Voltage-controlled oscillator
By introducing two control units and oscillation circuits into the voltage-controlled oscillator, adjusting the gain mode, and combining current bias and frequency calibration, the negative correlation between gain and frequency coverage is solved, ensuring frequency stability and phase-locked loop performance, making it suitable for CMOS on-chip systems.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-13
- Publication Date
- 2026-03-10
AI Technical Summary
In CMOS on-chip systems, the gain of a voltage-controlled oscillator is negatively correlated with its frequency coverage, making it difficult to support the same target frequency under changes in process, voltage, and temperature, thus affecting the overall performance and frequency stability of the phase-locked loop.
A voltage-controlled oscillator was designed, comprising two control units and an oscillation circuit. The gain mode is changed by adjusting the switching module of the control unit. Combined with the current bias circuit and frequency calibration unit, it ensures stable coverage of the target frequency under changes in process, voltage and temperature.
It achieves stable coverage of the target frequency under changes in process, voltage, and temperature, improving the overall performance and frequency stability of the phase-locked loop, while minimizing the impact on the function and performance of the voltage-controlled oscillator when the additional control unit is not in operation.
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Figure CN121643643A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of electronics, and in particular to a voltage-controlled oscillator. BACKGROUND
[0002] A voltage-controlled oscillator (VCO) is an electronic device that generates different frequency output signals according to the input voltage. By adjusting the control voltage of the VCO, the frequency of its output changes within a certain range. VCOs are widely used in modern communication systems, radars, radio equipment, etc., and are an important part of frequency modulation, frequency synthesis and clock signal generation.
[0003] In a CMOS system on chip (SOC) chip, a clock generation circuit is a necessary component, which is generally realized by a reference source and a phase-locked loop, and the VCO is an important component module. In order to meet the strict requirements of high-speed digital circuits and high-speed digital-to-analog and analog-to-digital converters for clock jitter, the gain (KVCO) of the VCO is usually reduced to improve the overall performance of the phase-locked loop, but KVCO and the frequency coverage range of the VCO are naturally negatively correlated, which makes it difficult for low-gain KVCO to support the same target frequency under process, voltage, and temperature (PVT) changes. SUMMARY
[0004] To solve the above technical problems, the present application provides a voltage-controlled oscillator, comprising: a first control unit, the first control unit outputs a first current based on a control voltage; a second control unit, the second control unit outputs a second current based on the control voltage, and the second control unit further comprises a switch module for controlling the on-off of the second control unit; an oscillation circuit connected to the first control unit and the second control unit, which changes the gain of the voltage-controlled oscillator by adjusting the switch module of the second control unit.
[0005] In one embodiment, when the second control unit is turned on, the oscillation circuit takes the first current and the second current as input current, and the voltage-controlled oscillator is in a first gain mode; when the second control unit is turned off, the oscillation circuit takes the first current as input current, and the voltage-controlled oscillator is in a second gain mode.
[0006] In one embodiment, the first control unit comprises: a first transistor, a gate of the first transistor is used to obtain the control voltage, and a source of the first transistor is connected to a power supply; a second transistor, a gate of the second transistor is used to obtain the control voltage, a source of the second transistor is connected to the zero potential, and a drain of the second transistor is connected to the drain of the first transistor.
[0007] In one embodiment, the second control unit comprises: a third transistor, a gate of the third transistor is used to obtain the control voltage, a source of the third transistor is connected to the power supply via the first switch transistor; a fourth transistor, a gate of the fourth transistor is used to obtain the control voltage, a source of the fourth transistor is connected to the zero potential via the second switch transistor, and a drain of the fourth transistor is connected to the drain of the third transistor.
[0008] In one embodiment, a connection point of the drain of the first transistor and the drain of the second transistor is an output terminal of the first control unit, an input terminal of the oscillation circuit is connected to the output terminal of the first control unit; a connection point of the drain of the third transistor and the drain of the fourth transistor is an output terminal of the second control unit, and the input terminal of the oscillation circuit is connected to the output terminal of the second control unit.
