Low-noise ring oscillator insensitive to process, voltage and temperature

Abstract

The invention discloses a low-noise ring oscillator insensitive to process, voltage and temperature. The low-noise ring oscillator comprises an oscillator body, a process and temperature compensation module and an alternating current coupling buffer. Wherein the process and temperature compensation module utilizes a structure matched with a transistor pair used in a phase inverter of the oscillator main body to generate a voltage synchronously changed with the process, and utilizes a current positively correlated with the temperature to generate a voltage synchronously changed with the temperature. The voltage compensated by the process and temperature compensation module is transmitted to the oscillator main body through the two transistors to serve as the power supply voltage of the oscillator main body, so that the power supply voltage of the ring oscillator can synchronously change along with the process and the temperature, and the sensitivity degree of the oscillation frequency to the process, the voltage and the temperature is resisted. And finally, a clock signal with the duty ratio of 50% is output through the alternating current coupling buffer.

Description

Technical Field

[0001] The present invention belongs to the field of on-chip high-performance clock design, and relates to a low-noise ring oscillator that is insensitive to process, voltage, and temperature, and optimizes the problem that the oscillation frequency of the ring oscillator is sensitive to process, voltage, and temperature. Background Art

[0002] The oscillation frequency of a ring oscillator with a traditional structure is affected by the process parameters of transistors and the threshold voltage. For example, the mobility and oxide capacitance of transistors are different under different processes, the power supply voltages of the produced chips are inconsistent, and the temperature causes the threshold voltage of transistors to change. These parameters will greatly affect the oscillation frequency of the ring oscillator. Therefore, the oscillation frequency of the ring oscillator is extremely sensitive to process, voltage, and temperature (PVT).

[0003] In addition, compared with an inductor-capacitor (LC) oscillator, due to its lower quality factor, the phase noise performance of the ring oscillator is also worse.

[0004] Regarding the problem that the oscillation frequency of the ring oscillator is sensitive to PVT, some academic studies have improved the structure of the ring oscillator. For example, some scholars proposed in the literature "K.R. Lakshmikumar, V. Mukundagiri and S.L.J. Gierkink, A Process and Temperature Compensated Two-Stage Ring Oscillator, 2007 IEEE Custom Integrated Circuits Conference, 2007, pp. 691-694." that by changing the reference voltage input to the LDO (low dropout linear regulator), its output voltage will also change synchronously with the process and temperature, and finally make the change in the oscillation frequency of the ring oscillator as small as possible. However, this approach will introduce an additional LDO, and the noise of its power supply voltage will further deteriorate the phase noise of the ring oscillator. At the same time, the additional LDO will also occupy additional area. Summary of the Invention

[0005] The purpose of the present invention is to propose a low-noise ring oscillator, which can solve the problem that the oscillation frequency of the ring oscillator is sensitive to process, voltage, and temperature, and at the same time can achieve better phase noise performance.

[0006] To achieve the above object, the present invention provides a ring oscillator, which includes:

[0007] An oscillator body, comprising a plurality of inverters connected end to end, each of the inverters comprising a first transistor pair, and each of the inverters receiving an equivalent power supply voltage from a first node;

[0008] A process and temperature compensation module, comprising:

[0009] A first transistor disposed between the power supply voltage and the first node and a second transistor disposed between the power supply voltage and a second node, the first transistor and the second transistor being matched to keep the voltage of the first node and the voltage of the second node consistent;

[0010] A second transistor pair disposed between the second node and the ground terminal, the second transistor pair being matched with the first transistor pair in the inverter to make the variation trends of the first transistor pair and the second transistor pair consistent with process and temperature changes;

[0011] An AC coupling buffer connected to the output of the oscillator body, for forming and outputting a square wave clock signal,

[0012] Wherein, the matching of the second transistor pair with the first transistor pair means that the sizes of the two transistor pairs are the same or maintained in a certain proportion, and the positions on the layout are adjacent.

[0013] Optionally, the oscillator body further comprises a variable capacitor located between the output terminal of each inverter and the ground terminal.

[0014] Optionally, the process and temperature compensation module further comprises a current source connected between the power supply voltage and the second transistor and positively correlated with temperature.

