JP2002185268A - Leakage current compensation circuit and IC using the same - Google Patents

Abstract

(57) Abstract: A leakage current compensating circuit capable of compensating for a leakage current caused by a reverse current of a protection diode and an IC using the same are realized. SOLUTION: In a leakage current compensating circuit for compensating for a leakage current which is a difference current of a reverse current of two protection diodes provided on a pad of an IC, the same current as a difference current of a reverse current of the protection diode is generated. And a current mirror circuit that outputs a compensation current of the same value using a current generated by the replica circuit as an input current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an IC such as an amplifier or an A / D converter, and more particularly to a leakage current compensating circuit capable of compensating for a leakage current generated at a pad portion of an IC and an IC using the same. About

[0002]

2. Description of the Related Art In a conventional IC such as an amplifier or an A / D converter, a protection diode is provided on a pad of the IC for circuit protection to cope with excessive input and the like.

FIG. 3 is a configuration block diagram for explaining a configuration around a pad of such a conventional IC. In FIG. 3, 1 is a signal source for supplying an input voltage signal to the IC, 2 is a signal source resistor, 3 is a pad of the IC, 4 and 5 are protection diodes, and 6 is an amplifier formed in the IC.

One end of a signal source 1 is connected to one end of a signal source resistor 2, and the other end of the signal source resistor 2 is connected to a pad 3.
The pad 3 is connected to the input terminal of the amplifier 6 and to the anode of the protection diode 4 and the cathode of the protection diode 5, respectively.

The cathode of the protection diode 4 is a positive voltage source.
VDD ", and the anode of the protection diode 5 is connected to the negative voltage source" VSS ". The other end of the signal source 1 is grounded.

Here, the operation of the conventional example shown in FIG. 3 will be described. Since the protection diodes 4 and 5 are in reverse bias, respectively, when the value of the input voltage signal supplied from the signal source is between the positive voltage source “VDD” and the negative voltage source “VSS”, 5 remains "OFF".

On the other hand, when the value of the supplied input voltage signal exceeds the positive voltage source "VDD", the protection diode 4 turns "O".
N ", and the voltage value of the pad 3 is limited to" VDD + Vf4 "if the forward voltage of the protection diode 4 is" Vf4 ".

Similarly, when the value of the supplied input voltage signal becomes lower than the negative voltage source "VSS", the protection diode 5 is turned "ON" and the voltage value of the pad 3 becomes the forward voltage of the protection diode 5. Is “Vf5”, then “VSS−Vf”
Limited to 5 ".

As a result, when the value of the input voltage signal exceeds the value of the positive / negative voltage source, one of the protection diodes is set to "O".
N ", and the voltage value of the pad 3 is limited to a constant voltage, so that the amplifier 6 which is an internal circuit of the IC can be protected from overvoltage.

[0010]

However, in the conventional example shown in FIG. 3, the protection diodes 4 and 5 are reverse-biased in a normal state, but a slight reverse current actually flows as a leakage current. For example, “Idp” and “I
A reverse current flows through the protection diodes 4 and 5 as indicated by dn ″.

When the input resistance of the amplifier 6 as the internal circuit is sufficiently high, these reverse currents flow into the signal source resistance 2 via the pad 3. Set the resistance value of the signal source resistor 2 to "R
s ", the current flowing through the signal source resistor 2, in other words, if the leakage current is" Iin ", then Iin = Idn-Idp (1) Iin (2).

Therefore, the input voltage "Vin" of the amplifier 6 is
If the output voltage signal of the signal source 1 is "Vs", Becomes

That is, the input voltage "V" of the amplifier 6 which is an internal circuit of the IC due to the reverse current of the protection diode.
There is a problem that an error of "-Rs.times.Iin" occurs in "in." In particular, when the operating atmosphere is at a high temperature, the leakage current "Iin" flowing through the signal source resistor 2 increases. However, there is a problem that the error also increases.
Accordingly, an object of the present invention is to realize a leakage current compensating circuit capable of compensating for a leakage current caused by a reverse current of a protection diode and an IC using the same.

[0014]

In order to achieve the above object, according to the first aspect of the present invention, the present invention is directed to a method for detecting the difference between the reverse currents of two protection diodes provided on an IC pad. In a leakage current compensating circuit for compensating for a certain leakage current, a replica circuit for generating the same current as the difference current of the reverse current of the protection diode, and the current generated by the replica circuit having the same value as an input current. The provision of the current mirror circuit for outputting the compensation current makes it possible to compensate for the leakage current caused by the reverse current of the protection diode.

