JPS6091702A - Constant voltage circuit - Google Patents

Abstract

PURPOSE:To obtain a reference voltage any temperature characteristic by outputting the sum between a base-emitter voltage of a transistor (TR) having a negative temperature characteristic and a voltage drop of a resistor having a positive temperature characteristic. CONSTITUTION:A band gap reference circuit is provided with a resistor R2, a TRQ2, a path of a current I2 flowing to a resistor R3 and a path of a current I3 flowing to resistors R2, R4. The voltage drop having a positive temperature characteristic generated across the resistor R2 is changed by the sum of the currents I2, I3 by adjusting the resistance value of the resistors R2-R4. A desired reference voltage VREF1 without any temperature characteristic is obtained by adding a base-emitter voltage of a TRQ3 having a negative temperature characteristic to said voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a constant voltage circuit used in obtaining a reference voltage in various electronic devices.

[Background technology]

There are various types of constant voltage circuits, one of which is called a bandgap reference circuit among those skilled in the art. A bandgap reference circuit is a circuit that obtains a stable and highly accurate reference voltage without temperature characteristics, and has a negative temperature coefficient of the base-emitter junction and a pair of base-emitter junctions biased at different current densities.
Temperature compensation is performed using the positive temperature coefficient of the voltage difference between the emitter junctions.

The overall temperature coefficient of the bandgap reference circuit is
The output voltage (constant voltage) becomes zero only when it exactly matches the forbidden band width of silicon, that is, the value of the p-band gap (approximately 1.2 V). This means that the output voltage obtained when the temperature coefficient is zero is fixed at approximately 1.2 .mu. and cannot be varied. However, various electronic circuits require different reference voltage levels; for example, TT L (Transister 'I'
As the reference voltage for the ister Logic) circuit, 1, 4■, which is an intermediate voltage between the low level (O, SV) and the level (2■), is optimal as the reference voltage. However, studies by the present inventor have revealed that when a bandgap reference circuit is used as a reference power source for a TTL circuit, the reference voltage of 1.4■ has a temperature coefficient, making it impossible for the TTL circuit to operate stably. was made into The present invention has been made in view of the above-mentioned problems.

[Purpose of the invention]

An object of the present invention is to provide a constant voltage circuit that can arbitrarily set an output voltage that does not have a temperature coefficient.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief summary of the invention disclosed in this application is as follows.

That is, in the bandgap reference circuit, a first current path is made up of resistor R7 and transistor Q2 r, and a second current path is made up of resistor R2 and resistor R4.
By providing a current path and adjusting the resistance value of the resistor, the resistance value is increased by the sum of the currents obtained from the two current paths.

By changing the amount of voltage drop with positive temperature characteristic that occurs in Q, and adding to this the pace-emitter voltage of transistor Q, which has negative temperature characteristic, it can be set arbitrarily and has no temperature characteristic. This achieves the object of the present invention, which is to obtain a reference voltage.

[Embodiment 1] Hereinafter, a first embodiment of a constant voltage circuit to which the present invention is applied will be described with reference to FIG. In this embodiment, a case will be considered in which the output voltage of the bandgap reference circuit is made to have no temperature coefficient at 1.4. It is assumed that the constant voltage circuit shown in FIG. 1 is a bandgap reference circuit, and is constituted by a semiconductor integrated circuit.

+VCC power is supplied to the No. 1 terminal. The output voltage, that is, the reference voltage VREF□ appears at the second terminal. The resistor paste defines the current t flowing through the transistor Q together with the power supply Vcc. For example, 1. =600
It is set to μA. For example, if it is ■cc-10■. Pace-emitter voltage of transistor Q1■
BEI is applied to the gate of transistor Q, turning transistor Q2 on. Therefore, it is one ■. ,
The current flowing from the power supply to the line t via the constant current circuit C8 flows through the following two current paths.

That is, from line t, to resistance R, ,) running star Q
■ To the ground line via t+resistance R8! flows. Here, the emitter size of transistor Q2 is the same as that of transistor Q1, for example, L=60
Resistor R1 is set so that μA. That is, I,
: I, = 10:1 relationship. Further, a resistor R4 is connected in series to the resistor R6, and the series line 1. resistance R from
,,R.

