Crystal oscillator driver circuit having adaptive current regulation function

Abstract

The crystal oscillator driving circuit includes an amplifier, a current generation circuit, a reference voltage generation circuit, a driver circuit, and a detection circuit. The amplifier generates a control voltage based on a reference voltage and a detection voltage. The current generation circuit generates a first current and a second current based on the control voltage. The reference voltage generation circuit receives the first current and generates the reference voltage. The driver circuit receives the second current and drives a crystal based on the second current. The detection circuit generates a detection voltage based on a first voltage related to the crystal. The ratio between the first current and the second current is less than 1.

Description

Technical Field

[0001] This case concerns crystal oscillator drive circuits, particularly crystal oscillator drive circuits with adaptive current regulation. Prior Technology

[0002] Crystal oscillators are commonly used in clock generation and related applications to provide a stable reference frequency or reference clock signal. In existing crystal oscillator driver circuits, a complex array of low-pass filters is typically used to obtain a reference voltage based on the crystal's terminal voltage, and this reference voltage is then used to drive the crystal. However, the more low-pass filters used, the larger the circuit area required for the crystal oscillator driver circuit becomes, leading to an increase in both overall cost and power consumption. Summary of the Invention

[0003] In some embodiments, one of the objectives of this invention is to provide a crystal oscillator drive circuit with adaptive current regulation to improve upon the shortcomings of prior art.

[0004] In some embodiments, the crystal oscillator driving circuit includes an amplifier, a current generating circuit, a reference voltage generating circuit, a driver circuit, and a detection circuit. The amplifier generates a control voltage based on a reference voltage and a detection voltage. The current generating circuit generates a first current and a second current based on the control voltage. The reference voltage generating circuit receives the first current and generates the reference voltage. The driver circuit receives the second current and drives a crystal based on the second current. The detection circuit generates a detection voltage based on a first voltage related to the crystal. The ratio between the first current and the second current is less than 1.

[0005] Regarding the features, implementation, and effects of this case, the preferred embodiments are described in detail below with reference to the drawings. Simple Explanation of the Diagram

[0006] [Figure 1] is a schematic diagram of a crystal oscillator driving circuit according to some embodiments of this case; [Figure 2] is a circuit diagram of the crystal oscillator drive circuit of Figure 1 drawn according to some embodiments of this case; and [Figure 3] is a schematic diagram of the waveforms of the control voltage, reference voltage, detection voltage and voltage related to the crystal in Figure 2, according to some embodiments of this case. Implementation

[0007] All terms used herein have their common meanings. The definitions of the terms mentioned above in commonly used dictionaries, and any examples of the use of any term discussed herein, are merely illustrative and should not limit the scope or meaning of this application. Similarly, this application is not limited to the various embodiments shown in this specification.

[0008] As used herein, "coupling" or "connection" can refer to two or more components making direct physical or electrical contact with each other, or indirectly making direct physical or electrical contact with each other, or to two or more components operating or moving together. As used herein, the term "circuit" can refer to a device in which at least one transistor and / or at least one active or passive component are connected in a certain manner to process signals.

[0009] Figure 1 is a schematic diagram of a crystal oscillator drive circuit 100 according to some embodiments of this invention. In some embodiments, the crystal oscillator drive circuit 100 can be applied to real-time clock (RTC) applications to provide high-accuracy clock signals. In some embodiments, real-time clock applications typically require the related circuitry to operate continuously for extended periods in a battery-powered environment; therefore, the crystal oscillator drive circuit 100 needs to provide relatively low power consumption and operate in a relatively low-voltage environment to meet the aforementioned requirements of real-time clock applications.

