JPH0377686B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a Schmitt circuit used in bipolar integrated circuits.

(Prior Art) A Schmitt circuit conventionally used in bipolar integrated circuits is shown in FIG.

In this Schmitt circuit, a constant current circuit (constant current value I ₀ ) consisting of transistors Q ₁₃ , Q ₁₄ and resistor R ₂ is connected to the emitter side connection point of two transistors Q ₁₁ and Q ₁₂ that constitute a differential amplifier circuit. Furthermore, two transistors are connected to the collector sides of these transistors Q ₁₁ and Q _12.
Two current mirror circuits 6 and 7 are connected in a so-called cross-over configuration.

The current mirror circuit 6 is composed of a transistor Q ₁₅ connected to a transistor Q ₁₂ , a transistor Q ₁₆ connected to a transistor Q ₁₁ which acts as a so-called diode junction, and a resistor R ₃ . In addition, the current mirror circuit 7 is
Transistor Q ₁₇ connected to transistor Q ₁₁
and a transistor Q ₁₈ connected to transistor Q ₁₂ acting as a so-called diode junction,
It is composed of a resistor _R4 .

In a Schmitt circuit with such a configuration, the base sides of transistors Q ₁₁ and Q ₁₂ are respectively input terminals A and B, the potential difference between A and B is V _AB , and the collector current flowing through each transistor Q _{o is}
Assuming _Ico , equations (1) and (2) shown below hold regardless of the state of the output (collector potential of transistor _Q12 ).

V _AB = kT/ql _o I _C12 /I _C11 ... I _C11 + I _C12 = I ₀ ... However, q: Electron charge k: Boltzmann's constant T: Absolute temperature Also, when the output is at "L" level, the following The following relationship holds true.

I _C11 = I _C16 ... I _C15 = I _C12 ... I _C18 = I _C17 ... On the other hand, when the output switches from "L" level to "H" level, in addition to the above formula, R ₃・I _C16 =kT/ql _o I _C15 /I _C16 holds true, and when the above equation is substituted into this relationship, R ₃・I _C11 =kT/ql _o I _C12 /I _C11 ... holds true.

Therefore, the potential difference V _{AB (L} ‖ _H) when the output switches from "L" level to "H" level is expressed by the formula,
determined by.

By the way, when the output is switched to the "H" level, the following formulas are established: I _C12 = I _C18 ... I _C17 = I _C11 ... I _C16 = I _C15 = 0...

Next, when the output switches from the "H" level to the "L" level, in addition to the above equation, the relationship R ₄ · I _C18 = kT / ql _o I _C17 / I _C18 is established, and this relationship Substituting the above equation into , R ₄ · I _C12 = kT / ql _o I _c11 / I _c12 ... is established.

Therefore, the potential difference V _{AB (L} ‖ _H) when the output switches from "H" level to "L" level is expressed by the formula,
determined by. At this time, the hysteresis width is defined as {V _AB(L ‖ _H) −V _AB(H ‖ _L) }.

(Problem to be Solved by the Invention) However, since the characteristics of this type of Schmitt circuit are defined by the above equation, the threshold level, V _AB(L ‖ _H) ,
V _AB(H ‖ _L) and the hysteresis width depend on the constant current value I ₀ of the constant current circuit.

That is, the output of the Schmitt circuit shown in FIG. 2 switches when the collector currents I _c11 and I _c12 of the transistors Q ₁₁ and Q ₁₂ reach the current ratio set in the two current mirror circuits 6 and 7. It is.

Here, if the set current ratios of the two current mirror circuits 6 and 7 are respectively I _c16 : I _c15 = 1:2 (current mirror circuit 6) I _c17 : I _c18 = 2:1 (current mirror circuit 7) , the output of the Schmitt circuit switches from the "L" level to the "H" level when the current ratio between I _c11 and I _c12 reaches the set ratio of the current mirror circuit 6. That is, when I _c11 :I _c12 =I _c16 :I _c15 =1:2...

