JPS6222087A - Battery check circuit - Google Patents

Abstract

PURPOSE:To remove the temperature dependency of the battery check voltage, and to improve the reliability of the circuit, by combining PN-junction diodes, resistors, and a comparator. CONSTITUTION:If VI1>VI2, for input terminal voltages VI1, VI2, the output terminal voltage VO of a comparator 15 is 'H', while if VI1<VI2, VO is 'L'. The current I1 varies substantially in proportion to the power supply voltage VDD. If VDD is lowered, and I1.R2 is decreased, it occurs VI1<VI2, thus the voltage VO goes to 'L'. Also, if VDD is raised and the value of I1.R2 becomes higher than (VF1-VF2), it occurs VI1>VI2, thus the voltage VO goes to 'H'. Therefore, by the presence of VDD=VB as the boundary condition between 'L' and 'H' of the voltage VO, battery check faculty is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a battery-powered computer for electronic thermometers, watches, etc.
This relates to a battery check circuit built into a MOS monolithic IC or the like.

(Prior Art) Conventionally, as a technology in this field, there has been a technology as shown in FIG. 2, for example. The configuration will be explained below.

FIG. 2 is a circuit diagram showing an example of the configuration of a conventional battery check circuit.

In Figure 2, 1 is an NMOS transistor whose source is grounded and a resistor 2 is connected between its drain and gate.
is connected. NMOS) The drain of transistor 1 is connected to output terminal 4 via inverter 3 consisting of 0MO8.
It is connected to the. The power supply voltage VDD is applied to the resistor 2, and the drain current I of the transistor 1 flows through the resistor 2 (NN09). In addition, Vl in FIG. 2 is 1. The input voltage of the inverter 3, vO, is the output voltage of the inverter 3.

Next, the operation will be explained with reference to the voltage characteristic diagram shown in FIG. In addition, in FIG. 3, the horizontal axis is the power supply voltage VDD, and the vertical axis is the voltage axis, which shows the power supply voltage VDD straight line, the input voltage VI convex curve, the input threshold voltage VTI straight line of the inverter 3, and the output voltage vO level. .

The circuit in Fig. 2 has an output voltage v when the power supply voltage VDD is low.
It operates to set the output voltage VO to the "L" level and to set the output voltage vO to the "H" level when the power supply voltage VDD exceeds a certain voltage level VB (hereinafter referred to as battery check voltage).

That is, when the power supply voltage VDD is low, the transistor l
The gate voltage of the transistor is the threshold voltage VT2 specific to that transistor.
, the drain current I decreases and the input voltage v■ shown by the following equation increases.

VI=VDD-IR However, R: resistance value of resistor 2.

As the input voltage vI increases, the threshold voltage V of the inverter 3
When it exceeds TI, the output voltage VO becomes "L" level.

Conversely, when the power supply voltage VDII is high, transistor 1
As the gate voltage increases, the drain current I increases,
Input voltage VI decreases. Input voltage vI is inverter 3
When the output voltage VO becomes smaller than the threshold voltage VTI, the output voltage VO becomes "H" level.゛Here, the power supply battery of the device is exhausted and its power supply voltage VDD becomes VDD <V
B, that is, the output voltage vO reaches the "H" level.
When the "L" level changes, a light emitting element or the like is made to blink, for example, to warn of a drop in battery voltage based on this "°L" level signal.

(Problems to be Solved by the Invention) However, the circuit with the above configuration has a problem in that the reliability as a battery check function is low because the battery check voltage VB has a large temperature dependence due to the following reasons. was there.

When considering the temperature dependence of the battery check voltage VB, first, assuming that the transistor operates in a non-saturated manner and VDD=VB, the drain current is given by the following equation.

However, β: conductance coefficient of transistor l.

The input voltage of inverter 3 (i.e., the drain voltage of transistor l) LI is VD[1=VB, VI
=VT1, so the following equation holds.

VTI=VB-I-R-(2) When v■ in equation (1) is substituted into equation (2) as VTI, the following equation is obtained.

...(3) Furthermore, by differentiating equation (3) with respect to temperature T and rearranging it, the following equation representing the temperature dependence of battery check voltage VB is obtained.

ΔVB= (4) However, it is assumed that Δ=d/dT, ΔR=0, and AVT1=0. In equation (4), Δβ/β and ΔVT2 are generally both negative values, so if one condition is set well,
It is possible to reduce ΔVB. and colo are the expression (
4) is AVB under the condition of 1/2VT1=VT2(7)
becomes infinite.

For example, VB=1.3V, VT1=0.65V, β=0.1m
Z'/V, VT2=0.5V, Δβ/p=-40
In the case of 00PPg/'C1ΔVT2=-3mV/0C and the current condition, ΔVB=-4.1mV/°C, but if only VT2 becomes VT2=0.3V under these conditions.

