JP2002040060A - Monitoring circuit - Google Patents

Abstract

(57) Abstract: The present invention relates to a monitoring circuit, and an object of the present invention is to provide a monitoring circuit that can accurately detect a current flowing through a current detection resistor with a simple circuit. The transistor circuit includes a current detection resistor Re and generates a signal corresponding to a current flowing through the current detection resistor; a current mirror pair 20 connected to the transistor circuit 10; A current detection circuit 3 for detecting a current signal corresponding to the current flowing through the resistor Re;
0 is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a monitoring circuit, and more particularly to a monitoring circuit for detecting a loop current in a subscriber circuit.

[0002]

2. Description of the Related Art A so-called BORSCHT function is known as a main function of an analog subscriber circuit mounted on a time-division electronic exchange. BORSCHT means B (direct current supply), O (overvoltage protection), R (call signal transmission), S (monitoring), C (codec), H (hybrid (2-wire / 4-wire conversion)), T (test ).

Here, in the monitoring function S, a main function of the monitoring function is to monitor a DC current (loop current) value supplied to the subscriber and to transmit the state of the subscriber to a higher-level device. At present, most of the main functions of the subscriber circuit are realized by a semiconductor integrated circuit (IC), and each circuit needs to have a circuit configuration suitable for the semiconductor integrated circuit. Therefore, conventionally, a mirror circuit as shown in FIG. 5 has been used, or a differential amplifier using an operational amplifier as shown in FIG. 6 has been used.

FIG. 5 is a diagram showing an example of a conventional circuit using a current mirror circuit. A current mirror circuit is formed by the transistors Q1 and Q2. I0 is used as a program current, and a current flowing through the collector of Q2 is connected to the current detection circuit 1 as If. The emitter of the transistor Q0 is connected to the emitter of Q1, and the base of Q0 is connected to the current detection resistor Re.

A mirror current ratio setting resistor R1 is connected to the emitter side of the transistor Q2, then the emitter of the transistor Q3 is connected, and the base of Q3 is connected to the other end of the current detecting resistor Re. The operation of the circuit thus configured will be described as follows.

In the above connection, the current flowing through the current detection resistor Re (loop current: hereinafter simply abbreviated as current) IIf
, And a current detection circuit 1 monitors IIf. Here, the current If flowing through the current detection circuit 1 is represented by the following equation.

If = (((IIf × Re) + Vbe0 + Vbe1)-(Vbe2 + Vbe3)) / R1 (1) However, the identification code is used as it is as the resistance value (the same applies hereinafter), and Vbei is the base of the i-th transistor.・
It indicates the voltage between the emitters. Here, the base-emitter voltage Vbe of the transistor used is Vb
If e0 ≒ Vbe3 and Vbe1 ≒ Vbe2, the equation (1) is simplified as follows.

If = IIf × (Re / R1) (2) From the equation (2), it can be seen that If corresponds to the current IIf flowing through the current detection resistor Re. Therefore, the current flowing through the current detection resistor Re can be monitored based on the current If detected by the current detection circuit 1.

FIG. 6 is a diagram showing an example of a conventional circuit using an operational amplifier. A current detection resistor Re is connected between two input terminals of a differential amplifier using the operational amplifier U1. A resistor R1 'is connected in series to the output of the differential amplifier. The input side resistance of the differential amplifier is Rs1, Rs2, and Rs1 = Rs2 = R
s. Let the feedback side resistance be Rf1 and Rf2,
f1 = Rf2 = Rf.

With such a connection, the current detecting resistor R
The following equation holds between the current IIf flowing through the resistor e and the current If flowing through the resistor R1 '. The output Vo of the differential amplifier is expressed by the following equation.

Vo = (Rf / Rs) × (Vsp−Vsm) (3) Here, Vsp and Vsm are voltages applied to both ends of the current detection resistor Re. Vsp−Vsm = IIf × Re, V
Since o = If × R1 ′, the following equation is obtained by solving equation (3) for If.

If = (Rf / Rs) × IIf × Re × (1 / R1 ′) (4) Equation (4) indicates that the current If flowing through the resistor R1 ′ corresponds to the current IIf flowing through the current detection resistor Re. It shows that they have a relationship. Therefore, the current IIf can be detected by measuring If.

Similarly, the following equation is established between the current IIr flowing through the current detecting resistor Re in the opposite direction and the current Ir flowing through the resistor R1 ', and IIr can be monitored. Ir = (Rf / Rs) × IIr × Re × (1 / R1 ′) (5)

[0014]

In the case of the conventional circuit shown in FIG. 5, when it is necessary to detect the reverse current flowing through the current detecting resistor Re, a reverse current detection circuit is also required. Becomes complicated. When the program current I0 of the current mirror circuit is fixed, errors occur in Vbe0 and Vbe3, Vbe1 and Vbe2 due to the change of IIf,
The linearity of If and IIf cannot be obtained. That is,
Equation (2) does not hold.

