CN204142381U - Temperature measuring circuit - Google Patents

Abstract

The utility model provides a temperature measuring circuit, which includes a temperature sensing circuit, which outputs first and second voltages representing temperature changes, and the temperature sensing circuit includes: a bias current source, which includes outputting first and second voltages respectively The first and second output ends of the current; the first and second MOS transistors are configured such that the gate and drain are connected and grounded, the source of the first MOS transistor is connected to the first output end, and the The source of the second MOS transistor is connected to the second output terminal, wherein the first voltage is the difference between the gate-source voltages of the first and second MOS transistors, and the second voltage is the first Or the gate-source voltage of the second MOS transistor. The temperature measuring circuit of the utility model is suitable for on-chip integration, has the characteristics of low power consumption and high precision, and can be applied to chip circuit systems with low power supply voltage.

Description

temperature measurement circuit

technical field

The utility model relates to a temperature measuring circuit.

Background technique

At present, the market development of environmental monitoring, medical devices and high-precision electronic devices has put forward requirements for temperature measurement solutions with low power consumption, high precision and easy integration. In order to obtain accurate temperature values, a common solution is to use high-precision temperature measuring instruments, but this method is not easy to integrate, and is only suitable for laboratory measurement and other occasions, and cannot be applied to emerging fields such as using RFID tags to collect ambient temperature.

The prior art, such as patent document CN102435336A, discloses a temperature measurement circuit suitable for on-chip integration, which uses a conventional temperature sensing element triode for temperature measurement, but requires a high power supply voltage and does not use system power consumption. In addition, the analog-to-digital conversion precision of the temperature measurement circuit in the prior art is too low to meet the current market demand.

Utility model content

To this end, the utility model provides a temperature measurement circuit, including a temperature sensing circuit, which outputs first and second voltages representing temperature changes, and the temperature sensing circuit includes: a bias current source, which includes outputting first and second voltages respectively and the first and second output ends of the second current; the first and second MOS transistors are configured such that the gate and the drain are connected and grounded, and the source of the first MOS transistor is connected to the first output end , the source of the second MOS transistor is connected to the second output terminal, wherein the first voltage is the gate-source voltage of the first or second MOS transistor, and the second voltage is the first and the difference between the gate-source voltage of the second MOS transistor.

Further, the temperature measurement circuit also includes an analog-to-digital conversion circuit for converting the analog quantity representing the ratio of the first voltage to the second voltage into a bit stream, and the analog-to-digital conversion circuit includes a SAR ADC and a Sigma- Delta modulator, wherein, the SAR ADC converts the integer part of the analog quantity, and the Sigma-Delta modulator converts the fractional part of the analog quantity.

Further, the temperature measurement circuit further includes a digital processing circuit, which filters and extracts the bit stream to obtain the measured temperature value and stores the temperature value.

Preferably, both the first and second MOS transistors are PMOS transistors.

Preferably, the first current is 5-10 times of the second current.

Preferably, said digital processing circuit includes a sinc ³ digital filter for said filtering and decimation processing.

The temperature measurement circuit of the utility model is suitable for on-chip integration, and uses the characteristics of the diode-connected MOS tube to generate a temperature-related voltage signal. It has the characteristics of low power consumption and can be applied to chip circuit systems with low power supply voltage; using SAR The combination of ADC and Sigma-Delta modulator for analog-to-digital conversion enables it to reach the level required by the current market.

Description of drawings

Fig. 1 is the composition block diagram of the temperature measurement circuit of the present utility model;

FIG. 2 is a schematic diagram of an embodiment of the temperature measurement circuit of the present invention.

Detailed ways

The temperature measurement circuit of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, but this is not intended to limit the present invention.

Referring to Fig. 1, it is a block diagram of the temperature measurement circuit of the present invention. In this architecture, the temperature measurement circuit includes a temperature sensing circuit 100 , an analog-to-digital conversion circuit 200 and a digital processing circuit 300 .

Wherein, the temperature sensing circuit 100 is used for outputting a first voltage V ₁ and a second voltage V ₂ representing temperature changes. The temperature sensing circuit 100 includes a bias current source 110 having a first output terminal outputting a first current I ₁ and a second output terminal outputting a second current I ₂ . The temperature sensing circuit 100 also includes a first MOS transistor M ₁ and a second MOS transistor M ₂ , both of which are configured as a diode-connected type, that is, the gates and drains of the two MOS transistors M ₁ and M ₂ are connected and grounded, and, The source of the first MOS transistor M ₁ is connected to the first output terminal, that is, receives the first current I ₁ , and the source of the second MOS transistor M ₂ is connected to the second output terminal, that is, receives the second current I ₂ . The first voltage V ₁ output by the temperature sensing circuit 100 is the gate-source voltage V _GS1 of the first MOS transistor M ₁ or the gate-source voltage V _GS2 of the second MOS transistor M ₂ , and the second voltage V ₂ output by it is M ₁ and The difference between the gate-source voltage of M ₂ is ΔV _GS shown in FIG. 2 .

