Low-power-consumption temperature sensor based on MOS tube

Abstract

The invention belongs to the field of analog integrated circuits, and particularly relates to a low-power-consumption temperature sensor based on an MOS tube. A relaxation oscillator with a negative temperature characteristic is used as a temperature sensor, and the output square wave period and the temperature are in a linear relation. The MOS tube M1 in the oscillator has the dual functions of signal amplification and temperature sensing: on one hand, the common-gate amplifier is used for amplifying the voltage of an upper pole plate of a capacitor, increasing the input swing of a comparator and reducing the charge quantity of single charge and discharge, so that the power consumption is remarkably reduced; and on the other hand, the amplified signal improves the input slope at the overturning point of the comparator, the comparison speed is increased, and the influence of circuit noise on oscillator jitter is effectively suppressed. According to the invention, temperature sensing is carried out by using the voltage temperature characteristic of the MOS tube working in the sub-threshold region, the limitation of a traditional sub-threshold region current temperature sensing mode is avoided, low-power-consumption, high-resolution and high-precision measurement in a wide temperature range is realized, and the effective temperature sensing range of the MOS type temperature sensor is obviously widened.

Description

A low-power temperature sensor based on MOSFET Technical Field

[0001] This invention belongs to the field of analog integrated circuits and relates to temperature sensors in integrated circuits, specifically a low-power temperature sensor based on a MOS transistor. Background Technology

[0002] Temperature, as a crucial physical quantity, has a significant impact on the performance parameters of electronic devices. Therefore, temperature sensors are widely used in industrial production, food processing, smart homes, and other fields. Based on size, temperature sensors can be categorized into traditional discrete sensors and emerging integrated sensors.

[0003] Traditional discrete temperature sensors are based on discrete components, typically thermistors or thermocouples. However, they are relatively large and difficult to integrate directly into microchips. Emerging integrated temperature sensors, on the other hand, are manufactured directly on integrated circuits using semiconductor processes, offering advantages such as small size and high integration. Furthermore, integrated temperature sensors also offer advantages such as low power consumption, low cost, and fast response. Therefore, integrated temperature sensors are favored by the microelectronics industry.

[0004] Based on the temperature sensing device, integrated temperature sensors can be classified into BJT (bipolar transistor) type, resistive type, TD (thermal diffusivity) type, and MOSFET (metal-oxide-semiconductor field-effect transistor) type. BJT type sensors offer high temperature sensing accuracy but require a complex analog-to-digital converter (ADC) for readout, resulting in typically long conversion times. Resistive type sensors offer flexible power supply voltage selection but occupy a significant area. TD type sensors offer high temperature sensing accuracy and a wide sensing range, but power consumption is typically in the milliwatt range. MOSFET type sensors typically utilize the subthreshold current of the MOSFET for temperature sensing, offering low power consumption and a small area, but power consumption varies greatly with temperature, and leakage current limits the temperature sensing accuracy and range of MOSFET type sensors. Summary of the Invention

[0005] To address the aforementioned problems and shortcomings, this invention provides a low-power temperature sensor based on a MOSFET, utilizing both the temperature-sensing and amplification characteristics of the MOSFET. This invention uses a MOSFET operating in the subthreshold region to sense temperature, embedding the MOSFET within a relaxation oscillator to output a frequency- and temperature-dependent clock signal. Unlike traditional MOSFET subthreshold current-based temperature sensing methods, this invention directly utilizes the voltage characteristics of the MOSFET in the subthreshold region, broadening the temperature sensing range. Furthermore, the MOSFET also functions as a common-gate amplifier, amplifying the small voltage swing of the capacitor's upper plate into a large-swing signal for the comparator input. This significantly reduces the charge required for a single charge-discharge cycle, thereby reducing system power consumption, and also greatly improves the conversion slope of the comparator input signal, accelerating the comparison speed and effectively suppressing the impact of circuit noise on oscillator jitter.

[0006] A low-power temperature sensor based on a MOSFET includes: a reference voltage source V REF Reference current source I REF Capacitor C L The components include an NMOS transistor M1, a switch S1, a comparator, and a delay module.

