JPS5991721A - Comparison circuit - Google Patents

Abstract

PURPOSE:To change optionally a threshold voltage by providing a current sharing circuit to a differential circuit comprising two transistors (TRs). CONSTITUTION:TRs 35-38, resistors 30, 39 and a variable resistor 40 form the current sharing circuit. The TR35 has two collectors of identical characteristic and a current flowing to the two collectors is designed equal. Thus, a potential difference V30 produced across a resistor 30 is dependent on a resistance value of the resistors 30 and 40. On the other hand, the threshold voltage of the differential circuit formed by TRs 26, 27 is equal to the potential difference V30. Thus, the threshold voltage is changed optionally by mounting externally a resistor between terminals 41 and 16 and changing the resistance value of the resistor 40.

Description

[Detailed description of the invention] (Technical field to which the invention pertains) The present invention relates to a comparison circuit using differential transistors,
In particular, the present invention relates to a comparison circuit that can change the threshold level of differential transistors.

[Description of prior art]

FIG. 2 is a circuit diagram of a conventional comparison circuit. In the figure, two transistors 1 and 2 constitute a differential transistor, and their emitters are commonly connected and connected to a constant current source 3. A bias resistor 4 is installed at the base of the transistor l.
．． 5, a bias resistor 6.7 is connected to the base of the transistor 2, and an output circuit 1t'& consisting of a transistor 18.8 and a resistor 9 is connected to the collector of the transistor 1. Diode 10. zener diode 1
1. A resistor 12 is a voltage stabilized power supply circuit, which supplies a stabilized power supply voltage Vs to the differential transistors 1.2 and the like. In addition, each terminal in the same figure is input terminal 13, output terminal 1
4, an unregulated power supply terminal 15, a ground terminal 16, and a stabilized power supply terminal 17.

In this circuit, when the base potentials of the transistors 12 are Va and Vb, the base potential vb is set higher than the base potential Va, and this base potential V
a and Vb are the following formulas. However, R4, Rs, R6, and Rv are the resistance values of resistor 4, 5, 6, and 7, respectively.

is required.

In this comparator circuit, the threshold voltage vth required for the transistor 1 to enter the normal state when there is no signal input from the input terminal 13 is V th = V b
-V a -(denoted by 31).

Input terminal Vin and output voltage V of this conventional circuit.

The relationship between is as shown in Figure 2, and the input voltage Vi
When n exceeds the threshold voltage Vtl+, the output voltage VO is output to the output terminal 14.

As is clear from the above equations (1) to (3), the threshold voltage vth is fixed in this conventional comparison circuit, and when configured in a semiconductor integrated circuit, the threshold voltage vth can be changed depending on the application. There are drawbacks that cannot be changed.

[Purpose of the invention]

The present invention has been made in order to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a comparison circuit that can easily change the threshold voltage vth according to the application by changing the control current by external operation. shall be.

[Key points of the invention]

The present invention provides a circuit that provides a potential difference between the bases of two transistors of a differential circuit even when there is no input signal, and the voltage applied to this circuit is configured so that it can be changed depending on the value of Il (resistor) connected from the outside. It is characterized by what it did.

[Explanation based on examples]

Hereinafter, the present invention will be explained based on the drawings.

FIG. 3 is a circuit diagram showing an embodiment of the comparison circuit according to the present invention.

In FIG. 3, the signal input from the input terminal 13 is led to the base of the transistor 21 via the capacitor 920,
The emitters of the transistors 21 are connected via resistors 22, 23 respectively to the bases of l transistors 24, 25. Further, the collectors of the transistors 24 and 25 are commonly connected and lead to the stabilized power supply terminal 17.

Transistors 26 and 27 constitute a differential circuit, and the emitters of the transistors 26 and 27 are commonly connected and led between constant current sources. The base of transistor 26 connects the emitter of transistor 24 and
1 (grounded via the resistor 29. Also, the l transistor 27
The base of the resistor 30 is connected to one end of a resistor garden, and the other end of this resistor 30 is connected to the emitter of the transistor 25 and grounded via a resistor 31. An output circuit consisting of transistors 32 and 33, a resistor 34, and an output terminal 14 is connected to the collector of the transistor 26.

Transistors 35, 36, 37, cold resistors 30, 39 and variable resistor 40 constitute a current distribution circuit. Transistor 35 has two collectors of equal characteristics, the two
The structure is such that the current flowing through each collector is equal. Transistor 36 is diode-connected with its base and collector coupled. The variable resistor 40 is configured to be externally connected between the terminal 41 and the terminal 16, and its resistance value can be arbitrarily selected. In this current distribution circuit, when the control current flowing from the transistor 36 to the variable resistor 40 is 11, and the current flowing to each collector of the transistor 35 is 2, the ratio between the currents 11 and 12 is 1 m.

Next, the operation of this embodiment circuit will be explained.

'The control current 11 flowing to the control terminal 41 is expressed as R40, where Vs is the stabilized power supply voltage, V[+e36 is the forward voltage between the emitter and base of the transistor 36, and 1-4o is the resistance value of the variable resistor 40. The ratio of this current 11 to the current I2 flowing through one collector of the transistor 35 is l:m as described above.
Since the base current flowing through the transistor 27 can be ignored, the potential difference V30 generated across the resistor 30 is V2O-12°R3o=m°'l 1°R30. If the resistors 22 and 23, the transistors 24 and 25, and the resistors 29 and 31 are matched, the emitter-collector voltages of the transistors 24 and 25 cancel each other out, and the differential transistor composed of the transistors 26 and 27 The threshold voltage vth' of becomes equal to V2O, and V tl+e '=V2O---(61).

In this way, as is clear from the above equations (5) and (6), the threshold voltage can be arbitrarily changed by varying the resistance value of the resistor 40 in the present invention.

FIG. 4 is a diagram showing the relationship between the threshold voltage vth' and the resistor 40 of the comparator circuit according to the present invention.
The figure shows how the threshold voltage Vth' decreases as the zero resistance value V40 increases.

〔Effect of the invention〕

As described above, since the threshold level of the comparator circuit according to the present invention can be changed arbitrarily, it is suitable for various detection applications and is extremely suitable for use in semiconductor integrated circuits.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional comparison circuit. FIG. 2 is a diagram showing input/output characteristics of a conventional comparison circuit. FIG. 3 is a circuit diagram of an embodiment of a comparison circuit according to the present invention. FIG. 4 is a diagram showing the relationship between the threshold voltage Vtb'' of the comparator circuit according to the present invention and the variable resistor 4o. 2G, 27... differential transistor, 3o... resistor,
4o...variable resistance.

Claims (1)

[Claims] +1.1 It includes a differential circuit in which the emitters of two I transistors (26, 27) are connected in common, and is configured to provide a difference in bias voltage between the bases of these two transistors. , In a comparator circuit configured such that an input signal is applied to the base of one of these two transistors and an output signal is taken out from the collector of at least one of these two transistors, A receiver circuit of another transistor (35) is connected to the base bias circuit, and the base circuit of this other transistor includes a resistor (40) that determines a bias current to be applied to the base of this other transistor. The resistance value of the device (40) is the same as that of the two terminals (41, 16
) A comparison circuit characterized in that the comparison circuit is configured such that the value can be changed by the value of a resistor externally connected between ).