JPH07336200A - Comparison circuit - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to a comparison circuit, and an object thereof is to easily improve the accuracy of a hysteresis voltage. [Structure] The differential pair transistor 21 has an emitter area ratio set to 1: 3, and a common source has a current source 30.
Are connected, and V _{S, which} is a voltage obtained by dividing V _Z and the detection target voltage V cc, is supplied to each base. The current mirror circuit 22 is connected to each collector of the differential pair transistor 21 as an active load, and has a current ratio of 1: 1 or 1.
You can switch to pair 3. The output circuit 23 is connected to one collector of the differential pair transistor 21, and generates an output voltage according to the level of the collector voltage. The transistor Q _{45 of the} switching circuit is a differential pair transistor 2
According to the level of one collector voltage of 1, the current ratio of the current mirror circuit 22 is switched to a ratio of 1: 1 or 1: 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a comparison circuit, and more particularly,
The present invention relates to a comparison circuit having hysteresis and comparing a detection target voltage with a threshold voltage.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram of a conventional comparison circuit.
Indicates. The circuit of FIG. 3 compares the power supply voltage Vcc with the threshold voltage.
It is a circuit to do. PNP type transistor Q₁, Q₂When
The differential pair transistor is composed of a transistor Q
₁, Q₂The common emitter of the₆Current source 6
It is connected. Transistor Q₁, Q₂Each of these
The current mirror circuit as an active load.
Transistor Q₃, Q _FourConnected to their respective collectors
ing.

The emitters of the transistors Q ₃ and Q ₄ are grounded via resistors R ₃ and R ₄ , respectively. In addition, the base of the output stage transistor Q ₅ is the transistor Q ₁
Of the transistor Q _{3 and} the emitter thereof is connected to the emitter of the transistor Q ₃ . The collector of the transistor Q ₅ is connected to the current source 7 having the current value I ₇ and the output terminal 9.

Voltage V_ZConstant voltage diode D₁Anno
The cathode is grounded and the cathode has a current value I _FiveConnect to current source 5
Has been done.

The base of the transistor Q ₁ is connected to the cathode of the diode D ₁ and is supplied with the voltage V _Z. A voltage V _{S obtained} by dividing the power supply voltage Vcc, which is the detection target voltage, by the resistors R ₁ and R ₂ is supplied to the base of the transistor Q ₂ .

If R ₂ / (R ₁ + R ₂ ) = 1 / k, the voltage V _S is V _S = (1 / k) Vcc.

The resistors R ₃ and R ₄ have the same value. The current I ₆ is set to a smaller value than the current I ₇ . Further, the voltage V _Z is constant regardless of the fluctuation of the power supply voltage Vcc.

The transistors Q ₁ and Q ₂ and the transistors Q ₃ and Q ₄ have emitter area ratios of 1: 1 and are matched in characteristics.

Next, the operation of the comparison circuit shown in FIG. 3 will be described. When the voltage V _S is sufficiently higher than V _Z (that is, the power supply voltage Vcc is sufficiently higher than the threshold voltage), the transistor Q ₂ is turned off and the transistor Q ₁ is turned on. At this time, the collector current of the transistor Q ₁ is to flow into the base of the transistor Q _5, the transistor Q ₅ is turned on, a current I ₇ flows to the resistor R ₃ from the emitter of the transistor Q _5. Therefore, the resistor R ₃ has both ends of R ₃
-The voltage of I ₇ is generated. At this time, the transistor Q ₃
Is almost off because the emitter potential increases by the amount of R ₃ · I ₇ .

At this time, since the transistor Q ₅ is on, the voltage at the output terminal 9 becomes a low level voltage.
Thus, when the detection target voltage Vcc is higher than the threshold voltage, the voltage of the output terminal 9 becomes low level.

Next, consider a case where the voltage V _S drops from a value sufficiently higher than V _Z to reach the voltage V _Z. At this time, the collector currents of the transistors Q ₁ and Q ₂ have almost the same value. On the other hand, since the current I ₇ flows from the transistor Q ₅ , a voltage of R ₃ · I ₇ is generated across the resistor R ₃ .

[0012] Therefore, the collector current of the transistor Q ₁ is little flow to the base of the transistor Q _5, the transistor Q ₅ is kept turned on.

Next, the voltage V _S further falls below V _Z and V
_{When Z−} R ₃ · I ₇ , the base-emitter voltage V _{BE2 of} the transistor Q ₂ becomes R ₃ · I more than in the balanced state.
_{Increases by 7} . At this time, the base-emitter voltage V _{BE4 of the} transistor Q ₄ whose characteristics are matched with those of the transistor Q ₂ also becomes larger than that in the balanced state by R ₃ · I ₇ . Thus, the base-emitter voltage V _BE3 of the transistor Q ₃ is increased, the transistor Q ₃ are fully turned on.