[0010] The crystal oscillator drive circuit 100 includes an amplifier 110, a current generation circuit 120, a reference voltage generation circuit 130, a driver circuit 140, and a detection circuit 150. The amplifier 110 generates a control voltage VC based on a reference voltage VB and a detection voltage VA. The current generation circuit 120 generates currents I1 and I2 based on the control voltage VC, wherein the ratio between currents I1 and I2 is set to be less than 1. The reference voltage generation circuit 130 receives current I1 and generates a reference voltage VB accordingly. The driver circuit 140 receives current I2 and drives the crystal 101 based on current I2. The detection circuit 150 generates a detection voltage VA based on a voltage relative to the crystal 101 (which may be, for example, but is not limited to, the voltage XIN at one terminal of the crystal 101). In some embodiments, the crystal 101 may be, but is not limited to, a quartz crystal. The driver circuit 140 can provide a negative impedance to the crystal 101, allowing the crystal 101 to enter an oscillation state based on current I2, thereby generating a reference signal XO. In some embodiments, a reference signal XO may be provided to a comparator (not shown) so that the comparator generates a stable clock signal based on the reference signal XO.

[0011] Figure 2 is a circuit diagram of the crystal oscillator drive circuit 100 of Figure 1, drawn according to some embodiments of this invention. The negative input terminal of amplifier 110 receives a detection voltage VA, and the positive input terminal of amplifier 110 receives a reference voltage VB. The current generation circuit 120 includes transistors M1 and M2. The first terminal (e.g., the source) of transistor M1 and the first terminal of transistor M2 receive a power supply voltage VDD. The control terminal (e.g., the gate) of transistor M1 and the control terminal of transistor M2 are coupled to the output terminal of amplifier 110 to receive a control voltage VC. The second terminal (e.g., the drain) of transistor M1 generates a current I1 and transmits current I1 to the reference voltage generation circuit 130. The second terminal of transistor M2 generates a current I2 and transmits current I2 to the driver circuit 140. In other words, by the above arrangement, transistor M1 can generate current I1 according to the control voltage VC, and transistor M2 can generate current I2 according to the control voltage VC. In this embodiment, the current generation circuit 120 is implemented by a current mirror circuit. As mentioned earlier, the ratio between current I1 and current I2 is less than 1, meaning current I2 is greater than current I1. Accordingly, the aspect ratio of transistor M1 can be set to be less than that of transistor M2 to establish the proportional relationship between current I1 and current I2.

[0012] The driver circuit 140 includes a resistor R1 and a transistor M3. A first terminal (e.g., drain) of transistor M3 is coupled to transistor M2 to receive current I2, a second terminal (e.g., source) of transistor M3 is coupled to ground, and a control terminal (e.g., gate) of transistor M3 is coupled to the detection circuit 150. Resistor R1 and transistor 101 are connected in parallel between the control terminal of transistor M3 and the first terminal of transistor M3, wherein the first terminal of transistor 101 provides the aforementioned voltage XIN, and the second terminal of transistor 101 generates a reference signal XO. In some embodiments, the driver circuit 140 may further include a load capacitor (not shown) coupled to the second terminal of transistor 101. With the above configuration, the driver circuit 140 can provide a negative impedance to transistor 101 to assist transistor 101 in entering an oscillation state. Since transistor M3 is driven by current I2, the transconductance of transistor M3 will be determined by the current. The transconductance of transistor M3 determines the magnitude of the aforementioned negative impedance. In some embodiments, when crystal 101 is not in an oscillation state (i.e., before it starts oscillating), the reference voltage VB is lower than the detection voltage VA, causing amplifier 110 to generate a lower control voltage VC. Under this condition, transistor M2 will generate a larger current I2, causing the transconductance of transistor M3 to increase, thereby generating a higher negative impedance to make it easier for crystal 101 to enter an oscillation state (i.e., reducing the time required for crystal 101 to start oscillating).

[0013] In some embodiments, the detection circuit 150 includes a capacitor C1, which can be charged or discharged according to a voltage XIN relative to the crystal 101 to generate a detection voltage VA. For example, the capacitor C1 is charged or discharged to generate a voltage VD. In some embodiments, the detection circuit 150 further includes a low-pass filter 154. The low-pass filter 154 generates the detection voltage VA according to the voltage VD. Specifically, the detection circuit 150 includes a current source 152, a capacitor C1, a crystal M4, and a low-pass filter 154. The current source 152 receives a power supply voltage VDD and provides a bias current IB to charge the capacitor C1. A first terminal of the crystal M4 is coupled to the current source 152, a second terminal of the crystal M4 is coupled to ground, and a control terminal of the crystal M4 is coupled to the capacitor C1, the crystal 101, and the driver circuit 140 to receive the voltage XIN. The first terminal of capacitor C1 is coupled to current source 152, the first terminal of transistor M4, and the input terminal of low-pass filter 154, and the second terminal of capacitor C1 is coupled to ground. Transistor M4 selectively conducts according to voltage XIN to discharge capacitor C1.