Further, in the case of the conventional circuit shown in FIG. 6, since the operational amplifier circuit is used, the circuit scale becomes very large and the unit price of the semiconductor integrated circuit increases. The present invention has been made in view of such problems,
It is an object of the present invention to provide a monitoring circuit capable of accurately detecting a current flowing through a current detection resistor Re with a simple circuit.

[0016]

(1) FIG. 1 is a principle circuit diagram of the present invention. In the figure, reference numeral 10 denotes a current detection resistor R
e, a transistor circuit that generates a signal corresponding to the current flowing through the current detection resistor Re, and 20 is a current mirror pair including transistors Q7 and Q8 connected to the transistor circuit 10. Reference numeral 30 denotes a current detection circuit that detects a current signal corresponding to the current flowing through the current detection resistor Re.

With this configuration, the current detecting resistor R
By configuring the transistor circuit 10 such that the current flowing through e and the current detected by the current detection circuit 30 have a corresponding relationship, the current can be accurately detected with a simple circuit.

(2) The invention according to claim 2 is characterized in that one transistor is cascade-connected to the current mirror pair 20 to form a Wilson type. With this configuration, a constant voltage drop of 2 Vbe is given as the base-emitter voltage of the added transistor,
Stable constant current characteristics can be obtained.

(3) The invention according to claim 3 is characterized in that a feedback current corresponding to the current detected by the current detection circuit 30 is applied to a current source provided in the transistor circuit 10.

With this configuration, the current detecting resistor R
It is possible to reduce power consumption in a state where no current flows through e or in a state close to it. Further, in the present invention, by adding an emitter resistor to the transistor forming the current mirror pair, it is possible to reduce the influence of Vbe fluctuation due to a change in Vce voltage of the transistor forming the mirror circuit.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a circuit diagram showing a first embodiment of the present invention. 1 are denoted by the same reference numerals. In the figure, reference numeral 20 denotes a current mirror pair composed of transistors Q7 and Q8;
Reference numeral 30 denotes a current detection circuit that detects a loop current flowing through the current detection resistor Re. Reference numeral 10 denotes a transistor circuit connected to the current mirror pair 20, and transistors Q11 to Q11
Q16 and resistors R11 and R12. Re
Is a current detecting resistor for detecting a loop current, both ends of which are connected to the bases of the transistors Q11 and Q16, respectively. The operation of the circuit thus configured will be described as follows.

This circuit also generates a current If proportional to the current IIf and a current Ir proportional to the current IIr, and monitors the currents IIf and IIr, as in the conventional circuit described above.
When no current flows through the current detection resistor Re, both ends of Re are at the same potential, and the transistor Q16 of the resistor R12
And the emitter side of the transistor Q11 of the resistor R11 are also at the same potential. Therefore, the current from the constant current source I1 passes through the transistors Q15 and Q13, and
Flow through the resistors R12 and R11. Transistor Q1
4 and Q12, the bases and the emitters are connected in the same manner as the transistors Q15 and Q13, so that
Is flowing.

The circuit operation for detecting the loop current IIf in this state is as follows. When the current IIf flows, the potential on the emitter side of the transistor Q11 of the resistor R11 increases by １ ／ of the voltage generated in the current detection resistor Re. Conversely, the emitter side of the transistor Q16 of the resistor R12 drops by half the voltage generated at the resistor Re.

These voltage fluctuations are transferred to transistor Q1
4 increases the flowing current, and the transistor Q12 functions to decrease and correct. At this time, the transistor Q14
And the current flowing through Q12 is output as If.

When the base-emitter voltage of the transistor is Vbe, Vbe11 ≒ Vbe16, Vbe12 = Vbe
When 13 = Vbe14 = Vbe15, the current detection circuit 30
Is output as follows. If = I1 / 2 + (((IIf × Re) / 2) / R12) / 2− (I1 / 2 − (((IIf × Re) / 2) / R11) / 2) = (((IIf × Re)) / (2) / R12) / 2 + (((IIf × Re) / 2) / R11) / 2 = ((IIf × Re) / 2) × (1 / R12) × (1/2) + ((IIf) × (Re) / 2) × (1 / R11) × (1/2) = ((IIf × Re) / (2 × R12 × 2) + ((IIf × Re) / (2 × R11 × 2) = ( (IIf × Re) / (4 × R12) + ((IIf × Re) / (4 × R11) (6) Here, if a constant is set so that R11 = R12 = N × Re, the equation (6) becomes It is as follows: If = (IIf × Re) / (4 × N × Re) + (IIf × Re) / (4 × N × Re) = 2 × (IIf × Re) / (4 × N × Re) ) = IIf / When 2 × N) (7) is set to N = 500 as an example, If the equation (7) =
IIf / 1000, which indicates that If is proportional to the loop current IIf.