Transistor Q₃When is turned on,
Dista Q₁The collector current of all is transistor Q₃of
Flowed into collector, transistor Q_FiveThe base current of
It becomes 0. This allows the transistor Q_FiveTurns off,
Transistor Q_FiveTo resistance R ₃The current flowing into is 0
It At this time, the output terminal has a high level voltage.

Thus, the voltage V_SFrom high level
-Voltage V when changing to level _SThreshold voltage for
V_RLIs expressed by the following equation (1).

V _RL = V _Z −R ₃ · I ₇ (1) As described above, when the voltage V _S is equal to or lower than the threshold voltage V _RL (that is, when the detection target voltage Vcc is equal to or lower than the threshold voltage V _RL · k). ), The voltage of the output terminal 9 becomes high level.

Next, consider a case where the voltage V _S rises from a voltage of V _Z -R ₃ · I ₇ or less.

Voltage V_SBut V_Z-R₃・ I₇Below voltage
, As described above, the transistor Q_FiveIs off
And transistor Q_FiveTo resistance R₃Current flowing into
Is. Voltage V_SRises to V_ZWhen the tiger is reached
Register Q₁And transistor Q ₂Is in a balanced state
Transistor Q₁, Q₂Have the same collector current
It At this time, the transistor Q₃And transistor Q_FourAlso
Be in a balanced state.

From this balance state, the voltage V_SIs V_ZOr
When it rises a little, the transistor Q₂Collector of
Current decreases, transistor Q₁Collector current increases
It As a result, the transistor Q_FiveBase current flows
And transistor Q_FiveChanges from off to on and the output
The voltage of the terminal 9 becomes low level. Transistor Q_Five
Is turned on, the current I₇Is resistance R₃Flowing into the resistance
R₃R at both ends of₃・ I ₇Voltage is generated.

Thus, the voltage V_SFrom low level to
Voltage V when changing to a level _SThreshold voltage for
V_RHIs expressed by the following equation (2).

V_RH= V_Z (2) Once voltage V_SWhen becomes high level, as above,
Resistance R₃R at both ends of ₃・ I₇Since the voltage of
Again, the threshold voltage is V_RL= V_Z-R₃・ I₇Becomes

Hysteresis voltage V _{RHYS with} respect to voltage V _S
Is expressed by the following equation (3).

V _RHYS = V _RH −V _RL = R ₃ · I ₇ (3) Further, the threshold voltages V _CH and V _CL of the power supply voltage Vcc, which is the detection target voltage, and the hysteresis voltage V _CHYS are as follows. Become.

V _CH = V _Z · k (4) V _CL = (V _Z −R ₃ · I ₇ ) · k (5) V _CHYS = R ₃ · I ₇ · k (6)

[0025]

[SUMMARY OF THE INVENTION] As described above, in the conventional circuit of FIG. 3, the hysteresis voltage is related value of the resistor R _3, to increase the accuracy of the hysteresis voltage, the resistor R ₃ We have to improve precision. Therefore, there is a problem that it is difficult to improve the accuracy of the hysteresis voltage.

The present invention has been made in view of the above points, and an object of the present invention is to provide a comparison circuit capable of easily increasing the accuracy of the hysteresis voltage.

[0027]

According to the present invention, an emitter area ratio is set to 1: n, a current source having a predetermined current value is connected to a common emitter, and a threshold voltage is compared between each base. The differential pair transistor to which a voltage that changes corresponding to the voltage change of the detection target voltage is supplied, and the collectors of the differential pair transistor are connected as active loads, and the current ratio is 1: 1 or 1. A current mirror circuit capable of switching to a ratio other than 1 and an output connected to one collector of the differential pair transistor and generating an output voltage according to the level of one collector voltage of the differential pair transistor A circuit and a switching circuit for switching the current ratio of the current mirror circuit to a ratio of 1: 1 or a ratio other than 1: 1 according to the level of one collector voltage of the differential pair transistor. Configured to have.

[0028]

In the present invention, the hysteresis voltage of the threshold voltage and the emitter area ratio are set to 1 to n by switching the current ratio of the current mirror circuit according to the level of the collector voltage of one of the differential pair transistors. It can be generated by utilizing the difference between the base-emitter voltage of the differential pair transistor.

With this, unlike the conventional circuit, a resistor is not required for generating the hysteresis voltage, and the accuracy of the hysteresis voltage can be easily increased.