According to a second aspect of the present invention, there is provided a leakage current compensating circuit according to the first aspect of the present invention, further comprising a potential adjusting circuit for adjusting the potential of the output terminal of the replica circuit, thereby providing a reverse current caused by a potential difference. Mismatch of the direction current values can be prevented, and more accurate leakage current compensation becomes possible.

According to a third aspect of the present invention, in the leakage current compensating circuit according to the first and second aspects of the present invention, the replica circuit includes a pad serving as an output terminal and an anode or a cathode connected to the pad. Since the protection diode is applied with the reverse bias and the two diodes having the same characteristics, it is possible to compensate for a leakage current caused by a reverse current of the protection diode.

According to a fourth aspect of the present invention, in the leakage current compensating circuit according to the second aspect, the potential adjusting circuit is connected between an input terminal of the current mirror circuit and an output terminal of the replica circuit. In addition, since the transistor has the gate or base to which the set voltage is applied, the mismatch of the reverse current value due to the potential difference can be prevented, and the leakage current can be compensated with higher accuracy.

According to a fifth aspect of the present invention, the compensation current of the leakage current compensation circuit according to any one of the first to fourth aspects is applied to an input pad, an output pad, or an input / output pad connected to an internal circuit of the IC. The supply makes it possible to compensate for leakage currents due to the reverse current of the protection diode.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an IC using a leakage current compensating circuit according to the present invention. 1, reference numerals 1 to 6 denote the same reference numerals as in FIG. 3, reference numeral 7 denotes a pad, reference numerals 8 and 9 denote diodes having the same characteristics as the protection diodes 4 and 5, and reference numeral 10 denotes a current mirror circuit.

7, 8, and 9 are replica circuits 50.
7, 8, 9 and 10 constitute a leakage current compensation circuit 51, respectively.

One end of the signal source 1 is connected to one end of the signal source resistor 2, and the other end of the signal source resistor 2 is connected to the pad 3.
The pad 3 is connected to the input terminal of the amplifier 6 and to the anode of the protection diode 4 and the cathode of the protection diode 5, respectively.

On the other hand, the pad 7 is connected to the anode of the diode 8 and the cathode of the diode 9 and to the input terminal of the current mirror circuit 10, and the output current of the current mirror circuit 10 is supplied to the pad 3.

The protection diode 4 and the diode 8
Is connected to a positive voltage source "VDD", and the anodes of the protection diodes 5 and 9 are connected to a negative voltage source "VSS".
S ". The other end of the signal source 1 is grounded.

Here, the operation of the embodiment shown in FIG. 1 will be described. Diodes 8 and 9 are reverse-biased, but with small reverse currents "Idp '" and "Idn'" as described above.
Flows as a leakage current.

However, since there is no external connection to the pad 7, the leakage current becomes the input current of the current mirror circuit as it is. The input current, which is the leakage current, is referred to as “Ii
If n ′ ″, Iin ′ = Idn′−Idp ′ (4)

The current mirror circuit 10 supplies an output current equal to the leakage current "Iin '", which is an input current, to the pad 3. Therefore, this output current is used as a compensation current and its value is set to "Ic".
omp (= Iin ′) ”, the current“ Iin ”flowing through the signal source resistor 2 from the equation (1) is Iin = Idn−Idp−Icomp = Idn−Idp−Iin ′ = Idn−Idp− (Idn ′) −Idp ′) (5)

Here, since the protection diodes 4 and 5 and the diodes 8 and 9 have the same characteristics, the reverse currents are also equal, respectively, and Idn = Idn '(6) Idp = Idp' (7)

Therefore, Equations (6) and (7) are replaced by Equation (5).
, Iin = Idn−Idp− (Idn′−Idp ′) = Idn−Idp−Idn + Idp = 0 (8), and the leakage current can be compensated.

By substituting equation (8) into equation (3), And the error can be compensated.

As a result, a leakage current, which is a difference current of a reverse current of a diode connected to the dummy pad and having the same characteristic as the protection diode, is detected, and a compensation current is supplied to the pad. Can compensate for the leakage current caused by the

However, the reverse currents of the protection diodes 4 and 5 and the diodes 8 and 9 have some dependence on the potential of the pad 3 or pad 7. That is, when the potential difference between the pad 3 and the pad 7 becomes large, a mismatch in the value of the reverse current may occur, and accurate compensation of the leakage current may not be performed.

