Zener zapping device and zener zapping method

Details Zener zapping device and zener zapping method Zener zapping device and zener zapping method

1999-07-13

2001-05-22

Leja, Ronald W. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Impedance insertion

C323S313000

Reexamination Certificate

active

06236547

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Zener zapping device forming a voltage setting circuit for generating a highly accurate voltage supplied to analog integrated circuitry etc., and to a Zener zapping method using the Zener zapping device.
2. Description of the Background Art
Conventionally, the Zener zapping technique has been widely used as a method for controlling variations in analog integrated circuits etc. caused in manufacture after the manufacture so as to generate highly accurate voltage.
FIG. 5
is a circuit diagram showing part of a structure of a semiconductor integrated circuit. The semiconductor integrated circuit shown in
FIG. 5
has a terminal
101
at which the voltage is to be set (the potential at the terminal
101
is taken as V
ref
), a Zener diode
106
a
having its one end connected to the terminal
101
, a resistor
105
a
(having a resistance value R
1
) having its one end connected to the terminal
101
, a Zener diode
106
b
having its one end connected to the other end of the resistor
105
a
and to the other end of the Zener diode
106
a
, a resistor
105
b
(having a resistance value R
2
) having its one end connected to the other end of the resistor
105
a
and to the other end of the Zener diode
106
a
, a Zener diode
106
c
having its one end connected to the other end of the resistor
105
b
and to the other end of the Zener diode
106
b
and its other end grounded, and a resistor
105
c
(having a resistance value R
3
) having its one end connected to the other end of the resistor
105
b
and to the other end of the Zener diode
106
b
and its other end grounded.
The semiconductor integrated circuit shown in
FIG. 5
also has a resistor
104
a
(having a resistance value R
4
) having its one end connected to a voltage source
103
(having a potential VB) and its other end connected to the terminal
101
, and a resistor
104
b
(having a resistance value R
5
) having its one end connected to the terminal
101
and its other end grounded. Further, the semiconductor integrated circuit shown in
FIG. 5
has a terminal
108
a
connected to the one end of the Zener diode
106
a
, a terminal
108
b
connected to the other end of the Zener diode
106
a
and to the one end of the Zener diode
106
b
, a terminal
108
c
connected to the other end of the Zener diode
106
b
and to the one end of the Zener diode
106
c
, and a terminal
108
d
connected to the other end of the Zener diode
106
c.
Generally, when a Zener voltage in reverse direction is not applied to a Zener diode, the Zener diode is in an open state between its one end and the other end. When an excessive current in the reverse direction is instantaneously passed to the Zener diode, the Zener diode causes a Zener breakdown and one end and the other end of the Zener diode are short-circuited.
FIG. 6
is a circuit diagram showing an example of a voltage setting circuit for setting the potential V
ref
. In
FIG. 6
, the part surrounded by the one-dot chain line corresponds to the semiconductor integrated circuit shown in
FIG. 5
, and the outside of the one-dot chain line is a Zener zapping device connected to the semiconductor integrated circuit. A current source
102
has its one end grounded, and the grounded end is connected to the terminal
108
c
and its other end is connected to the terminal
108
a
, so that a current I is supplied from the current source
102
to the terminal
108
a
. Then a current I
1
flows to the Zener diodes
106
a
and
106
b
in the reverse direction to cause the Zener diodes
106
a
and
106
b
to undergo Zener breakdown. While part of the current I flows also to the resistors
104
b
,
105
a
, and
105
b
as a current I
2
, it is possible to cause Zener breakdown at the Zener diodes
106
a
and
106
b
by setting the current value of the current I sufficiently large.
With the Zener breakdown of the Zener diodes
106
a
and
106
b
, one end and the other end of the Zener diode
106
a
and one end and the other end of the Zener diode
106
b
are respectively short-circuited. As a result, one end and the other end of the resistor
105
a
connected in parallel to the Zener diode
106
a
and one end and the other end of the resistor
105
b
connected in parallel to the Zener diode
106
b
are shorted respectively by the Zener diodes
106
a
and
106
b
, and then the resistors
105
a
and
105
b
do not function as resistance from the circuit standpoint. In this case, the potential V
ref
at the terminal
101
is given as (R
5
//R
3
)·VB/(R
4
+(R
5
//R
3
)).
As stated above, the combined resistance value of the resistors
104
a
,
104
b
,
105
a
to
105
c
can be varied by causing arbitrary ones of the Zener diodes
106
a
to
106
c
to undergo Zener breakdown to short both ends of arbitrary ones of the resistors
105
a
to
105
c
, which enables the potential V
ref
at the terminal
101
to be highly accurately set to a desired value.
However, such a conventional Zener zapping device has the following problems.
FIG. 7
is a circuit diagram showing another example of the voltage setting circuit, which is intended particularly to cause the Zener diodes
106
a
and
106
c
to undergo Zener breakdown. A current source
102
a
has its one end grounded, and the grounded end is connected to the terminal
108
b
and its other end is connected to the terminal
108
a
; a current source
102
b
has its one end grounded, and the grounded end is connected to the terminal
108
d
and its other end is connected to the terminal
108
c.
Passing a reverse current from the current source
102
a
to the Zener diode
106
a
through the terminal
108
a
causes the Zener diode
106
a
to undergo a Zener breakdown, and passing a reverse current from the current source
102
b
to the Zener diode
106
c
through the terminal
108
c
causes the Zener diode
106
c
to undergo a Zener breakdown.
However, when the current Ib is supplied from the current source
102
b
to the terminal
108
c
, part of the current Ib, the current Ib
2
, flows to the terminal
108
b
through the Zener diode
106
b
. Accordingly, when the current Ia from the current source
102
a
and the current Ib from the current source
102
b
are supplied at the same time, the current Ib
2
functions as a current in the forward direction for the Zener diode
106
a
to clamp the potential at the terminal
108
b
, so that the Zener diode
106
a
cannot cause a Zener breakdown. Accordingly, when causing the Zener diodes
106
a
and
106
c
to undergo Zener breakdown in the voltage setting circuit shown in
FIG. 7
, it is necessary to separately supply the current Ia from the current source
102
a
and the current Ib from the current source
102
b
, which causes the problem that the Zener-zapping takes long time. Further, the need of the two current sources
102
a
and
102
b
causes the device scale of the Zener zapping device to be large.
SUMMARY OF THE INVENTION
A first aspect of the present invention is directed to a Zener zapping device for selectively Zener-zapping a plurality of Zener diodes in a semiconductor integrated circuit having the plurality of Zener diodes connected in series and a plurality of external terminals connected to one end, respective series connection points, and the other end of the series connection of the Zener diodes. According to the present invention, the Zener zapping device comprises: a current source having its one end grounded and its other end connected to the external terminal corresponding to the one end of the series connection; and a plurality of switches for selectively making a conductive state between the plurality of external terminals which are adjacent to each other along the connected sequence of the series connection.
According to a second aspect of the present invention, a Zener zapping method using the Zener zapping device according to the first aspect comprises the steps of: (a) turning off/on the switches in correspondence with Zener-zapping or not each of the plurality of Zener diodes; and (b) supplying a cu

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