[0007] The gate of the NMOS transistor M1 is connected to the reference voltage source V. REF Connected and fixed at a constant potential; the source of NMOS transistor M1 is connected to capacitor C. L The upper plate is connected and grounded through switch S1, C L The voltage of the upper plate is V C The drain of M1 is connected to the reference current source I. REF Connected together, and simultaneously connected to the input of the comparator, the input voltage of the comparator is V. CMP The comparator's output is connected to the input of the delay module. Furthermore, the design of M1 must ensure that its on-resistance is low when it is in the linear region, while also minimizing the introduction of parasitic capacitance to achieve optimal performance.

[0008] The reference voltage source V REF Provides a temperature-independent reference voltage V ref V ref The voltage needs to be higher than the threshold voltage of M1 to ensure that M1 is within V. C When reset to ground, it is in the linear region. Furthermore, simultaneously, V ref The temperature cannot be too high, otherwise it will increase the oscillator period and the temperature sensor's switching time.

[0009] The comparator, when the input voltage is lower than the comparator switching voltage V TC When the input voltage is higher than the comparator's switching voltage V, the output is high; when the input voltage is higher than the comparator's switching voltage V, the output is high. TC When this occurs, the output is low.

[0010] The delay module outputs a square wave voltage signal CLK. When the input switches to a high level, it outputs a low level after a delay; when the input switches to a low level, it outputs a high level after a delay. The voltage signal CLK controls the on and off of switch S1 and serves as the output of the entire temperature sensor. The delay module ensures that capacitor C... L The potential V of the upper plate C It was completely reset to ground.

[0011] When the signal CLK output by the delay module is high, switch S1 is turned on. L Upper plate voltage V C Reset to ground; when the delay module output signal CLK is low, switch S1 is open, C L The upper electrode plate is referenced by current source I REF Charging, reference current source I REF Provide a constant current I that is independent of temperature. ref .

[0012] The reference voltage source V REF Reference current source I REF Capacitor C L A common-gate amplifier NMOS transistor M1, switch S1, comparator, and delay module are combined to form a relaxation oscillator with a negative temperature characteristic output frequency. The period of the output square wave voltage signal CLK is linearly related to the temperature.

[0013] Furthermore, the NMOS transistor M1 operates in the subthreshold region when the comparator is critically flipped, and functions as a common-gate amplifier.

[0014] Furthermore, the delay module's function is not only to ensure that capacitor C remains in operation before switch S1 is turned off. L The potential V of the upper plate C It must be completely reset to ground; it is also necessary to ensure that the delay time accounts for less than 0.1% of an oscillation cycle in order to avoid having too much impact on the temperature sensing accuracy.

[0015] Furthermore, the specific workflow of the aforementioned low-power temperature sensor based on MOSFETs includes:

[0016] When CLK is high, switch S1 is turned on, and capacitor C... L Upper plate potential V C When reset to ground, M1 is in the on state, and its drain-source voltage is very small. Therefore, the comparator input potential V CMP It is also reset to ground, so the input of the comparator becomes low and the output becomes high; after the delay module, the output CLK is switched to low.

[0017] When CLK is low, switch S1 is off, and the reference current source I... REF Through M1 to capacitor C L Upper plate charging, V C As the temperature gradually increases, the working region of M1 will gradually switch to the subthreshold region, V C Amplified by a common-gate amplifier based on M1, therefore V CMP It will also gradually increase until it reaches the comparator's switching voltage V. TC This causes the comparator output to go low; after a delay, the output CLK is switched to high, thus initiating the next cycle.

[0018] In summary, this invention effectively amplifies the voltage signal on the upper plate of the capacitor by introducing a common-gate amplifier M1. On the one hand, this structure significantly reduces the amount of charge change required during a single charge-discharge cycle, thereby effectively reducing overall power consumption. On the other hand, the amplified signal serves as the input to the comparator, converting the original small voltage swing of the upper plate of the capacitor into a large swing signal, significantly improving the slope of the input signal at the comparator's flip point. This not only speeds up the comparison process but also effectively suppresses the impact of circuit noise on oscillator jitter, improving system stability. Crucially, this invention innovatively utilizes the threshold voltage of the common-gate amplifier as the temperature sensing parameter, rather than relying on the traditional subthreshold current. This mechanism results in smaller power consumption fluctuations for the sensor over a wide temperature range and significantly expands the effective temperature sensing range of the MOSFET-type temperature sensor. Ultimately, this invention achieves wide-range, low-power, high-resolution, and high-precision temperature measurement while maintaining a simple circuit structure. Attached Figure Description

[0019] Figure 1 is a schematic block diagram of the overall circuit structure of the present invention.