As shown in FIG. 2 , the first MOS transistor M ₁ and the second MOS transistor M ₂ are preferably PMOS transistors, and the first current I ₁ is m times, preferably 5-10 times, the second current I ₂ . Thus, the temperature sensing circuit 100 uses diode-connected PMOS transistors biased at different current densities to sense the external temperature, and can obtain the first voltage V ₁ , that is, the negative temperature coefficient voltage V _GS (V _GS1 or V _GS2 ), by changing the current ratio between the first current I ₁ and the second current I ₂ , the second voltage V ₂ , that is, the positive temperature coefficient voltage ΔV _GS , can be adjusted, and the temperature can be measured through subsequent circuits.

Since the gate-source voltage V _GS of the MOS tube is approximately equal to 0.3V at normal temperature, and the base-emitter voltage V _BE of the conventional temperature sensing element triode is approximately equal to 0.7V, it can be seen that the V _GS of the MOS tube is lower than the V _BE of the triode Many, so it can work at lower supply voltages. Compared with the prior art, the temperature sensing circuit 100 uses MOS transistors to sense temperature, which reduces the power consumption of the system while simplifying the circuit design. At the same time, since it can work at a lower power supply voltage, its application range is wider.

The principle of obtaining the measured temperature value from the first voltage V ₁ (ie, the negative temperature coefficient voltage V _GS ) and the second voltage V ₂ (ie, the positive temperature coefficient voltage ΔV _GS ) outputted by the temperature sensing circuit 100 is described as follows. The positive temperature coefficient voltage ΔV _GS and the negative temperature coefficient voltage V _GS can be combined into a zero temperature coefficient voltage V _REF . And the zero temperature coefficient voltage V _REF =V _GS +α·ΔV _GS , where α is a constant value of 14˜18.

Then, according to the following formula (1), the coefficient r positively correlated with temperature can be obtained:

$r=\frac{\mathrm{\α}\·{\mathrm{\ΔV}}_{\mathrm{GS}}}{\mathrm{\α}\·{\mathrm{\ΔV}}_{\mathrm{GS}}+V_{\mathrm{GS}}}=\frac{\mathrm{\α}}{\mathrm{\α}+\frac{V_{\mathrm{GS}}}{{\mathrm{\ΔV}}_{\mathrm{GS}}}},$ Formula 1)

Among them, α is a constant, the value is 14~18, is the ratio of the first voltage V ₁ (ie, the negative temperature coefficient voltage V _GS ) output by the temperature sensing circuit 100 to the second voltage V ₂ (ie, the positive temperature coefficient voltage ΔV _GS ).

Finally, according to the principle of determining a straight line based on two points, the mapping relationship between the coefficient r positively correlated with temperature and the temperature value Temp can be obtained, namely:

Temp＝A*r-B, Formula (2)

Among them, A=580-620, B=260-280.

In order to improve the digitization accuracy of the ratio of the first voltage _V1 to the second voltage _V2 , the temperature measurement circuit of the present invention further includes an analog-to-digital conversion circuit 200, which is used to convert the analog quantity of the voltage signal containing temperature information into A bit stream with a data bit width of 1 bit. Wherein, the analog quantity of the voltage signal containing temperature information is the ratio of the first voltage _V1 to the second voltage _V2 , that is, the ratio of the negative temperature coefficient voltage V _GS to the positive temperature coefficient voltage ΔV _GS

in the analog When digitizing, the integer part and the fractional part are converted separately. The analog quantity can be decomposed, namely:

$\frac{V_{\mathrm{GS}}}{{\mathrm{\ΔV}}_{\mathrm{GS}}}=\mathrm{no}+\mathrm{\μ},$ Formula (3)

Where n is the integer part and μ is the fractional part.

The analog-to-digital conversion circuit 200 includes a SAR (Successive Approximation Register) ADC (Analog-Digital Converter) 210 and a Sigma-Delta modulator 220, wherein the SAR ADC 210 converts the integer part n of the analog quantity, and the Sigma-Delta modulation The device 220 converts the fractional part μ of the analog quantity.

Referring to FIG. 2 , the analog-to-digital conversion process of the analog-to-digital conversion circuit 200 is described.

Firstly, use SAR ADC (preferably 5-bit SAR ADC) 210 to perform rough conversion, and compare V _GS with an integer multiple of ΔV _GS to obtain an integer part n and store it in a register.

