JPH0326564B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the configuration of a drive stage of a comparison circuit, and more particularly to the arrangement of drive stage transistors of a comparison circuit in which a reference potential is set small in advance.

FIG. 1 shows a gain control circuit using a conventional comparison circuit. In FIG. 1, 1 is a signal input terminal, 2 is an amplifier, 3 is a constant current source, and 4 is a power supply terminal. A region 5 surrounded by a broken line indicates a comparison circuit. In the comparison circuit 5, a first transistor _Q1 having a second conductivity type, a second transistor _Q2 having a first conductivity type, a second resistor _R2 ,
A buffer stage is established by the fourth capacitor _C4 . The differential amplification stage includes third to fifth transistors.
It consists of Q ₃ to Q ₅ , DC voltage sources V _A and V _B , third and fourth resistors R ₃ and R ₄ , and constant current source 3 .

The fourth and fifth transistors Q ₄ and Q ₅ have a differential amplification configuration, and have voltages V A and V _A at their respective bases.
V _B is given. Since the potential relationship is set to V _A > V _B , all of the current I ₀ sent from the constant current source 3 flows to the fourth transistor Q ₄ when there is no signal. Therefore, since no current flows through the second, third and fifth transistors Q ₂ , Q ₃ , Q ₅ , no voltage appears on the pace of the first transistor Q ₁ and the first transistor _Q1 is in the off state. Next, an input signal is applied to the signal input terminal 1, and the pace of the fifth transistor _Q5 is V _A and V _B
When a signal equal to or higher than the voltage difference [V _A −V _B ] is applied, the fifth transistor Q ₅ is turned on. When the fifth transistor Q ₅ turns on, a current I ₀ flows from the constant current source to the second and third transistors Q ₂ and Q ₃ , which causes the first transistor
Since a voltage is applied to the pace of Q ₁ , the first transistor Q ₁ is turned on, and the impedance between the collector and emitter of the first transistor Q ₁ changes. Therefore, gain control can be performed by the ratio between this impedance and the resistor _R1 .
By the way, in the conventional comparison circuit shown in FIG. 1, in order to turn on the first transistor _Q1 , the pace voltage V _C is generally the forward voltage between the pace and emitter of the transistor, that is, about 0.7V.
is necessary. However, in a circuit that requires a fast response speed, such as a pulse noise removal circuit, it is preferable that the pace voltage V _C be as small as possible.

An object of the present invention is to turn on a second transistor of a first conductivity type, thereby turning on a first transistor of a second conductivity type, which has a time constant circuit constituted by a parallel circuit of a resistor and a capacitor connected to its base.
In a differential amplification comparison circuit that controls a feedback loop by turning on a transistor of the second conductivity type, a pace voltage that is slightly lower than that of turning on a transistor of the second conductivity type is set in advance, and thereby the second conductivity type transistor is turned on. It is an object of the present invention to provide a comparator circuit equipped with a drive circuit configured to slightly increase the pace potential of a transistor of conductivity type and easily turn on the transistor.

A comparator circuit according to the present invention turns on a second transistor of a first conductivity type, and a time constant circuit constituted by a parallel circuit of a resistor and a capacitor is connected to a base of a second transistor of a second conductivity type. This is an improved differential amplification type comparison circuit that controls a feedback loop by turning on one transistor. In the present invention, the second
A drive circuit is inserted between the base terminal of the first transistor of conductivity type and the time constant circuit, and the drive circuit has a constant current circuit, and divides the constant current of the constant current circuit, and divides the constant current of the constant current circuit. The shunt circuit is connected to the base terminal of the first transistor of the second conductivity type via a dividing resistor or a differential circuit of transistors, and the other shunt circuit is connected to the base terminal of the first transistor of the second conductivity type. connected, the base terminal of a transistor of the same conductivity type as the first conductivity type is connected to the time constant circuit, and when there is no output from the differential amplification type comparison circuit, the base terminal of the transistor of the same conductivity type as the first conductivity type is connected to the time constant circuit. The base voltage of the first transistor is set to a voltage slightly lower than the voltage that turns on this transistor, and the second transistor of the first conductivity type is turned on by the output of the differential amplification type comparison circuit. , the transistor of the same conductivity type as the first conductivity type is turned off, and the first transistor of the second conductivity type is turned on.