FIG. 2 is a configuration block diagram showing another embodiment of an IC using a leakage current compensating circuit according to the present invention which solves such a problem. In FIG. 2, 1 to 10 and 50
Denotes the same reference numerals as in FIG. 1, 11 denotes a transistor,
A voltage source 12 supplies a set voltage. Also, 8 to 1
1 is a leakage current compensating circuit 52, 11 is a potential adjusting circuit 53
Respectively.

The connection is almost the same as that of the embodiment shown in FIG.
, The drain of the transistor 11 is connected to the input terminal of the current mirror circuit 10, the gate of the transistor 11 is connected to one end of the voltage source 12, and the voltage source 1
2 is a point to be grounded.

The operation of the embodiment shown in FIG. 2 will now be described. Although the transistor 11 is cascode-connected to the current mirror circuit 10, the input current "I" of the current mirror circuit 10 is
Since in ′ ″ flows as it is, the basic operation is the same as that of the embodiment shown in FIG.

Since the potential of the source terminal of the transistor 11 is determined by the set voltage of the voltage source 12, the potential of the pad 7 can be adjusted by adjusting the set voltage.

That is, by adjusting the value of the set voltage which is the output voltage of the voltage source 12 and setting the potential of the pad 7 to be equal to the output voltage signal “Vs” of the signal source 1, the pad 3 and the pad 7, it is possible to prevent a mismatch in the value of the reverse current due to the potential difference between the current and the current, and to more accurately compensate for the leakage current.

In the embodiment shown in FIGS. 1 and 2, the IC
Although the amplifier 6 is illustrated as an example of the internal circuit of the present invention, it is needless to say that the present invention is not limited to this. The internal circuit may deteriorate the DC accuracy or hinder the operation due to the leakage current caused by the reverse current of the protection diode. Anything is fine.

Although the transistors constituting the current mirror circuit 10 and the potential adjusting circuit 53 are exemplified by MOS transistors, they may be ordinary bipolar transistors.

In FIG. 1 and the like, input pads are assumed as IC pads, but they may be output pads or input / output pads.

[0040]

As is apparent from the above description,
According to the present invention, the following effects can be obtained. According to the first, third and fifth aspects of the present invention, a compensation current is supplied to the pad by detecting a leakage current which is a difference current of a reverse current of a diode connected to the dummy pad and having the same characteristic as the protection diode. This makes it possible to compensate for leakage current caused by the reverse current of the protection diode.

According to the second and fourth aspects of the present invention, by adjusting the value of the set voltage to equalize the potential difference between the pads, it is possible to prevent the mismatch of the reverse current value due to the potential difference. And the leakage current can be compensated with higher accuracy.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram showing an embodiment of an IC using a leakage current compensation circuit according to the present invention.

FIG. 2 is a configuration block diagram showing another embodiment of an IC using the leakage current compensation circuit according to the present invention.

FIG. 3 is a configuration block diagram illustrating a configuration around a pad of a conventional IC.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 signal source 2 signal source resistance 3,7 pad 4,5 protection diode 6 amplifier 8,9 diode 10 current mirror circuit 11 transistor 12 voltage source 50 replica circuit 51,52 leakage current compensation circuit 53 potential adjustment circuit

Claims (5)

[Claims] 1. A leakage current compensating circuit for compensating a leakage current, which is a difference current between two reverse currents of two protection diodes provided on a pad of an IC, wherein the leakage current is the same as the difference current of the reverse current of the protection diode. A leakage current compensating circuit comprising: a replica circuit that generates a current; and a current mirror circuit that uses the current generated by the replica circuit as an input current and outputs a compensation current having the same value. 2. The leakage current compensating circuit according to claim 1, further comprising a potential adjusting circuit for adjusting a potential at an output terminal of said replica circuit. 3. The replica circuit according to claim 1, wherein said replica circuit comprises a pad serving as an output terminal, and an anode or a cathode connected to said pad, said protection diode having the same characteristics as said protection diode to which a reverse bias is applied.
3. The leakage current compensating circuit according to claim 1, wherein said leakage current compensating circuit is constituted by two diodes. 4. The potential adjusting circuit is a transistor connected between an input terminal of the current mirror circuit and an output terminal of the replica circuit and having a gate or a base to which a set voltage is applied. The leakage current compensation circuit according to claim 2. 5. An input pad connected to an internal circuit of the IC,
5. An IC for supplying the compensation current of the leakage current compensation circuit according to claim 1 to an output pad or an input / output pad.