Next, the Sigma-Delta modulator 220 completes the fine conversion, that is, when the comparator outputs the first state (for example, the output is 1), the Sigma-Delta modulator 220 integrates V _GS -(n+1)·ΔV _GS , when the comparator When the second state is output (for example, the output is 0), V _GS −n·ΔV _GS is integrated. After working for a period of time, according to the principle of charge conservation, that is:

(1-μ)·(V _GS −n·ΔV _GS )+u·(V _GS −(n+1)·ΔV _GS )=0, formula (4)

According to the following formula (5), the value of the fractional part can be obtained:

$\mathrm{\μ}=\frac{V_{\mathrm{GS}}}{{\mathrm{\ΔV}}_{\mathrm{GS}}}-\mathrm{no},$ Formula (5)

Wherein, the integer part n has been converted by the SAR ADC 210.

Thus, the analog-to-digital conversion circuit 200 obtains The digitized value of the integer part n and the fractional part μ, that is, we get It is output to the digital processing circuit 300 . The digital processing circuit 300 includes a sinc ³ digital filter, which is used to extract and filter the 1-bit bit stream output by the analog-to-digital conversion circuit 200 to become a digital signal. The bit width of the digital signal can be selected according to the accuracy requirements, for example , the optional data bit width is 12 bits. Dividing the 12-bit data by 4096 can obtain the coefficient r positively correlated with temperature in formulas (1) and (2), thereby obtaining the temperature value Temp to be measured. The obtained temperature value Temp can be stored in a memory, and can be directly read by an external entity through a digital communication interface.

The analog-to-digital conversion circuit 200 of the temperature measurement circuit of the present utility model adopts a structure combining a SAR ADC210 and a Sigma-Delta modulator 220 to form a high-speed and high-precision analog-to-digital converter. Since the integer and the fractional part are quantized separately, while ensuring the high precision of quantization, the accuracy requirement of the Sigma-Delta modulator 220 is reduced (for example, it is not necessary to adopt the double-precision Sigma-Delta modulator as disclosed in the patent document CN102435336A, can also achieve digitization accuracy higher than that of the literature). Since the accuracy requirement of the Sigma-Delta modulator 220 is reduced, that is, its oversampling rate does not need to be too high, its working time is greatly shortened, thereby reducing the average power consumption of the system; at the same time, the output swing of the operational amplifier and the sampling capacitor Requirements are also reduced, further reducing system power consumption.

The temperature measurement circuit of the utility model is suitable for on-chip integration, and uses the characteristics of the diode-connected MOS tube to generate a temperature-related voltage signal. It has the characteristics of low power consumption and can be applied to chip circuit systems with low power supply voltage; using SAR The combination of ADC and Sigma-Delta modulator for analog-to-digital conversion enables it to reach the level required by the current market.

The above specific implementations are only exemplary implementations of the utility model, and cannot be used to limit the utility model, and the protection scope of the utility model is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements to the present invention within the spirit and protection scope of the present invention, and these modifications or equivalent replacements should also be deemed to fall within the protection scope of the present invention.

Claims (6)

1. A temperature measurement circuit comprising a temperature sensing circuit which outputs first and second voltages representing temperature variations, said temperature sensing circuit comprising: a bias current source comprising first and second output terminals outputting first and second currents, respectively; The first and second MOS transistors are both configured such that the gate and the drain are connected and grounded, the source of the first MOS transistor is connected to the first output terminal, and the source of the second MOS transistor is connected to the The second output, where, The first voltage is a gate-source voltage of the first or second MOS transistor, and the second voltage is a difference between the gate-source voltages of the first and second MOS transistors. 2. The temperature measurement circuit according to claim 1, characterized in that, the temperature measurement circuit further comprises an analog-to-digital conversion circuit for converting the analog quantity representing the ratio of the first voltage to the second voltage into bit The analog-to-digital conversion circuit includes a SAR ADC and a Sigma-Delta modulator, wherein the SAR ADC converts the integer part of the analog quantity, and the Sigma-Delta modulator converts the fractional part of the analog quantity. 3. The temperature measurement circuit according to claim 2, characterized in that, the temperature measurement circuit also includes a digital processing circuit, which filters and extracts the bit stream to obtain the measured temperature value and stores the temperature value . 4. The temperature measurement circuit according to claim 1, wherein the first and second MOS transistors are both PMOS transistors. 5. The temperature measuring circuit according to claim 1, wherein the first current is 5-10 times of the second current. 6. The temperature measurement circuit according to claim 3, wherein the digital processing circuit includes a sin c ³ digital filter to perform the filtering and decimation processing.