[0020] Figure 2 is a schematic diagram of the circuit principle of the embodiment.

[0021] Figure 3 shows the timing waveform of the key node voltage in the embodiment. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0023] This embodiment provides a low-power temperature sensor based on a MOSFET, including a reference voltage source V. REF Reference current source I REF Capacitor C L The common-gate amplifier transistor NMOS transistor M1, switch S1, comparator and delay module are shown in Figure 1.

[0024] Reference voltage source V REF Reference current source I REF Capacitor CL A common-gate amplifier NMOS transistor M1, switch S1, comparator, and delay module are combined to form a relaxation oscillator with a negative temperature characteristic output frequency. The period of the output square wave voltage signal CLK is linearly related to the temperature.

[0025] In this embodiment:

[0026] The switch S1 is composed of an NMOS transistor M2, whose gate is connected to the output of the delay module and whose drain is connected to a capacitor C. L The upper plate of the common-gate amplifier is grounded, and the source is grounded. The input of the common-gate amplifier is the source voltage Vc of M1, and the output is the drain voltage V of M1. CMP .

[0027] The comparator consists of a PMOS transistor M3 and an NMOS transistor M4. The gates of M3 and M4 are connected to the drain of M1. The source of M3 is connected to the power supply, and the source of M4 is grounded. The drains of M3 and M4 are connected to the input of the delay module.

[0028] The delay module is composed of an odd number of cascaded inverters. The input of the first inverter serves as the input of the delay module, the output of the first inverter serves as the input of the second inverter, and so on, with the output of the last inverter serving as the output of the delay module. This ensures that when the input of the delay module is high, it outputs a low level after the delay, and when the input is low, it outputs a high level after the delay.

[0029] The working principle of the relaxation oscillator with negative temperature characteristic output frequency is explained below with reference to Figures 2 and 3. Figure 3 is the timing waveform diagram of the key node voltage in this embodiment:

[0030] When CLK is high, switch M2 is turned on, and C... L Upper plate voltage V C When reset to ground, M1 is in the on state, and its drain-source voltage is very small. Therefore, the input voltage V of the comparator is... CMP It is also reset to ground, so the comparator output becomes high. After passing through the delay module, its output CLK is switched to low.

[0031] When CLK is low, switch M2 is turned off, and the reference current source charges the upper plate of the capacitor through M1. C As the temperature gradually increases, the working region of M1 will gradually switch to the subthreshold region, V C Amplified by a common-gate amplifier based on M1, therefore V CMP It will also gradually increase until it reaches the comparator's switching voltage V. TC This causes the comparator output to go low; after passing through the delay module, its output CLK is switched to high, thus initiating the next cycle.

[0032] The temperature characteristic of the threshold voltage of the MOSFET is derived below. The threshold voltage V of the MOSFET... th It can be represented as:

[0033]

[0034] in, The difference in work function between the metal and semiconductor contacts. The effective positive charge surface density of the gate oxide layer, The capacitance per unit area of ​​the gate oxide layer. It is the dielectric constant of silicon. The charge of an electron. The concentration of acceptor impurities, The Fermi potential of the substrate, This represents the potential difference between the substrate and source of the MOS transistor. Among these parameters, and It is unrelated to temperature, but among them, the ones that are strongly correlated with temperature are .therefore, Temperature Differentiation yields:

[0035]

[0036] in:

[0037]

[0038] in, Boltzmann's constant, For the effective density of states in the conduction band, This represents the effective density of states in the valence band. In summary, we can obtain... right The derivative is:

[0039]

[0040] because Since the logarithmic term is negative, the threshold voltage of the NMOS transistor is... It has a negative temperature coefficient, decreasing as temperature increases. It can be approximated as... The change with temperature is linear:

[0041]

[0042] in, This represents the threshold voltage of the MOSFET at temperature T. for Threshold voltage measured at temperature is the temperature coefficient of the threshold voltage, and is a positive value.

