Crystal oscillator with adaptive amplifier conduction angle control

Abstract

This invention provides a crystal oscillator whose conduction angle can be digitally defined and adaptively adjusted according to the current oscillation amplitude, thereby enabling the sustain amplifier of the crystal oscillator to operate in Class C mode. System-level simulation results show that when a subthreshold inverter with θ modulation characteristics is used as the sustain amplifier, the overall power efficiency can reach approximately 80% to 90%. Furthermore, the adaptive conduction angle crystal oscillator can effectively reduce circuit power consumption while maintaining the inherent startup capability and stability of the crystal oscillator, even with a small chip area.

Description

Technical Field

[0001] This invention generally relates to crystal oscillator technology, and more specifically to a crystal oscillator employing an amplifier with adaptive conduction angle control to improve energy efficiency. Background Technology

[0002] Crystal oscillators are widely used in real-time clocks (RTCs) in various electronic systems. When used as wake-up timers, their performance is particularly critical for battery-powered Internet of Things (IoT) sensor nodes. To extend battery life, crystal oscillators need extremely low power consumption while always on. Simultaneously, they also require good frequency stability; otherwise, the system must extend the communication guard time slot for synchronization, causing the transceiver to remain active for longer periods, resulting in additional energy loss. Based on these requirements, recent research has begun exploring alternatives to traditional inverter-based Pierce oscillators. While Pierce oscillators have a simple structure, they typically consume approximately 10 to 100 nanowatts (nW) of power, which is insufficient to meet more stringent ultra-low power requirements.

[0003] Crystal oscillators are typically constructed by combining an oscillator amplifier with a piezoelectric crystal into a closed feedback loop. To achieve higher energy efficiency, the amplifier can be designed to operate under specific operating categories, which introduces the concept of conduction angle. The conduction angle is defined as the proportion of the amplifier's period that is turned on with the power supply, and the on-time typically needs to occur near the peak or trough of the oscillation waveform to improve energy injection efficiency.

[0004] Pulse-injection crystal oscillators (PIOs) are a type of design that utilizes conduction angle modulation to reduce power consumption. These oscillators typically employ a very small conduction angle to inject energy into the oscillation system in short pulses, thereby reducing power consumption. However, this topology has several limitations. First, to accurately inject current at the optimal timing point, a high-precision delay signal is usually required, resulting in a larger chip area occupied by the pulse generator. Second, delay-chain-based timing mechanisms cannot independently initiate oscillation because the delay chain relies on the zero-crossing point of the oscillation signal as the trigger moment, and this zero-crossing point only occurs after oscillation has been established. Therefore, PIOs typically require an additional independent startup circuit to establish the initial oscillation, which not only increases the complexity of the control logic but also introduces robustness issues in the face of strong transient disturbances. Therefore, in cost-sensitive IoT applications, the market still needs a novel crystal oscillator solution that is compact, easy to use, and has extremely low power consumption. Summary of the Invention

[0005] This invention provides a crystal oscillator that, by employing an amplitude modulation mechanism and digitally defining the conduction angle, enables the Pierce inverter to operate in Class C mode, thereby meeting the requirements for ultra-low power consumption and ease of use of crystal oscillators.

[0006] According to one aspect of the invention, the crystal oscillator comprises: a crystal resonator having a pair of first and second terminals; an oscillation amplifier having an input terminal and an output terminal respectively connected to the first and second terminals of the crystal resonator; a high-side power gate switch connected between a first reference terminal of the oscillation amplifier and a first reference voltage; a low-side power gate switch connected between a second reference terminal of the oscillation amplifier and a second reference voltage; a high-side oscillation amplitude detector having: a first high-side sensing input terminal and a second high-side sensing input terminal respectively connected to the first and second terminals of the crystal resonator; a high-side driver having a high-side driver input terminal connected to the high-side sensing output terminal of the high-side oscillation amplitude detector; and a high-side driver output terminal connected to a control terminal of the high-side power gate switch; a low-side oscillation amplitude detector having: a first low-side sensing input terminal and a second low-side sensing input terminal respectively connected to the first and second terminals of the crystal resonator; and a low-side driver having a low-side driver input terminal connected to the low-side sensing output terminal of the low-side oscillation amplitude detector; and a low-side driver output terminal connected to the control terminal of the low-side power gate switch.