[0014] When crystal 101 is not yet oscillating, the bias current IB is greater than the current flowing through transistor M4, causing capacitor C1 to begin charging and generate a higher voltage VD. Under this condition, low-pass filter 154 can generate a higher detection voltage VA based on this voltage VD, allowing transistor M2 to generate a higher current I2. When crystal 101 enters the oscillation state, the amplitude of voltage XIN gradually increases, causing the current in transistor M4 to be higher than the bias current IB, causing capacitor C1 to begin discharging through transistor M4 and generate a lower voltage VD. Under this condition, low-pass filter 154 can generate a lower detection voltage VA based on this voltage VD, causing amplifier 110 to generate a higher control voltage VC, thereby allowing transistor M2 to generate a lower current I2, effectively reducing overall power consumption after crystal 101 enters the oscillation state. In other words, the above operation forms an adaptive current regulation function. That is, when crystal 101 is not yet oscillating, current generation circuit 120 generates a higher current I2 to reduce the start-up time of crystal 101. When the crystal 101 enters the oscillation state, the current generating circuit 120 can generate a lower current I2, thereby reducing the overall power consumption.

[0015] In some embodiments, the low-pass filter 154 may include a resistor R2 and a capacitor C2. A first terminal of resistor R2 is coupled to capacitor C1 to receive voltage VD, a second terminal of resistor R2 is coupled to the first terminal of capacitor C2, the second terminal of capacitor C2 is coupled to ground, and the second terminal of resistor R2 generates a detection voltage VA and transmits the detection voltage VA to the negative input terminal of amplifier 110. The above embodiments of the low-pass filter 154 are merely examples and are not intended to limit the scope of this invention. Various related embodiments that can implement low-pass filtering are within the scope of this invention.

[0016] The reference voltage generation circuit 130 includes a current source 132, transistor M5, and transistor M6. The current source 132 receives the power supply voltage VDD and generates a reference current IREF. A first terminal of transistor M5 is coupled to a second terminal of transistor M1 to receive current. The first terminal of transistor M5 is further coupled to a control terminal of transistor M5 to generate a bias voltage VE, and the second terminal of transistor M5 is coupled to ground. A first terminal of transistor M6 is coupled to the current source 132 to receive the reference current IREF and generate a reference voltage VB. The second terminal of transistor M6 is coupled to ground, and the control terminal of transistor M6 is coupled to the control terminal of transistor M5 to receive the bias voltage VE. With this configuration, transistor M5 is configured as a diode-connected transistor to generate a corresponding bias voltage VE based on the current I1. Transistor M6 can generate a corresponding reference voltage VB based on the bias voltage VE and the reference current IREF.

[0017] Figure 3 is a waveform diagram of the control voltage VC, reference voltage VB, detection voltage VA, and voltage XIN related to crystal 101 in Figure 2, drawn according to some embodiments of this case. Before time T0, crystal 101 has not entered the oscillation state (i.e., it has not yet stabilized). As mentioned above, the current generating circuit 120 is implemented by a current mirror circuit, which, by configuring the ratio between current I1 and current I2, makes the reference voltage VB lower than the detection voltage VA (when crystal 101 has not entered the oscillation state). Thus, amplifier 110 will generate a lower control voltage VC. In response to the lower control voltage VC, current I2 will increase, allowing driver circuit 140 to accelerate crystal 101 into the oscillation state. After time T0, crystal 101 enters the oscillation state, causing the amplitude of voltage XIN at one end of crystal 101 to increase. This will cause capacitor C1 to discharge, resulting in detection circuit 150 generating a lower detection voltage VA. At the same time, reference voltage generating circuit 130 will generate a higher reference voltage VB. In other words, after crystal 101 enters the oscillation state, the reference voltage VB will be higher than the detection voltage VA. Under this condition, amplifier 110 will generate a higher control voltage VC, thereby reducing current I2 and current I1 to save overall power consumption.