Current ■3 flows to the ground line via. Therefore, a current of I, +I flows through the resistor R7.

The reference voltage VREF□ obtained at this time is expressed as follows.

VBIP□=■t+r, qa + (It + Is
) By partially differentiating both sides of Rt(1) equation with respect to temperature T, we obtain:

avBgq:1 =α3, equation (2) can be written as follows.

θT In equation (3), α is the temperature coefficient of VREF, α1. α
2°α3 are transistors Q1 . Qt, Qs
represents the temperature coefficient of the base-emitter voltage of

Equation (3) is further It can be transformed into

Here, α3 in equation (4). Pay attention to (α, −α,). In general, a PN junction has a negative temperature coefficient, so α,
is a negative temperature coefficient. Specifically, according to the research of the present inventors, α = 2.1 mV/C.
The temperature coefficient of the N junction depends on the current density flowing through the diode, and the larger the current density, the smaller the temperature dependence of the diode, and the smaller its negative temperature coefficient. In this embodiment, as described above, for example, the current density I, :I,
= 10:1, the absolute value of the negative temperature coefficient of Vile of transistor Qt is larger than the negative temperature coefficient of Vilg of transistor Q, and as a result, α, -α , has a positive value. That is, it has a positive temperature coefficient. Specifically, according to research by the present inventors, α, -αt = +0.21 mV.

0 is obtained. In other words, the reference voltage VREF□ is expressed as shown in equation (1). Here, VBEQI VIllCQ2 ”△V
Letting it be BIC, △■ can be calculated as follows. In other words, as mentioned above, when setting <I, :I, = 10:1, V
BE□ and VBゎ have the following relationship.

Here, K is Boltzmann's constant and T is the absolute temperature.

q is the electron charge * "I41s IB2tj dark current in the PN junction. Therefore, in transistors Q, , Q, with the same emitter size, if the dark current I, 1 = I, , then kTI.

△VBE =tn-=2.3 x 26 (mV) l
0g1610q I! Obtain 60mV = 0.06V in the middle.

Also VB, 0. = 0.7 V, then R,,R,
.

VREF□=0.7+-0,7+-0,06=1.
4 ・Song・(6) R, R.

Also, as mentioned above, set <I, = 60μA, dR3 =
”” ”EQ2=!=1000Q=lK1”AI,
60 (μA).

Therefore, equations (5) and (6) can be written as follows.

Considering (7) and (8) as simultaneous quadratic equations with R2 and R4 as variables, and subtracting the values of Rt and R4, we obtain Ω in R, #10.7Kfl, and R4, #129.

Therefore, in the circuit in FIG. 1, Vcc=lOV
, Ω at R,1=15.5, Ω at R,=10.7.

If we set Rs ” I KΩ, R, = 129 as Ω, we get
A stable reference voltage that does not have a temperature coefficient of 1.4■ can be obtained. However, in this example, R4=
129 requires a high resistance of Ω, which poses a problem when fabricated into a semiconductor integrated circuit.

For this reason, the inventor of the present invention has further studied the constant voltage circuit and has come up with a circuit technology suitable for semiconductor integrated circuits without significantly changing the resistance value.

[Embodiment 2] Next, a second embodiment of the present invention will be described with reference to FIG. Note that the same reference numerals are given to parts that perform the same circuit operations as in the first embodiment, and the explanation thereof will be omitted. In addition,
In this embodiment as well, consider the case where ■REF□ is 1.4V and has no temperature coefficient.

1. First, set the reference voltage REF1. In this embodiment, there are three current paths. That is, line t,, R2°Rt',
Qt, the path through which the electrician flows through Rs, line t+
There is a path through which current 14 flows through lines t, , R, , t', and Qs through rTLt+Rr+. Therefore, VREFI is as follows.

VREFI −VBEQ3 + I; + (It
+ Is ) Rt ... (1) Here I3 is (2)
It is expressed as the formula.