[0007] Preferably, the oscillator amplifier includes: a high-side amplifying transistor having a source connected to a high-side power-gated switch, a drain connected to a second terminal of a crystal resonator, and a gate connected to a first terminal of a crystal resonator; and a low-side amplifying transistor having a source connected to a low-side power-gated switch, a drain connected to a second terminal of a crystal resonator, and a gate connected to a first terminal of a crystal resonator.

[0008] Preferably, the high-side amplification transistor is a PMOS transistor, and the low-side amplification transistor is an NMOS transistor.

[0009] Preferably, the high-side driver includes one or more inverters connected in series between the high-side driver input terminal and the high-side driver output terminal.

[0010] Preferably, the low-side driver includes one or more inverters connected in series between the low-side driver input terminal and the low-side driver output terminal.

[0011] Preferably, the high-side power gate switch includes a PMOS transistor having a source connected to the first reference voltage, a drain connected to the oscillating amplifier, and a gate connected to the output terminal of the high-side driver.

[0012] Preferably, the high-side driver includes an even number of inverters connected in series between the input terminal and the output terminal of the high-side driver.

[0013] Preferably, the low-side power supply gate switch includes an NMOS transistor having a source connected to the second reference voltage, a drain connected to the oscillating amplifier, and a gate connected to the low-side driver output terminal.

[0014] Preferably, the low-side driver includes an even number of inverters connected in series between the input terminal and the output terminal of the low-side driver.

[0015] Preferably, the high-side power supply gate switch includes an NMOS transistor having a drain connected to the first reference voltage, a source connected to the oscillating amplifier, and a gate connected to the output terminal of the high-side driver.

[0016] Preferably, the high-side driver includes an odd number of inverters connected in series between the input terminal and the output terminal of the high-side driver.

[0017] Preferably, the low-side power supply gate switch includes a PMOS transistor having a drain connected to the second reference voltage, a source connected to the oscillating amplifier, and a gate connected to the low-side driver output terminal.

[0018] Preferably, the low-side driver includes an odd number of inverters connected in series between the input terminal and the output terminal of the low-side driver.

[0019] Preferably, the high-side oscillation amplitude detector includes: a high-side capacitor having a first terminal connected to a first high-side sensing input terminal and a second terminal connected to a high-side sensing output terminal; a first high-side diode having an anode connected to a second high-side sensing input terminal and a cathode connected to a high-side sensing output terminal; and a second high-side diode having an anode connected to a high-side bias voltage and a cathode connected to a high-side sensing output terminal, wherein the second reference voltage causes the second high-side diode to be in a reverse bias state.

[0020] Preferably, the low-side oscillation amplitude detector includes: a low-side capacitor having a first terminal connected to a first low-side sensing input terminal and a second terminal connected to a low-side sensing output terminal; a first low-side diode having a cathode connected to a second low-side sensing input terminal and an anode connected to a low-side sensing output terminal; and a second low-side diode having a cathode connected to a low-side bias voltage and an anode connected to a low-side sensing output terminal, wherein the first reference voltage causes the second low-side diode to be in a reverse bias state.

[0021] Compared to pulse-injection crystal oscillators, the adaptive conduction angle crystal oscillator of this invention avoids the need for precise timing delays by employing a larger θ value, thereby saving chip area and reducing power consumption. When the sustain amplifier uses a subthreshold inverter with θ modulation characteristics, system-level simulation results show that its power efficiency can reach approximately 80% to 90%. This result demonstrates that the adaptive conduction angle crystal oscillator can achieve ultra-low power consumption with a smaller chip area while maintaining the inherent startup capability and stable operating performance of a crystal oscillator. Attached Figure Description

[0022] Embodiments of the invention are described in more detail below with reference to the accompanying drawings, in which:

[0023] Figure 1 This is a circuit block diagram of a crystal oscillator according to an embodiment of the present invention.

[0024] Figure 2 Show Figure 1 A more detailed schematic diagram of the crystal oscillator.

[0025] Figure 3 This illustrates the working principle of adaptive conduction angle control of a crystal oscillator.