ΔVB=-5(,8m/''O) It is quite possible that VT2 changes by this amount, considering the variations in the normal IC manufacturing process.As the temperature rises, the battery check voltage VB changes. The change to VBD is shown as the input voltage VID curve in FIG.

A VB=-54,8m/'Ctealto, VB=1
, 3V. With a change in temperature + lO°C (7), V
BD' = 0.75V this is,
This is the type of change that makes the battery check circuit useless. As described above, the conventional circuit has a problem in that the reliability of the battery check function is low because the temperature dependence of the battery check voltage VB may become very large.

The present invention provides a battery check circuit that solves the problem of the prior art in that the battery check voltage has a large temperature dependence.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a battery check circuit for detecting changes in power supply voltage.
first and second PN junction diodes which are connected in the forward direction to the power supply and whose PN junction areas are related in size;
．． second and third resistors and a voltage comparison circuit, the first and second resistors being connected in series to the first PN junction diode, and the third resistor being connected in series to the second PN junction diode. The first and second resistance voltages and the voltage between the second PN junction diode and the third resistor are compared by a '12 voltage comparator circuit.

(Function) According to the present invention, since the batch IJ-check circuit is configured as described above, the diode acts to cancel the temperature change of the entire circuit due to the forward voltage drop having a negative temperature coefficient. This allows the voltage between the re-input terminals in the voltage comparator circuit to match (battery check voltage)
It becomes possible to reduce the temperature dependence of therefore.

The above problem can be eliminated.

(Embodiment) (I) Description of the battery check circuit in FIG. 1 FIG. 1 is a circuit diagram of a battery check circuit showing an embodiment of the present invention. In FIG. 1, 10 is a first PN junction diode, and 11 is a second PN junction diode, with the diode 11 having a larger junction area. A power supply voltage VDD is applied to the anode of the diode 10, and its source is grounded via first and second resistors 12 and 13 connected in series. The diode 11 has a power supply voltage VD at its 7th node.
D is applied, and its terminal is grounded via the third resistor 14. A voltage comparison circuit (hereinafter referred to as a comparator) 15 is provided to determine the difference between the voltage across the resistors 12 and 13 and the cathode voltage of the diode 11.

The converter 15 has its (+) input terminals 15A connected to the cathode side of the diode 11, its (-) input terminals 15B connected to the connection point between the resistors 12 and 13, and its output terminal 1
5G is connected to the output terminal 16, respectively. In addition, in FIG. 1, 11 is the current flowing through the resistor 12.13, R2
is the current flowing through the resistor 14, and VII is the current flowing through the comparator 15.
(+) input terminal voltage, VI2 is comparator 15
(-) input terminal voltage, and vO is the output terminal voltage of the comparator 15.

Next, the operation will be explained with reference to the voltage characteristic diagram shown in FIG. In addition, FIG. 4 shows the power supply voltage vDD straight line, the curves of the input terminal voltages VII and VI2, and the output voltage vO level, with the horizontal axis as the power supply voltage van and the vertical axis as the voltage axis. Further, in FIG. 4, VB is the power supply voltage when V11=VI2.

First, input terminal voltage Vll, VI2 is VII>VI2
In case (7), the output terminal voltage vO of the comparator 15 goes to “H” level, and when VII < VI2, vO goes to “L” level.
The voltages VII and VT2 are expressed by the following equations.

VH=V[l[l −VF2 ・(5)
VI2=VDI)-VFI-11-R2-(8) However,
R2: resistance value of resistor 13.

VFl, diode lO order Directional voltage drop.

VF2, diode 11 in order Directional voltage drop.

In equations (5) and (6), since the junction area of diode 11 is larger than that of diode IO, in the case of 11 bottles I2, the relationship is VFI>VF2.

The current I'l changes almost in proportion to the power supply voltage VD[l, so when VDD is low and It-R2 is small, the equation (5
).

From (6), since VII<VI2, the output voltage V
O becomes lmL" level. Conversely, when VD[] becomes high and the value of It-R2 becomes large enough to exceed (VFI-VF2), VII>VI2 and the output voltage vO becomes °"H. Therefore, the presence of the boundary point between the "L" level and "H" level of the output voltage vO, VDD=VB, provides a battery check function.

Next, the temperature dependence of the battery check voltage VB will be explained.

First, the effective junction area ratio of diodes 10 and 11 is set to 1:N.
,! -S6. VDD=VB, that is, V11=VI
2. Under the condition (7), the following equation holds true.

VB=VF2+12-R3・(7) VF2=VFl+11・R2-(8)11-R1=r
2・R3...(9) However, R1: resistance value of resistor 12.

R2, resistance value of resistor 13.

R3: resistance value of resistor 14.

When VFI and VF2 are expressed by the current flowing through the diode 10.11, the following equation is obtained.

