JPS64759B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-wire temperature transmission semiconductor device that obtains an output current proportional to absolute temperature by operating two transistors with different emitter areas with equal collector currents.

Conventionally, this type of temperature-sensitive element includes a temperature-measuring resistor, a thermistor, and the like. Since all of these elements are large, there are problems when embedding or pasting them in the temperature measuring section. Furthermore, since the outputs of temperature sensing elements such as resistance temperature detectors and thermistors are not linear, it is necessary to linearize these outputs as necessary when attempting to utilize these outputs.

The present invention has been made in view of these points, and can be realized with a single part and has a small size.
A two-wire temperature transmission semiconductor device that can obtain a linearized output with respect to temperature has been realized.

FIG. 1 is an electrical connection diagram showing an embodiment of the present invention. FIG. 2 is a diagram showing the relationship between the base potential and collector current of each of transistors Q ₁ , Q ₂ , and Q ₃ in the circuit shown in FIG. 1. The present invention will be explained in detail below using the drawings.

In FIG. 1, transistors Q ₁ to Q ₃ and resistor R ₁ constitute a temperature sensing section. Here, the emitter area of transistor Q ₁ is expressed as transistor Q ₂ , Q ₃
(K is a constant greater than 1). Generally, the emitter current density Je of a transistor is given by the following equation.

Je=1/αJ _s (e ^qVb/kT −1) (1) However, J _e ; Emitter current density J _s ; Emitter saturation current density α ; Base-grounded current gain V _b ; Base-emitter voltage q ; Electron charge k: Boltzmann's constant T: absolute temperature Solving equation (1) for the base-emitter voltage V _b yields V _b = kT/qln (αJe/Js+1) (2). Generally, since Je≫Js, it can be considered that αJe/Js≫1, and V _b is approximately expressed by the following equation.

V _b =kT/qlnαJe/Js (3) Transistors Q ₁ and Q ₂ are operated with the same collector current, and their emitter current densities are Je ₁ , Je ₂ ,
If the emitter saturation current density is Js ₁ , Vs ₂ and the common base current gain is α ₁ , α ₂ , then the difference voltage between the base-emitter voltage V _b1 of transistor Q ₁ and the base-emitter voltage V _b2 of transistor Q ₂ is △ V _b can be expressed as follows using equation (3).

△V _b ＝V _b2 −V _b1 ＝kT／qlnα ₂ Je ₂ Js ₁ ／α ₁ Je ₁ Js ₂ (4
) If transistors Q ₁ and Q ₂ are manufactured on the same silicon chip, their characteristics will be well matched, so α ₁ =
It may be considered that α ₂ , J _s1 = J _s2 . Therefore, equation (4) can be simplified as shown below.

△V _b =kT/qlnJ _e2 /J _e1 (5) Since the emitter current density J _e is inversely proportional to the emitter area, equation (5) can be further simplified as the following equation.

△V _b = kT/qlnK (6) This differential voltage △V _b occurs across the resistor R ₁ shown in Figure 1, so the current I ₁ flowing through this resistor R ₁
can be expressed by the following equation.

I ₁ = △V _b / R ₁ = kT / qR ₁ lnK (7) As can be seen from Figure 1, the current flowing through transistor Q ₁ is I ₁ , the current flowing through Q ₂ is I ₂ and the current is flowing through Q ₃ .
I ₃ each takes the same value. Therefore, the output current I ₀ of the circuit shown in FIG. 1 can be expressed by the following equation.

I ₀ = I ₁ + I ₂ + I ₃ = 3I ₁ = 3kT/qR ₁ lnK (8) Here, K is the transistor Q ₁ as described above.
The ratio of the emitter area of Q2 to the emitter area of transistor _Q2 is a constant greater than 1. As can be seen from equation (8), the output current of the temperature sensing circuit, ie, the output current I ₀ of the circuit according to the present invention, is proportional to the absolute temperature T. By drawing this output current I ₀ to the outside through two wires from terminals 1 and 2, the circuit shown in FIG. 1 can be used as a two-wire temperature transmission circuit. In FIG. 1, R _L is a load that receives this output current. Although a resistor is shown as a load in the figure, any device that can input current in place of the resistor may be used. Among the output terminals, terminal 1 is connected to a junction point A of currents I ₁ , I ₂ , and I ₃ , and terminal 2 is connected to a negative polarity power source V ⁻ .