[0009] In one embodiment, the gate of the first transistor, the gate of the second transistor, the gate of the third transistor, and the gate of the fourth transistor are connected to each other.
[0010] In one embodiment, the first transistor comprises a PMOS transistor, the second transistor comprises an NMOS transistor, the third transistor comprises a PMOS transistor, and the fourth transistor comprises an NMOS transistor.
[0011] In one embodiment, based on the same control voltage, a working frequency range of the first gain mode is greater than a working frequency range of the second gain mode, and an output noise of the first gain mode is greater than an output noise of the second gain mode.
[0012] In one embodiment, the voltage-controlled oscillator further comprises: a current biasing circuit connected to the oscillation circuit, the current biasing circuit being used to adjust the center frequency.
[0013] In one embodiment, the current biasing circuit is connected to the frequency calibration unit, and is used to calibrate the center frequency of the voltage-controlled oscillator based on the target frequency in the second gain mode.
[0014] According to the voltage-controlled oscillator provided in the present application, two control units are included, and the oscillation circuit is connected to both of the control units, and the switches of the control units are adjusted to change the gain of the voltage-controlled oscillator. By additionally adding the control units, not only is the coverage of the target frequency under the changes of process, voltage, and temperature guaranteed, but also the functions and performance of the voltage-controlled oscillator are almost not affected when the additionally added control units are not working. BRIEF DESCRIPTION OF DRAWINGS
[0015] The accompanying drawings, which are incorporated herein and constitute part of the specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.
[0016] Figure 1 A schematic diagram of the frequency coverage of a voltage-controlled oscillator; Figure 2 A schematic diagram of the structure of a voltage-controlled oscillator of the application; Figure 3 A schematic diagram of the frequency coverage of a voltage-controlled oscillator of the application in different modes; Figure 4 A schematic diagram of the frequency calibration of a voltage-controlled oscillator of the application. DETAILED DESCRIPTION
[0017] In order to more clearly understand the above-mentioned purposes, features and advantages of the application, the embodiments of the application will be further described below. It should be noted that the embodiments of the application and the features in the embodiments can be combined with each other without conflict.
[0018] In the following description, many specific details are set forth in order to provide a thorough understanding of the application. However, the application can be practiced in different ways without the specific details described herein. It is apparent that the embodiments described in the specification are only a part of the embodiments of the application, not all the embodiments.
[0019] Figure 1 A schematic diagram of the frequency coverage of a voltage-controlled oscillator, it can be seen that the operating frequency changes with the input voltage. At the same time, with the change of process, voltage, temperature (PVT) and other conditions, the voltage-frequency curve S0 will have an overall shift, Figure 1 The highest position S1 and the lowest position S2 of the shift are shown in FIG. 1. In order to make the VCO work stably at the target frequency under any condition, it is necessary to make the high and low curves cover the operating frequency and leave a certain margin, that is Figure 1 the shaded area in FIG. 1, which is the actual operating frequency range that the VCO can support. It can be seen directly that the greater the slope of the voltage-frequency curve, the greater the actual operating frequency range of the VCO, and the slope corresponds to the gain (KVCO) of the VCO. If KVCO is too small, the high and low curves may not overlap, which means that the VCO cannot work normally. On the other hand, the gain of the VCO also determines the conversion of control voltage noise to phase noise, the higher KVCO, the more easily the VCO is affected by voltage noise. Therefore, there is a conflict between the VCO frequency range and the overall performance of the phase-locked loop.
[0020] In view of the above problems, the application provides a voltage-controlled oscillator, referring to FIG. 1, Figure 2 comprising: The first control unit 110 outputs a first current I1 based on the control voltage; The second control unit 120 outputs a second current I2 based on the control voltage, and further comprises a switch module for controlling the on-off of the second control unit; The oscillation circuit 130 is connected to the first control unit 110 and the second control unit 120, and changes the gain of the voltage-controlled oscillator based on adjusting the switch module of the second control unit 120.
