JP2014011433A - Electronic circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a leakage current from flowing to the external input terminal side from an internal circuit.SOLUTION: An internal circuit 8 includes a differential amplifier circuit 11. The differential amplifier circuit 11 is constituted of an operational amplifier 9 including a negative feedback circuit 10. An external input terminal 2 is connected with the inverted input terminal of the operational amplifier 9. First and second electrostatic protective elements 5, 6 are connected in series between the external input terminal 2 and the ground. A reference voltage source 3 applies a bias voltage Vref to the joint P of the first and second electrostatic protective elements 5, 6, and the non-inverted input terminal of the operational amplifier 9. Since the bias voltage Vref is also applied to the external input terminal 2 connected with the non-inverted input terminal of the operational amplifier 9 by imaginary short circuit, both ends of the first electrostatic protective element 5 have the same potential.

Description

  The present invention relates to an electronic circuit having a protection function against static electricity.

  2. Description of the Related Art An electronic circuit that inputs a signal from an external input terminal to an internal circuit is known that includes an electrostatic protection element that protects the internal circuit from static electricity applied to the external input terminal (see, for example, Patent Document 1). This electrostatic protection element is connected, for example, between an external input terminal and a constant potential portion such as a ground. However, a leakage current flows through the electrostatic protection element during high temperature operation, etc., and this leakage current causes abnormal operation of the internal circuit. May cause etc. For this reason, the electronic circuit described in Patent Document 1 includes a leakage current cancellation circuit, and a current equal to the leakage current is supplied to the electrostatic protection element by the leakage current cancellation circuit to cancel the leakage current.

JP 2009-170589 A

  By the way, since the leak current cancel circuit described in Patent Document 1 is configured by a folded structure circuit such as a current mirror circuit in order to flow a current equal to the leak current, the circuit tends to be complicated. is there. In addition, since a circuit having a folded structure is employed, it is difficult to generate a current equal to the leakage current with high accuracy, and the influence of the leakage current tends to remain.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an electronic circuit capable of preventing leakage current from flowing from an internal circuit to the external input terminal side.

  In order to solve the above problem, an electronic circuit according to the invention of claim 1 includes an external input terminal to which a bias voltage is applied, an internal circuit connected to the external input terminal, the external input terminal and a constant voltage portion. First and second electrostatic protection elements connected in series between each other, and the internal circuit has a bias voltage of the same potential at the connection point between the external input terminal and the first and second electrostatic protection elements. And a functional circuit for processing a signal input from the external input terminal.

  According to a second aspect of the invention, the internal circuit includes a differential amplifier circuit in which a negative feedback circuit is provided in an operational amplifier, and the equipotential application circuit includes the non-inverting input terminal of the operational amplifier and the first and second amplifiers. By applying the bias voltage to the connection point of the electrostatic protection element and connecting the external input terminal to the inverting input terminal of the operational amplifier, the bias voltage having the same potential is applied to both ends of the first electrostatic protection element. The functional circuit is configured to differentially amplify the signal input from the external input terminal by the differential amplifier circuit.

  According to the first aspect of the present invention, the bias voltage having the same potential is applied to the connection point between the external input terminal and the first and second electrostatic protection elements by the same potential application circuit. The voltage across the electrostatic protection element 1 is equal. Thereby, a leak current does not flow from the internal circuit to the external input terminal side, and the potential of the external input terminal is stabilized. As a result, the influence of the leakage current in the internal circuit can be eliminated, and the operation of the internal circuit can be stabilized.

  According to the invention of claim 2, since the internal circuit is configured to include the differential amplifier circuit in which the operational amplifier is provided with the negative feedback circuit, the non-inverting input terminal of the operational amplifier and the first and second electrostatic protection elements By applying a bias voltage to the connection point and connecting an external input terminal to the inverting input terminal of the operational amplifier, the same potential application circuit can be configured. That is, since the inverting input terminal and the non-inverting input terminal of the operational amplifier are set to the same potential due to an imaginary short, the first electrostatic protection element connected to the external input terminal is applied with a bias voltage of the same potential at both ends. Is done. For this reason, a leak current does not flow from the internal circuit to the external input terminal side, and the potential of the external input terminal can be stabilized.

  The functional circuit differentially amplifies the signal input from the external input terminal by the differential amplifier circuit. For this reason, the operational amplifier can be used both as the same potential application circuit and the functional circuit, and the circuit configuration can be simplified as compared with the case where the operational amplifier is configured as a separate circuit.

It is a circuit diagram which shows the electronic circuit by embodiment of this invention. It is a circuit diagram which shows the electronic circuit by a 1st modification. It is a circuit diagram which shows the electronic circuit by the 2nd modification. It is a circuit diagram which shows the electronic circuit by the 3rd modification.

