Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2001-02-15
2004-08-24
Luu, Thanh X. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C330S308000
Reexamination Certificate
active
06781108
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photosensor-amplifier device that converts an optical signal incident thereon into an electric signal and that then amplifies the electric signal for output.
2. Description of the Prior Art
First, a conventional photosensor-amplifier device will be described with reference to
FIGS. 4A and 4B
.
FIG. 4A
is a schematic sectional view showing the structure of a principal portion of a conventional photosensor-amplifier device, and
FIG. 4B
is an equivalent circuit diagram of the photosensor-amplifier device shown in
FIG. 4A. A
common photosensor-amplifier device as shown in these figures is composed of a photodiode chip
100
functioning as a photoelectric conversion element and an IC chip
200
incorporating an amplifier circuit and other components, with the photodiode chip
100
and the IC chip
200
sealed in a single package.
The photodiode chip
100
has an N-type semiconductor substrate
101
and a P-type semiconductor region
102
formed in a top portion of the substrate
101
, the PN junction in between constituting a photodiode PD. The top surface of the photodiode chip
100
is coated with an insulating film
103
, of which a small portion above the P-type semiconductor region
102
is removed. In this portion where the P-type semiconductor region
102
is exposed, the anode electrode
104
of the photodiode PD is provided. On the other hand, the bottom surface of the substrate
101
is die-bonded to a frame
50
, and a supply voltage V
DD
is applied to the frame
50
from outside. That is, the frame
50
serves as the cathode electrode of the photodiode PD.
The anode electrode
104
of the photodiode PD is electrically connected by way of a wire W to an electrode
201
of the IC chip
200
. As shown in
FIG. 4B
, the IC chip
200
incorporates an amplifier circuit AMP and a resistor R, and the electrode
201
is connected to the input terminal of the amplifier circuit AMP and also through the resistor R to ground.
In this photosensor-amplifier device built as described above, an optical signal incident on the photodiode chip
100
is sensed by the photodiode PD and is detected as a current signal that flows through the photodiode PD. The current signal thus obtained as a result of photoelectric conversion performed in the photodiode chip
100
is then fed by way of the wire W to the IC chip
200
, where the current signal is converted into a voltage signal by the resistor R. This voltage signal is then amplified to a predetermined voltage level by the amplifier circuit AMP, and is then fed to a signal processing circuit (not shown) provided in the succeeding stage.
In this conventional photosensor-amplifier device built as described above, the path connecting the photodiode chip
100
to the IC chip
200
(i.e., the wire W and other wiring elements) has a high impedance, and therefore electromagnetic noise coming from outside the device or electromagnetic noise generated inside the device tends to cause electromagnetic induction whereby noise signals tend to be induced in the wire W and other components. Moreover, the path connecting the photodiode chip
100
to the IC chip
200
is susceptible also to noise signals induced by the coupling capacitance that accompanies the path.
Despite these facts, the conventional photosensor-amplifier device is provided with no means of reducing such noise signals, and therefore noise signals are amplified, unchecked, by the amplifier circuit AMP and tend to cause malfunctioning of the IC chip
200
. To solve this problem, some measure against electromagnetic noise, such as an electromagnetic shield, is essential, which inconveniently increases the total number of components, and thus the cost, of the photosensor-amplifier device.
Moreover, as shown in
FIG. 4A
, in the photosensor-amplifier device built as described above, the anode electrode
104
of the photodiode PD is connected to the electrode
201
of the IC chip
200
by way of a single wire W. Thus, the wire W is, at both ends, die-bonded directly to the anode electrode
104
and to the electrode
201
, respectively.
In the wire-bonding process of this wire W, first, one end of the wire W is bonded to one of the anode electrode
104
and the electrode
201
(this operation is called the first bonding), and then the other end of the wire W is bonded to the other of those electrodes (this operation is called the second bonding). Here, on the chip where the wire W was bonded as the second bonding, it is subsequently necessary to cut the wire W. Inconveniently, the mechanical force accompanying the wire cutting here is applied to the chip and may cause chip breakage.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a photosensor-amplifier device that, despite having a photoelectric conversion circuit and an amplifier circuit connected together by way of a wire, is less likely than ever to malfunction under the influence of noise signals induced in the wire and other components.
Another object of the present invention is to provide a photosensor-amplifier device that is less likely than ever to suffer chip breakage in a wire-bonding process.
To achieve the above object, according to the present invention, a photosensor-amplifier device has a photoelectric conversion circuit that converts an optical signal into an electric signal, a first electrode by way of which the electric signal is extracted from the photoelectric conversion circuit, a second electrode that is not directly connected to the electric signal, an amplifier circuit that has a first input terminal and a second input terminal and that amplifies and then outputs the difference between the electric signals fed to the first and second input terminals, a first wire that connects the first electrode to the first input terminal, and a second wire that connects the second electrode to the second input terminal.
REFERENCES:
patent: 4626678 (1986-12-01), Morita et al.
patent: 4629882 (1986-12-01), Matsuda et al.
patent: 4891519 (1990-01-01), Nohira et al.
patent: 5132532 (1992-07-01), Watanabe
patent: 5610395 (1997-03-01), Nishiyama
patent: 5652425 (1997-07-01), Sawada et al.
patent: 5724967 (1998-03-01), Venkatachalam
patent: 5781233 (1998-07-01), Liang et al.
patent: 6175438 (2001-01-01), Agarwal et al.
Arent & Fox PLLC
Luu Thanh X.
Rohm & Co., Ltd.
Yam Stephen
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