A temperature sensing circuit based on bjt and a detection method thereof

Abstract

The application discloses a temperature sensing circuit based on BJT and a detection method thereof. The temperature sensing circuit comprises a current source, a current mirror, a clamping circuit and a functional circuit. The current source provides bias for the functional circuit through the copy of the current mirror. The current mirror is also used for copying and outputting circuit signals. The clamping circuit is used for voltage clamping of the functional circuit. The functional circuit comprises a first functional circuit and a second functional circuit, and is used for outputting two currents positively and negatively correlated with temperature respectively. During detection, the related output of temperature can be obtained through simple conversion and calculation of the two output currents by an auxiliary circuit. The circuit structure of the application is simple in structure and compatible with standard integrated circuit technology, and can realize effective and rapid temperature detection.

Description

Technical Field

[0001] This invention relates to a temperature sensing circuit and detection method based on a BJT (Bipolar Junction Transistor), belonging to the field of temperature sensors, and particularly to a temperature detection sensor. Background Technology

[0002] A temperature sensor is a common type of sensor used to detect parameters such as temperature changes, patterns of change, and ranges. It converts the detected temperature parameters into electrical signals, enabling electronic devices to respond promptly. Temperature sensors have applications in various fields, such as automatic control, environmental measurement, and temperature measuring instruments. They are also used for industrial equipment maintenance and safety alarms, providing effective support for temperature control, measurement, and recording.

[0003] The working principles of temperature sensors can be divided into two types: one is the physical change caused by temperature changes; the other is the conversion of physical parameters characterizing temperature changes into electrical signals through the application of electronic technology. The physical change principle refers to the fact that temperature changes cause certain physical effects, and temperature changes can be measured by detecting these physical effects; this includes resistive temperature sensors and specific heat sensors, etc. The electrical principle relies on the fact that temperature changes cause changes in the characteristic parameters of specific operational amplifiers in a circuit, and temperature changes can be simulated by monitoring changes in certain specific circuit parameters, such as variable resistors and variable capacitors.

[0004] Because minute physical changes are difficult to observe and quantify, temperature sensors based on this principle generally have low accuracy and poor timeliness. In contrast, temperature sensors based on electrical principles, which measure temperature changes through variations in variable resistance and capacitance, suffer from excessively large layout requirements. Therefore, currently, the most widely used temperature sensors are generally based on bipolar junction transistors (BJTs).

[0005] According to classical theory, at a given temperature, the base-emitter voltage V of a BJT is... BE The temperature coefficient is related to the voltage itself; when V BE ≈750mV, at T=300K, That is, V BE It is a physical quantity with a negative temperature coefficient. For two BJTs operating at different currents and composed of different numbers of unit cells connected in parallel, their V... BE The difference ΔV BE It is a physical quantity with a positive temperature coefficient, and this temperature coefficient is independent of temperature and the collector current characteristics of the BJT, exhibiting good linearity. In summary, based on V... BEand ΔV BE By understanding the relationship between temperature and electrical parameters, and using certain circuit structures, temperature detection can be achieved by converting these parameters into electrical parameters that characterize temperature changes.

[0006] However, the temperature characteristics of BJT under different working conditions cannot be perfectly described by formulas. How to use BJT to detect temperature more accurately remains a worthy and challenging task to study. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a temperature sensing circuit and detection method based on BJT, which has a simple circuit structure, can achieve effective and rapid temperature detection, and is compatible with standard integrated circuit technology.

[0008] The technical solution adopted in this invention is as follows:

[0009] A temperature sensing circuit based on BJT includes a current source, a current mirror, a clamping circuit, and a functional circuit. The current source provides bias to the functional circuit through a copy of the current mirror; the current mirror is also used for copying and outputting circuit signals; the clamping circuit is used for voltage clamping of the functional circuit; the functional circuit includes a first functional circuit and a second functional circuit, used to output two currents that are positively and negatively correlated with temperature, respectively.

[0010] Furthermore, the current mirror comprises four structures: four N-type transistors NM0 to NM3 constitute the first current mirror; four P-type transistors PM1, PM2, PM3, and PM4 constitute the second current mirror; transistors PM1 and PM2, along with P-type transistors PM5 and PM6, constitute the third current mirror; and transistors PM1, PM2, and P-type transistors PM7 and PM8 constitute the fourth current mirror. The drain of the current source input transistor NM0 is replicated through the first current mirror and output from the drain of transistor NM2. The output current flows into transistor PM0 to form a bias voltage, which biases the second, third, and fourth current mirrors.