[0015] Optionally, the process and temperature compensation module further comprises a low-pass filter connected between the first transistor and the second transistor.

[0016] Optionally, the AC coupling buffer comprises a pair of inverters, a DC blocking capacitor connected between the oscillator body and the pair of inverters, and a resistor connected between the pair of inverters.

[0017] Optionally, the AC coupling buffer comprises a pair of inverters, a DC blocking capacitor connected between the oscillator body and the pair of inverters, and a resistor connected between the pair of inverters.

[0018] Optionally, the inverters used in the AC coupling buffer have the same structure as the inverters used in the oscillator body, but different sizes.

[0019] Optionally, the AC coupling buffer is used to output a square wave clock signal with a 50% duty cycle.

[0020] According to the test results, the frequency of the ring oscillator of the present invention varies by no more than 10% with the process, and within the temperature range of -40°C to 125°C, the frequency varies by less than 1% with the temperature.

[0021] The present invention uses a structure that matches the NMOS (N-type metal-oxide-semiconductor) and PMOS (P-type metal-oxide-semiconductor) used in the inverters of the ring oscillator main body to generate a voltage that changes synchronously with the process; in addition, a voltage that changes synchronously with the temperature is generated through a current that has a positive correlation with the temperature. Finally, this voltage is transmitted to the ring oscillator main body through two NMOS transistors as its power supply voltage, so that the power supply voltage of the ring oscillator will change synchronously with the process and temperature, thereby resisting the sensitivity of its oscillation frequency to the process, voltage, and temperature. And the high output impedance of the NMOS can effectively reduce the influence of power supply noise on the ring oscillator. Finally, a clock signal with a duty cycle of 50% is output through an AC-coupled buffer. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1A is a schematic structural diagram of a ring oscillator according to an embodiment of the present invention.

[0023] Figure 1B is Figure 1A the specific structure of the inverter in

[0024] Figure 2 shows the curve of the oscillation frequency of the ring oscillator according to an embodiment of the present invention changing with temperature.

[0025] Figure 3 shows the phase noise curve of the ring oscillator according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0027] According to an embodiment of the present invention, a ring oscillator with an improved structure is proposed. Please refer to Figure 1A , three inverters connected end to end and three variable capacitors C var constitute the oscillator main body of the ring oscillator. The specific structure of each inverter is as Figure 1B shown, which is formed by connecting a PMOS transistor PM0 and an NMOS transistor NM0. As described in the background art, the power supply voltage of the ring oscillator will change synchronously with the process and temperature. To solve this problem, the present invention provides a process and temperature compensation module. Specifically, the Figure 1A voltages AVDD_RO and Vx in are kept consistent through a pair of matching transistors M1 and M2, where AVDD_RO is the equivalent power supply voltage of the oscillator main body, and the node where it is located is called the first node, Vx is the source voltage of transistor M3, and the node where it is located is called the second node. Further, the transistor pair M3 and M4 connected between the second node and the ground terminal match the transistor pair PM0 and NM0 in the inverter. Therefore, their variation trends with process and temperature are the same. Here, "matching" means that the sizes of the two pairs of transistors are the same or maintain a certain ratio, and their positions on the layout are adjacent, thus ensuring that their process deviations are the same. For example, at the ff process corner, the threshold voltage of the transistor decreases, the oscillation frequency of the ring oscillator will increase, and at this time, the voltage of AVDD_RO will decrease, causing the frequency to decrease again. The two cancel each other out to keep the frequency unchanged.

[0028] In addition, for the influence of temperature on the oscillation frequency, a current source I1 that is positively correlated with temperature is set between the power supply voltage AVDD and transistor M2 to ensure that the voltage of Vx increases as the temperature rises, thereby compensating for the characteristic that the oscillation frequency of the ring oscillator decreases as the temperature rises.

[0029] Meanwhile, the high-frequency noise of the bias circuit is suppressed by a low-pass filter composed of a resistor R1 and a capacitor C1, and the noise of the power supply is suppressed by the high output impedance of transistor M1 located between the power supply AVDD and the first node, thereby better improving the phase noise performance of the ring oscillator.