FIG. 2 shows an embodiment of a comparator circuit according to the present invention. Elements having the same functions as those in the conventional comparative circuit example shown in FIG. 1 are given the same numbers in FIG. 2 as well. In the circuit of Fig. 2, the first
In addition to the configuration shown in the figure, a drive circuit 7 is added.

When no signal is applied to the pace of the fifth transistor Q ₅ , no collector current flows through the second and third transistors Q ₂ and Q ₃ , so the following equation holds true.

V _D =V _BEQ6 +IQ ₆ /1+h _FEQ6 ×R ₂ ≒V _BEQ6 ……(1) V _E =R ₆ /R ₅ +R ₆ ×V _D ≒R ₆ /R ₅ +R ₆ ×V _BEQ6 ……(2) I ₆ = IQ ₆ + IR ₅ where V _BEQ6 is the pace-to-emitter forward voltage of the sixth transistor Q ₆ (which is a transistor of the same conductivity type as the first conductivity type described in the claims), and h _FEQ6 is the current amplification factor of the sixth transistor _Q6 . Also, IQ ₆ is the emitter current of the sixth transistor Q ₆ and V _D is the emitter current of the sixth transistor Q ₆
is the emitter potential of IR ₅ is the current flowing through the fifth and sixth resistors R ₅ and R ₆ .

Note that the second transistor of the first conductivity type refers to the transistor _Q2 , and also refers to the first transistor of the second conductivity type.
The transistor refers to transistor _Q1 .

The current I ₆ from the constant current source 6 is divided into a current IR ₅ and a current IQ ₆ , thereby causing the first transistor Q ₁
A voltage V _E is applied to the pace of . Voltage V _E is the second (2)
The fifth and sixth resistors, as shown in Eq.
It can be set arbitrarily depending on the ratio of R ₅ and R ₆ . For example, if the ratio of _the fifth resistor R ₅ to the sixth resistor R ₆ is 1:4, in order for the first transistor Q 1 to turn on, the base-emitter voltage V _BEQ1 of the transistor Q ₁ must be approximately Must be 0.7V or higher. That is, R ₆ (V _BEQ6 + V _B ) / (R ₅ + R ₆ ) ≧V _BE = V _BEQ1 ……(4) 4/5×(V _BEQ6 +V _B )≧V _BEQ1 ……(4)′ V _B ≧ 1/4×V _BEQ1 ...(4)'' In the circuit of FIG. 2 showing the comparison circuit according to the present invention, no signal is input from the amplifier 2, and the signal is input to the base of the fifth transistor _Q5 . When is not applied, the second transistor Q ₂ is turned off and the constant current I ₆ is shunted and IQ ₆
and IR ₅ . The current IR ₅ flows through the resistors R ₅ and R ₆ , and the first transistor Q ₁ is turned off with the voltage of 4/5V _BEQ1 applied to the base of the first transistor Q ₁ .

On the other hand, IQ ₆ flows through the sixth transistor Q ₆ and it is turned on.

In this state, when a signal is generated from the amplifier 2, the transistor _Q5 turns on and the second transistor _Q2 turns on, so the base potential _VB applied to the base of the sixth transistor _Q6 becomes high and the IQ of the transistor _{Q6 increases} . The current in _{IR 5} decreases and the current in IR ₅ increases. 1/4V _BE at the base of transistor Q ₆
When V BEQ1 is applied, the base potential of the first transistor Q ₁ reaches V _BEQ1 , so the first transistor Q ₁ is turned on. Therefore, this makes it possible to realize a circuit with a high response speed.