[0030]

1 is a circuit diagram of a comparison circuit according to an embodiment of the present invention. Differential pair transistors 21 consists NPN type transistor Q _31, Q _32, transistor Q ₃₁ and the transistor Q ₃₂ is is set to the emitter area ratio to 1: 3. The common emitter of the transistors Q _31, Q _32, the current source 30 of a current value I ₃₀ is connected.

The current mirror circuit 22 includes PNP type transistors Q ₃₃ , Q ₃₄ and Q ₃₅ and a Schottky diode D.
_It consists of ₃₆ . The collector of the diode-connected transistor Q ₃₃ is connected to the collector of the transistor Q ₃₁ , and the collector of the transistor Q ₃₄ is connected to the transistor Q _32.
Connected to the collector. Also, the transistor Q ₃₅
Is connected to the collector of the transistor Q ₃₂ via the diode D ₃₆ .

The output circuit 23 is a Schottky diode.
D₃₇, Transistor Q₃₈, Q₃₉, Q ₄₁, Current value I₄₀Electric power
Source 40, current value I₄₂Current source 42, resistor R₄₁Empty
It Diode D₃₇Is the transistor Q₃₂The
Connected to the lector. Transistor Q₃₈Base of
Is the diode D₃₇Connected to the anode of the emitter
Is the transistor Q₃₉Connect to the power supply terminal together with the
Has been continued.

The base of the transistor Q ₃₉ is connected to its own collector, the collector of the transistor Q ₃₈ , and the current source 40.

The other collector of the transistor Q ₃₉ is connected to the base of the transistor Q ₄₁ and also has a resistance R _41.
Grounded through. The emitter of the transistor Q ₄₁ is grounded, the collector is connected to the current source 42 and the output terminal 48.

The base of the switching transistor Q ₄₅ is connected to the collector of the transistor Q ₄₁ , the emitter is grounded, and the collector is connected to the anode of the diode D ₃₆ . The switching circuit is composed of the output circuit 23 and the switching transistor Q ₄₅ .

The anode of the constant voltage diode D ₄₆ is grounded, and the cathode is connected to the current source 47 having the current value I ₄₇ . The constant voltage V _Z is supplied from the constant voltage diode D ₄₆ to the base of the transistor Q ₃₂ .

The base of the transistor Q ₃₁ is supplied with a voltage V _{s obtained} by dividing the power supply voltage Vcc which is the detection target voltage by the resistors R ₁ and R ₂ .

When R ₂ / (R ₁ + R ₂ ) = 1 / k, the voltage V _S is V _S = (1 / k) Vcc.

Next, the operation of the comparison circuit of this embodiment
explain. First, the voltage V_SIs V_ZIf higher enough (immediately
If the power supply voltage Vcc is sufficiently higher than the threshold voltage),
Langista Q₃₁Turns on and transistor Q₃₂Is off
Becomes At this time, the transistor Q₃₂The collector voltage of
High level, diode D₃₇And transistor Q ₃₈
Turn off. This allows the transistor Q₃₉Is on
Transistor Q₃₉Collector current of transistor Q
₄₁Flows into the base of transistor Q₄₁Is on
It Therefore, the voltage of the output terminal 48 becomes low level.
It

Thus, when the power supply voltage Vcc is higher than the threshold voltage, the output voltage becomes low level.

At this time, the transistor Q45 is off and no collector current flows. Therefore, the diode D ₃₆ is turned on by forward bias, and the transistor Q ₃₅ of the current mirror circuit 22 operates. As a result, the transistor Q ₃₃ side of the current mirror circuit 22 and the transistors Q ₃₄ ,
The current ratio on the Q ₃₅ side is 1: 3.

Therefore, when the base voltages of the transistor Q ₃₁ and the transistor Q ₃₂ are equal, the transistor Q ₃₁
And the collector current ratio of the transistor Q ₃₂ becomes 1: 3,
In addition, the current ratio between the transistor Q ₃₃ side of the current mirror circuit 22 and the transistors Q ₃₄ and Q ₃₅ side becomes 1: 3, which is balanced. That is, when the voltage V _S = V _Z ,
Be balanced.

[0043] Therefore, when the voltage V _S becomes voltage V _Z drops from sufficiently higher than V _Z, as described above, the collector current ratio of the transistor Q ₃₁ and the transistor Q ₃₂ is 1
The current ratio between the transistor Q ₃₃ side of the current mirror circuit 22 and the current ratio of the transistors Q ₃₄ and Q ₃₅ is 1: 3.