[0030] Since the output swing of the ring oscillator will change with process and temperature, the output of the oscillator main body is passed through an AC-coupled buffer to obtain a square-wave clock signal output CK with a 50% duty cycle. OUT where the capacitor C c is used to block the DC operating point and transfer AC signals, and the resistor R f is used to provide a new DC operating point. The inverter used in the AC-coupled buffer has the same structure as the inverter used in the oscillator main body, but different sizes.

[0031] Finally, after the chip fabrication and test verification of the present invention, its frequency variation with process is no more than 10%, within the extreme temperature range of -40°C to 125°C, the frequency variation is less than 1%, and when the oscillation frequency is 1 GHz, the phase noise is -107.4 dBc / Hz at a 1 MHz frequency offset.

[0032] The oscillation frequency variation of the uncompensated traditional ring oscillator with process will be about 30%. The final simulation results of the present invention are shown in Table 1. When the oscillation frequency is 1 GHz at the tt process corner, the frequency variation at other process corners is less than 9%. Each process corner represents the speed of PMOS and NMOS respectively, where t represents typical, f represents fast, and s represents slow.

[0033] Table 1 Oscillation frequencies of the oscillator at different process corners

[0034]

[0035] The oscillation frequency of the uncompensated traditional ring oscillator changes by about 20% within the temperature range of -40°C to 125°C. However, the final test results of the present invention show that the frequency change within the temperature range of -40°C to 125°C is less than 1%, and the temperature coefficient is about 100 ppm / °C. The specific temperature drift curve is as Figure 2 shown, where the abscissa is temperature and the ordinate is the oscillation frequency.

[0036] The change in the power supply voltage has little effect on the ring oscillator. For a voltage change of plus or minus 10%, the oscillation frequency change is less than 0.1%.

[0037] The test results show that when the oscillation frequency of the ring oscillator of the present invention is 1 GHz, the phase noise is -107.4 dBc / Hz at a frequency offset of 1 MHz. The overall phase noise curve is as Figure 3 shown.

[0038] Although the present invention is disclosed as above, it is not limited thereto. Those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. A ring oscillator, characterized in that, Comprising: An oscillator body, including a plurality of inverters connected end to end, each of the inverters including a first transistor pair, and each of the inverters receiving an equivalent power supply voltage from a first node; A process and temperature compensation module, including: A first transistor disposed between the power supply voltage and the first node and a second transistor disposed between the power supply voltage and a second node, the first transistor and the second transistor being matched to keep the voltage of the first node consistent with the voltage of the second node; A second transistor pair disposed between the second node and the ground terminal, the second transistor pair being matched with the first transistor pair in the inverter to make the variation trends of the first transistor pair and the second transistor pair consistent with respect to process and temperature; An AC coupling buffer connected to the output of the oscillator body for forming and outputting a square wave clock signal, wherein the matching of the second transistor pair with the first transistor pair means that the sizes of the two transistor pairs are the same or maintained in a certain ratio, and their positions on the layout are adjacent.

2. The ring oscillator according to claim 1, wherein The oscillator body further includes a variable capacitor between the output terminal of each inverter and the ground terminal.

3. The ring oscillator according to claim 1, characterized in that, The process and temperature compensation module further includes a current source that is positively correlated with temperature and is connected between the power supply voltage and the second transistor.

4. The ring oscillator according to claim 1 or 3, characterized in that The process and temperature compensation module further includes a low-pass filter connected between the first transistor and the second transistor.

5. The ring oscillator according to claim 1, wherein The AC coupling buffer includes a pair of inverters, a DC blocking capacitor connected between the oscillator body and the pair of inverters, and a resistor connected between the pair of inverters.

6. The ring oscillator according to claim 5, characterized in that The inverters used in the AC coupling buffer have the same structure as those used in the oscillator body, but different sizes.

7. The ring oscillator according to claim 5 or 6, characterized in that, The AC coupling buffer is used to output a square wave clock signal with a 50% duty cycle.

8. The ring oscillator according to claim 1, characterized in that, The frequency of the ring oscillator varies by no more than 10% with the process.

9. The ring oscillator according to claim 1, wherein Within the temperature range of -40°C to 125°C, the frequency of the ring oscillator varies by less than 1% with temperature.

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