However, K: Portzmann's constant.

Q: Amount of electric charge.

T: Absolute temperature.

Is, saturation of diode 11 sum current.

Substituting equations (9), (10), and (11) into equation (8), I
When we find 2, we get . Substituting this equation (12) into equation (7) yields.

In this equation (13), the first term, VF2, has a negative temperature coefficient. The second term is the temperature coefficient proportional to T, assuming that R1/R2 and R1/R3 have no temperature dependence.
.

Therefore, the first term and the second term cancel each other out,
It can be seen that the temperature coefficient of the battery check voltage VB becomes smaller.

VF2 of the amount related to the temperature coefficient of I2 included in VF2
The ratio of VB to the temperature coefficient is very small, so if this is ignored, the temperature dependence of VB can be expressed by the following equation from equation (13).

However, Δ=d/dT In this equation (14), for example, 1, a VF2--2mV/℃, T = 300°,
If VB=1.3V, VF2=OJV, ΔVB=
÷0.3mV/”C, which is a small value. Also, V
B=1.2V-r becomes AVB=0. Therefore, if configured as in this embodiment, a battery check circuit with low temperature dependence can be realized, thereby significantly improving reliability.

(II) Description of the battery check circuit in FIG. 5 FIG. 5 is a diagram showing a more specific example of the circuit configuration of FIG. 1.

When actually forming the circuit shown in Fig. 1 in a CMOS monolithic IC, for example, if an N-silicon substrate is used, an N--P" junction can be used for the diodes to and tt. Also, lower power consumption can be achieved. In order to calculate The circuit shown in Figure 5 will be explained in detail.

In FIG. 5, A1. -A4 is a control signal line, C is a capacitor, G1 and G2 are inverters composed of CMO9, LT is a latch circuit, 5l-S5 is an analog type switch, VGI is the input terminal voltage of inverter G1, and VB2 is the inverter This is the output terminal voltage of G1.

Resistor 12.14 is connected to terminal SIA of switch S1 and via terminal SIB of switch S1.

A control terminal SIG of the switch Sl is connected to a control signal line A1, and terminals SIA and SIB of the switch S1 are turned on and off by a signal applied from the control signal line A1.

The (+) input terminals 15A of the comparator 15 are connected to one end of the capacitor C via the terminals S2A and S2B of the switch S2, and the (-) input terminals 15B of the comparator 15 are connected to the terminals S3A and 93B of the switch S3.
It is connected to one end of the capacitor C via. The control terminal S2C of the switch S2 is connected to the control signal line A2, and the control terminal 53G of the switch S3 is connected to the control signal 11A3.

The other end of capacitor C is connected to terminal S4A of switch S4, input terminal of inverter G1, and terminal S of switch S5.
5A respectively. The switch S4 has its terminal 54B connected to the output terminal of the inverter G1 and the input terminal of the inverter G3, and its control terminal 84C connected to the control signal line A.
3 are connected to each other. The switch S5 has its terminal S5B grounded, and its control terminal S5G connected to the control signal line A1 via an inverter G2 in the opposite direction.

The output terminal of inverter G3 is connected to the data input terminal of latch circuit LT. The latch circuit LT has its latch control input terminal connected to the control signal MA4, and its output terminal Q (i.e., the output terminal 14G of the comparator 14).
) are connected to the output terminal 15, respectively.

Here, each switch 81 to S5 has its respective control terminal st
c When N5sc is at L” level, it turns off and each terminal SIA
, 5IB-95A, and S5B are open, and conversely “
When the level is “H”, it turns on and each terminal SIA, SIB -5
5A.

It operates so that S5B is short-circuited. The latch circuit LT is connected to the terminal Q when the terminal RI is at "H" level.

The signal levels of D become equal, and the terminal changes from “H” to
When it reaches the "L" level, it operates to hold the previous signal level of the terminal Q until the next terminal becomes the "H" level.

Next, the operation will be explained with reference to the signal waveform diagram in FIG. Note that FIG. 6 shows the control signal lines A1 to A4. Output voltage vO
1 and inverter G1 input/output terminal voltages VGI, VG
2 signal waveforms are shown respectively. Also, in Figure 6,
tl-t8 is time, VC is the threshold voltage of inverter G1, X is the waveform when VDD>VB, and
"Y indicates the waveform when VDD<VB.

(i) Time chart in Fig. 6 When the overall control signal line A1 is at the "H" level between times t1 and t6, the battery check circuit is in the operating state, and AI is "L".
``At level, it enters a standby state with zero power consumption.

That is, when the control signal line A1 becomes "H" level, the switch St is turned on and the switch S5 is turned off, so that the resistor 12.14 is grounded and the power supply voltage V[l
[A battery chain 2 state is created in which the magnitude relationship between the input terminal voltages Vll and VI2 changes depending on the magnitude of +. Therefore, the comparator 15 has two input terminal voltages Vll
, VI2.