FIG. 3 shows a second embodiment of the comparison circuit according to the present invention. 8 is a power supply, 9 is a ground terminal, 10 is a signal input terminal, and 11 is a signal source.

This figure omits that the output of the amplifier 2 is connected to the signal source 11.

The transistor Q ₈ corresponds to the second transistor of the first conductivity type, and the transistor Q ₁₄ corresponds to the first transistor of the second conductivity type. Also, the first
The transistor _Q10 has the same conductivity type as the transistor Q10.

The drive circuit includes a constant current source 12, a transistor Q ₉ ,
It consists of Q ₁₀ , Q ₁₁ , Q ₁₂ , Q ₁₃ and a reference voltage V _ref . This embodiment is an example in which a differential circuit is used for the drive circuit.

Transistors Q ₉ , Q ₁₀ , Q ₁₁ , Q ₁₂ and Q ₁₃ are matched, and a reference potential V _ref is applied to the base of transistor Q ₁₂ . When no signal is input to the signal source 11, the transistor _Q8 is turned off and the base potential _VB of the transistor _Q10 is not increased, so the transistor _Q10 is turned on.

On the other hand, transistors Q ₁₁ , Q ₁₂ and Q ₁₃ are turned off, and current from constant current source 12 is not flowing.

When a signal is input to the signal source 11, the transistor
_Q8 turns, base on potential _VB rises, and transistor _Q10 is forced to turn off. Therefore, the current of the constant current source 12 flows through the transistors Q ₁ , Q ₁₂ and Q ₁₃ , turns on the transistor Q ₁₄ , and changes the impedance between the collector and emitter of the transistor Q ₁₄ . Since all of the comparison circuits shown in FIG. 3 have a differential configuration, there is no temperature dependence and it is possible to easily realize a circuit with a fast response speed.

As described above, the comparison circuit according to the present invention has the effect that the reference potential can be made small, and further has the effect that it can be extremely easily adapted to a comparison circuit with a fast response speed such as a noise removal circuit. .

[Brief explanation of drawings]

FIG. 1 is a block diagram of a gain control circuit using a conventional comparison circuit. FIG. 2 is a block diagram showing a first embodiment of a gain control circuit using a comparison circuit according to the present invention. FIG. 3 is a block diagram showing a second embodiment of a gain control circuit using a comparison circuit according to the present invention. 1, 10...signal input terminal, 2...amplifier,
3, 6... constant current source, 4, 8... power supply terminal,
5...Comparison circuit, 7...Drive circuit, 9...Ground terminal, 11...Signal source, _Q1 to _Q14 ...Transistor, _R1 to _R6 ...Resistor, _C1 to _C4 ...Capacitor ,
V _A , V _B ... DC voltage source, V _ref ... Reference voltage.

Claims (1)

[Claims] 1 By turning on the second transistor of the first conductivity type, the time constant circuit constituted by a parallel circuit of a resistor and a capacitor turns on the first transistor of the second conductivity type connected to the base. In the differential amplification comparison circuit that controls the feedback loop by controlling the state, a drive circuit is inserted between the base terminal of the first transistor of the second conductivity type and the time constant circuit, and the drive circuit is configured to a constant current circuit, the constant current of the constant current circuit is shunted, and one of the shunt circuits is connected to the base terminal of the first transistor of the second conductivity type via a dividing resistor or a differential circuit of transistors. and the other shunt circuit is connected to a transistor of the same conductivity type as the first conductivity type, and is configured by connecting a base terminal of the transistor of the same conductivity type as the first conductivity type to the time constant circuit, When there is no output from the differential amplification type comparison circuit, the base voltage of the first transistor of the second conductivity type is set to a voltage slightly lower than the voltage that turns on this transistor. The second transistor of the first conductivity type is turned on by the output, and the transistor of the same conductivity type as the first conductivity type is turned off. A comparison circuit characterized in that it is configured to turn on a first conductive type transistor.