JPH0347608B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is used as a comparison circuit that compares an input signal level with one threshold voltage and outputs the magnitude thereof.

[Summary] In a comparator circuit that uses a differential circuit and sets the threshold voltage by self-bias, the current of a resistor circuit that provides self-bias is controlled by two current mirror circuits, and the input current of this current mirror circuit is connected to an external terminal. By changing it according to the external circuit to be connected, it is possible to set an arbitrary threshold voltage.

[Conventional technology]

2. Description of the Related Art Conventionally, a comparator circuit is widely known in which an input signal is applied to one input using a differential circuit, and a resistor circuit is connected to the other input to set a threshold voltage using a self-bias.

FIG. 1 is a circuit diagram of such a conventional comparison circuit. In the same figure, two transistors 1 and 2
Their emitters are commonly connected and connected to a constant current source 3 to form a differential circuit. Bias resistors 4 and 5 are connected to the base of transistor 1, and self-biasing resistors 6 and 7 are connected to the base of transistor 2, respectively. An output circuit consisting of transistors 18, 8, and a resistor 9 is connected to the collector of the transistor 1. A diode 10, a Zener diode 11, and a resistor 12 constitute a voltage stabilizing power supply circuit, which supplies a stabilized power supply voltage Vs to the differential transistors 1 and 2. Note that the terminals in the figure are designated by the input terminal 13, the output terminal 14, the unregulated power supply terminal 15, the ground terminal 16, and the stabilized power supply terminal 17.

In this circuit, if the base bias potentials of transistors 1 and 2 are Va and Vb, then
Base bias potential Vb is base bias potential Va
Va＝R ₅ /R ₄ +R ₅・Vs ……(1) Vb＝R ₇ /R ₆ +R ₇・Vs ……(2) (However, R ₄ , R ₅ , R ₆ , _R7 are resistors 4,
5, 6, 7 resistance values).

In this comparator circuit, a signal input from input terminal 13 sets a threshold voltage, which is the minimum value required for transistor 1 to become conductive.
Vth is expressed as Vth=V _B −V _A (3).

The relationship between the input voltage Vin and the output voltage _V0 of this conventional example circuit is as shown in Figure 2, and the input voltage
When Vin exceeds the threshold voltage Vth, an output voltage V ₀ is output to the output terminal 14.

[Problem that the invention seeks to solve]

Although this conventional comparison circuit is a convenient circuit that does not require an external voltage to be applied to set the threshold voltage, the threshold voltage is fixed at a constant value. Particularly when this circuit is configured as a semiconductor integrated circuit, the threshold voltage cannot be changed depending on the application because the elements cannot be changed. Therefore, there is a drawback that a separate circuit must be designed and manufactured for each threshold voltage.

Furthermore, in conventional circuits, when trying to compare minute input AC signal levels, there is a problem that deviations and variations between the input side bias voltage and the reference voltage side bias voltage deteriorate the accuracy of the detection level.
There was a drawback that the detection accuracy could not be improved.

The present invention has been made to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a comparator circuit that can easily change the threshold voltage according to the application by external operation and that can provide high detection accuracy. .

[Means for solving problems]

The present invention provides an external terminal for connecting an external circuit, and provides a first circuit that generates an output current proportional to an input current generated by an external circuit (generally a resistor) connected to the external terminal. A current mirror circuit is provided, and the output current of this first current mirror circuit is connected to pass through a resistor circuit that provides the self-bias voltage of the differential circuit, and the current passing through this resistor circuit is further controlled to a stable value. The second current mirror circuit is characterized in that a low-pass filter for removing alternating current components of the input signal is inserted between the input signal terminal and the resistance circuit.

[Effect]

With this configuration, by changing the value of the external circuit connected to the external terminal, the output current of the first current mirror circuit is changed, the current of the resistor circuit is changed, and the threshold voltage of the comparison circuit is changed.

One resistor is sufficient for the external circuit connected to the external terminal, and by selecting the value of this resistor, the threshold voltage can be substantially changed.

The set threshold voltage is maintained stably by the action of the second current mirror circuit.

Furthermore, the threshold voltage, which is the difference between the bias voltage of the input signal and the bias voltage of the reference voltage, can be arbitrarily set externally by the current value of the above-mentioned resistor circuit, making it possible to compare input signals with high precision.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

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

In FIG. 3, the input signal Vin input from the input terminal 13 is led to the base of a transistor 21 via a capacitor 20, and the emitter of the transistor 21 is connected to the bases of transistors 24 and 25 via resistors 22 and 23, respectively. Further, the collectors of the transistors 24 and 25 are commonly connected and led to the stabilized power supply terminal 17. Further, a capacitor 42 whose other end is connected to a common potential is connected between one end of the resistor 23 and the base of the transistor 25.

Transistors 26 and 27 constitute a differential circuit. The emitters of the transistors 26 and 27 are commonly connected and led to a constant current source 28. An input signal is applied to the base of the transistor 26 from the emitter of the transistor 24. Further, the base of transistor 27 is connected to one end of a resistor circuit composed of resistors 30 and 39 to provide a bias voltage. 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. Further, the emitter of the transistor 25 is connected to the connection point between the resistors 30 and 39.