The above explanation is based on the assumption that currents of the same value are flowing through the transistors Q ₁ and Q ₂ . In reality, the circuit tends to become unbalanced due to various factors such as temperature changes and power supply voltage fluctuations.
In the present invention, an unbalance detection circuit is provided which extracts the unbalance amount of the collector current _Ic1 flowing through the transistor _Q1 and the collector current _Ic2 flowing through the transistor _Q2 as a differential voltage, and the differential voltage generated by this unbalance detection circuit is provided. is amplified by a differential amplifier, and this amplified signal is transmitted to the transistors that make up the differential amplifier.
Collector currents I _c1 and I _c2 are stabilized by negative feedback to the unbalance detection circuit through a circuit including Q ₄ , Q ₅ and transistors Q ₁ , Q ₂ , and _{Q 3} .

In FIG. 1, it is assumed that the current gain β of all transistors is sufficiently large. Transistor Q ₆ ,
Since Q ₇ and Q ₈ constitute a current mirror circuit, the collector current I ₆ flowing through transistor Q ₆ and
The collector current I ₇ flowing through the transistor Q ₇ is equal to
I ₆ = I ₇ . In the collector of transistor Q ₆ ,
The base of transistor _Q10 of the unbalance detection circuit is connected to form a feedback circuit. Further, the collector of transistor _Q7 and the base of transistor _Q8 are connected. Furthermore, the collector of transistor Q ₆ is connected to the collector of transistor Q ₄ , and the collector of transistor Q ₇ is connected to the collector of transistor Q ₅ , respectively. Here, transistors Q ₄ and Q ₅ constitute a differential amplifier circuit that amplifies the differential voltage ΔV _b . In such a connection, the collector current I ₄ of the transistor Q ₄ and the collector current I ₅ of the transistor Q ₅ are respectively expressed by the following equations.

I ₄ = I ₆ + I _L (9) I ₅ = I ₇ + I _B (10) Here, current I _L is the feedback current flowing from the base of transistor Q ₁₀ to the collector of transistor Q ₄ , and current I _B is the feedback current flowing from the base of transistor Q 10 to the collector of transistor Q ₈ . is the current flowing from the base of Q5 to the collector of transistor _Q5 . The value of the feedback current I _L is I _L = (I _c1 + I _c2 )/assuming the current amplification factors of transistors Q ₉ and Q ₁₀ to be β ₉ and β ₁₀ , respectively.
It is expressed as β ₉ β ₁₀ and is sufficiently small compared to the current I ₆ so it can be ignored. Furthermore, the current I _B shown in equation (10) can be ignored compared to the current I ₇ for the same reason. Therefore, the current I ₄ flowing through the transistor Q ₄ and the current I ₅ flowing through the transistor Q ₅ are equal.

In the circuit shown in Figure 1, in an equilibrium state, the current I _c flowing through the transistors Q ₁ and Q ₂ of the temperature sensing section is
₁ and I _c2 are equal. Also, in Figure 1,
Transistors Q ₉ and Q ₁₀ and resistors R ₂ and R ₃ connected between the collectors of these transistors and the collectors of transistors Q ₁ and Q ₂ , respectively, constitute an unbalance detection circuit. In this unbalance detection circuit, the base of transistor Q ₉ is connected to the emitter of Q ₁₀ , and the collector of transistor Q ₉ and Q ₁₀
The collectors of the transistor Q ₉ are connected,
Q ₁₀ is connected to Darlington. In the equilibrium state, the current I _c flowing through the temperature sensing transistor Q ₁
The voltage drop caused by the _current I _{c2 flowing through the detection resistor R 2} and the voltage drop caused by the current I _c2 flowing through the temperature sensing transistor Q ₂ flowing through the detection resistor R ₃ are equal to each other. Therefore, the voltage difference between the two is ΔV _d =0V.

