A low-power time-domain temperature sensor based on mosfet temperature sensing

Abstract

The application relates to a time-domain temperature sensor based on MOSFET temperature sensing, and belongs to the temperature sensor field. The temperature sensor comprises a temperature sensing unit and a frequency digital converter connected in sequence. The frequency digital converter comprises a voltage-controlled oscillator and a counter. The temperature sensor senses the external temperature through the temperature sensing unit, converts a physical signal into an analog signal, converts the analog signal into a frequency signal through the voltage-controlled oscillator, inputs the frequency signal into the counter, and reads out a digital code value representing temperature information from the counter. Compared with a traditional temperature sensor, the temperature sensor has the advantages of low power consumption, small area, simple structure and the like.

Description

Technical Field

[0001] This invention belongs to the field of temperature sensors and relates to a time-domain temperature sensor based on MOSFET temperature sensing. Background Technology

[0002] As CMOS process nodes shrink further, chip functions become increasingly complex and integration levels rise. Based on advanced photolithography, tens of thousands of transistors are integrated onto a tiny silicon substrate, leading to increasingly severe chip heat generation issues. Since self-heating can significantly degrade chip performance, thermal management is essential. In chip thermal management, on-chip temperature sensors are commonly used devices that sense temperature, providing information on thermal gradients and hot spots to prevent overheating and improve chip stability.

[0003] Among on-chip temperature sensors, resistor-based temperature sensors offer superior performance in terms of energy efficiency and resolution. These sensors utilize high-sensitivity thermistors as the sensor and employ a high-resolution analog-to-digital converter to read the digital code value representing temperature information. Thermistor temperature sensors are highly sensitive, easily detecting temperature changes and responding quickly. However, they also suffer from resistance nonlinearity and have a limited temperature range; exceeding the specified temperature range will cause the thermistor to malfunction.

[0004] Fiber optic temperature sensors utilize the principle that the spectrum absorbed by some substances changes with temperature. By analyzing the spectrum transmitted through the fiber optic cable, real-time temperature can be determined. Fiber optic temperature sensors have high temperature sensitivity, are electrically insulated, and are small in size. However, their application cost is relatively high, and they are easily affected by light source noise and interference from micro-vibrations in the environment, making it difficult to achieve stable measurements over a long period of time.

[0005] Transistor-based temperature sensors utilize transistors to generate voltages with a positive temperature coefficient, which are then read out as digital codes by a frequency-to-digital converter to characterize the temperature. Although transistor temperature sensors are highly accurate, they are often large, complex in structure, and consume a lot of power. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a low-power time-domain temperature sensor based on MOSFET temperature sensing, which reduces the power consumption and area of ​​the temperature sensor, widens the temperature sensing range, and improves the resolution.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A low-power time-domain temperature sensor based on MOSFET temperature sensing is disclosed. The temperature sensor includes a temperature sensing unit and a frequency-to-digital converter connected in sequence. The frequency-to-digital converter includes a voltage-controlled oscillator (VCO) and a counter. The temperature sensor senses the external temperature through the temperature sensing unit and converts the physical signal into an analog signal. The VCO then converts the analog signal into a frequency signal, which is input into the counter. The counter then reads out a digital code value representing the temperature information.

[0009] Optionally, the temperature sensing unit includes a temperature sensing element and an operational amplifier. The positive input terminal of the operational amplifier is connected to the temperature sensing element, and its negative input terminal is connected to its output terminal. The output terminal of the operational amplifier is also connected to a voltage-controlled oscillator.

[0010] Optionally, the temperature sensing element includes MOSFETs M1 to M3; the drain of MOSFET M1 is connected to the power supply, and its gate is connected to the source and substrate of M1 and the drain and gate of MOSFET M2, respectively; the source of MOSFET M2 is connected to the substrate of M2 and the gate and drain of MOSFET M3, respectively; the substrate of M3 is connected to its source, and its source is grounded.

[0011] The drain of MOSFET M2 serves as the output of a temperature sensing element and is connected to the positive input of the operational amplifier.

[0012] The drain-source leakage currents of MOSFETs M1 to M3 are equal.

