasts for a certain time, an enabling phase is entered, in the enabling phase, the switch control signal EN is set to be high level, the gates of the PMOS transistors in the switch a1 and the switch a2 are high level, the PMOS transistors are turned off, namely the switch a1 and the switch a2 are turned off, the connection between the upper plates of the capacitor C1 and the capacitor C2 and the power supply is broken, meanwhile, when EN is set to be high level, in the switch A3, the EN signal obtains a low level signal ENB opposite to the EN signal through the inverter INV2, the EN is connected to the gate of the NMOS transistor in the switch A3, the ENB is connected to the gate of the PMOS transistor in the switch A3, so that the NMOS gate in the switch A3 is in a high conducting state, the PMOS gate in the switch A3 is in a low conducting state, so that the switch A3 is closed, the output of the inverter INV1 is connected to the upper plate of the capacitor C2, and the crystal oscillator starts to enter a normal operating mode. At this time, because the upper plate voltage of the capacitor C1 connected to the input end of the inverter INV1 is still the power voltage, the low voltage output by the inverter INV1 quickly pulls the upper plate voltage of the capacitor C2 down to the ground voltage, that is, N2 is quickly lowered, and the voltage of the node X2 is quickly pulled down to the ground voltage through the equivalent resistor of the crystal oscillator equivalent model, and the voltage of the node X1 is pulled down to the ground voltage through the equivalent capacitor of the crystal oscillator equivalent model, while the voltage at one side where the equivalent inductor is connected to the capacitor C1 is still the power voltage, so that a voltage difference is generated across the equivalent inductor, and an effect of providing potential energy to the equivalent inductor of the crystal oscillator equivalent model is achieved, the potential difference across the equivalent inductor causes the equivalent inductor to generate a current flowing from N1 to X1, thereby gradually pulling down N1, pulling up X1, and simultaneously the voltage at the other end of the equivalent capacitor of the crystal oscillator equivalent model, that X2 is also pulled up, and the node voltage of N2 is affected by the equivalent resistor in the crystal oscillator equivalent model, the voltage of the node N2 is pulled high, the current of the equivalent inductor is maximum when N1 and X1 are equal, at the moment, the potential energy at two ends of the equivalent inductor is completely converted into the current of the equivalent inductor flowing from N1 to X1, the voltage of X1 starts to be pushed high due to the maintaining characteristic of the inductor on the current, the voltage of N1 continues to be reduced, and the voltage difference between N1 and X1 gradually reaches the maximum value. When the voltage difference between two ends of the equivalent inductor changes to the maximum value, the inductor current is zero, the equivalent inductor obtains the maximum potential energy, then the potential difference between two ends of the equivalent inductor can generate a current flowing from X1 to N1, so that X1 is gradually pulled down, N1 is pulled up, meanwhile, the voltage X2 at the other end of the equivalent capacitor of the crystal oscillator equivalent model is also pulled down, N2 is influenced by the equivalent resistor in the crystal oscillator equivalent model, the voltage of an N2 node is also pulled down, the current of the equivalent inductor is maximum when N1 and X1 are equal, at the moment, the potential energy at two ends of the equivalent inductor is completely converted into the current flowing from X1 to N1, and due to the maintaining characteristic of the inductor to the current, the voltage of N1 starts to be pushed up, the voltage of X1 continues to be reduced, and the voltage difference between N1 and X1 gradually reaches the maximum value. When the potential difference between N1 and X1 reaches the maximum, the potential energy of the equivalent inductor is the maximum, the voltage of each node finishes the change of one period, and the next period is carried out according to the same change trend. Meanwhile, due to the negative resistance provided by the inverter INV1, the equivalent resistance of the crystal oscillator equivalent model is offset, and the provided negative resistance value is greater than the equivalent resistance of the crystal oscillator, so that the specific working effect is as follows: when the voltage of the node N1 is reduced, the voltage of the node N2 is increased, the voltage of the node N1 is reduced and is reversely amplified through the inverter INV1, the increasing effect of the voltage of the node N2 is enhanced, when the voltage of the node N1 is increased, the voltage of the node N2 is reduced, the voltage of the node N1 is reversely amplified through the inverter INV1, the reducing effect of the voltage of the node N2 is enhanced, in the periodic variation process, the waveform of the node N1 is amplified and transmitted to the node N2 through the inverter INV1, then the amplitude of the node N1 is influenced, and therefore the periodically varying voltage of each node is continuously amplified, and finally clock output is achieved.

The pull-down mentioned above is caused by the crystal model characteristic that the voltage change of the node N1, N2 and X2 is small relative to the voltage change of the node X1, i.e. when the voltage of the node X1 changes from the power supply voltage to the ground voltage, the voltage change of the node N2 is very small, and when the amplitude change of the power supply voltage is presented by the N1 and N2, the voltage of the node X2 is already very large.

The above two connection considerations for the crystal oscillator model have better effects, but the difference lies in that the dc voltage of the voltage change node is provided by someone, and the dc voltage is finally half of the power supply voltage under the action of the feedback resistor R provided in the crystal oscillator circuit.

As an example, the connection of the switch a1 and the switch a2 is connected to the ground terminal at one end of the power supply, and the switch A3 is unchanged, so that the same quick oscillation starting effect can be realized; the switch a1 and the switch a2 can be replaced by NMOS transistors and adjusted accordingly, and the principle is similar, so that the details are not repeated.