[0021] Further, when the second control unit 120 is turned on, the oscillation circuit 130 takes the first current I1 and the second current I2 as input currents, and the voltage-controlled oscillator is in the first gain mode; when the second control unit 120 is turned off, the oscillation circuit 130 takes the first current I1 as the input current, and the voltage-controlled oscillator is in the second gain mode.
[0022] In one embodiment, referring to Figure 2 The first control unit 110 comprises a first transistor M1 and a second transistor M2. The first transistor M1 is a PMOS transistor, the gate of the first transistor M1 is used to obtain the control voltage V0, the source of the first transistor M1 is connected to the power supply Vcc, and the drain of the first transistor M1 is connected to the oscillation circuit 130.
[0023] In one embodiment, referring to Figure 2 The second transistor M2 is an NMOS transistor, the gate of the second transistor M2 is connected to the gate of the first transistor M1, the gate of the second transistor M2 is used to obtain the control voltage V0, the source of the second transistor M2 is grounded (i.e. zero potential), the drain of the second transistor M2 is connected to the drain of the first transistor M1, and the drain of the second transistor M2 is also connected to the oscillation circuit 130. Specifically, the connection point (also referred to as the midpoint) of the drain of the first transistor M1 and the drain of the second transistor M2 serves as the output end of the first control unit 110, and the input end of the oscillation circuit 130 is connected to the output end of the first control unit 110 to obtain the first current I1 output by the first control unit 110 as the input current of the oscillation circuit 130.
[0024] In one embodiment, referring to Figure 2As shown, the second control unit 120 includes a third transistor M3, a fourth transistor M4, and a switching module, wherein the switching module includes a first switching transistor M5 and a second switching transistor M6. The third transistor M3 is a PMOS transistor, and its gate is connected to the gates of the first transistor M1 and the second transistor M2. The gate of the third transistor M3 is used to obtain the control voltage V0. The source of the third transistor M3 is connected to the power supply Vcc via the first switching transistor M5; that is, the source of the third transistor M3 is connected to the first terminal of the first switching transistor M5, and the second terminal of the first switching transistor M5 is connected to the power supply Vcc. The drain of the third transistor M3 is connected to the oscillation circuit 130.
[0025] In one embodiment, refer to Figure 2 As shown, the fourth transistor M4 is an NMOS transistor. The gate of the fourth transistor M4 is connected to the gates of the first transistor M1, the second transistor M2, and the third transistor M3. The gate of the fourth transistor M4 is used to obtain the control voltage V0. The source of the fourth transistor M4 is grounded (i.e., zero potential) via the second switching transistor. Specifically, the source of the fourth transistor M4 is connected to the first terminal of the second switching transistor M6, and the second terminal of the second switching transistor M6 is grounded. The drain of the fourth transistor M4 is connected to the drain of the third transistor M3, and the drain of the fourth transistor M4 is also connected to the oscillation circuit 130. Specifically, the connection point (also called the midpoint) between the drains of the third transistor M3 and the fourth transistor M4 serves as the output terminal of the second control unit 120. The input terminal of the oscillation circuit 130 is connected to the output terminal of the second control unit 120 to obtain the second current I2 output by the second control unit 120 as the input current of the oscillation circuit 130.