[0043] The temperature characteristic of the oscillation frequency of the oscillator is derived below. At the critical switching point of the comparator, M1 operates in the subthreshold region. According to the subthreshold current formula of M1:

[0044]

[0045] in The reference current flowing through M1, The mobility of charge carriers, The gate oxide capacitance per unit area is given, W / L is the width-to-length ratio of the MOSFET, and the process factor is given. , It is the depletion layer capacitance under the channel, thermal voltage. , This is the gate-source voltage difference of the MOSFET. This represents the voltage difference between the drain and source of the MOSFET.

[0046] At the critical flip point of the comparator 3 Therefore, the formula can be rewritten as:

[0047]

[0048] In the above formula, This represents the gate-source voltage of M1 at the critical flip point. Considering lattice scattering and ionized impurity scattering, the expression for mobility can be written as:

[0049]

[0050] In the formula, This represents the migration rate at temperature T. Indicates reference temperature Mobility at (typically 300K) This is the temperature index, typically ranging from 1 to 1.5. Note that... The expression contains only temperature-related parameters. , and ,therefore right The derivative is:

[0051]

[0052] because ,and Therefore, the solution is:

[0053]

[0054] In the formula, Let be a constant. Clearly, since:

[0055]

[0056] In the formula, The reference voltage provided by the reference voltage source This represents the voltage across the upper plate of the capacitor at the critical reversal point. The value of . Therefore:

[0057]

[0058] Considering the temperature characteristics of the threshold voltage, the above equation can be written as:

[0059]

[0060] Applying the above formula to temperature Taking the derivative, we get:

[0061]

[0062] The formula contains The terms are negligible, therefore they can be approximated as... It has a linear relationship with temperature, that is:

[0063]

[0064] Ideally, the period of signal CLK is equal to that of capacitance C. L The upper plate is charged from 0 to Time required. Signal CLK frequency F CLK The expression is:

[0065]

[0066] Indicates capacitance The capacitance value. and Both are independent of temperature, therefore F CLK and The relationship is inversely proportional, so the period of signal CLK has a good linear relationship with temperature.

[0067] The amplification characteristics of M1 are derived below. For a MOSFET operating in the subthreshold region, its transconductance... It can be calculated using the subthreshold current formula:

[0068]

[0069] By analyzing the amplification characteristics of the common-gate amplifier M1 using small-signal analysis, the gain can be obtained. The expression:

[0070]

[0071] In the formula, This characterizes the M1 channel length modulation effect. Typically, the gain... It is at least several tens of times greater, therefore M1 can amplify the voltage. The function of this is to increase the swing amplitude without changing the power consumption, thereby reducing the impact of circuit noise on oscillator jitter and increasing the comparison speed.

[0072] As can be seen from the above embodiments, this invention effectively amplifies the voltage signal on the upper plate of the capacitor by introducing a common-gate amplifier. On the one hand, this structure significantly reduces the amount of charge change required during a single charge-discharge cycle, thereby effectively reducing overall power consumption. On the other hand, the amplified signal, used as the input to the comparator, converts the original small voltage swing of the upper plate of the capacitor into a large swing signal, significantly improving the slope of the input signal at the comparator's flip point. This not only speeds up the comparison process but also effectively suppresses the impact of circuit noise on oscillator jitter, improving system stability. Crucially, this invention innovatively utilizes the threshold voltage of the common-gate amplifier as the temperature sensing parameter, rather than relying on the traditional subthreshold current. This mechanism results in smaller power consumption fluctuations for the sensor over a wide temperature range and significantly expands the effective temperature sensing range of the MOSFET-type temperature sensor. In summary, this invention achieves wide-range, low-power, high-resolution, and high-precision temperature measurement while maintaining a simple circuit structure, demonstrating outstanding practicality and technological advancement.