[0011] Furthermore, transistors PM1 and PM2, transistors PM3 and PM4, and transistors PM5 and PM6 respectively constitute common-source cascode current mirrors to ensure that the operating current of the three BJTs in the circuit structure remains consistent.

[0012] Furthermore, the first functional circuit is composed of bipolar junction transistors Q0 and Q1 and resistor R0, used to generate a current that is positively correlated with temperature; the second functional circuit is composed of bipolar junction transistor Q2 and resistor R1, used to generate a current that is negatively correlated with temperature; the clamping circuit includes a first clamping circuit and a second clamping circuit, wherein the positive terminal of resistor R0 is connected to the positive input terminal of the first clamping circuit, and the negative terminal of resistor R0 is connected to the emitter of transistor Q1; the positive terminal of resistor R1 is connected to the negative input terminal of the second clamping circuit, and the negative terminal of resistor R1 is grounded.

[0013] Furthermore, the positive and negative input terminals of the first clamping circuit are connected to the positive terminal of resistor R0 and the emitter of transistor Q0, respectively, and the voltage at the positive terminal of resistor R0 is equal to the voltage at the emitter of transistor Q0. The output terminal of the first clamping circuit is connected to the gate terminals of transistors PM1, PM3, PM5, and PM7. The positive and negative input terminals of the second clamping circuit are connected to the emitter of transistor Q2 and the positive terminal of resistor R1, respectively, and the voltage at the positive terminal of resistor R1 is equal to the voltage at the emitter of transistor Q2. The output terminal of the second clamping circuit is connected to the gate terminal of transistor NM4.

[0014] Furthermore, both the first clamping circuit and the second clamping circuit employ operational amplifiers, which use a classic folded cascode structure.

[0015] The present invention also provides a detection method using the above-mentioned BJT-based temperature sensing circuit, the steps of which include:

[0016] First, the temperature sensing circuit generates two output currents that are positively and negatively correlated with the temperature at a certain operating temperature. Then, these two currents are used to alternately charge and discharge the capacitor. At the same time, a counter is used to time the charging and discharging process. Finally, the temperature value can be obtained by proportionally calculating the charging and discharging time.

[0017] This invention provides a temperature sensing circuit structure based on BJT. Compared with existing temperature sensors, it utilizes the temperature correlation characteristics between BJT terminal voltages for simple derivation and achieves temperature detection with a relatively simple circuit structure, achieving a detection accuracy of ±1℃ over a millisecond time span. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall circuit structure of the present invention, which includes a current source, 9 PMOS transistors and 5 NMOS transistors, 2 resistors, 3 BJTs and 2 operational amplifiers;

[0019] Figure 2 This is the overall circuit diagram of an embodiment of the present invention;

[0020] Figure 3 This is a timing diagram of the circuit operation in an embodiment of the present invention, with an operating frequency of 50MHz;

[0021] Figure 4 Figure (a) shows the simulation results of an embodiment of the present invention, and Figure (b) shows the correspondence between the simulation output and the simulation temperature. Figure (b) is a schematic diagram of the slope change of the curve in Figure (a). Detailed Implementation

[0022] This invention provides a temperature sensing circuit structure based on BJT, and the circuit schematic is shown below. Figure 1 As shown, it can output two types of currents, one positively correlated with temperature and the other negatively correlated with temperature. A current source IDC and five transistors (PM0, NM0, NM1, NM2, and NM3) are used to generate a bias voltage. Transistors NM0 to NM3 form a current mirror to replicate the current source IDC. The use of a cascode current mirror reduces the influence of temperature. The voltage across resistor R0 is clamped to V by the operational amplifier. BE0 The voltage across R0 is V. BE1 The ratio of the number of BJTs on both sides is 8. At this time, the pressure difference V across R0 is... BE0 -V BE1 The current flowing through R0 is proportional to temperature, so it is a PTAT current proportional to temperature. This current is copied by the current mirror formed by transistors PM1, PM2, PM7, and PM8 and output. The voltage across resistor R1 is clamped at V by the operational amplifier. BE2 The voltage across the lower end of the resistor is 0, so the current flowing through this large resistor R1 is the CTAT current, which is inversely proportional to the temperature. This current is output through NM4. Subsequently, the capacitor can be alternately charged and discharged using two different currents, while a counter at a certain operating frequency records the time required for the same charging and discharging value. The temperature value can then be calculated using the correlation between charging / discharging time and temperature. Transistors PM1, PM2, PM3, PM4, PM5, PM6, PM7, and PM8 each form a common-source cascode current mirror, ensuring that the operating current of the three BJTs and the output PTAT current remain consistent. Both operational amplifiers use a classic folded common-source cascode structure, with a gain of approximately 60dB when a suitable bias voltage is provided, which basically meets the requirements for clamping stability.