[0026] Figure 4 Typical signal waveforms are shown to illustrate the working principle of a crystal oscillator. Detailed Implementation

[0027] In the following description, details of the invention are set forth as preferred embodiments. It will be apparent to those skilled in the art that modifications, including additions and / or substitutions, can be made without departing from the scope and spirit of the invention. Specific details may be omitted to avoid obscuring the invention; however, this disclosure is prepared to enable those skilled in the art to practice the teachings herein without requiring extensive experimentation.

[0028] Figure 1This is a circuit block diagram of a crystal oscillator 100 according to an embodiment of the present invention. As shown, the crystal oscillator 100 includes a crystal resonator 110 having a pair of terminals XIN and XOUT; and an oscillation amplifier 120 having an input terminal and an output terminal respectively connected to terminals XIN and XOUT.

[0029] The crystal oscillator 100 further includes a high-side power supply gate switch 131 that connects a first reference terminal of the oscillator amplifier to a first reference voltage VDD; and a low-side power supply gate switch 132 that connects a second reference terminal of the oscillator amplifier to a reference node VSS (e.g., ground GND).

[0030] The crystal oscillator 100 further includes a high-side oscillation amplitude detector 141, which is configured to generate conduction information for the high-side power gating switch 131. The high-side oscillation amplitude detector 141 has a first sensing input terminal and a second sensing input terminal connected to terminals XIN and XOUT of the crystal resonator 110, respectively.

[0031] The crystal oscillator 100 further includes a high-side driver 151 configured to drive the high-side power gating switch 131 to either be on or off. The high-side driver 151 has an input terminal connected to the sensing output terminal of the high-side oscillation amplitude detector 141; and an output terminal connected to the control terminal of the high-side power gating switch 131.

[0032] The crystal oscillator 100 further includes a low-side oscillation amplitude detector 142, which is configured to generate conduction information for the low-side power gating switch 132. The low-side oscillation amplitude detector 142 has a first sensing input terminal and a second sensing input terminal connected to terminals XIN and XOUT of the crystal resonator 110, respectively.

[0033] The crystal oscillator 100 further includes a low-side driver 152 configured to drive the low-side power gating switch 132 to either be on or off. The low-side driver 152 has an input terminal connected to the sensing output terminal of the low-side oscillation amplitude detector 142; and an output terminal connected to the control terminal of the low-side power gating switch 132.

[0034] Figure 2 A more detailed schematic diagram of the crystal oscillator 100 is shown. The oscillator amplifier 120 includes: a high-side amplification transistor M. INVP It has a source connected to the high-side power gate switch 131, a drain connected to the terminal XOUT of the crystal resonator, and a gate connected to the terminal XIN of the crystal resonator. The oscillator amplifier 120 further includes a low-side amplification transistor M. INVNIt has a source connected to the low-side power supply gate switch 132, a drain connected to the terminal XOUT of the crystal resonator, and a gate connected to the terminal XIN of the crystal resonator. Preferably, the high-side amplification transistor M... INVP It is a PMOS transistor, and the low-side amplification transistor M INVN It is an NMOS transistor.

[0035] The high-side oscillation amplitude detector 142 includes: a high-side capacitor C 1P It has a first terminal connected to a first high-side sensing input terminal and a second terminal connected to a high-side sensing output terminal; the first high-side diode D 1P It has an anode connected to the second high-side sensing input terminal and a cathode connected to the high-side sensing output terminal; and a second high-side diode D. 2P It has an anode connected to a reference voltage VSS and a cathode connected to a high-side sensing output terminal, wherein the reference voltage VSS causes the second high-side diode to be reverse biased.

[0036] The low-side oscillation amplitude detector 142 includes: a low-side capacitor C 1N It has a first terminal connected to a first low-side sensing input terminal and a second terminal connected to a low-side sensing output terminal; the first low-side diode D 1N It has a cathode connected to a second low-side sensing input terminal and an anode connected to a low-side sensing output terminal; and a second low-side diode D. 2N It has a cathode connected to a reference voltage VDD and an anode connected to a low-side sensing output terminal, wherein the reference voltage VDD causes the second low-side diode to be reverse biased.

[0037] High-side driver 151 includes one or more inverters INV connected in series between the high-side driver input terminal and the high-side driver output terminal. 1P INV 2P The low-side driver 152 includes one or more inverters INV connected in series between the low-side driver input terminal and the low-side driver output terminal. 1N INV 2N .