[0026] In one embodiment, refer to Figure 2As shown, the first switching transistor M5 and the second switching transistor M6 are synchronously turned on or off. When both the first switching transistor M5 and the second switching transistor M6 are off, the second control unit 120 is off. At this time, the third transistor M3 and the fourth transistor M4 are not connected to the circuit, the second control unit 120 does not output current, and the oscillation circuit 130 only obtains the first current I1 as the input current. When both the first switching transistor M5 and the second switching transistor M6 are on, the second control unit 120 is on. At this time, the third transistor M3 and the fourth transistor M4 are both in working state, the second control unit 120 outputs the second current I2, and the oscillation circuit 130 obtains the first current I1 and the second current I2 as the input current. The first control unit 110 and the second control unit 120 are used to realize voltage-to-current conversion. The ratio of the change in current value with the change in control voltage V0 is the voltage-to-current conversion gain. The oscillation circuit 130 is used to realize current-to-frequency conversion. The ratio of the change in frequency value with the change in input current is the current-to-frequency conversion gain. The voltage-to-frequency conversion gain obtained based on the voltage-to-current conversion gain and the current-to-frequency conversion gain is the gain of the voltage-controlled oscillator. Therefore, when the second control unit 120 is turned on, the oscillation circuit 130 obtains the first current I1 and the second current I2 as input current, and the voltage-controlled oscillator is in the first gain mode, that is, the high gain mode; when the input current of the oscillation circuit 130 is low, the gain of the voltage-controlled oscillator is low. Therefore, when the second control unit 120 is turned off, the oscillation circuit 130 only obtains the first current I1 as input current, and the voltage-controlled oscillator is in the second gain mode, which is called the low gain mode or normal mode.
[0027] In one embodiment, based on the same control voltage, the operating frequency range of the first gain mode is greater than that of the second gain mode, and the output noise of the first gain mode is greater than that of the second gain mode. Therefore, when stable frequency coverage is required but frequency calibration cannot be completed, such as during the packaging test phase, the voltage-controlled oscillator can be switched to high-gain mode, in which the second control unit 120 operates and outputs a second current I2. During normal use, the voltage-controlled oscillator can be switched to low-gain mode, in which the second control unit 120 does not operate.
[0028] In one embodiment, refer to Figure 3 As shown, A0 displays the voltage-frequency curve of the voltage-controlled oscillator in low-gain mode, and B0 displays the voltage-frequency curve of the voltage-controlled oscillator in high-gain mode. According to... Figure 3As can be seen, the slope of curve B0 is greater than that of curve A0, and the slope corresponds to the VCO gain (KVCO). With changes in PVT, curve A0 will shift overall, with the highest shift point being curve A1 and the lowest point being curve A2. Curve B0 will also shift overall, with the highest shift point being curve B1 and the lowest point being curve B2. Clearly, curves B1 and B2 have an overlapping region, which represents the operating frequency range of the VCO in high-gain mode. Curves A1 and A2 do not overlap, indicating that the VCO is not functioning properly.
[0029] In one embodiment, refer to Figure 2 As shown, the voltage-controlled oscillator also includes a current bias circuit 140, which is connected to the oscillation circuit 130. The current bias circuit 140 is used to adjust the center frequency. Specifically, the first terminal of the current bias circuit 140 is connected to the power supply Vcc, the second terminal of the current bias circuit 140 is connected to the oscillation circuit 130, the current bias circuit 140 outputs a third current I3, and the oscillation circuit 130 is connected to the current bias circuit 140 to obtain the third current I3. Further, refer to... Figure 4 As shown, the current bias circuit 140 is externally connected to a frequency calibration unit to calibrate the center frequency of the voltage-controlled oscillator (VCO) based on the target frequency in the second gain mode. The frequency calibration unit includes a counter that obtains the VCO's output frequency based on the number of cycles recorded within a fixed time period. Specifically, in low-gain mode, the gain is at a lower value, which is beneficial to the clock quality of the phase-locked loop (PLL), and the deviation of the VCO's center frequency can be compensated by the frequency calibration unit. During calibration, the VCO operates in open-loop mode, and its output signal is fed into a counter. The counter uses a relatively accurate reference clock as the start and end trigger signals to record the number of cycles of the VCO output within a fixed time period, thereby calculating the VCO's operating frequency. Based on the measured frequency, the output current I3 of the current bias circuit 140 can be adjusted to regulate the VCO's center frequency. Through several measurements and adjustments, the VCO's center frequency is adjusted to near the target frequency, achieving frequency calibration. It should be noted that the output current I3 of the current bias circuit 140 is not affected by the control voltage V0.