[0023] Specifically, the overall circuit framework of this embodiment of the invention is as follows: Figure 2 As shown, the core part is the temperature sensing circuit structure of this invention, with two outputs (a current I that is positively correlated with temperature). PTAT Current I, which is negatively correlated with temperature CTAT This can be simply represented as:

[0024] I PTAT =ΔV BE / R0;I CTAT =V BE / R1

[0025] Among them, V BE The base-emitter voltage difference of Q2 is ΔV. BE V is the difference in base-emitter voltage between Q0 and Q1. BE0 -V BE1 .

[0026] Connect the output to the other end of a capacitor C with one end grounded to charge and discharge it, and record the charging and discharging time T corresponding to the same change in capacitor voltage ΔV. ptat and T ctat :

[0027] T ptat =C×ΔV / I PTAT ;T ctat =C×ΔV / I CTAT

[0028] Then the discharge time T ctat Total charging and discharging time T ctat +T ctat The ratio is:

[0029] T ctat / (T ptat +T ctat ) = I ptat / (I ptat +I ctat )=R1×ΔV BE / (R1×ΔV BE +R0×V BE )

[0030] Due to V BE and ΔV BE Since they have negative and positive temperature coefficients respectively, the denominator of the above equation can be made a constant by adjusting the ratio of resistors R0 and R1, and finally a parameter with a positive temperature coefficient can be obtained.

[0031] The two comparators connected after the capacitor have reference voltages of 0.8V and 1.6V, respectively, clamping the voltage change of the capacitor during charging and discharging to 0.8V. Two counters (counter9 and counter10) count the charging and discharging time of the capacitor within the 0.8V voltage range. These two time values ​​are obtained by a 10-bit counter operating at a 50MHz clock frequency and are serially output after passing through parallel-to-serial conversion modules (PtoS9 and PtoS10). Then, the two output values ​​(T...) are converted off-chip. ptat and Tctat By performing proportional calculations, a value proportional to temperature can be obtained. Finally, the corresponding temperature value can be obtained by looking up a table. At an operating frequency of 50MHz, T ptat The counter count values ​​differ by 1 when the temperature changes by 1℃, and it only takes 30us for counters counter10 and counter9 to be fully counted in one cycle. Considering the system's response delay and other influencing factors, a detection accuracy of ±1℃ can be achieved in the millisecond time span.

[0032] Figure 3 This is a timing diagram of the system operation. The system clock frequency is 50MHz. After power-on, the capacitor is first pre-charged to 1.8V. At this time, the system enable signal (EN) is low, and the capacitor charge / discharge switch (ENswitch) is high. Subsequently, the EN signal goes high, and the comparator starts working. At this time, since the 1.6V comparator output (COMP2OUT) is high, ENswitch goes low, and the capacitor begins to discharge. When the capacitor discharges to 1.6V, COMP2OUT goes low, and the 9-bit counter (ENcounter9) starts counting. When the capacitor discharges to 0.8V, the 0.8V comparator (COMP1OUT) toggles, and ENcounter9 stops counting. The obtained count value is the discharge time of the capacitor from 1.6V to 0.8V. This value is output after parallel-to-serial conversion, and ENswitch goes high to charge the capacitor. When the capacitor voltage returns to 0.8V, COMP1OUT toggles again, and the output returns to high. At this time, the 10-bit counter (ENcounter10) starts counting until the capacitor is charged to 1.6V. Then, COMP2OUT toggles, and ENcounter10 stops counting. The obtained count value is the charging time of the capacitor from 0.8V to 1.6V. This value is output after parallel-to-serial conversion, and ENswitch goes low to discharge the capacitor. This process repeats.