In addition, as mentioned above, the potential difference V _{AB (L} ‖ _H) when the output of the Schmitt circuit switches from the "L" level to the "H" level is determined by the equation, so from the relationship of the equation When calculating V _AB(L ‖ _H) , from the formula, I _c11 = 1/R ₃・kT/ql _o I _c12 /I _c11 = 1/R ₃・kT/ql _o 2 ... Also, from the formula, I _c12 = I ₀ − I _c11 = I ₀ −1/R ₃・kT/ql _o 2 ..., substituting the formula into the formula, V _AB(L ‖ _H) = kT/ql _o I _c12 / I _c11 = kT/ql _o I ₀ −1/R ₃・kT/ql _o 2/1/R ₃・kT/
ql _o 2...

Further, the output of the Schmitt circuit switches from the "H" level to the "L" level when the current ratio between I _C11 and I _C12 reaches the set ratio of the current mirror circuit 7. That is, when I _C11 :I _C12 =I _C17 :I _C18 =2:1...

Also, as mentioned above, the potential difference V _{AB (H} ‖ _L) when the output of the Schmitt circuit switches from the "H" level to the "L" level is determined by the formula, , From the formula, I _C12 = 1/R ₄・kT/ql _o I _C11 /I _C12 = 1/R ₄・kT/ql _o 2 ... Also, from the formula, I _C11 = I ₀ −I _c12 = I ₀ −1/ R ₄・kT/ql _o 2 ..., substituting the formula into the equation, V _AB(H ‖ _L) = kT/ql _o I _C11 /I _C12 = kT/ql _o 1/R ₃・kT/ql _o 2 /I ₀ −1/R ₃・kT
/ql _o 2... becomes.

As can be seen from the above equation, the threshold level, V _{AB (L} | _H) , V _{AB (H} | _L) , and the hysteresis width, which is the difference therebetween, depend on the constant current value I ₀ .

This constant current value I ₀ is determined by the power supply voltage V _CC and the resistor R ₂ , so the change in the power supply voltage V _CC and the resistance R ₂
The threshold levels, V _AB(L ‖ _H) , V _AB(H ‖ _L) ,
There was a problem that the hysteresis width fluctuated, making it impossible to unify the characteristics.

By the way, as a hysteresis comparator with hysteresis characteristics suitable for integration,
No. 59-104817 has been proposed.

As shown in FIG. 6 of the same publication, this hysteresis comparator mainly consists of transistors Q ₁ ,
A differential amplifier circuit consisting of Q ₂ and transistors Q ₃ ,
Two current mirror circuits consisting of Q ₄ and transistors Q ₆ and Q ₇ , and transistors Q ₈ , Q ₁₀ , and Q ₁₁
The circuit consists of constant current sources consisting of a switching transistor _Q5 , a resistor _R3 , and a diode D, and the resistor R3 and the resistor _R3 are connected to one input terminal (base of the transistor _Q2 ) of the differential amplifier circuit. Diode D
The reference power source 3 is connected via the .

That is, the hysteresis is controlled by changing the voltage applied to one input terminal (base of transistor _Q2 ) of the differential amplifier circuit depending on the change in the forward voltage of diode D.

In other words, in order to control hysteresis, the voltage applied to one input terminal of the differential amplifier circuit (the base of transistor _Q2 ) is changed by changing the forward voltage of diode D. The voltage of the reference power supply 3 connected to the anode of D must be managed very precisely. If the voltage of the reference power supply 3 fluctuates, this voltage fluctuation will be directly applied to the diode D, which will affect the hysteresis control.
Furthermore, it is generally well known that the forward voltage characteristics of a diode change significantly due to temperature changes, and it is inevitable that this will have an effect on hysteresis control.

Furthermore, since the forward voltage change of the diode D is utilized, one input terminal of the differential amplifier circuit must ultimately be connected to the reference power supply 3 having a fixed voltage value. The only variable input to be compared in the differential amplifier circuit is the signal voltage input to the other input terminal 1.

The present invention was made in view of such circumstances, and
The purpose of this is to allow the two inputs of the differential amplifier circuit to be compared as variable inputs without any relationship for hysteresis control, and to eliminate variations in characteristics without depending on the constant current value itself of the constant current circuit. The purpose is to provide the Schmitt circuit that has been lost.

(Means for Solving the Problems) In order to solve the above problems, the Schmitt circuit of the present invention includes a pair of transistors constituting a differential amplifier circuit, and a first transistor connected to the emitter side connection point of the pair of transistors. a constant current circuit, a first current mirror circuit that compares collector currents flowing through the pair of transistors, a second constant current circuit that is proportional to the first constant current circuit, and this second constant current circuit. is connected between the output side of the first current mirror circuit and the output side of the differential amplifier circuit, and changes the current value for threshold setting of the first current mirror circuit by flowing the output side current of the differential amplifier circuit. The configuration includes a second current mirror circuit to control, and a switching element to switch the second current mirror circuit according to the output of the differential amplifier circuit.