Now, for some reason, the equilibrium state of the current has been disrupted.
Suppose that I _c1 ≠ I _c2 . As an example of this, the base potentials of transistors Q ₁ , Q ₂ , Q ₃ shown in FIG.
Consider the case where the equilibrium point shifts from point a to point b. That is,
The value of current I _c2 is I _c2 = I _c1 +i. Here, if we use the identification signal as it is as the value of the resistor, the differential voltage to the differential amplifier is △V _d = i・
It becomes _R3 . In an unbalanced signal amplification circuit consisting of transistors Q ₄ and Q ₅ receiving this differential voltage △V _d ,
Transistor Q ₄ receives the differential voltage ΔV _d and is biased more shallowly than in the balanced state. Therefore, the collector current I ₄ flowing through the transistor Q ₄ decreases by Δi ₄ .

Naturally, the feedback current I _L to the unbalance detection circuit also decreases by Δi ₄ . If the current amplification factors of transistors Q ₉ and Q ₁₀ are β ₉ and β ₁₀ , respectively, then transistors Q ₉ and
Collector current I _c1 +I _c2 flowing through transistors Q ₁ and Q ₂ is reduced by β ₉ and β ₁₀ △i ₄ due to Q ₁₀ . Therefore, since the base currents flowing to transistors Q ₄ and Q ₅ of the differential amplifier both decrease, current I ₃ flowing to transistor Q ₃ decreases. As the current I ₃ decreases, the base potential V _b3 of the transistor Q ₃ decreases,
At the same time, the base potential of transistors Q ₁ and Q ₂
V _b1 +RI ₁ and V _b2 also decrease. Conversely, when the operating point in FIG. 2 changes from point a to point C, the operation is the opposite of the above operation, and a feedback loop is constructed so that it is always stabilized at the equilibrium point a. In FIG. 1, the capacitor _C1 connected between the base and collector of the transistor _Q4 is for circuit stabilization.

As explained in detail above, in the circuit shown in FIG. 1, the collector currents I _c1 and I _c2 flowing through the temperature sensing transistors Q ₁ and Q ₂ are always equal in value and stable. This simply means that the output current I ₀ of the circuit according to the present invention is stable. In order for the above-mentioned currents I _c1 and I _c2 to be stable, it is necessary that the unbalance detection resistors R ₂ and R ₃ have the same value and have the same temperature coefficient of resistance. By manufacturing the resistors R ₂ and R ₃ from thin film resistors, for example, it is possible to achieve very good matching of characteristics. On the other hand, two-wire signal transmitters require particularly high output stability against power supply voltage fluctuations. When this two-wire signal transmitter is configured with a differential amplifier using a current mirror, the collector potential of one of the differential pairs, which are the components of the differential amplifier, is normally swung to the power supply voltage, so the transistor This results in constant current imbalance due to the finite collector output resistance of the output current, resulting in large fluctuations in the output current. In the circuit configuration according to the present invention, as shown in FIG. 1, the collector potential of transistors Q ₆ and Q ₇ forming a current mirror is
By maintaining a constant potential difference (approximately twice the base-emitter voltage of the transistor) with respect to the positive power supply voltage V ⁺ , the output current is highly stabilized against fluctuations in the power supply voltage.

Now the bases of transistors Q ₆ , Q ₇ , Q ₈ , Q ₉
If the emitter voltages are V _B6 , V _B7 , V _B8 , and V _B9 respectively, then the collector potentials V _A and V B9 of transistor Q ₆ are
The collector potential V _B of Q ₇ is expressed by the following equations.