[0033] Considering that temperature is a slow variable relative to time, the enable signal EN can provide a periodic square wave signal with a certain duty cycle.

[0034] The entire circuit was simulated within a temperature range of -40℃ to 80℃. The output charge and discharge time counts were recorded. The circuit output results were processed using the positive temperature coefficient parameter calculation method, and T was plotted. ctst / (T ptat +T ctat The relationship between temperature and other factors is as follows: Figure 4 As shown in (a), it can be seen that the final result measured using the temperature sensing circuit structure of the present invention can achieve a good linear correspondence with the temperature value. For easier observation... Figure 4The linearity of the corresponding curve in (a) is shown in the curve of its slope change. Figure 4 As shown in (b), the slope variation range does not exceed two per thousand, indicating a high degree of linearity.

Claims

1. A temperature sensing circuit based on BJT, comprising a current source, a current mirror, a clamping circuit, and a functional circuit, characterized in that, The current source provides bias to the functional circuit through a copy of the current mirror; the current mirror is also used for copying and outputting circuit signals; the clamping circuit is used for voltage clamping of the functional circuit; the functional circuit includes a first functional circuit and a second functional circuit, used to output two types of currents that are positively and negatively correlated with temperature, respectively. The current mirror comprises four structures: four N-type transistors NM0~NM3 form the first current mirror; four P-type transistors PM1, PM2, PM3, and PM4 form the second current mirror; transistors PM1 and PM2, along with P-type transistors PM5 and PM6, form the third current mirror; and transistors PM1, PM2, PM7, and PM8, along with P-type transistors PM7 and PM8, form the fourth current mirror. The drain of the current source input transistor NM0 is replicated through the first current mirror and output from the drain of transistor NM2. The output current flows into transistor PM0 to form a bias voltage, which biases the second, third, and fourth current mirrors. The first functional circuit consists of bipolar junction transistors Q0 and Q1 and a resistor R0, used to generate a current that is positively correlated with temperature; the second functional circuit consists of bipolar junction transistor Q2 and a resistor R1, used to generate a current that is negatively correlated with temperature; the clamping circuit includes a first clamping circuit and a second clamping circuit, wherein the positive terminal of the resistor R0 is connected to the positive input terminal of the first clamping circuit, and the negative terminal of the resistor R0 is connected to the emitter of transistor Q1; the positive terminal of the resistor R1 is connected to the negative input terminal of the second clamping circuit, and the negative terminal of the resistor R1 is grounded; The positive and negative input terminals of the first clamping circuit are connected to the positive terminal of resistor R0 and the emitter of transistor Q0, respectively. The voltage at the positive terminal of resistor R0 is equal to the voltage at the emitter of transistor Q0. The output terminal of the first clamping circuit is connected to the gate terminals of transistors PM1, PM3, PM5, and PM7. The positive and negative input terminals of the second clamping circuit are connected to the emitter of transistor Q2 and the positive terminal of resistor R1, respectively. The voltage at the positive terminal of resistor R1 is equal to the voltage at the emitter of transistor Q2. The output terminal of the second clamping circuit is connected to the gate terminal of transistor NM4.

2. The temperature sensing circuit based on BJT according to claim 1, characterized in that, Transistors PM1 and PM2, PM3 and PM4, and PM5 and PM6 respectively constitute common-source cascode current mirrors to ensure that the operating current of the three BJTs in the circuit structure remains consistent.

3. The temperature sensing circuit based on BJT according to claim 1, characterized in that, Both the first clamping circuit and the second clamping circuit employ operational amplifiers, which use a classic folded cascode structure.

4. The detection method using the BJT-based temperature sensing circuit as described in claim 1, characterized in that, The steps of this detection method include: First, the temperature sensing circuit generates two output currents that are positively and negatively correlated with the temperature at a certain operating temperature. Then, these two currents are used to alternately charge and discharge the capacitor. At the same time, a counter is used to time the charging and discharging process. Finally, the temperature value can be obtained by proportionally calculating the charging and discharging time.

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