(ii) Between times t1 and t2, when the control signal line A1 is at "H" level and the control signal line A3 is at "L" level, switch S3. S4 is turned on and S2 is turned off. In this state, the switch S4 short-circuits the input and output terminals of the inverter G1, so that the voltage at the input and output terminals becomes VG. Since the input type terminal voltage VI2 is applied to one end of the capacitor C and the voltage VC is applied to the other end, the capacitor C is charged with the voltage difference between the two (VC-Vr2).

(iii) Between times t2 and t4 Next, when the control signal line A2 goes to "L" level and the control signal line A3 goes to "H" level, switch S3. Since S4 is turned off and S2 is turned on, input terminal voltage VII is applied to one end of capacitor C, and only inverter G1 is connected to the other end of capacitor C. Since the inverter G1 is a CMOS inverter and has infinite input impedance, the input terminal voltage VG13 of the inverter G1 is.

VGI = V11+ (VG-VI2) -(
15). At this time, the output terminal voltage VC2 of the inverter Gl is at the "L" level if VG1 = VC, if VGI > VC, )dL, and "H" if VGI < VC.
” becomes.

From formula (15), VI2 > Vll (7),! : When V is 1 < VG to lX, when VI2 < VII, VGI > VC. The former is a case where VDD<VB, and the latter is a case where VDD<VB. Therefore, the signal level of the output terminal voltage VG2 is VDD<VBTE”H.
"L/HeJL/, V [ID >VBte" level.

(iv) Between time t4 and 78 At time t4, when the control signal line A4 becomes "H" level, the inverted signal of VO2 is output from the output terminal Q of the latch circuit LT.

While the control signal line A3 is at “H” level, the control signal line A4
When the signal returns from the "H" level to the "L" level, the output terminal Q maintains the signal level at that time and does not change until the next time the control signal line A4 goes to the "H" level.

At time t5, when the control signal line A4 changes from the "H" level to the "L" level, the battery check operation is completed.

At time 0, when the control signal line A1 goes to the "H" level, the switch S1 is turned off, the switch S5 is turned on, and the control signal iA2 is at the "L" level, so the switch S4 is turned off. Therefore, the diode 10.
Since no current flows through the inverter 11 and the input terminal of the inverter 01 (7) is fixed at the "L" level, the power consumption of the entire circuit becomes zero.

As a result of the above operation, the output voltage VO becomes H" level when VDD>VB, and the output voltage VO becomes L" level when VDD<VB, and a battery check operation is performed.

In the application of iQ and CMOS nanolithic ICs, there is often no need to constantly perform batch reach errors, so using the method described above, for example, you can check the battery every time a certain period of time elapses. By performing this operation, a battery check function with low temperature dependence can be realized without impairing the CMOS feature of low power consumption operation.

Note that the present invention is not limited to the illustrated embodiment, and various modifications are possible. It is also possible to obtain the effects of the above embodiment by reversing the polarities of diodes 10, 11 and comparator 15 in FIG. 1, or by increasing or decreasing the number of resistors 12-14.

(Effects of the Invention) As explained above in detail 9. According to the present invention 9, jf.
.

Since the battery check circuit is configured using at least two PN junction diodes, three resistors, and a comparator, the temperature dependence of the battery check voltage is extremely small, and reliability can be expected to be improved. Furthermore, since it can be easily incorporated into a CMOS monolithic IC, etc., it is very effective for use in applied products such as battery-powered 0MO5 ICs.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a battery check circuit showing an embodiment of the present invention, Figure 2 is a circuit diagram of a conventional battery check circuit, Figure 3 is a voltage characteristic diagram of Figure 2, and Figure 4 is the diagram of Figure 1. FIG. 5 is a more specific circuit diagram of FIG. 1, and FIG. 6 is a voltage waveform diagram of FIG. 10...First diode, 11...
Second diode, 12...First resistor, 13
......Second resistor, 14...Third resistor, 15...Voltage comparison circuit (comparator), 1
6... Output terminal, VDD... Power supply voltage. Applicant's agent Yasushi Kakimoto Figure 1 Figure 2 Voltage characteristic diagram of Figure 2 Figure 3 Voltage characteristic diagram of Figure 1 Figure 4 Voltage waveform diagram of Figure 5 Figure 6

Claims (1)

[Claims] A battery check circuit for detecting a change in power supply voltage, comprising: first and second PN junction diodes connected in the forward direction to the power supply and having a size relationship in PN junction area; a first and second resistor connected in series to the first PN junction diode; a third resistor connected in series to the second PN junction diode; a voltage between the first and second resistors; A battery check circuit comprising: a voltage comparison circuit that detects a difference between a voltage between a second PN junction diode and a third resistor and outputs a signal according to the difference.