JP2578886B2 - Schmitt trigger circuit - Google Patents

Description

The present invention relates to a circuit configuration of a Schmitt trigger circuit,
In particular, the present invention relates to a circuit configuration of a Schmitt trigger circuit that operates stably and at a high speed at a low voltage and can be used for an electronic device such as a pager that operates at a power supply voltage of about 1.0 V.

[Conventional technology]

Conventionally, transistor Schmitt trigger circuit of this type receives an input signal V _IN to the base of the transistor Q ₆₁ having a feedback resistor R ₆₃ as in FIG. 6 to the emitter, the emitter to the transistor Q ₆₁ are connected in common the base of Q ₆₂ is connected to the collector of the transistor Q _61, each transistor Q ₆₁
And the load resistance R ₆₁ between the collector of Q ₆₂ and the constant voltage power supply V _CC ,
R ₆₂ is connected to each other, and the output is taken out from the collector of the transistor Q ₆₂ . The operation of such a conventional circuit is described as follows.

In Figure 6, the transistor Q ₆₁ is OFF, the transistor Q ₆₂ is ON, the common emitter potential and V _E2, Can be expressed as

Here, V _CC is a power supply voltage, V _BEon2 , V _CE2 are a base-emitter voltage and a collector-emitter voltage of the transistor Q ₆₂ , respectively, and R ₁ , R ₂ , R ₃ are resistors R ₆₁ , R ₆₂ , respectively. R
The resistance value is ₆₃ .

By _gradually increasing the input V _IN , V _IN > V _E2 + V _BEon1 (V _BEon1
When became transistor base-emitter voltage of the ON state of the Q _61), the transistor Q ₆₁ is ON from OFF, the transistor Q ₆₂ in the reverse state is inverted to OFF from ON. Reversal in this state, because it is performed by the positive feedback through an emitter resistor R _63, it is made rapidly.

Then Toranjisuta Q ₆₁ is ON, the common emitter potential V _E1 of time of the transistor Q ₆₂ is turned OFF, ignoring the base current of the transistor Q _61, The state by lowering the input V _IN; (V _CE1 collector-emitter voltage of the transistor Q ₆₁₎ gradually is inverted is similarly done by positive feedback via the emitter resistor R _63.

[Problems to be solved by the invention]

Since the above-mentioned conventional Schmitt trigger circuit normally uses one transistor in a saturated state, the switching speed cannot be expected to be high despite the positive feedback operation, and the hysteresis width is not increased. Is V
It is determined by the value of _BEon . However, in general V
_Although the value of _BE is considered to be stable, fluctuations of V _BE of several tens of mV are not necessarily negligible at low voltages such as the power supply voltage of about 1.0 V, and the temperature dependence is particularly small compared to the power supply voltage. However, there is a disadvantage that the hysteresis width cannot be stably realized.

[Means for solving the problem]

A Schmitt trigger circuit according to the present invention includes a first transistor receiving an input voltage at a base, a second transistor having an emitter connected to the emitter of the first transistor, and an emitter connection of the first and second transistors. A current source connected to the point, first and second resistors connected in series between a collector of the first transistor and a power supply terminal, and an output terminal connected to the collector of the first transistor. The connection point of the first and second resistors is connected to the collector of the second transistor, and the collector potential of the first transistor is fully fed back to the base of the second transistor.

That is, the present invention increases the high-speed operation as a non-saturated circuit configuration, and increases the stability of the hysteresis width by using a collector resistor as a feedback resistor.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of one embodiment of the present invention. Transistors Q ₁₁ and Q whose emitters are commonly connected to the constant current power supply IQ
It connects the input terminal V _IN to the base of one transistor Q ₁₁ of the ₁₂ is connected to its collector to the base and the output terminal V _OUT of the other transistor Q _12. Transistor Q ₁₁
The collector resistors R _11, via R ₁₂ is connected to a constant voltage source V _CC, the resistors collector of the transistor Q ₁₂ R ₁₁ and R
Connected to the connection point with ₁₂ .

Here, the input terminal V _IN is connected to the base of the transistor Q _11, as an initial state, the transistor Q ₁₁ is O
FF, transistor Q ₁₂ forming the emitter to the common connected to differential pair Consider that that is turned ON. Since this circuit is biased by the constant current power supply IQ, the base potential V _B21 of the transistor Q ₁₂ is V _B21 ≒ V _CC −Iq · R ₁₂ (3) (V _CC ; the voltage value of the constant voltage power supply V _CC , Iq; the current value of the constant current power supply IQ, R ₁₂ ; the resistance value of the resistor R ₁₂ ), and when the input voltage V _IN ≪V _B21 , the transistor Q ₁₁
OFF, the transistor Q ₁₂ is not changed state of ON. When the input voltage V _IN gradually increases and V _IN = V _B21 , the transistor
Both Q ₁₁ and Q ₁₂ are turned on. At that time, positive feedback is applied to the base of the transistor Q ₁₂ which is one input of the differential pair via the resistors R ₁₁ and R ₁₂ , and the state is rapidly inverted, transistor Q ₁₁ is oN, the transistor Q ₁₂ is turned OFF. At this time,
Base potential V _B22 of the transistor Q ₁₂ is _{V B22 ≒ V CC -Iq (R} 11 + R 12) ...... (4); a (R ₁₁ the resistance value of the resistor R _11). Thereafter, if V _IN BV _B22 , this state is maintained,
Input voltage V _IN conversely go lowered, when the V _IN = V _B22, state is inverted by the positive feedback to the base of the transistor Q ₁₂ as opposed to above. From equations (3) and (4), V _B21 > V
_Since it is _B22 , the input and output characteristics of this circuit are roughly
A hysteresis characteristic as shown in FIG. 2 is exhibited, and a Schmitt trigger circuit can be realized.

