Semiconductor integrated circuit

Details Semiconductor integrated circuit Semiconductor integrated circuit

2000-09-14

2002-05-21

Young, Brian (Department: 2819)

Coded data generation or conversion

Analog to or from digital conversion

Analog to digital conversion

C341S137000

Reexamination Certificate

active

06392582

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor integrated circuit and, more particularly, to a semiconductor integrated circuit having a current output sensor and a means for processing an output signal from the current output sensor.
2. Related Background Art
An output signal from a current output sensor is conventionally processed by a circuit having an arrangement shown in FIG.
1
. Referring to
FIG. 1
, the current output sensor is a photodiode.
Referring to
FIG. 1
, a current output from a photodiode
1
must have a dynamic range of about 80 dB or more from a dark state to a bright state. When this current signal is processed by, e.g., a 5-V single power source, the signal is first logarithmically compressed by an operational amplifier
23
and a diode
33
. An output V
o1
from the operational amplifier
23
is
V
O1
=
V
c
-
kT
q
⁢
ln
⁢
I
OP
I
S1
(
1
)
where V
C
is the reference voltage, I
S1
is the reverse saturation current of the photodiode, and I
OP
is the output current from the photodiode.
The output V
O1
is changed into an output V
O2
by a transistor
43
for compensating a dark current. The output V
O2
is
V
O2
=
V
O1
+
kT
q
⁢
ln
⁢
I
B
I
S2
(
2
)
where I
B
is the value of a constant current
53
, and I
S2
is the reverse saturation current of the transistor
43
.
The output
O2
is therefore
V
O2
=
V
C
-
kT
q
⁢
ln
⁡
(
I
OP
I
B
·
I
S2
I
S1
)
(
3
)
For
⁢
 
⁢
I
S1
=
I
S2
 
V
O2
=
V
C
-
kT
q
⁢
ln
⁢
I
OP
I
B
(
4
)
Referring to
FIG. 1
, a buffer
63
changes the impedance. An operational amplifier
93
adjusts a signal to an input range for an AD (analog-to-digital) converter in cooperation with resistors
73
and
83
. An output V
O
from the operational amplifier
93
is
V
O
=
V
C
-
R
2
R
1
·
kT
q
⁢
ln
⁢
I
OP
I
B
(
5
)
where R
1
is the value of the resistor
73
, and R
2
is the value of the resistor
83
. This output V
O
is A/D-converted and then transmitted to a CPU or the like.
In the conventional circuit, however, a plurality of circuit blocks such as an operational amplifier, constant current source, reference power source, and AD converter are required to process an output signal from the current output sensor. This increases the number of elements and the power consumption, resulting in a large chip size and high cost.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has as its object to process an output from a current output sensor with a smaller number of elements (simple circuit arrangement).
It is another object of the present invention to provide a semiconductor integrated circuit which can directly A/D-convert a current to achieve high-speed operation at low cost with a simpler circuit arrangement without any current-to-voltage conversion (logarithmic compression), impedance conversion, and gain adjustment.
To achieve the above objects, according to the present invention, there is provided a semiconductor integrated circuit comprising a current output sensor, and current AD conversion means connected to an output side of the current output sensor to connect an output from the current output sensor to an input side of a comparator via a current mirror circuit and A/D (analog-to-digital)-convert the output from the current output sensor.


REFERENCES:
patent: 4379285 (1983-04-01), Dooley
patent: 5729122 (1998-03-01), Nakamura
patent: 5966087 (1999-10-01), Koifman et al.
patent: 6150967 (2000-11-01), Nakamura
patent: 2695523 (1994-11-01), None

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