The above embodiments are performed on the basis of a crystal oscillator equivalent model, and the actual crystal oscillator outputs periodic signals by mutual conversion between voltage and deformation at two ends of the crystal oscillator, and the electric potential energy constructed for the inductance of the crystal oscillator equivalent model in the above circuits and analysis has the same effect as the deformation potential energy generated by the voltage at two ends of the actual crystal oscillator, so that the same rapid oscillation starting effect can be achieved, and through the verification of the current piece, the effect consistent with the expectation can be achieved, and the oscillation starting time is reduced by about 50%.

The features of the above embodiments may be arbitrarily combined, and for the sake of brevity, all possible combinations of the above embodiments are not described, but should be considered as within the scope of the present specification as long as there is no contradiction between the combinations of the features.

The above embodiments only express a few embodiments of the present invention, and the description thereof is specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application.

Claims (10)

1. A crystal oscillator circuit capable of starting oscillation rapidly comprises a capacitor C1, a capacitor C2, a crystal oscillator, a feedback resistor and an inverter INV1, wherein the crystal oscillator is arranged between the capacitor C1 and the capacitor C2, the other end of the capacitor C1 and the other end of the capacitor C2 are both provided with grounding ends, the crystal oscillator circuit is characterized by comprising a switch A1, a switch A2, a switch A3 and a power supply end, the input end of the inverter INV1 is connected with the power supply end through a switch A1, the output end of the inverter INV1 is connected with the power supply end through a switch A3 and a switch A2, a series circuit formed by the switch A3 and the inverter INV1 is respectively connected with the crystal oscillator and the feedback resistor in parallel, and the switch A1, the switch A2 and the switch A3 work in a combined mode to start oscillation of the crystal oscillator circuit.

2. The crystal oscillator circuit with fast oscillation starting according to claim 1, wherein the switch a1 comprises a PMOS transistor, the gate of the PMOS transistor of the switch a1 is used for receiving the switch control signal EN, the source is connected to the power supply terminal, and the drain is connected to the input terminal of the inverter INV 1.

3. The crystal oscillator circuit with fast oscillation starting according to claim 1, wherein the switch a2 comprises a PMOS transistor, the gate of the PMOS transistor of the switch a2 is used for receiving the switch control signal EN, the source is connected to the power supply terminal, and the drain is connected to the switch A3.

4. The crystal oscillator circuit with rapid oscillation starting of claim 2 or 3, wherein the gates of the PMOS transistors of the switch A1 and the switch A2 are connected to receive the same switch control signal EN.

5. The crystal oscillator circuit with fast oscillation starting according to claim 2 or 3, wherein the switch A3 comprises an NMOS transistor, the gate of the NMOS transistor of the switch A3 receives the same switch control signal EN with the gate of the PMOS transistor of the switch A1 and the gate of the PMOS transistor of the switch A2, the source is connected with the output end of the inverter INV1, and the drain is connected with the switch A2.

6. The crystal oscillator circuit with fast oscillation starting according to claim 2 or 3, wherein the switch A3 comprises a NOT gate and a PMOS transistor, the gate of the PMOS of the switch A3 receives the same switch control signal EN with the gate of the PMOS of the switch A1 and the gate of the PMOS of the switch A2 through the NOT gate, the source is connected with the output end of the inverter INV1, and the drain is connected with the switch A2.

7. The crystal oscillator circuit with rapid oscillation starting of claim 1, wherein the inverter INV1 comprises two fets, the two fets comprise a PMOS transistor and an NMOS transistor, the gates of the two fets are connected as the input terminal of the inverter INV1, the drains of the two fets are connected to the switch A3, the source of the PMOS fet is connected to the power supply terminal, and the source of the NMOS fet is connected to the ground terminal.

8. The crystal oscillator circuit with fast oscillation starting of claim 7, wherein the switch A3 is disposed in an inverter INV1, the switch A3 includes two fets and an inverter INV2, the two fets include a PMOS transistor and an NMOS transistor, a gate of the NMOS fet of the switch A3 and an input of the inverter INV2 are connected to the switch control signal EN, an output of the inverter INV2 is connected to a gate of the PMOS fet of the switch A3, sources of the two fets of the switch A3 are respectively connected to drains of the two fets of the inverter INV1, a source of the PMOS transistor of the switch A3 is connected to a drain of the PMOS transistor of the inverter INV1, a source of the NMOS transistor of the switch A3 is connected to a drain of the NMOS transistor of the inverter INV1, and drains of the two fets of the switch A3 are connected to serve as an output of the inverter INV 1.

9. A control method of a crystal oscillator circuit with rapid oscillation starting, which is used for controlling the crystal oscillator circuit with rapid oscillation starting of any one of claims 1 to 8, the control method comprising the steps of:

s1: the switch A1 and the switch A2 are closed, the switch A3 is opened, and the crystal oscillator circuit enters a preparation stage;

s2: after the crystal oscillator circuit is in the preparation phase and continues for the set time, the switch A1 and the switch A2 are opened, and the switch A3 is closed, so that the crystal oscillator circuit enters the working phase.

10. The method as claimed in claim 9, wherein the set time is 10ns after the switches a1 and a2 are closed and the voltages of the capacitors C1 and C2 change from occurring to reaching a stable voltage.

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