[0038] exist Figure 2 In the illustrated embodiment, the high-side power gate switch 131 includes a PMOS transistor M. SP It has a source connected to a reference voltage VDD, a drain connected to an oscillator amplifier 120, and a gate connected to the output terminal of a high-side driver 151; and the high-side driver 151 includes an even number of inverters connected in series between the high-side driver input terminal and the high-side driver output terminal.

[0039] The low-side power supply gate switch 132 includes a low-side NMOS transistor M SN It has a source connected to a reference voltage VSS, a drain connected to an oscillator amplifier 120, and a gate connected to the output terminal of a low-side driver 152; and the low-side driver 152 includes an even number of inverters connected in series between the low-side driver input terminal and the low-side driver output terminal.

[0040] Alternatively, in another embodiment, the high-side power supply gate switch 131 may include an NMOS transistor M. SN It has a drain connected to a reference voltage VDD, a source connected to an oscillator amplifier 120, and a gate connected to the output terminal of a high-side driver 151; and the high-side driver 151 includes an odd number of inverters connected in series between the high-side driver input terminal and the high-side driver output terminal.

[0041] The low-side power supply gate switch 132 may include a PMOS transistor M SP It has a drain connected to a reference voltage VSS, a source connected to an oscillator amplifier 120, and a gate connected to the output terminal of a low-side driver 152; and the low-side driver 152 includes an odd number of inverters connected in series between the low-side driver input terminal and the low-side driver output terminal.

[0042] Figure 3 This illustrates the working principle of amplifier conduction angle control. As the oscillation amplitude increases, an amplitude detector senses this amplitude information and generates a corresponding control signal to the switch driver to operate the power gating switch. Before the oscillation amplitude reaches a certain threshold, the conduction angle is 360°, indicating that the oscillation amplifier is always connected to VDD and VSS to ensure proper oscillation initialization, similar to that of a Pierce oscillator.

[0043] More specifically, the high-side amplitude detector 141 is configured to utilize a DC offset voltage V related to the amplitude. DC The voltage V at XIN IN Level shifting is performed to reduce the conduction angle θ, the amplitude-related V DC In the oscillating voltage amplitude V A It remains negative when it is low, but as V... A It increases rapidly. Therefore, in the voltage amplitude V A Reaching threshold V A,TH Previously, the conduction angle θ was maintained at 360°. When V A Exceeding the threshold voltage V A,TH At that time, due to C 1P and D 1P This constitutes a charge pump (with two input signals XIN and XOUT), and the output of the amplitude detector detects a waveform higher than that of the inverter INV. 1PThe time proportion of the threshold voltage will gradually increase. In a steady state, due to V... IN With V OUT Maintaining 180° out-of-phase in parallel oscillation, C 1P Both ends (from V) IN The voltage will be maintained at 2V at the output of the amplitude detector. A -V D DC voltage difference (where V) D Indicates diode D 1P (Forward conduction voltage drop). Meanwhile, V IN The AC component is directly coupled to the output of the amplitude detector. Therefore, due to C 1P and D 1P The resulting charge pump, under ideal conditions, produces an AC-to-DC gain of 2 and an AC-to-AC gain of 1. Diode D 2P Under reverse bias, the output of the amplitude detector is connected to V. SS Between, to generate a negative DC voltage shift, the negative DC voltage shift being V A,TH The root cause. In one embodiment, D 2P Multiple Ds implemented as parallel connections 1P (For example, D) 2P =5x D 1P This allows when V A,TH When = 0, the output voltage of the amplitude detector depends only on the shape of the diode's IV characteristic.

[0044] When there is no oscillation (i.e., θ = 360°), the overall structure of the high-side amplitude detector 141 produces an amplitude that is always below INV. 1P The waveform of the threshold voltage. With the oscillation amplitude (V at the XIN terminal) IN V at the XOUT end OUT Increase, below INV 1P The output voltage (V) of the threshold voltage amplitude detector 141 SP The duration of ( ) is shortened. (Reference) Figure 4 The V SP After the waveform is processed by the high-side switch driver 151, it is then processed by the high-side power supply gate transistor M. SP The gate generates control signal V GP Its frequency is the same as the fundamental frequency of the crystal resonator, but as the oscillation amplitude increases, the duty cycle (i.e., the duration of the power-gated switch being on divided by the period of the clock signal) decreases. This is achieved via M... SP This effectively reduces the conduction angle, allowing the oscillator amplifier (in this case, the Pierce oscillator) to be connected to the supply voltage only when energy efficiency is high.