[0013] Optionally, the voltage-controlled oscillator includes MOSFETs Mp1-Mp3, Mc1-Mc3, and Mn1-Mn3, and inverters INV1 and INV2; the source of MOSFET Mp1 is connected to its substrate and the power supply, and the drain of Mp1 is connected to the drain of MOSFET Mc1 and the gates of MOSFETs Mp2 and Mn2; the source of MOSFET Mc1 is connected to its substrate and the drain of Mn1; the source of MOSFET Mn1 is connected to its substrate and grounded; the source of MOSFET Mp2 is connected to its substrate and the power supply, and its drain is connected to the drain of MOSFET Mc2 and the gates of MOSFETs Mp3 and Mn3. Gate connections; the source of MOSFET Mc2 is connected to its substrate and the drain of Mn2; the source of MOSFET Mn2 is connected to its substrate and grounded; the source of MOSFET Mp3 is connected to its substrate and the power supply, and its drain is connected to the drain of MOSFET Mc3, the gates of Mp1 and Mn1, and the input of inverter INV1; the source of MOSFET Mc3 is connected to its substrate and the drain of Mn3; the source of MOSFET Mn3 is connected to its substrate and grounded; the output of inverter INV1 is connected to the input of inverter INV2, and the output of INV2 is connected to the counter;

[0014] The gates of MOS transistors Mc1 to Mc3 are all connected to the output signal of the temperature sensing unit.

[0015] The beneficial effects of the present invention are: low power consumption, small area, simple structure, large temperature sensing range, and high resolution.

[0016] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0018] Figure 1 This is a block diagram illustrating the principle of the low-power time-domain temperature sensor of the present invention.

[0019] Figure 2 This is the circuit diagram of the temperature sensing unit;

[0020] Figure 3 This is a partial circuit diagram of a voltage-controlled oscillator. Detailed Implementation

[0021] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0022] Please see Figures 1-3 This is a low-power time-domain temperature sensor based on MOSFET temperature sensing. It mainly consists of two parts: a temperature sensing unit and a frequency-to-digital converter. The frequency-to-digital converter comprises a voltage-controlled oscillator and a counter. Figure 1 As shown. The basic mechanism of this temperature sensor is that the temperature on the chip is converted into an analog electrical signal by the temperature sensing unit. The analog electrical signal is then converted into a digital signal by a frequency-to-digital converter. Inside the frequency-to-digital converter, the analog electrical signal is first converted into a frequency, and then read out by a counter, which represents it as a binary digital code value.

[0023] The temperature sensing unit mainly includes a temperature sensing element and an operational amplifier A1 connected in a negative feedback configuration. The temperature sensing element includes MOSFETs M1 to M3, such as... Figure 2As shown. The drain of MOSFET M1 is connected to the power supply, and its gate is connected to the source and substrate of M1, as well as the drain and gate of MOSFET M2. The source of MOSFET M2 is connected to the substrate of M2, as well as the gate and drain of MOSFET M3. The substrate of M3 is connected to its source, and its source is grounded. The drain of MOSFET M2 is the output V of the entire temperature sensing element. sense The negative input of operational amplifier A1 is connected to its positive input terminal. The negative input of operational amplifier A1 is connected to its output terminal, which then outputs the control voltage V for the next stage voltage-controlled oscillator. ctrl .

[0024] The theoretical derivation of the functional relationship between temperature and voltage of the temperature sensing unit is as follows:

[0025] The general equation for the subthreshold current of a MOSFET is:

[0026]

[0027] In the formula, μ0 represents the mobility of the MOS transistor, and C ox It is the gate oxide capacitance per unit area. V represents the width-to-length ratio of a MOSFET. T It is the temperature equivalent, V th It is a threshold voltage mismatch, V gs It is the gate-source voltage of the MOSFET, V th V is the threshold voltage of the MOSFET, γ is the body effect coefficient, and V sb It is the voltage between the substrate and source of the MOSFET, η is the DIBL effect coefficient, V ds is the drain-source voltage of the MOSFET, and m is the process factor.

[0028] Because NMOS transistors using a long-channel deep-well process can have γ and η approximated as 0, and because of the V used... ds ≥3V T Therefore MOSFETs M1 through M3 all operate in the subthreshold region, and because they use the same channel length, V th1 V th2 V th3 They can be considered approximately equal, hence the following three expressions can be obtained:

[0029]

[0030]

[0031]

[0032] If we set the drain-source currents of MOSFETs M1 to M3 to be equal, we can obtain the expression for the output voltage:

[0033]

[0034] From equation (5), it can be deduced that V sense With V T The relationship is linear, increasing with increasing temperature.