V _A =V ⁺ −V _B9 −V _B10 (11) V _B =V ⁺ −V _B7 −V _B8 (12) From equations (11) and (12), the potentials of V _A and V _B are equal to the power supply voltage V It can be seen that even if ⁺ changes, the potential is maintained at the same potential. Since the collector output resistances of the transistors Q ₄ and Q ₅ can be considered to be almost the same, no imbalance occurs between the collector currents I ₄ and I ₅ of these transistors. Therefore, the output current I ₀ is hardly affected by power supply voltage fluctuations.

In addition, the bases of temperature sensing transistors Q ₁ and Q ₂
The collector-to-collector voltage is kept constant over the entire operating temperature range for the following reasons. In Figure 1, the bases of differential amplification transistors Q ₄ and Q ₅
Both emitter voltages have a temperature coefficient of -2 mV/K. A current _{I 3 flowing} through the transistor Q 3 receiving the emitter currents of the transistors Q ₄ and Q ₅ .
can have a temperature coefficient of +0.33 μA/K by appropriately selecting the value of resistor R ₁ in equation (8). Here, the point where the emitters of transistors Q ₄ and Q ₅ are joined and the point where the emitters of transistors Q 4 and Q 5 are connected
The resistor R ₄ connected between the collector of Q ₃ ,
If the value of the resistor R ₄ is designed to be 6KΩ, the temperature coefficient of the voltage drop caused by the flow of the current I ₃ will be 6KΩ×0.33μA/K=+2mV/K. This +
Since 2 mV/K and the temperature coefficient of the base-emitter voltage of the transistor Q ₄ or Q ₅ -2 mV/K cancel each other out, the base-collector voltage of the transistors Q ₁ and Q ₂ is always kept constant, and as a result, A stable output current I ₀ can be supplied. In FIG. 1, a junction point B between the collector of the transistor Q ₃ and one end of the resistor R ₄ is a connection point to the silicon substrate. In actual design, the value of the output current I ₀ is determined as follows. That is, in equation (8), the value of the emitter area ratio K is determined to be 2. And the output current _I0 is 1μA/
If it is designed so that K, the difference in resistor _R1 will be 179.2Ω from equation (8). As the resistor _R1 , for example, a thin film resistor can be used as described above.

In FIG. 1, the field effect transistor Q ₁₁ is used to operate the temperature sensing transistors Q ₁ and Q ₂ by passing a drive current through the detection resistors R ₂ and R ₃ of the unbalance detection circuit when the power is turned on. It is unnecessary once the circuit starts working.

As can be seen from FIG. 1 and the above description, the present invention is aimed at integrated circuits. Therefore, by integrating this, it can be housed in one package, resulting in extremely compact size. This is useful when the temperature signal transmitter according to the present invention is embedded or attached to a temperature measuring section and the temperature measuring section is small or narrow.

As described in detail above, according to the present invention, it is possible to realize a two-wire temperature transmission semiconductor device that can obtain a linearized output with respect to temperature and is highly stable with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is an electrical connection diagram showing an embodiment of the present invention. FIG. 2 is a characteristic diagram showing the characteristics of the circuit shown in FIG. 1. _R1 to _R4 ...Resistor, _Q1 to _Q10 ...Transistor,
Q ₁₁ ...Field effect transistor, 1, 2...Output terminal, C ₁ ...Capacitor.

Claims (1)

[Claims] 1. At least one of them is composed of first, second, and third transistors with different emitter areas, the bases of which are connected to each other to obtain an output current proportional to the absolute temperature to be measured, and a temperature sensing section that receives a feedback signal. Unbalance detection comprising: a feedback section that supplies collector current flowing to the collectors of the first and second transistors; and a detection section that is connected between the collectors of these transistors and detects an unbalanced amount of these collector currents. an unbalanced signal amplifying circuit connected to the collector of the third transistor and amplifying the unbalanced amount as input; A two-wire temperature transmission semiconductor device, characterized in that the output current is the sum of currents that flow back to the emitters of the first, second, and third transistors.