[0045] The low-side oscillation amplitude detector 142 operates in a similar manner to generate a voltage, and as the oscillation amplitude increases, the proportion of time in its output voltage waveform that exceeds the inverter threshold voltage gradually decreases, thus reducing inversion. This further enables the M... SN Control signal V generated at the gate GN It has a duty cycle that decreases as the oscillation amplitude increases. Therefore, the circuit topology of this invention is via M SN The conduction angle was reduced, so that the oscillator amplifier could be connected to the reference voltage VSS only when energy efficiency was high.

[0046] Therefore, the oscillation circuit provided by this invention maintains the maximum conduction angle before the oscillator amplifier starts oscillating, and can self-adjust the conduction angle by reducing it according to the current oscillation amplitude.

[0047] Compared to existing low-power crystal oscillators, this invention exhibits a stable efficiency improvement over a wide θ range, with lower power consumption and a simpler structure. Furthermore, through an amplitude-based modulation mechanism, this invention achieves inherent self-starting capability, a unique advantage in ultra-low-power crystal oscillators operating at sub-nanowatt power. These characteristics make this invention a competitive solution for future RTC applications in IoT sensor nodes: its record-low power consumption significantly extends system battery life; its extremely small chip area reduces manufacturing costs; and its single-supply architecture, relying on inherent startup capability, provides high ease of use, making it a potential pin-compatible alternative to classic Pierce oscillators.

[0048] The functional units and modules according to the embodiments disclosed herein may be implemented in computing devices, computer processors, or electronic circuit systems, including but not limited to analog electronic devices / modules, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), microcontrollers, and other programmable logic devices configured or programmed according to the teachings of this disclosure. Based on the teachings of this disclosure, those skilled in the art of software or electronics can readily perform specialized development for computer instructions or software code running on computing devices, computer processors, or programmable logic devices.

[0049] All or part of the methods according to the embodiments can be performed in one or more computing devices, including server computers, personal computers, laptops, and mobile computing devices such as smartphones and tablets. The embodiments may relate to computer storage media, transient and non-transient memory devices in which computer instructions or software code are stored, which can be used to program or configure computing devices, computer processors, or electronic circuit systems to perform any of the processes of the present invention. The storage media, transient and non-transient memory devices may include, but are not limited to, floppy disks, optical disks, Blu-ray discs, DVDs, CD-ROMs and magneto-optical disks, ROMs, RAMs, flash memory devices, and any type of medium or device suitable for storing instructions, code, and / or data.

[0050] Each functional unit and module described according to various embodiments can be implemented in a distributed computing environment and / or a cloud computing environment. In such environments, all or part of the machine instructions are executed in a distributed manner by one or more processing devices interconnected via communication networks, such as intranets, wide area networks (WANs), local area networks (LANs), the Internet, and other forms of data transmission media. While this disclosure has been described and illustrated with reference to specific embodiments, such descriptions and illustrations are not limiting. Illustrations are not necessarily drawn to scale. Due to manufacturing processes and tolerances, there may be differences between the illustrations in this disclosure and actual devices. Other embodiments may exist in this disclosure that are not explicitly shown. Adaptive modifications may be made to the specific circumstances, materials, combinations of substances, methods, or processes based on the objectives and scope of this disclosure, and such modifications should fall within the scope of the appended claims. Although the methods described herein have been described with reference to specific operations performed in a particular order, it should be understood that these operations can be combined, subdivided, or reordered to form equivalent methods without departing from the teachings of this disclosure. Therefore, unless expressly indicated herein, the order and grouping of operations are not limiting.