From this balanced state, when the voltage V _S drops very slightly, the transistor Q ₃₁ turns off, the transistor Q ₃₂ turns on, and the collector of the transistor Q ₃₂ becomes low level. As a result, the diode D ₃₇ and the transistor Q ₃₈ are turned on, the transistor Q ₃₉ is turned off, and the collector current of the transistor Q ₃₉ becomes zero. Therefore, the transistor Q ₄₁ is turned off and the output terminal 48
The voltage of changes from low level to high level.

Thus, the threshold voltage V _RL for the voltage V _S when the voltage V _S changes from the high level to the low level
Is as shown in equation (7) below.

V _RL = V _S (7) When the voltage V _S is less than or equal to the threshold voltage V _RL (that is, the power supply voltage V
If cc is less than the threshold voltage of V _RL · k), output terminal 48
Voltage becomes high level.

When the voltage at the output terminal 48 changes to the high level, the transistor Q45 is turned on and the collector current flows, and the collector becomes the low level. Therefore, the diode D ₃₆ is turned off by the reverse bias, and the transistor Q ₃₅ of the current mirror circuit 22 becomes inoperative. As a result, the current ratio between the transistor Q ₃₃ side and the transistors Q ₃₄ , Q ₃₅ side of the current mirror circuit 22 becomes 1: 1.

In this state, the current ratio of the transistor Q ₃₃ side and the transistors Q ₃₄ and Q ₃₅ side of the current mirror circuit 22 is 1: 1, while the transistors Q ₃₁ and Q _35.
The emitter area ratio of ₃₂ is 1: 3.

_Therefore , when the relationship between the base-emitter voltage of the transistor Q _{32 and} the base-emitter voltage V _BE31 of the transistor Q ₃₁ becomes as shown in the following equation (8), the collectors of the transistors Q ₃₁ and Q ₃₂ are: The currents are equal and the current ratio between the transistor Q ₃₃ side and the transistor Q ₃₄ side of the current mirror circuit 22 is 1: 1 so that the current is balanced.

V _BE32 = V _BE31 − (KT / q) · ln3 (8) (where K is the Boltzmann constant, T is the absolute temperature, and q is the electron charge). Therefore, V _S is V _S = When V _Z + (KT / q) · ln3, the above-mentioned balanced state is achieved.

Next, the voltage V_SBut V_ZAbove voltage below
Consider the case of rising. Voltage V _SBut V_ZThe following
If it is a pressure, as described above, the current mirror circuit 22
Transistor Q₃₃Side and transistor Q₃₄, Q₃₅Side power
The flow ratio is 1: 1. Voltage V _SRises to V_Z+ (K
T / q) · ln3, the transistor Q₃₁, Q
₃₂Collector currents are equal and the current mirror
Transistor Q of circuit 22₃₃Side and transistor Q₃₄On the side
The current ratio is 1: 1 and the balance is good.

From this balance state, the voltage V _S is V _Z +
When (KT / q) · ln3 rises slightly, transistor Q ₃₁ turns on and transistor Q ₃₂ turns off. At this time, the collector voltage of the transistor Q ₃₂ becomes high level, and the diode D ₃₇ and the transistor Q ₃₈ are turned off. This turns on transistor Q ₃₉ ,
The collector current of the transistor Q ₃₉ flows into the base of the transistor Q _41, the transistor Q ₄₁ is turned on. Therefore, the voltage of the output terminal 48 becomes low level.

[0053] Thus, when the V _S changes from low level to high level, the threshold voltage V _RH for the voltage V _S
Is expressed by the following equation (9). The threshold voltage for the power supply voltage Vcc is V _RH · k.

V _RH = V _Z + (KT / q) · ln3 (9) Once the voltage V _S becomes the high level, the voltage of the output terminal 48 becomes the low level, and as described above, the transistor Q45 Turns off, the diode D ₃₆ turns on with forward bias, and the transistor Q ₃₅ of the current mirror circuit 22 operates. As a result, the current mirror circuit 2
The current ratio between the second transistor Q ₃₃ side and the transistors Q ₃₄ and Q ₃₅ side is 1: 3. Therefore, the threshold voltage for the voltage V _S becomes V _RL = V _S again.

Hysteresis voltage V _{RHYS with} respect to voltage V _S
Is expressed by the following equation (10).

V _RHYS = V _RH −V _RL = (KT / q) · ln3R ₃ · I ₇ (10) Further, the threshold voltages V _CH and V _CL of the power supply voltage Vcc, which is the detection target voltage, and the hysteresis voltage V _CHYS. Is as follows.