This circuit is basically the differential amplifier configuration, the non-saturation type circuit, since it consists of a resistor and NPN transistors are capable of operating at V _CC 1.0 V as low voltage and high speed operation Can be expected. Furthermore, the hysteresis width ΔV becomes ΔV = V _B21 −V _B22 = IqR ₁₁ (5), but it is easy and general to create a constant current source that is inversely proportional to the resistance value on the integrated circuit. It can be seen that the circuit configuration is easy to keep the hysteresis width ΔV constant.

In the description so far, the threshold voltages of this Schmitt trigger circuit have been V _B21 and V _B22 ,
More accurate values of the threshold voltages V _TH1 and V _TH2 are shown here. The state inversion of the present circuit is performed by positive feedback as described above, but positive feedback occurs when the loop gain of the feedback loop is greater than 1. To obtain the loop gain as shown in FIG. 3 (a), assuming that the loop is equivalently open, the input / output characteristics when the reference voltage Vref is biased to the base of the transistor Q ₁₂ And positive feedback occurs when | ∂V _OUT / ∂V _IN |> 1. FIG. 3 (b) shows this diagrammatically.
Positive feedback occurs because the slope of the input / output characteristics in FIG.
Vref ± dV. In this way, the positive feedback actually occurs and the state is inverted when the reference voltage
Since it is shifted from Vref by dV, the accurate hysteresis characteristic of the circuit of FIG. 1 is as shown in FIG. here
dV is the solution of ∂V _OUT / ∂V _IN = 1.

FIG. 5 is a circuit diagram of another embodiment of the present invention. In the embodiment shown in FIG. 1, the minimum configuration is used to show the basic points of the present invention. Therefore, (1) Since the amplifier has a single-stage configuration, a large loop gain cannot be obtained, and the amplifier tends to be slightly unstable. (2) for feedback resistor R ₁₁ is as load resistance of the output, setting a logic amplitude setting of the output of the hysteresis width can not independently has a drawback that. Therefore, in the embodiment shown in FIG.
(I) Amplifying stage constituting a feedback loop is a transistor
A differential amplifier composed of Q ₅₀₁ , Q ₅₀₂ , Q ₅₀₈ and resistors R ₅₀₁ , R ₅₀₂ , transistors Q ₅₀₃ , Q ₅₀₄ , Q ₅₀₉ and resistors R ₅₀₃ , R ₅₀₄ , R ₅₀₅
And a differential amplifier consisting of
i) To match the logic amplitude of the output, the transistors Q ₅₀₅ ,
An output stage differential amplifier composed of Q ₅₀₆ , Q ₅₁₀ and resistors R ₅₀₆ , R ₅₀₇ is added to provide a total of three stages of differential amplifier. The basic operation principle is exactly the same as the description of the embodiment of FIG. 1, and the description is omitted here.

In addition to the above-mentioned improvements, this embodiment has the same features of low voltage operation, high speed operation, and stability of hysteresis width as shown in the embodiment of FIG.
It has a practical configuration.

〔The invention's effect〕

As described above, the present invention operates stably even at a low power supply voltage of about V _CC 1.0 V by configuring a positive feedback circuit based on a basic configuration of a simple differential amplifier circuit having a resistive load, thereby achieving a high speed operation. There is an effect that a Schmitt trigger circuit that can expect a response and easily control the hysteresis width stably can be configured.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention, FIG. 2 is a diagram for explaining the outline of hysteresis characteristics according to one embodiment of the present invention,
FIG. 3 (a) is an equivalent circuit diagram for explaining the loop gain, FIG. 3 (b) is a characteristic diagram for explaining the loop gain, and FIG. 4 is an accurate circuit diagram according to one embodiment of the present invention. FIG. 5 is a circuit diagram illustrating a hysteresis characteristic, FIG. 5 is a circuit diagram of another embodiment of the present invention, and FIG. 6 is a circuit diagram of a conventional Schmitt trigger circuit. Q ₁₁ ...... transistor, Q ₁₂ ...... transistor, R ₁₁ ......
Resistance, R ₁₂ … Resistance, IQ …… Constant current power supply, V _CC …… Constant voltage power supply, V _IN …… Input terminal, V _OUT …… Output terminal, V _REF ……
Reference constant voltage source, _Q501 , _Q502 , _Q503 , _Q504 , _Q505 , _Q506 , _Q507 , Q
_{508, Q 509, Q 510,} Q 61, Q 62, Q 63 ...... transistor, R _501, R
₅₀₂ , R ₅₀₃ , R ₅₀₄ , R ₅₀₅ , R ₅₀₆ , R ₅₀₇ , R ₆₁ , R ₆₂ , R ₆₃ ... resistance.

Claims (1)

(57) [Claims] 1. A first transistor receiving an input voltage at a base, a second transistor having an emitter connected to an emitter of the first transistor, and the first and second transistors.
Current source connected to the emitter connection point of the first transistor, first and second resistors connected in series between the collector of the first transistor and a power supply terminal, and connected to the collector of the first transistor A connection point of the first and second resistors is connected to a collector of the second transistor, and a collector potential of the first transistor is completely connected to a base of the second transistor. Schmitt trigger circuit being fed back.