Claims

1. A low-power temperature sensor based on a MOSFET, characterized in that, include: Reference voltage source V REF Reference current source I REF Capacitor C L The system includes an NMOS transistor M1, a switch S1, a comparator, and a delay module; the gate of the NMOS transistor M1 is connected to the reference voltage source V. REF Connected and fixed at a constant potential; the source of NMOS transistor M1 is connected to capacitor C. L The upper plate is connected and grounded through switch S1, C L The voltage of the upper plate is V C The drain of M1 is connected to the reference current source I. REF Connected together, and simultaneously connected to the input of the comparator, the input voltage of the comparator is V. CMP The comparator's output is connected to the input of the delay module; the reference voltage source V REF Provides a temperature-independent reference voltage V ref V ref A voltage higher than the threshold voltage of M1 is required to ensure that M1 operates at V. C When reset to ground, it is in the linear region; the comparator, when the input voltage is lower than the comparator switching voltage V TC When the input voltage is higher than the comparator's switching voltage V, the output is high; when the input voltage is higher than the comparator's switching voltage V, the output is high. TC When the input switches to a high level, the output is low; the output of the delay module is a square wave voltage signal CLK. When the input switches to a low level, after a delay, the output is low; when the input switches to a low level, after a delay, the output is high; the voltage signal CLK controls the on and off of switch S1 and serves as the output of the entire temperature sensor; the delay module ensures that before switch S1 is turned off, capacitor C... L The potential V of the upper plate C The switch S1 is fully reset to ground; when the delay module output signal CLK is high, the switch S1 is turned on, and C L Upper plate voltage V C Reset to ground; when the delay module output signal CLK is low, switch S1 is open, C L The upper electrode plate is referenced by current source I REF Charging; the reference voltage source V REF Reference current source I REF Capacitor C L A common-gate amplifier NMOS transistor M1, switch S1, comparator, and delay module are combined to form a relaxation oscillator with a negative temperature characteristic output frequency. The period of the output square wave voltage signal CLK is linearly related to the temperature.

2. The low-power temperature sensor based on a MOS transistor as described in claim 1, characterized in that: The NMOS transistor M1 operates in the subthreshold region when the comparator is critically flipped.

3. The low-power temperature sensor based on a MOS transistor as described in claim 1, characterized in that: The delay time of the delay module accounts for less than 0.1% of one oscillation cycle.

4. The low-power temperature sensor based on a MOS transistor as described in claim 1, characterized in that, The specific workflow is as follows: When CLK is high, switch S1 is turned on, and capacitor C... L Upper plate potential V C When reset to ground, M1 is in the ON state, and the comparator input potential V CMP The circuit is also reset to ground, so the comparator's input becomes low and the output becomes high; after the delay module, the output CLK is switched to low; when CLK is low, switch S1 is turned off, and the reference current source I... REF Through M1 to capacitor C L Upper plate charging, V C As the value gradually increases, the working region of M1 gradually switches to the subthreshold region, V C Amplified by a common-gate amplifier based on M1, therefore V CMP It also gradually increases until it reaches the comparator's switching voltage V. TC This causes the comparator output to go low; after passing through the delay module, the output CLK is switched to high; thus, the next cycle begins.

5. The low-power temperature sensor based on a MOS transistor as described in claim 1, characterized in that: The switch S1 uses an NMOS transistor M2, with the gate of M2 connected to the output of the delay module and the drain connected to a capacitor C. L The upper electrode plate is grounded.

6. The low-power temperature sensor based on a MOS transistor as described in claim 1, characterized in that: The comparator consists of a PMOS transistor M3 and an NMOS transistor M4; the gates of M3 and M4 are connected to the drain of M1, the source of M3 is connected to the power supply, and the source of M4 is grounded; the drains of M3 and M4 are connected to the input of the delay module.

7. The low-power temperature sensor based on a MOS transistor as described in claim 1, characterized in that: The delay module is composed of an odd number of cascaded inverters. The input of the first inverter serves as the input of the delay module, the output of the first inverter serves as the input of the second inverter, and so on, with the output of the last inverter serving as the output of the delay module.

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