  Hereinafter, an electronic circuit according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an electronic circuit 1 according to the first embodiment. The electronic circuit 1 includes an external input terminal 2, a reference voltage source 3, electrostatic protection elements 5 and 6, an internal circuit 8, and the like.

  The reference voltage source 3 outputs a bias voltage Vref. The reference voltage source 3 includes a voltage follower by an operational amplifier 4, for example. An inverting input terminal and an output terminal of the operational amplifier 4 are connected, and a bias voltage Vref is applied to the non-inverting input terminal of the operational amplifier 4.

  The first electrostatic protection element 5 and the second electrostatic protection element 6 are connected in series to each other and provided between the external input terminal 2 and a ground (GND) as a constant voltage part. At this time, one end of the first electrostatic protection element 5 is connected to the external input terminal 2, and the other end of the first electrostatic protection element 5 is connected to one end of the second electrostatic protection element 6. The other end of the element 6 is connected to the ground.

  The connection point P between the first electrostatic protection element 5 and the second electrostatic protection element 6 is connected to the output terminal of the operational amplifier 4. As a result, the bias voltage Vref is applied to the connection point P.

  The first electrostatic protection element 5 is configured using, for example, an n-type MOSFET 7, the drain D is connected to the external input terminal 2, the source S is connected to the connection point P, and the gate G is connected to the source via the resistor R. The back gate B is connected to the ground.

  The second electrostatic protection element 6 is configured in substantially the same manner as the first electrostatic protection element 5. For this reason, also in the MOSFET 7 of the second electrostatic protection element 6, the gate G is connected to the source S via the resistor R, and the back gate B is connected to the ground. Further, the MOSFET 7 of the second electrostatic protection element 6 has a drain D connected to the connection point P and a source S connected to the ground.

  The internal circuit 8 has a high impedance input terminal, and the external input terminal 2 is connected to this input terminal. When the signal Sin is input from the external input terminal 2, the internal circuit 8 performs various signal processing on the signal Sin.

  Specifically, the internal circuit 8 includes a differential amplifier circuit 11 in which an operational amplifier 9 is provided with a negative feedback circuit 10. The external input terminal 2 is connected to the inverting input terminal of the operational amplifier 9, and the bias voltage Vref of the reference voltage source 3 is applied to the non-inverting input terminal of the operational amplifier 9. At this time, the differential amplifier circuit 11 constitutes a functional circuit 12 that differentially amplifies the signal Sin input from the external input terminal 2.

  Further, the inverting input terminal and the non-inverting input terminal of the operational amplifier 9 become the bias voltage Vref having the same potential due to the imaginary short. For this reason, the bias voltage Vref is also applied to the external input terminal 2 connected to the inverting input terminal of the operational amplifier 9. On the other hand, a bias voltage Vref is applied to the connection point P between the first electrostatic protection element 5 and the second electrostatic protection element 6 by the reference voltage source 3. Therefore, the differential amplifier circuit 11 and the reference voltage source 3 have the same potential application circuit that applies the bias voltage Vref having the same potential to the external input terminal 2 and the connection point P between the first and second electrostatic protection elements 5 and 6. 13 is configured. The equipotential application circuit 13 applies a bias voltage Vref having the same potential to the source S and drain D of the MOSFET 7 which is both ends of the first electrostatic protection element 5.

  The electronic circuit 1 according to the present embodiment is configured as described above. When the signal Sin is input from the external input terminal 2, the internal circuit 8 differentially amplifies the signal Sin by the differential amplifier circuit 11. The amplified signal Sout is output.

  In addition, when an excessive surge voltage is applied to the external input terminal 2 due to electrostatic discharge (ESD), the electrostatic protection elements 5 and 6 pass a current caused by the surge voltage to the ground to protect the internal circuit 8.

  However, in the present embodiment, the same potential application circuit 13 applies the bias voltage Vref having the same potential to the external input terminal 2 and the connection point P between the first and second electrostatic protection elements 5 and 6. The voltage across the first electrostatic protection element 5 connected to the terminal 2 becomes equal. Thereby, no leak current flows from the internal circuit 8 to the external input terminal 2 side, and the potential of the external input terminal 2 is stabilized. As a result, the influence of the leakage current in the internal circuit 8 can be eliminated, and the operation of the internal circuit 8 can be stabilized.

  Since the internal circuit 8 includes the differential amplifier circuit 11 provided with the negative feedback circuit 10 in the operational amplifier 9, the non-inverting input terminal of the operational amplifier 9 and the first and second electrostatic protection elements 5, 6 By applying a bias voltage Vref to the connection point P and connecting the external input terminal 2 to the inverting input terminal of the operational amplifier 9, the same potential application circuit 13 can be configured. That is, because the imaginary short causes the inverting input terminal and the non-inverting input terminal of the operational amplifier 9 to have the same potential, the first electrostatic protection element 5 connected to the external input terminal 2 has a bias having the same potential at both ends. A voltage Vref can be applied.