[0035] A voltage-controlled oscillator (VCO) includes MOSFETs Mp1-Mp3, Mc1-Mc3, and Mn1-Mn3, as well as inverters INV1 and INV2. The MOSFETs are the main components of the VCO, while the inverters INV1 and INV2 form a buffer, making signal transmission more accurate and stable. Figure 3 As shown, the specific connection method of the voltage-controlled oscillator is as follows: the source of MOSFET Mp1 is connected to its substrate and the power supply, and the drain of Mp1 is connected to the drain of MOSFET Mc1 and the gates of MOSFETs Mp2 and Mn2; the source of MOSFET Mc1 is connected to its substrate and the drain of Mn1; the source of MOSFET Mn1 is connected to its substrate and grounded; the source of MOSFET Mp2 is connected to its substrate and the power supply, and its drain is connected to the drain of MOSFET Mc2 and the gates of MOSFETs Mp3 and Mn3; the source of MOSFET Mc2 is connected to its substrate and the drain of Mn2; the source of MOSFET Mn2... The source of MOSFET Mp3 is connected to its substrate and grounded; its drain is connected to the drain of MOSFET Mc3, the gates of Mp1 and Mn1, and the input of inverter INV1; the source of MOSFET Mc3 is connected to its substrate and the drain of Mn3; the source of MOSFET Mn3 is connected to its substrate and grounded; the output of inverter INV1 is connected to the input of inverter INV2, and the output of INV2 outputs a square wave signal with a frequency of Freq, which is input to the counter; the gates of MOSFETs Mc1 to Mc3 are all connected to the output signal V of the temperature sensing unit. ctrl .

[0036] The theoretical derivation of the frequency generation expression for a voltage-controlled oscillator is as follows:

[0037] For a single-stage inverter, assume its equivalent capacitance to ground is C. eq1 If the input signal is a step signal, the output voltage will be [voltage value] when the equivalent capacitor is charged. When the equivalent capacitance is discharged, the output voltage is In the formula, t is the charging / discharging time, τ is the time constant, and V DD This is the power supply voltage.

[0038] So V out Rise or fall to V DD When half of the output voltage rise time t is reached, the rise time is t. h and descent time t lThe expression is as follows:

[0039] t h =(ln2)R p C eq1 ≈0.7R p C eq1 (6)

[0040] t l =(ln2)R n C eq1 ≈0.7R n C eq1 (7)

[0041] In the formula, R p R represents the equivalent resistance of the PMOS transistor used as part of the inverter section. n This represents the equivalent resistance of the NMOS transistor used as part of the inverter.

[0042] The period of the three-stage oscillator is: 3(t) h +t l )≈2.1(R p +R n C eq1 .

[0043] For the equivalent resistance of an NMOS transistor in the deep linear region, the following relationship holds:

[0044]

[0045] Where, μ n This represents the mobility of the NMOS transistor. Therefore, a voltage-controlled oscillator can be designed using the variable resistor shown in the above formula:

[0046] In the designed voltage-controlled oscillator, the input control signal is V ctrl The output frequency is Freq. The input signal V... ctrl Three MOSFETs Mc1-Mc3 are directly connected to form the variable resistor section of the voltage-controlled oscillator. Mp1 and Mn1 form a first-stage inverter, Mp2 and Mn2 form a second-stage inverter, and Mp3 and Mn3 form a third-stage inverter, totaling three inverter stages forming an oscillating loop with no steady state. The signal output from the third-stage inverter Mp3 / Mn3 has a 180° phase difference with the signal input to the first-stage inverter Mp1 / Mn1. With each inverter stage, the voltage gain is greater than 1, meaning the circuit satisfies the Barkhausen condition. This cycle repeats continuously, resulting in self-oscillation.

[0047] The resonant signal output by the oscillating loop is in the range of 0 to V. DD The input of the three-stage inverter is determined by V. DD At the instant the voltage drops to 0V, the three signals generated by the input signal V...ctrl The connected MOSFETs Mc1 through Mc3 are all in the deep linear region. At this instant, the three MOSFETs, which act as variable resistors, are each equivalent to a small resistor. Then, the output of the three-stage inverter begins to change until the output voltage becomes V. DD Half of the time is lost, and NMOS transistors Mc1 to Mc3 are no longer in the deep linear region. The time of this output voltage change can be regarded as the delay of this stage of inverter, which is affected by the equivalent resistance of the deep linear region of MOS transistors Mc1 to Mc3.