The same applies to the current IIr in the opposite direction to IIf. In the case of IIr, unlike IIf, the voltage applied to the resistor R11 increases compared to the voltage applied to the resistor R12 due to the voltage generated at the current detection resistor Re. Therefore, the current Ir flowing to the current detection circuit 30 is as follows: The current value is the same as If and the current direction is reversed. Ir = I1 / 2 + (((IIr × Re) / 2) / R11) / 2− (I1 / 2 − (((IIr × Re) / 2) / R12) / 2) = (((IIr × Re) / (2) / R11) / 2 + (((IIf × Re) / 2) / R12) / 2 = ((IIr × Re) / 2) × (1 / R11) × (1/2) + ((IIr × (Re) / 2) × (1 / R12) × (1/2) = ((IIr × Re) / (2 × R11 × 2) + ((IIr × Re) / (2 × R12 × 2) = ( (IIr × Re) / (4 × R11) + ((IIr × Re) / (4 × R12) (8) Here, if it is set so that R11 = R12 = N × Re, the equation (8) becomes Ir = (IIr × Re) / (4 × N × Re) + (IIr × Re) / (4 × N × Re) = 2 × (IIr × Re) / (4 × N) × Re) = II The / (2 × N) (9) (9) is found. Over that Ir is proportional to the IIr from the equation, and the current flowing through the current detection resistor Re,
By configuring the transistor circuit 10 so that the currents detected by the current detection circuit 30 have a corresponding relationship, the current can be accurately detected with a simple configuration.

In the circuit configuration shown in FIG. 2, the following problems remain. Problem 1 Due to the circuit configuration, it is possible to output to the current detection circuit 30 only a current value within the current value of I1. It is necessary to supply a current equal to or more than (1 / N) times the maximum detection loop current value as I1, but if I1 is fixed under the above conditions, the loop current does not flow or extra power is consumed when the loop current is small. .

Problem 2 The voltages generated in the resistors R11 and R12 are different due to the flow of the loop current. Thereby, the transistors Q7 and Q8
And a collector-emitter voltage V
A difference occurs between ce7 and Vce8. Early effect (described later)
Then, when the mirror ratio is shifted, the current (If = IIf / 2 × N, Ir = IIr / 2 ×) output to the current detection circuit 30 is output.
N) has an error.

The following measures are taken against these problems. Countermeasure for Problem 1 I1 has a fixed current required by the loop current detection circuit and a feedback current configuration of the current output to the current detection circuit.

Countermeasure for Problem 2 By adding an emitter resistor to the mirror circuit 20,
Collector-emitter potential Vc of transistors Q7 and Q8
e) the influence of the change in the base-emitter voltage Vbe due to the voltage change is apparently reduced, or the transistor Q8
The transistor Q9 is cascaded to form a Wilson-type transistor so that the transistor Q9
A stable constant current characteristic can be obtained by giving a constant voltage drop of 2 × Vbe as the base bias of the transistor.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals. In this embodiment, in addition to the circuit shown in FIG. 1, a point that one transistor Q9 is cascaded to the current mirror pair 20, and a feedback signal is supplied from the current detection circuit 30 to the constant current source I1. It is a point that was made. Other configurations are the same as those of the circuit shown in FIG. The operation of the circuit thus configured will be described as follows.

Since the detailed operation of the circuit is as described with reference to FIG. 1, here, the effect of adding the transistor Q9 and the effect of providing a feedback signal will be described.

(A) Description of Basic Current Mirror Circuit Generally, the current amplification factor hfe of a transistor is
It fluctuates according to the emitter-to-emitter voltage Vce. Vce of the output transistor Q8 of the current mirror pair 20 is equal to Vbe because the base and the collector are connected. On the other hand, in the transistor Q7 on the program side, Vce also fluctuates due to the fluctuation of the load. The output current deviates from the set value due to the difference between Vce between the program side and the output side transistor (early effect).

(B) Description of Wilson-type current mirror circuit In the case of the Wilson-type current mirror shown in FIG. 3, a transistor Q9 is cascade-connected to a basic current mirror pair 20. Therefore, Vce of the program side transistor Q7 becomes 2 × Vbe, and Vce of the output side transistor Q8 becomes Vbe. For this reason, Vce of the added transistor Q9 is responsible for the load fluctuation.
Therefore, the output side transistor Q of the current mirror pair 20
The Vce of 8 is not affected by the fluctuation of the load, and the output current also becomes the value as set.