[0030] Although the VCO's center frequency can be calibrated in low-gain mode using the current bias circuit 140 and the frequency calibration unit to adjust the frequency coverage range and alleviate frequency coverage pressure, the clock generation circuit still needs to provide a fixed-frequency clock for digital scan testing during package testing. Due to limitations in the production testing environment, frequency calibration is difficult to complete at this time, requiring the uncalibrated VCO to support the target operating frequency under PVT variations. Therefore, during the package testing phase, the voltage-controlled oscillator can be switched to high-gain mode to address the VCO's frequency stability issues before frequency calibration and during production testing.
[0031] The voltage-controlled oscillator provided in this application includes two control units, with an oscillation circuit connected to both control units. The oscillation circuit draws input current from one or both control units to change the gain of the voltage-controlled oscillator. By adding additional control units, coverage of the target frequency is ensured under variations in process, voltage, and temperature. Furthermore, when the additional control units are not in operation, the function and performance of the voltage-controlled oscillator are almost unaffected.
[0032] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0033] The above descriptions are merely embodiments of this application, which enable those skilled in the art to understand and implement this application. Various modifications to the embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
Claims
1. A voltage controlled oscillator characterized by, Comprising: a first control unit, outputting a first current based on a control voltage; a second control unit, outputting a second current based on the control voltage, the second control unit further comprising a switch module for controlling the on-off of the second control unit; an oscillation circuit, connected to the first control unit and the second control unit, changing the gain of the voltage-controlled oscillator based on adjusting the switch module of the second control unit.
2. The voltage-controlled oscillator of claim 1, wherein: when the second control unit is on, the oscillation circuit takes the first current and the second current as input current, and the voltage-controlled oscillator is in a first gain mode; when the second control unit is off, the oscillation circuit takes the first current as input current, and the voltage-controlled oscillator is in a second gain mode.
3. The voltage controlled oscillator of claim 1, wherein, The first control unit comprises: a first transistor, the gate of the first transistor being used to obtain the control voltage, the source of the first transistor being connected to a power supply; a second transistor, the gate of the second transistor being used to obtain the control voltage, the source of the second transistor being connected to zero potential, and the drain of the second transistor being connected to the drain of the first transistor.
4. The voltage controlled oscillator of claim 3, wherein, The second control unit comprises: a third transistor, the gate of the third transistor being used to obtain the control voltage, the source of the third transistor being connected to a power supply via a first switch transistor; a fourth transistor, the gate of the fourth transistor being used to obtain the control voltage, the source of the fourth transistor being connected to zero potential via a second switch transistor, and the drain of the fourth transistor being connected to the drain of the third transistor.
5. The voltage controlled oscillator of claim 4, wherein, The connection point of the drain of the first transistor and the drain of the second transistor is the output of the first control unit, and the input of the oscillation circuit is connected to the output of the first control unit; The connection point of the drain of the third transistor and the drain of the fourth transistor is the output of the second control unit, and the input of the oscillation circuit is connected to the output of the second control unit.
6. The voltage controlled oscillator of claim 4, wherein, The gates of the first transistor, the second transistor, the third transistor, and the fourth transistor are connected to each other.
7. The voltage controlled oscillator of claim 4, wherein, The first transistor comprises a PMOS transistor, the second transistor comprises an NMOS transistor, the third transistor comprises a PMOS transistor, and the fourth transistor comprises an NMOS transistor.
8. The voltage controlled oscillator of claim 2, wherein, Based on the same control voltage, the operating frequency range of the first gain mode is greater than that of the second gain mode, and the output noise of the first gain mode is greater than that of the second gain mode.
9. The voltage controlled oscillator of claim 2, wherein, Further comprising: a current biasing circuit, connected to the oscillation circuit, for adjusting the center frequency.
10. The voltage controlled oscillator of claim 9, wherein, The current biasing circuit is connected to a frequency calibration unit, and the center frequency of the voltage-controlled oscillator is calibrated based on a target frequency in the second gain mode.