[0018] It should be noted that the signal waveform in Figure 3 is only used to explain the timing of related operations and the relationship between voltage level changes, and is not intended to limit this case. The actual frequency or actual amplitude change of voltage XIN is not limited to the example waveform in Figure 3.

[0019] In summary, the crystal oscillator driving circuits provided in some embodiments of this invention have an adaptive current regulation function. They can self-regulate the overall current according to the crystal's oscillation state, increasing the current to reduce the start-up time before the crystal begins oscillation and automatically reducing the current to reduce power consumption after the crystal stabilizes. Furthermore, the crystal oscillator driving circuits provided in some embodiments of this invention can use circuit techniques such as current mirror circuits to generate a reference voltage without requiring a complex array of low-pass filters, thus reducing the overall circuit area.

[0020] Although the embodiments of this case are described above, these embodiments are not intended to limit this case. Those skilled in the art can make variations to the technical features of this case based on the express or implied content of this case. All such variations may fall within the scope of patent protection sought in this case. In other words, the scope of patent protection in this case shall be determined by the scope of the patent application in this specification.

[0021] 100: Crystal oscillator drive circuit 101: Crystal 110: Amplifier 120: Current generating circuit 130: Reference voltage generation circuit 132: Current Source 140: Driver circuit 150: Detection circuit 152: Current Source 154: Low-pass filter C1, C2: Capacitors I1, I2: Current IB: Bias Current IREF: Reference Current M1, M2, M3, M4, M5, M6: Transistors R1, R2: Resistors T0: Time VA: Detection Voltage VB: Reference Voltage VC: Control Voltage VD: Voltage VDD: Power supply voltage VE: Bias voltage XIN: Voltage XO: Reference signal

Claims

1. A crystal oscillator driving circuit, comprising: an amplifier for generating a control voltage based on a reference voltage and a detection voltage; a current generating circuit for generating a first current and a second current based on the control voltage; a reference voltage generating circuit for receiving the first current and generating the reference voltage; a driver circuit for receiving the second current and driving a crystal based on the second current; and a detection circuit for generating the detection voltage based on a first voltage related to the crystal, wherein... The ratio between the first current and the second current is less than 1.

2. The crystal oscillator drive circuit of claim 1, wherein when the crystal is not in an oscillation state, the reference voltage is lower than the detection voltage.

3. The crystal oscillator drive circuit of claim 1, wherein when the crystal enters an oscillation state, the detected voltage is lower than the reference voltage.

4. The crystal oscillator drive circuit of claim 1, wherein the second current decreases when the crystal enters an oscillation state.

5. The crystal oscillator drive circuit of claim 1, wherein the detection circuit includes a capacitor, and the detection circuit charges or discharges the capacitor according to the first voltage to generate the detection voltage.

6. The crystal oscillator drive circuit of claim 5, wherein the capacitor is charged or discharged to generate a second voltage, the detection circuit further includes a low-pass filter, and the low-pass filter generates the detection voltage based on the second voltage.

7. The crystal oscillator drive circuit of claim 5, wherein the detection circuit further comprises: a current source that generates a bias current to charge the capacitor; and a transistor coupled to the current source and the capacitor, and selectively conducting according to the first voltage to discharge the capacitor.

8. The crystal oscillator drive circuit of claim 1, wherein the current generating circuit comprises: a first transistor that generates the first current according to the control voltage; and a second transistor that generates the second current according to the control voltage.

9. The crystal oscillator drive circuit of claim 1, wherein the reference voltage generation circuit comprises: a current source for generating a reference current; a first transistor for receiving the first current and configured as a diode-type transistor to generate a bias voltage; and a second transistor for generating the reference voltage based on the bias voltage and the reference current.

10. The crystal oscillator drive circuit of claim 1, wherein the driver circuit comprises: a transistor, wherein a first terminal of the transistor receives the second current, a second terminal of the transistor is coupled to ground, and the transistor is coupled between the first terminal of the transistor and a control terminal of the transistor; and a resistor coupled between the first terminal of the transistor and the control terminal of the transistor.

11. The crystal oscillator drive circuit of claim 1, wherein the current generating circuit is composed of a current mirror circuit.

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