TWI387736B - Low power temperature sensor operated in sub-threshold region - Google Patents

Description

Low power temperature sensor operating in the subcritical region

The present disclosure is directed to a temperature sensor, and more particularly to an ultra low power temperature sensor that is generated by operation of a MOS transistor in a subcritical region.

Taking Taiwan Patent No. I292474 as an example, it directly uses two ring oscillators which are positively and negatively correlated with temperature as a temperature sensing mechanism, and claims that it can greatly reduce wafer area, power consumption and complicated design. degree. However, the power required by various conventional temperature sensors is still too high, the required layout area is still too large, and the design complexity has not been improved.

Accordingly, one aspect of the present disclosure is to provide a low power temperature sensor that operates in a subcritical region that provides a smaller layout area, lower power consumption, and more, than various prior art techniques. Simplified design complexity.

According to an embodiment of the present disclosure, a low power temperature sensor operating in a subcritical region is mainly composed of a first field effect transistor, a second field effect transistor, a third field effect transistor, and a ring. The type of oscillator is composed. The drain of the first field effect transistor and the gate are electrically connected to a power source, and the source of the first field effect transistor is electrically connected to the gate of the second field effect transistor. The source of the second field effect transistor is electrically connected to the power source, the drain of the second field effect transistor is electrically connected to the gate of the third field effect transistor, and the second field effect crystal system is operated The critical region is to provide a critical current to a resistor, thereby generating a voltage to bias the gate of the third field effect transistor. The source of the third field effect transistor is electrically connected to the power source, and the drain of the third field effect transistor is electrically connected to the ring oscillator. Thereby, the third field effect transistor provides a driving current to bias the ring oscillator, so that the ring oscillator generates a pulse frequency signal to reflect the temperature, and the pulse wave frequency signal is negatively correlated with the absolute temperature.

According to still another embodiment of the present disclosure, a low power temperature sensor operating in a subcritical region is proposed, which is mainly composed of a first field effect transistor, a second field effect transistor and a ring oscillator. Wherein, the drain of the first field effect transistor and the gate are electrically connected to a power source, and the source of the first field effect transistor is electrically connected to the gate of the second field effect transistor, and the first field effect is The crystal system is operated in the subcritical region. The source of the second field effect transistor is electrically connected to the power source, the second field effect transistor is electrically connected to the ring oscillator, and the second field effect crystal system is operated in the subcritical region to provide A critical current is applied to the ring oscillator. Thereby, the ring oscillator is biased by the secondary critical current to generate a pulse frequency signal to reflect the temperature.

According to still another embodiment of the present disclosure, a low power temperature sensor operating in a subcritical region is proposed, which is mainly composed of a first field effect transistor and a second field effect transistor. Wherein, the drain of the first field effect transistor and the gate are electrically connected to a power source, and the source of the first field effect transistor is electrically connected to the gate of the second field effect transistor, and the second field effect is The crystal system is operated in the subcritical region. The source of the second field effect transistor is electrically connected to the power source, and the threshold voltage of the second field effect transistor is linearly positively correlated with the absolute temperature.

Through the long-term observation and years of practical experience of the present inventors, the linear correlation between the subcritical current and the absolute temperature when the transistor is operated in the subcritical region, combined with the ring oscillator, proposes a low power temperature operating in the subcritical region. The sensor is far superior to conventional techniques, such as the patent of Taiwan Patent No. I292474, which saves wafer area, lower power consumption, and has less design complexity.

Specifically, for a gold-oxygen half-field effect transistor, when V _GS >= V _TH , the transistor is in the conducting phase; and when the transistor is operated in the sub-critical region (or weak inversion) In the region), the gate voltage of the transistor gate-source V _GS is slightly smaller than the threshold voltage V _{TH of the} transistor itself (ie, V _GS <V _TH ); at this time, the gate current I _{D of the} transistor still exists. Not completely without current. Moreover, the drain current I _D is exponentially related to the gate-source voltage (V _GS ) rather than the linear region or saturation region characteristics when turned on.

Please refer to Figure 1 and Figure 2 together. Figure 1 is a diagram showing the relationship between the drain current I _D and the gate-source voltage (V _GS ) when the MOS transistor is turned on. Figure 2 is the graph. When the crystal is operated in the subcritical region, the relationship between the drain current I _D and the gate-source voltage (V _GS ) is exponential, wherein the ordinate uses logarithmic coordinates. It can be seen from FIGS. 1 and 2 that in the case of a general gold-oxygen half-field effect transistor, when the gate-to-source voltage is greater than 200 mV (ie, V _GS >200 mV), the voltage of the gate-source of the transistor is The relationship with the buckling current in the subcritical region can be expressed by the following formula: as well as Where η is a non-ideal factor (η>1), I _O is a process-related parameter, and V _T = KT / q . It can be found from the above formula that if I _D /I _O is constant, the relationship between V _GS and temperature V _T is a positive temperature coefficient.