[0048] For a MOSFET that functions as a variable resistor, the expression for its equivalent resistance in the deep linear region is as follows:

[0049]

[0050] The relationship between the frequency of the output signal and the input voltage is derived as follows:

[0051] First, referring to the aforementioned oscillator period expression, we obtain the frequency of the output signal:

[0052]

[0053] By adjusting the width-to-length ratio of the MOSFET, R... o ′>>R p AND R o ′>>R n Then we have the following expression:

[0054]

[0055] Due to V sense =V ctrl Then equation (11) becomes:

[0056]

[0057] Further simplification of equation (12) (due to V) sense -V ds -V th Some of the results are temperature-dependent and contain high-order terms. Therefore, in this invention, the high-order terms related to temperature are filtered out, and only the zero-order and first-order terms are retained, resulting in:

[0058]

[0059] In the formula, a and b are constants, and T represents temperature.

[0060] Finally, the square wave signal with a frequency of Freq output from the voltage-controlled oscillator is sent to the counter, and the counter reads out the digital code value that can characterize the temperature.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A low-power time-domain temperature sensor based on MOSFET temperature sensing, characterized in that: It includes a temperature sensing unit, a voltage-controlled oscillator, and a counter connected in sequence; the temperature sensing unit senses the external temperature and converts the physical signal into an analog signal; the voltage-controlled oscillator converts the analog signal into a frequency signal and inputs it into the counter; and the counter reads out the digital code value representing the temperature information. The voltage-controlled oscillator includes MOSFETs Mp1-Mp3, Mc1-Mc3, and Mn1-Mn3, as well as inverters INV1 and INV2. The source of MOSFET Mp1 is connected to its substrate and the power supply, and the drain of Mp1 is connected to the drain of MOSFET Mc1 and the gates of MOSFETs Mp2 and Mn2. The source of MOSFET Mc1 is connected to its substrate and the drain of MOSFET Mn1. The source of MOSFET Mn1 is connected to its substrate and grounded. The source of Mp2 is connected to its substrate and the power supply, and its drain is connected to the drain of MOS transistor Mc2 and the gates of Mp3 and Mn3, respectively; the source of MOS transistor Mc2 is connected to its substrate and the drain of Mn2, respectively; the source of MOS transistor Mn2 is connected to its substrate and grounded; the source of MOS transistor Mp3 is connected to its substrate and the power supply, and its drain is connected to the drain of MOS transistor Mc3, the gates of Mp1 and Mn1, and the input terminal of inverter INV1, respectively. The source of MOSFET Mc3 is connected to its substrate and the drain of MOSFET Mn3, respectively; the source of MOSFET Mn3 is connected to its substrate and grounded; the output of inverter INV1 is connected to the input of inverter INV2, and the output of INV2 is connected to the counter; the gates of MOSFETs Mc1 to Mc3 are all connected to the output signal of the temperature sensing unit. In this circuit, MOSFETs Mp1 and Mn1 form the first-stage inverter, MOSFETs Mp2 and Mn2 form the second-stage inverter, and MOSFETs Mp3 and Mn3 form the third-stage inverter. The first to third-stage inverters are cascaded, and there is a 180° phase difference between the input signals of the first-stage inverter and the third-stage inverter.

2. The temperature sensor according to claim 1, characterized in that: The temperature sensing unit includes a temperature sensing element and an operational amplifier. The positive input terminal of the operational amplifier is connected to the temperature sensing element, and its negative input terminal is connected to its output terminal. The output terminal of the operational amplifier is also connected to a voltage-controlled oscillator.

3. The temperature sensor according to claim 2, characterized in that: The temperature sensing element includes MOS transistors M1 to M3; the drain of MOS transistor M1 is connected to the power supply, and its gate is connected to the source and substrate of M1 and the drain and gate of MOS transistor M2, respectively; the source of MOS transistor M2 is connected to the substrate of M2 and the gate and drain of MOS transistor M3, respectively; the substrate of M3 is connected to its source, and its source is grounded. The drain of MOSFET M2 serves as the output of a temperature sensing element and is connected to the positive input of the operational amplifier.

4. The temperature sensor according to claim 3, characterized in that: The drain-source leakage currents of the MOS transistors M1 to M3 are equal.

5. The temperature sensor according to claim 3, characterized in that: The MOS transistors M1 to M3 all operate in the subthreshold region.

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