Next, the effect of the feedback circuit will be described. The current Ifb for the feedback must always be in a direction to be added to the fixed amount regardless of the direction of the current flowing through the current detection resistor Re. Specifically, Ifb
= If, and Ifb = -Ir, the fixed component can be reduced to a small value, and there is no need to supply useless current even when there is no or little loop current, and the power consumption is extremely low. Can be.

FIG. 4 is a circuit diagram showing a specific embodiment of the present invention. In the circuit shown in the figure, the circuit shown in FIG. 3 is provided on each of the A line side and the B line side. The A-line side component and the B-line side component are denoted by a and b, respectively.

This circuit is an analog subscriber circuit mounted on a time-division electronic exchange, which is generally used for an A line,
This is an application example in the case of having a DC current supply function to the B line and having current detection circuits 30a and 30b, respectively. A telephone 42 is connected between the A line and the B line. Here, A
The values of the DC currents flowing through the line and the line B are detected, and the values are added by the adder 40, and then halved by the arithmetic unit 41 to obtain the feedback for the lines A and B. Reference numeral 30c denotes a current detection circuit which receives the addition result of the adder 40.

The effects of the above-described embodiment of the present invention are listed below. The circuit scale is smaller than when an operational amplifier circuit is used. Higher accuracy can be obtained than when a simple mirror circuit is used. Bidirectional current detection is possible with a single circuit. This is a circuit configuration suitable for a semiconductor integrated circuit. Similarly, space can be saved. Similarly, weight reduction is possible.

(Supplementary Note 1) A monitoring circuit including a current detection resistor, generating a signal corresponding to a current flowing through the current detection resistor, a monitoring circuit including a current mirror pair connected to the transistor circuit, A monitoring circuit, comprising: a current detection circuit for detecting a current signal corresponding to a current flowing through a current detection resistor.

(Supplementary note 2) The monitoring circuit according to supplementary note 1, wherein one transistor is added to the current mirror pair to form a Wilson type. (Supplementary note 3) The monitoring circuit according to supplementary note 1, wherein a feedback current corresponding to the current detected by the current detection circuit is added to a current source provided in the monitoring circuit.

(Supplementary Note 4) The monitoring circuit according to Supplementary Note 1, wherein an emitter resistor is added to the transistor forming the current mirror pair.

[0042]

As described above, according to the present invention, the following effects can be obtained. (1) According to the first aspect of the present invention, the transistor circuit is configured so that the current flowing through the current detection resistor and the current detected by the current detection circuit have a corresponding relationship, thereby providing a simple circuit. The current can be accurately detected.

(2) According to the second aspect of the present invention, the base-emitter voltage of the added transistor is 2 V
The constant voltage drop of be can be provided, and stable constant current characteristics can be obtained.

(3) According to the third aspect of the invention, it is possible to reduce the power consumption in a state where a current does not flow through the current detecting resistor or in a state close thereto. Further, in the present invention, if an emitter resistor is added to the transistor constituting the mirror circuit, the effect of Vbe fluctuation due to Vce voltage change can be reduced.

As described above, according to the present invention, it is possible to provide a monitoring circuit capable of accurately detecting the current flowing through the current detecting resistor with a simple circuit.

[Brief description of the drawings]

FIG. 1 is a principle circuit diagram of the present invention.

FIG. 2 is a circuit diagram showing a first embodiment of the present invention.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a specific embodiment of the present invention.

FIG. 5 is a diagram showing a conventional circuit example using a current mirror circuit.

FIG. 6 is a diagram showing an example of a conventional circuit using an operational amplifier.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 transistor circuit 20 current mirror pair 30 current detection circuit Re current detection resistor Q7, Q8 transistor

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kenji Takato 4-1-1, Kamidadanaka, Nakahara-ku, Kawasaki-shi, Kanagawa F-term within Fujitsu Limited (reference) 2G035 AA09 AA20 AA26 AB01 AC02 AD02 AD10 AD20 5H420 NB03 NC02 NC27

Claims (3)

[Claims] 1. A transistor circuit comprising a current detection resistor, for generating a signal corresponding to a current flowing through the current detection resistor, a current mirror pair connected to the transistor circuit, and a current flowing through the current detection resistor A monitoring circuit, comprising: a current detection circuit for detecting a current signal corresponding to a current. 2. The monitoring circuit according to claim 1, wherein one transistor is cascaded to the current mirror pair to form a Wilson type. 3. The monitoring circuit according to claim 1, wherein a feedback current corresponding to the current detected by the current detection circuit is applied to a current source provided in the transistor circuit.