As shown in FIG. 3, when the transistor inside the absolute temperature-dependent transistor circuit 110 of the present embodiment operates in the sub-critical region, a critical current 101, that is, a drain current I _D , whose linear value is linearly positively correlated, can be output. At absolute temperature. At this time, the drain current I _D can be converted into a current signal that is positively correlated with the absolute temperature; of course, the drain current I _D can also be converted into a current signal that is negatively correlated with the absolute temperature through the circuit design.

Please refer to FIG. 3 and FIG. 4 together. FIG. 3 is an embodiment of the disclosure, which is a block diagram of a low power temperature sensor operating in a subcritical region, and FIG. 4 is a detail of FIG. Circuit diagram. In the figure, the transistor circuit 110 is mainly composed of a first field effect transistor 111 and a second field effect transistor 112. The drain of the first field effect transistor 111 and the gate are electrically connected to a power source V _DD , and the source of the first field effect transistor 111 is electrically connected to the gate of the second field effect transistor 112. The source of the two field effect transistor 112 is electrically connected to the power source V _DD , and the second field effect transistor 112 is operated in the subcritical region, and the threshold current 101 of the second field effect transistor 112 is linearly positively correlated with Absolute temperature.

In this embodiment, as shown in FIGS. 5 to 6, a ring oscillator 620 receives the critical current 101, and generates a pulse signal sufficient to reflect the current temperature, and the frequency and absolute temperature of the pulse signal are linear. Related. Please refer to FIG. 5 and FIG. 6 , which is another embodiment of the present disclosure. After the sub-critical current generated by the absolute temperature-dependent transistor circuit 110 flows through the resistor R, the driving voltage signal may be converted into a negative driving voltage signal. The voltage signal is electrically connected to the gate of the third field effect transistor 113 in the ring oscillator 620, whereby the third field effect transistor 113 provides a driving current to bias the multistage inverting series connected oscillator, and further The ring oscillator 620 generates a pulse signal to reflect the temperature, and the pulse signal frequency is inversely related to the absolute temperature.

Please refer to FIGS. 7 and 8 together. FIGS. 7 and 8 are still another embodiment of the present disclosure, and FIG. 8 is a detailed circuit diagram of FIG. 7. In the figure, the drain of the first field effect transistor 111 and the gate are electrically connected to a voltage source V _DD . The source of the second field effect transistor is electrically connected to the voltage source V _DD , the gate of the second field effect transistor 112 is electrically connected to the source of the first field effect transistor 111 , and the second field effect transistor 112 The drain is electrically connected to the ring oscillator 120. The second field effect transistor 112 is operated in the subcritical region, and the gate current generated by the second field effect transistor 112 is positively correlated with the absolute temperature. The sub-critical current generated by the second field effect transistor 112, that is, the drain current, can be supplied to the ring oscillator 120, so that the pulse signal frequency generated by the ring oscillator 120 is positively correlated with the absolute temperature.

In other words, the present embodiment does not use a conventional analog analog-to-digital converter (ADC) which is conventionally used, because the conventional analog-to-digital converter not only causes a large increase in the power of the chip, but also causes the wafer area to become large. Therefore, the present embodiment is replaced with a ring oscillator 120. In addition, the ring oscillator 120 can be implemented by a plurality of inverters by connecting a plurality of inverters into a ring shape and then externally connecting an inverter as a signal output terminal.

The low power temperature sensor operating in the subcritical region of the present embodiment only needs two field effect transistors with opposite properties, and a ring oscillator can convert the gate current positively correlated with the absolute temperature into Frequency parameters that are positively correlated with absolute temperature do not require an additional voltage source or current source, and are far more sophisticated than conventional techniques.

Next, please refer to FIG. 6 and FIG. 9. FIG. 9 is a waveform diagram of the pulse wave frequency signal of the low-power temperature sensor operating in the sub-critical region at minus one hundred and five degrees Celsius. In this embodiment, a ring oscillator 620 composed of seven inverters is taken as an example, and a low power temperature sensor operating in a subcritical region is implemented in a wafer by a semiconductor process, and measured under the following parameters. Figure 9 is shown.

It should be noted that in the above implementation, since the threshold voltage of the N-type transistor is slightly smaller than the threshold voltage of the P-type transistor (ie, V _THN <V _THP ), the present embodiment first utilizes an N-type transistor, that is, The first field effect transistor 111 generates a voltage drop from the voltage source V _DD ; the voltage drop is used to bias the P-type transistor, that is, the second field effect transistor 112, to generate an absolute temperature-dependent current. , that is, the subcritical current 101. Wherein, since the second field effect transistor 112 operates in the subcritical region in the circuit, the current 101 of the P-type transistor is a sub-critical current. In other words, the first field effect transistor 111 is an N-type field effect transistor, the second field effect transistor 112 is a P-type field effect transistor, and the third field effect transistor 113 is also a P-type field. Effect transistor.