(Function) A first constant current circuit is connected to the emitter side connection point of a pair of transistors constituting a differential amplifier circuit,
A first current mirror circuit is configured to compare the collector currents flowing through these pair of transistors. Further, a second constant current circuit supplies a current value (for example, 1/2) proportional to the current value of the first constant current circuit.
A constant current circuit is provided, and a second current mirror circuit is connected between the output side of the second constant current circuit and the output side of the differential amplifier circuit. Then, by flowing the output side current of the differential amplifier circuit into the second current mirror circuit, the current value for threshold setting of the first current mirror circuit is variably controlled. Further, this second current mirror circuit is switched by a switching element that switches according to the output of the differential amplifier circuit.

That is, the present invention essentially provides a first transistor for a pair of transistors constituting a differential amplifier circuit.
The configuration is such that only the current mirror circuit is connected. That is, when the output of the present Schmitt circuit is, for example, at the "H" level, the switching element is turned on, and the second current mirror circuit is substantially not connected. For example, when the output goes to the "L" level, the second current mirror circuit is connected, and the current value for setting the threshold of the first current mirror circuit is varied. . At this time,
The first constant current circuit changes in proportion to the second constant current circuit connected to the emitter side of the differential amplifier circuit, and therefore, according to the present invention, the two input terminals of the differential amplifier circuit The threshold level, V _{AB (L} ‖ _H) , V _{AB (H} ‖ _L) , and hysteresis width are determined without any relation to hysteresis control and without depending on the constant current value.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of an integrated circuit in which a Schmitt circuit according to the present invention is constructed using bipolar transistors.

A pair of transistors forming a differential amplifier circuit
Transistor Q ₆ is connected to the emitter side connection point of Q ₁ and Q ₂ .
A first constant current circuit 4 consisting of _Q8 and resistor _R1 ,
A second constant current circuit 5 consisting of transistors Q ₇ and Q ₈ and a resistor R ₁ is connected by a common base. The base-emitter junction area ratio of each transistor Q ₆ , Q ₇ , Q ₈ of the first constant current circuit 4 and the second constant current circuit 5 is set to 1:1/2:1. As a result, the collector current flowing through transistor Q ₆ is set to a constant current value I ₀ and the collector current flowing through transistor Q ₇ is set to a constant current value I ₀ /2.
It is said that

A first current mirror circuit 2 constituted by a transistor Q ₃ and a transistor Q ₉ acting as a so-called diode junction is connected to the collector side of the differential amplifier circuit, and the second current mirror circuit 2 is connected to the collector side of the differential amplifier circuit.
A second current mirror circuit 3 consisting of a transistor Q ₄ and a transistor Q ₅ acting as a so-called diode junction is connected to the collector side of the transistor Q ₇ and the output terminal side (collector of the transistor Q ₂ ) constituting the constant current circuit 5. It is connected.
This second current mirror circuit 3 is configured such that when the output is at the "H" level, the transistor (switching element) _Q10 connected to the output terminal side is conductive and does not function.

Next, the operation when the area ratio of the base-emitter junctions of the transistors Q ₉ , Q ₃ , Q ₄ , and Q ₅ is set to 2:3:1:6 will be described.

The potential difference between the bases of transistors Q ₁ and Q ₂ is V _AB
Then, V _AB = kT / ql _o I _C2 / I _C1 ... I _C1 + I _C2 = I ₀ ... holds, and when the output is at "L" level, I _C2 = I _C3 + I _C4 ... I _C5 = I ₀ /2 ...〓〓 holds true, and furthermore, when the output switches from "L" level to "H" level, in addition to the relationship of the above formula ~〓〓, I _C3 = 3/2 I _C1 ... I _C4 =1/6I _C5 =1/12I ₀ ...〓〓 holds true.