Transistors 35 and 36 constitute a first current mirror circuit. transistors 37 and 38
constitutes a second current mirror circuit. In this example, the transistor 35 has two collectors with equal characteristics, and is configured so that the current flowing through the two collectors is equal. An external circuit is connected between external terminal 41 and ground terminal 16. Here, the variable resistor 40 connects the external terminal 41 and the ground terminal 16.
An example is shown in which it is externally connected between. Its resistance value can be changed arbitrarily. The control current flowing from the transistor 36 to the external variable resistor 40 is
I ₁ and the current flowing through each collector of the transistor 35 is I ₂ , the first current mirror circuits 35 and 36
controls the ratio of its input current I ₁ to its output current I ₂ to a constant value of 1:m. Further, the second current mirror circuits 37 and 38 are configured so that one of the two collector currents of the transistor 35 is applied to the transistor 38 and becomes an input current, and the output current appearing in the transistor 37 is always equal to this input current. control.

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

The control current I ₁ flowing to the external terminal 41 is I ₁ = Vs − Vbe ₃₆ /R ₄₀ (4) (where, Vs is the stabilized power supply voltage, Vbe ₃₆ is the forward voltage between the emitter and base of the transistor 36, and R ₄₀ is the resistance value of the variable resistor 40). The ratio between this current I ₁ and the current I ₂ flowing through one collector of the transistor 35 is a constant value of 1:m due to the action of the first current mirror circuit as described above, and the base current flowing through the transistor 27 is ignored. Therefore, the potential difference V ₃₀ that occurs across the resistor 30 is: V ₃₀ = I ₂ · R ₃₀ = m · I ₁ · R ₃₀ = m · (Vs − Vbe ₃₆ ) · R ₃₀ /R ₄₀ ...(5) becomes. Resistors 22 and 23, transistors 24 and 2
5. If the resistors 29 and 31 are matched, the emitter-collector voltages of transistors 24 and 25 will cancel each other out, and the voltages between transistors 26 and 27 will cancel each other out.
The threshold voltage of a differential circuit consisting of
Vth′ is equal to V ₃₀ , and Vth′=V ₃₀ ……(6).

That is, the input AC signal is biased from the input terminal 13 via the capacitor 20 and is input to the base of the transistor 21 . The emitter output of this transistor 21 is inputted to a transistor 24 via a resistor 22, and the alternating current component is removed by a low-pass filter formed by a resistor 23 and a capacitor 42, and then inputted to the base of a transistor 25. Therefore, a bias voltage+AC component appears at the emitter of the transistor 24, and a bias voltage appears at the emitter of the transistor 25.
Therefore, transistor 24 and transistor 2
The DC potential difference between the emitters of No. 5 becomes zero.

Therefore, the DC potential difference between transistor 26 and transistor 27 is only the voltage V ₃₀ provided by resistor 30, and this voltage V ₃₀ becomes the threshold voltage Vth'. This threshold voltage can be precisely controlled by using the current mirror circuit as described above, and can be arbitrarily set using the variable resistor 40, so that the comparison levels of various input AC signals can be detected with high accuracy.

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

FIG. 4 is a diagram showing the relationship between the threshold voltage Vth' of the comparator circuit according to the present invention and the resistor 40. As the resistance value R ₄₀ of the resistor 40 increases,
This shows how the threshold voltage Vth' decreases.

[Effects of the Invention] As described above, the comparison circuit according to the present invention is a circuit that does not require a separate reference voltage;
The threshold voltage can be changed arbitrarily by an external circuit, and the dynamic range can be increased. Therefore, a comparison circuit with one type of design can be used for many different applications. Furthermore, since the threshold voltage can be precisely set from the outside, it is possible to improve the detection accuracy for minute input AC signals.

Therefore, the manufacturing cost becomes cheaper due to the mass production effect. Furthermore, since the circuit of the present invention can be configured by connecting differential transistors and resistors, it is extremely suitable for semiconductor integrated circuit implementation.

[Brief explanation of drawings]

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. Figure 4 shows the threshold voltage of the comparator circuit according to the present invention.
5 is a diagram showing the relationship between Vth' and variable resistor 40. FIG. 26, 27...Transistors forming a differential circuit 35, 36...Transistors forming a first current mirror circuit, 37, 38...Transistors forming a second current mirror circuit, 40...As an external circuit variable resistor, 41...external terminal.

Claims (1)

[Claims] 1. Resistor circuits 30, 3 to which the input signal Vin is applied to one input and which provides a bias potential to the other input.
In the comparator circuit including differential circuits 26 and 27 to which 9 is connected, low-pass filters 23 and 24 for removing alternating current components of the input signal are inserted between the input terminal of the input signal and the resistance circuit, and the external An external terminal 41 is provided for connecting the circuit, and two output currents proportional to the input current _I1 generated according to the external circuit connected to this external terminal are provided.
First current mirror circuit 35, 3 that generates I ₂ , I ₂
6, and one of these two output currents is connected to the input,
The other of these two output currents is the resistance circuit 30,
a second current mirror circuit 37, 38 connected to the output via 39.