Specifically, taking the embodiment of FIG. 6 as an example, the overall circuit performance of the low-power temperature sensor operating in the sub-critical region is as shown in the above table, and the wafer area is only 976.1 μm ² , and the power consumption can be reduced to 129 nW. The sensing temperature range is up to about 165 ° C, and the circuit in the sensible temperature range, the output frequency and temperature relationship curve, linearity (R-square) is about 0.9943, has excellent performance.

The present invention has been disclosed in the above embodiments, but it is not intended to limit the invention, and it is obvious to those skilled in the art that various modifications and refinements can be made without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application attached.

101. . . Subcritical current

110. . . Absolute temperature dependent transistor circuit

111. . . First effect transistor

112. . . Second field effect transistor

113. . . Third field effect transistor

120, 620. . . Ring oscillator

R. . . resistance

The above and other objects, features, advantages and embodiments of the present disclosure will become more apparent and understood.

Fig. 1 is a graph showing the relationship between the drain current I _D and the gate-source voltage (V _GS ) when the transistor is operated in the conduction region.

Figure 2 is an exponential plot of the drain current I _D and the gate-source voltage (V _GS ) when the transistor is operating in the subcritical region.

3 is a functional block diagram of a low power temperature sensor operating in a subcritical region in accordance with an embodiment of the present disclosure.

Fig. 4 is a detailed circuit diagram of Fig. 3.

Figure 5 is a functional block diagram of a low power temperature sensor operating in a subcritical region of another embodiment of the present disclosure.

Fig. 6 is a detailed circuit diagram of Fig. 5.

Figure 7 is a functional block diagram of a low power temperature sensor operating in a subcritical region in accordance with yet another embodiment of the present disclosure.

Figure 8 is a detailed circuit diagram of Figure 7.

Figure 9 is a waveform diagram of the pulse wave frequency signal of the circuit of Figure 8 operating at minus one hundred and five degrees Celsius.

110. . . Absolute temperature dependent transistor circuit

111. . . First effect transistor

112. . . Second field effect transistor

120. . . Ring oscillator

Claims (12)

A low-power temperature sensor operating in a sub-critical region is mainly composed of a first field effect transistor, a second field effect transistor, a third field effect transistor and a ring oscillator, wherein: The drain of the first field effect transistor and the gate are electrically connected to a power source, and the source of the first field effect transistor is electrically connected to the gate of the second field effect transistor; the second field effect The source of the transistor is electrically connected to the power source, the drain of the second field effect transistor is electrically connected to the gate of the third field effect transistor, and the second field effect crystal system is operated a critical region for providing a critical current to a resistor, thereby generating a driving voltage to the gate of the third field effect transistor; and a source of the third field effect transistor electrically connecting the power source, and the The drain of the three field effect transistors is electrically connected to the ring oscillator; thereby, the third field effect transistor provides a driving current to bias the ring oscillator, thereby causing the ring oscillator to generate a ring oscillator Pulse signal, and the pulse signal frequency is negatively correlated with absolute temperature. A low power temperature sensor operating in a subcritical region as claimed in claim 1, wherein the ring oscillator is composed of a plurality of inverters. The low power temperature sensor operating in the subcritical region according to claim 1, wherein the first field effect transistor is an N type field effect transistor. The low power temperature sensor operating in the subcritical region according to claim 1, wherein the second field effect transistor is a P-type field effect transistor. The low power temperature sensor operating in the subcritical region according to claim 1, wherein the third field effect transistor is a P-type field effect transistor. A low-power temperature sensor operating in a sub-critical region is mainly composed of a first field effect transistor, a second field effect transistor and a ring oscillator, wherein: the first field effect transistor The drain and the gate are electrically connected to a power source, the source of the first field effect transistor is electrically connected to the gate of the second field effect transistor; and the source of the second field effect transistor is electrically Connected to the power source, the second field effect transistor is electrically connected to the ring oscillator, and the second field effect crystal system operates in the subcritical region to provide a critical current to the ring oscillation. Thereby, the ring oscillator is biased by the critical current to generate a pulse signal, and the pulse signal frequency is positively correlated with the absolute temperature. A low power temperature sensor operating in a subcritical region as recited in claim 6, wherein the ring oscillator is comprised of a plurality of inverters. The low power temperature sensor operating in the subcritical region according to claim 6, wherein the first field effect transistor is an N type field effect transistor. The low power temperature sensor operating in the subcritical region according to claim 6, wherein the second field effect transistor is a P-type field effect transistor. A low-power temperature sensor operating in a sub-critical region is mainly composed of a first field effect transistor and a second field effect transistor, wherein: the first field effect transistor has a drain and a gate Electrically connecting a power source, the source of the first field effect transistor is electrically connected to the gate of the second field effect transistor; and the source of the second field effect transistor is electrically connected to the power source, And the drain current of the second field effect transistor is linearly positively correlated with the absolute temperature. The low power temperature sensor operating in the subcritical region as claimed in claim 10, wherein the first field effect transistor is an N type field effect transistor. A low power temperature sensor operating in a subcritical region as claimed in claim 10, wherein the second field effect transistor is a P-type field effect transistor.