Therefore, when the output switches from "L" level to "H" level, I _C1 is I _C1(L ‖ _H) , I _C2 is I _C2(L ‖ _H) ,
If V _AB is V _AB(L ‖ _H) , I _C1(L ‖ _H) = 11/30I ₀ ……〓〓 I _C2(L ‖ _H) = 19/30I ₀ ……〓〓 V _AB(L ‖ _H) = kT/ql _o 19/11 ……〓〓.

Therefore, when the output is switched to the "H" level, the following relationship is established: I _C5 =I _C4 =0...〓〓.

That is, when the output of the differential amplifier circuit switches from the "H" level to the "L" level, the second current mirror circuit 3 is substantially disconnected due to the conduction of the transistor _Q10 . They are in the same state.

On the other hand, when the output is switched from the "H" level to the "L" level, in addition to the above equations, the following equation holds true.

I _C2 = I _C3 ...〓〓 I _C3 = 3/2I _C1 ... Therefore, I _C1 when the output switches from "H" level to "L" level is I _C1(H ‖ _L) , and I _C2 is I _C2(H ‖ _L) ,
If V _AB is V _AB(H ‖ _L) , I _C1(H ‖ _L) = 2/5I ₀ ... I _C2(H ‖ _L) = 2/5I ₀ ... V _AB(H ‖ _L) = kT /ql _o 3/2 ...〓〓 becomes.

Therefore, according to the circuit of this example, the threshold level, V _AB(L ‖ _H) , V _AB(H ‖ _L) , and hysteresis width {V _AB(L ‖ _H) −V _AB(H ‖ _L) } is determined by the above formulas 〓〓, 〓〓.

By the way, as mentioned above, when the output of the differential amplifier circuit switches from the "H" level to the "L" level, the second current mirror circuit 3 is substantially disconnected due to the conduction of the transistor _Q10 . The situation is the same as if it had not been done. This means that when the transistor Q ₁₀ is non-conductive (when the output of the differential amplifier circuit switches from the "L" level to the "H" level), the collector current I _C2 of the transistor Q ₂ is transferred to the second current mirror circuit. By flowing the emitter current I _C4 of 3, the output becomes "L".
When switching from level to “H” level,
The current value of the collector current I _C3 of the first current mirror circuit 2 is set to a different value when switching from the "H" level to the "L" level (see formula, 〓〓),
By setting the threshold values of V _{AB (L} ‖ _H) and V _{AB (H} ‖ _L) , hysteresis characteristics are given to the Schmitt circuit.

(Effects of the Invention) The Schmitt circuit of the present invention essentially connects only a first current mirror circuit to a pair of transistors constituting a differential amplifier circuit, and connects a pair of transistors constituting a differential amplifier circuit with a switching element. A second current mirror circuit is connected to the second current mirror circuit, and the output side current of the differential amplifier circuit is fed into the second current mirror circuit to variably control the current value for setting the threshold value of the first current mirror circuit. Since the various parameters that determine the characteristics of the circuit are configured so that they do not depend on the constant current value itself, variations in characteristics can be reduced, and the threshold level,
Fluctuations in the potential difference and hysteresis width between two inputs of the differential amplifier circuit are suppressed, and stable circuit operation can be performed. In addition, unlike the conventional hysteresis comparator described above, it does not use a diode or reference power supply for hysteresis control, so it is not affected by changes in the diode's forward voltage characteristics due to temperature changes or fluctuations in the reference power supply. Therefore, stable circuit operation can be achieved. Furthermore, since the two inputs of the differential amplifier circuit can be compared as variable inputs, the scope of use is wide.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a Schmitt circuit according to the present invention, and FIG. 2 is a circuit diagram showing a conventional example. 1... Emitter side connection point, 2... First current mirror circuit, 3... Second current mirror circuit, 4... First constant current circuit, 5... Second constant current circuit, Q ₁ ~Q ₉ ...transistor.

Claims (1)

[Claims] 1. Comparison of a pair of transistors constituting a differential amplifier circuit, a first constant current circuit connected to the emitter side connection point of these pair of transistors, and collector current flowing through these pair of transistors. a first current mirror circuit proportional to the first constant current circuit; and between the output side of the second constant current circuit and the output side of the differential amplifier circuit. a second current mirror circuit that is connected to the differential amplifier circuit and variably controls a current value for threshold setting of the first current mirror circuit by flowing an output side current of the differential amplifier circuit; A Schmitt circuit comprising: a switching element that switches the second current mirror circuit according to an output.