  The functional circuit 12 differentially amplifies the signal Sin input from the external input terminal 2 by the differential amplifier circuit 11. For this reason, the operational amplifier 9 can be used both as the same potential application circuit 13 and the functional circuit 12, and the circuit configuration can be simplified as compared with a configuration including separate circuits.

  In the above embodiment, the case where the first electrostatic protection element 5 is configured using the n-type MOSFET 7 has been described as an example. However, the present invention is not limited to this. For example, like the electronic circuit 21 according to the first modification shown in FIG. May be. In this case, the first electrostatic protection element 22 has a drain D connected to the external input terminal 2, a source S connected to the connection point P, a gate G connected to the drain D via the resistor R, and a back surface. A bias voltage Vref is applied to the gate B. In the first electrostatic protection element 22, the gate G of the MOSFET 24 may be connected to the source S via the resistor R.

  On the other hand, in the second electrostatic protection element 23, the gate G is connected to the drain D through the resistor R and the bias voltage Vref is applied to the back gate B in order to suppress the leakage current. In the MOSFET 24 of the second electrostatic protection element 23, the drain D is connected to the connection point P, and the source S is connected to the ground.

  Further, as in the electronic circuit 31 according to the second modification shown in FIG. 3, the first and second electrostatic protection elements 32 and 33 may be configured using a diode 34. In this case, the diode 34 of the first electrostatic protection element 32 has a cathode connected to the external input terminal 2 and an anode connected to the connection point P. The diode 34 of the second electrostatic protection element 33 has a cathode connected to the connection point P and an anode connected to the ground.

  The first electrostatic protection elements 5, 22, and 32 can be exchanged with each other, and the second electrostatic protection elements 6, 23, and 33 can be exchanged with each other. The first electrostatic protection elements 5, 22, 32 and the second electrostatic protection elements 6, 23, 33 are not limited to those described above, and other elements such as various transistors and resistors are used. It may be configured.

  In the above-described embodiment, the differential amplifier circuit 11 of the internal circuit 8 is configured to serve both as the functional circuit 12 and the same potential application circuit 13. However, the present invention is not limited to this, and the internal circuit 42 may include a functional circuit 43 and a potential applying circuit 44 separately, such as an electronic circuit 41 according to a third modification shown in FIG. . In this case, the functional circuit 43 has a high impedance input terminal connected to the external input terminal 2, and performs various signal processing on the signal Sin input from the external input terminal 2. The equipotential application circuit 44 includes a reference voltage source 45, applies a bias voltage Vref to the connection point P of the first and second electrostatic protection elements 5 and 6, and via a pull-up resistor 45A. The bias voltage Vref is applied to the external input terminal 2.

  Note that the bias voltage Vref is not limited to a voltage higher than the ground, but may be a low voltage. In this case, a pull-down resistor is used instead of the pull-up resistor 43A.

  In the above-described embodiment, the case where the ground is used as the constant voltage portion has been described as an example. However, the present invention is not limited to the ground, and may be a portion to which a constant DC voltage is applied.

  Furthermore, the present invention may be applied to an electronic circuit composed of a semiconductor circuit formed integrally with a semiconductor substrate, or may be applied to an electronic circuit in which separate electronic components independent from each other are combined.

1, 2, 31, 41 Electronic circuit 2 External input terminal 3, 45 Reference voltage source 5, 22, 32 First electrostatic protection element 6, 23, 33 Second electrostatic protection element 8, 42 Internal circuit 9 Operational amplifier 10 Negative feedback circuit 11 Differential amplifier circuit 12, 43 Functional circuit 13, 44 Equipotential application circuit

Claims (2)

An external input terminal to which a bias voltage is applied;
An internal circuit connected to the external input terminal;
Comprising first and second electrostatic protection elements connected in series between the external input terminal and a constant voltage portion;
The internal circuit processes a signal input from the external input terminal, and an equipotential application circuit that applies a bias voltage of the same potential to the connection point of the external input terminal and the first and second electrostatic protection elements. And an electronic circuit having a functional circuit. The internal circuit includes a differential amplifier circuit provided with a negative feedback circuit in an operational amplifier,
The equipotential application circuit applies the bias voltage to a non-inverting input terminal of the operational amplifier and a connection point of the first and second electrostatic protection elements, and the external input terminal is connected to the inverting input terminal of the operational amplifier. By applying the bias voltage of the same potential to both ends of the first electrostatic protection element,
The electronic circuit according to claim 1, wherein the functional circuit is configured to differentially amplify a signal input from the external input terminal by the differential amplifier circuit.

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