[0057] _{V CH = (V Z + (} KT / q) · ln3) · k (11) V CL = V Z · k (12) V CHYS = (KT / q) · ln3 · k (13) above Thus, in this embodiment, the differential pair transistor 21
The current ratio of the current mirror circuit 22 is switched to 1: 1 or 1: 3 according to the level of the collector voltage of one side.
Thereby, the hysteresis voltage of the threshold voltage can be generated by utilizing the difference between the base-emitter voltages of the differential pair transistor 21 in which the emitter area ratio is set to 1: 3.

Therefore, unlike the conventional circuit, no resistor is required to generate the hysteresis voltage, and the accuracy of the hysteresis voltage can be easily increased.

The ratio of the emitter area of the differential-to-transistor 21 and the current ratio of the current mirror circuit 22 are not limited to 1: 3, but can be set appropriately according to the hysteresis voltage to be set.

FIG. 2 illustrates a comparison circuit according to a modification of the present invention.
The figure is shown. 2, the same components as in FIG.
A reference numeral is given and the description is omitted as appropriate. Differential pair Transis
Transistor Q that forms the transistor 51₅₂And transistor Q₅₃
The emitter area ratio is set to 1: N (N> 1). Tiger
Register Q₅₂, Q₅₃The common emitter of the₅₅of
The current source 55 is connected. The current mirror circuit 50 is
Transistor Q₅₆, Q ₅₇, Q₅₈, Diode D₅₉Empty
It The current mirror circuit 50 is the current mirror circuit 2
The circuit is the same as that of 2, and the current ratio is 1: 1 or 1: M (M
<N).

The collector of the transistor Q ₅₃ is connected to the diode D ₃₇ of the output circuit 23. The anode of the diode D ₅₉ is connected to the collector of the transistor Q ₄₅ .

A series circuit of a diode-connected transistor Q ₅₄ and resistors R ₁ , R ₂ and R ₃ is connected between the power supply terminal and ground. The connection point between the resistors R ₁ and R ₂ is connected to the base of the transistor Q ₅₂ , and the connection point between the resistors R ₂ and R ₃ is connected to the base of the transistor Q ₅₃ .

Here, p = (R ₁ + R ₂ + R ₃ ) / R ₂
And the base-emitter voltage of the transistor Q ₅₄ is V
_{Assuming BE54} , the threshold voltage of the power supply voltage Vcc and the hysteresis voltage are as shown in (14) to (16) below.

[0064] _{V CH = p · (KT /} q) · lnN + V BE54 (14) V CL = p · (KT / q) · lnN-ΔV BE53 + V BE54 (15) V CHYS = ΔV BE53 (16) In addition, [Delta] V _BE53 is the case the current ratio of the current mirror circuit 50 is a one-to-one, in the case of one-to-M, which is the difference between the base-emitter voltage of the transistor Q ₅₃ in the balance state of each case. The value of ΔV _BE53 can be appropriately set by changing M.

In this way, the hysteresis voltage can be set in the same manner as the circuit of FIG. Further, in this modified example, the constant voltage diode of the constant voltage V _Z which is the reference of the threshold voltage is not required.

The present invention is not limited to the above circuit,
In the circuits of FIGS. 1 and 2, the PNP type transistor and the NPN type transistor may be replaced with each other, and the power supply voltage may be set to a negative voltage accordingly. Further, instead of the transistor, an FET may be used.

[0067]

As described above, according to the present invention, the hysteresis voltage of the threshold voltage is generated by using the difference between the base-emitter voltage of the differential pair transistor whose emitter area ratio is set to 1: n. Therefore, unlike the conventional circuit, a resistor is not required to generate the hysteresis voltage, and the accuracy of the hysteresis voltage can be easily increased.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a comparison circuit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a comparison circuit according to a modified example of the present invention.

FIG. 3 is a circuit diagram of a conventional comparison circuit.

[Explanation of symbols]

21 differential pair transistor 22 current mirror circuit 23 output circuit Q ₄₅ switching transistor I ₃₀ current source D ₄₆ constant voltage diode

Claims (1)

[Claims] 1. An emitter area ratio is set to 1: n, a current source of a predetermined current value is connected to a common emitter, and a change in a detection target voltage compared with a threshold voltage is supported between each base. And a differential pair transistor to which a varying voltage is supplied, and an active load connected to each collector of the differential pair transistor, and the current ratio can be switched to 1: 1 or a ratio other than 1: 1. A current mirror circuit; an output circuit that is connected to one collector of the differential pair transistor and that generates an output voltage according to the level of one collector voltage of the differential pair transistor; According to the level of one collector voltage, the current ratio of the current mirror circuit is set to 1: 1.
Alternatively, a comparison circuit having a configuration including a switching circuit for switching to a ratio other than 1: 1.