Substituting equation (2) into equation (1) and transforming it, one-way work t =
(VBEQ to ■BEQ2)/Rs, so (3)
The formula can be further transformed as follows.

Next, when equation (4) is partially differentiated with respect to temperature T, equations (3) and (5) can be written as follows.

VREF□=AI, +BV□, 3...four times...song...
(6)■ In order to prevent REF1 from having a temperature characteristic at 1.4V, use equation (6), (in the force equation, VREF
□=1.4V.

Since α=0, from equation (8) and (9), when A and B are included, Rt = (B D ”4 −-0.Q21 Now, I,
=800μA, I, =80μA (i.e. I, : L
=10:1), and Vcc=
10■, R4 is set to 5 and Ω, and as in Example 1, α,
= -2,1mV/l z△α=+0.21 mV/
℃.

If VBE, 3 = 0.7 V, then the formula (1(1,00
From the formula, A=8076.92 B=1.077 2〇2. (R from 1:1, = 3829.8f)) # To 3.830, QR2=
3845 (c) #3.Obtain Ω to 845.

That is, in this embodiment, ■cc=1o■.

R,=11.63 is Ω, ,=3.83 is Ω, R+,
' = 3.85, Q, s = 0.75 K, Q,
By setting R4=5KO, a stable reference voltage without a temperature coefficient can be obtained. Further, the resistance values of the above-mentioned resistors are not so large, and there is no problem when this circuit is integrated into a semiconductor circuit.

In the embodiment, a case was considered in which a reference voltage of 1.4 square meters having no temperature coefficient was obtained, but it goes without saying that according to the present invention, the reference voltage value can be set freely. for example,
In Example 2, by substituting the desired voltage value into VRBF□ in equation (6) and solving the simultaneous equations with equation (7), the resistance value of the resistor constituting the constant voltage circuit can be found, and the temperature coefficient It is possible to set circuit constants to obtain a desired reference voltage. Note that the base and collector of the transistor Q1 do not need to be directly connected; a resistor may be connected to the collector, and the resistor and the base may be connected.

〔effect〕

The sum voltage of the pace-emitter voltage of the transistor Q, which has a negative temperature coefficient, and the voltage drop of the resistor R1, which has a positive temperature coefficient, is outputted, and further, the resistor R1,l 几! ' etc., and by carefully setting these resistance values, it is possible to obtain a stable constant voltage power supply that has temperature characteristics and is set at a desired voltage level.

[Application field]

In the above description, the invention made by the present inventor was mainly applied to a constant voltage circuit, which is the field of application to which the invention is based, but the invention is not limited thereto.

For example, it can be used not only as a reference power supply circuit for TTL circuits, but also for linear ICs and interface driver ICs.
It can also be used as a reference power supply circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a constant voltage circuit showing a first embodiment of the present invention, and FIG. 2 is a circuit diagram of a constant voltage circuit showing a twentieth embodiment of the present invention. Q,,Q,,Qs...transistor, dirt, R1゜R,
,R,'...Resistance, VB, l ■BE21 VBB
I...Pace-emitter voltage, I...Current, VR), Fl...Reference power supply.

Claims (1)

[Claims] 1. A first transistor Q whose collector and base are connected, and a first transistor Q connected to the collector Km of the transistor Q.
a second transistor Q whose base is biased by the base-emitter voltage of the transistor Qt; a second resistor R3 connected to the emitter of the transistor Q; and a second resistor R3 connected to the collector of the transistor Q. the third resistor hole, and the transistor Q! A third transistor Q whose base is biased by the collector of Q. and at least the base of the transistor Q3.
1. A constant voltage circuit whose output is a summed voltage of an emitter voltage and a voltage drop across a resistor R2, characterized in that a fourth resistor R4 is connected to the collector of a transistor Q. 2. An additional resistor Rt' is connected between the third resistor R1 and the collector of the transistor Q, and the common connection point of the third resistor R7 and the additional resistor R7' is connected to the fourth resistor Rt'. R4 is connected to the operating potential point, and the connection point between the additional resistor R1' and the collector of the transistor Q2 is connected to the base of the third transistor Q. Constant voltage circuit described in section.