Claims

1. A crystal oscillator with adaptive amplifier conduction angle control, characterized in that, include: A crystal resonator having a pair of first and second terminals; An oscillating amplifier having an input terminal and an output terminal respectively connected to the first terminal and the second terminal of the crystal resonator; A high-side power supply gate switch is connected between the first reference terminal of the oscillating amplifier and the first reference voltage. A low-side power supply gate switch is connected between the second reference terminal of the oscillating amplifier and the second reference voltage. A high-side oscillation amplitude detector having: a first high-side sensing input terminal and a second high-side sensing input terminal respectively connected to the first terminal and the second terminal of the crystal resonator; A high-side driver having a high-side driver input terminal connected to the high-side sensing output terminal of the high-side oscillation amplitude detector; and the high-side driver output terminal connected to the control terminal of the high-side power gate switch; A low-side oscillation amplitude detector having: a first low-side sensing input terminal and a second low-side sensing input terminal respectively connected to the first terminal and the second terminal of the crystal resonator; as well as A low-side driver having a low-side driver input terminal connected to the low-side sensing output terminal of the low-side oscillation amplitude detector; and the low-side driver output terminal connected to the control terminal of the low-side power gate switch.

2. The crystal oscillator according to claim 1, characterized in that, The oscillation amplifier includes: A high-side amplifier transistor having a source connected to the high-side power-gated switch, a drain connected to the second terminal of the crystal resonator, and a gate connected to the first terminal of the crystal resonator; and A low-side amplifying transistor having a source connected to the low-side power-gated switch, a drain connected to the second terminal of the crystal resonator, and a gate connected to the first terminal of the crystal resonator.

3. The crystal oscillator according to claim 2, characterized in that, The high-side amplification transistor is a PMOS transistor, and the low-side amplification transistor is an NMOS transistor.

4. The crystal oscillator according to claim 1, characterized in that, The high-side driver includes one or more inverters connected in series between the input terminal and the output terminal of the high-side driver.

5. The crystal oscillator according to claim 1, characterized in that, The low-side driver includes one or more inverters connected in series between the low-side driver input terminal and the low-side driver output terminal.

6. The crystal oscillator according to claim 1, characterized in that, The high-side power gate switch includes a PMOS transistor having a source connected to the first reference voltage, a drain connected to the oscillating amplifier, and a gate connected to the output terminal of the high-side driver.

7. The crystal oscillator according to claim 6, characterized in that, The high-side driver includes an even number of inverters connected in series between the input terminal and the output terminal of the high-side driver.

8. The crystal oscillator according to claim 1, characterized in that, The low-side power supply gate switch includes an NMOS transistor having a source connected to the second reference voltage, a drain connected to the oscillating amplifier, and a gate connected to the low-side driver output terminal.

9. The crystal oscillator according to claim 8, characterized in that, The low-side driver includes an even number of inverters connected in series between the input terminal and the output terminal of the low-side driver.

10. The crystal oscillator according to claim 1, characterized in that, The high-side power gate switch includes an NMOS transistor having a drain connected to the first reference voltage, a source connected to the oscillating amplifier, and a gate connected to the output terminal of the high-side driver.

11. The crystal oscillator according to claim 10, characterized in that, The high-side driver includes an odd number of inverters connected in series between the input terminal and the output terminal of the high-side driver.

12. The crystal oscillator according to claim 1, characterized in that, The low-side power supply gate switch includes a PMOS transistor having a drain connected to the second reference voltage, a source connected to the oscillating amplifier, and a gate connected to the low-side driver output terminal.

13. The crystal oscillator according to claim 12, characterized in that, The low-side driver includes an odd number of inverters connected in series between the input terminal and the output terminal of the low-side driver.

14. The crystal oscillator according to claim 1, characterized in that, The high-side oscillation amplitude detector includes: A high-side capacitor having a first terminal connected to the first high-side sensing input terminal and a second terminal connected to the high-side sensing output terminal; A first high-side diode has an anode connected to the second high-side sensing input terminal and a cathode connected to the high-side sensing output terminal; and The second high-side diode has an anode connected to a high-side bias voltage and a cathode connected to the high-side sensing output terminal, wherein the second reference voltage causes the second high-side diode to be in a reverse bias state.

15. The crystal oscillator according to claim 1, characterized in that, The low-side oscillation amplitude detector includes: A low-side capacitor having a first terminal connected to the first low-side sensing input terminal and a second terminal connected to the low-side sensing output terminal; A first low-side diode has a cathode connected to the second low-side sensing input terminal and an anode connected to the low-side sensing output terminal; and A second low-side diode has a cathode connected to a reference voltage and an anode connected to the low-side sensing output terminal, wherein the first reference voltage causes the second low-side diode to be reverse biased.

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