Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-07-09
2001-11-06
Ham, Seungsook (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C330S308000
Reexamination Certificate
active
06313458
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photoreceiver circuit and more particularly, to a photoreceiver or photoreceptor circuit equipped with a photoelectric conversion element and an amplifier circuit, which is capable of conversion-gain adjustment of the photoelectric conversion element and high-speed circuit operation. For example, this photoreceiver circuit is applicable to intelligent sensors for sensing a moving object or objects in an image formed by a photoelectric conversion element (i.e., a scene).
2. Description of the Prior Art
An example of the prior-art photoreceiver or photoreceptor circuits each having photoelectric conversion elements and amplifier circuits is disclosed in the U.S. Pat. No. 5,376,813 issued on Dec. 27, 1994, which is intended to expand the dynamic range with respect to the incident light, resulting in increase in response speed. The circuit configuration of this prior-art photoreceiver circuit thus patented is shown in FIG.
1
.
In
FIG. 1
, a photodiode
301
serves as a photoelectric conversion element. One terminal of the photodiode
301
is connected to the gate of an n-channel Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET)
302
. The other terminal of the photodiode
301
is connected to the ground. The source of the MOSFET
302
is connected to the ground. The drain of the MOSFET
302
is connected to the drain of a p-channel MOSFET
303
. The source of the MOSFET
303
is connected to a power supply (not shown) supplying a constant supply voltage V
cc
. The gate of the MOSFET
303
is applied with a suitable bias voltage V
bias
.
The combination of the MOSFETs
302
and
303
serves as an inverting, analog voltage amplifier circuit
310
for amplifying a voltage V
a
at the output terminal
300
A of the photodiode
301
with respect to the ground (i.e., an input voltage V
in
of the amplifier
310
). The MOSFET
302
is operated in the saturation region. The MOSFET
303
serves as a load resistor of the MOSFET
302
in the amplifier circuit
310
.
An output voltage V
out
of the voltage amplifier circuit
310
, which is an amplified voltage of the input voltage V
in
, is derived from the drain of the MOSEET
302
or an output terminal
300
B. The output voltage V
out
is fed back to the input side of the amplifier circuit
310
through a voltage-lowering circuit
330
and an n-channel MOSFET
307
. The voltage-lowering circuit
330
comprises two capacitors
304
and
305
. The capacitor
304
, which as a capacitance C
1
, is connected to the output terminal
300
B and a terminal
300
D connected to the gate of the MOSFET
307
. The capacitor
305
, which has a capacitance C
2
, is connected to the terminal
300
D and the ground.
A current-leaking circuit
320
, which comprises a p-channel MOSFET
306
, is connected in parallel to the voltage-lowering circuit
330
between the terminals
300
B and
300
D. The gate and the drain of the MOSFET
306
are coupled together to be connected to the terminal
300
B. The source of the MOSFET
306
, which is connected to the substrate, is connected to the terminal
300
D.
The source of the MOSFET
307
is connected to the terminal of the photodiode
301
at the terminal
300
A. The drain of the MOSFET
307
is connected to the power supply and applied with the supply voltage V
cc
.
The current leaking circuit
320
serves to leak a current between the terminals
300
B and
300
D. Specifically, when a potential difference occurs between the terminals
300
B and
300
D, a current flows gradually (i.e., leaks) through the MOSFET
306
from the terminal
300
B to the terminal
300
D and vice versa, thereby eliminating the potential difference after a specific relaxation time.
Next, the operation of the prior-art photoreceiver circuit shown in
FIG. 1
is explained below.
When the incident light PH applied to the photodiode
301
has a constant intensity with time, i.e., the photodiode
301
is in the steady state, the electric potentials or voltages at the terminals
300
B and
300
D with respect to the ground are equal to each other because of the current-leaking operation of the MOSFET
306
. On the other hand, a voltage V
d
at the terminal
300
D (i.e., the gate voltage of the MOSFET
307
) with respect to the ground is determined in such a way that a current flowing through the MOSFET
307
is equal to an output current I
PH
of the photodiode
301
.
Thus, the output voltage V
out
of the prior-art photoreceiver circuit of
FIG. 1
produced at the output terminal
300
B is equal to the voltage V
d
at the terminal
300
D, i.e., V
out
=V
d
, when the photodiode
301
is in the steady state.
On the other hand, when the intensity of the incident light PH applied to the photodiode
301
varies with time, i.e , the photodiode
301
is in the changing state, the magnitude of the output current I
PH
of the photodiode
301
varies with time according to the intensity change of the light PH, thereby changing the magnitude of the voltage V
a
at the terminal
300
A. The change of the voltage V
a
at the terminal
300
A is applied to the amplifier circuit
310
as its input voltage V
in
and is amplified therein, producing an amplified change of the output voltage V
out
at the terminal
300
B. This amplified change of V
out
is opposite in phase to the change of V
a
and therefore, the latter is decreased if the former is increased, and vice versa. The amplified change of the output voltage V
out
is sent to the gate of the MOSFET
307
through the voltage-lowering circuit
330
, causing an amplified change of the current flowing through the MOSFET
307
. Thus, the current flowing through the MOSFET
307
is equalized with the output current I
PH
of the photodiode
301
.
As explained above, the output voltage V
out
of the photoreceiver circuit is fed back to the input side of the amplifier circuit
310
through the voltage-lowering circuit
330
and the n-channel MOSFETs
307
, thereby suppressing the change of the voltage V
a
at the terminal
300
A caused by the change of the output current I
PH
. As a result, the value of the voltage V
a
is kept approximately constant independent of the intensity change of the incident light PH.
The above-described circuit operation of the prior-art photoreceiver circuit of
FIG. 1
is unlike that of another prior-art photoreceiver circuit shown in FIG.
2
. The circuit in
FIG. 2
is simply comprised of a photodiode
401
and an n-channel MOSFET
402
without any feedback path. An output terminal
400
A of the photodiode
401
is connected to the source of the MOSFET
402
. The gate of the MOSFET
401
is applied with a fixed bias voltage V
b
. An output voltage V
out
of the photoreceiver circuit is derived from the output terminal
400
A.
In the circuit of
FIG. 2
, since no feedback path is provided, the output voltage V
out
produced at the terminal
400
A varies largely in order to equalize the current flowing through the MOSFET
402
with the output current I
PH
of the photodiode
401
. This is quite different from that of the prior-art photoreceiver circuit shown in
FIG. 1
where the current flowing through the MOSFET
307
is equalized with the output current I
PH
of the photodiode
301
by changing the gate voltage V
d
of the MOSFET
307
.
In the circuit of
FIG. 2
, the parasitic capacitors existing in the vicinity of the terminal
400
A (e.g., the parasitic capacitors of the photodiode
401
and the source region of the MOSFET
402
) need to be charged and discharged by the output current I
PH
itself of the photodiode
401
. Since the output current I
PH
is usually very small, it takes a long time to fully charge or discharge these parasitic capacitors. This means that the necessitated relaxation time of the photoreceiver circuit of
FIG. 2
from the changing state to the steady state is extremely long.
In contrast, in the photoreceiver circuit of
FIG. 1
, the voltage V
a
at the terminal
300
A is always kept approximately constant because of the operation of the MOSFET
307
.
Ham Seungsook
NEC Corporation
Spears Eric
Young & Thompson
LandOfFree
Gain-adjustable photoreceiver circuit with photoelectric... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Gain-adjustable photoreceiver circuit with photoelectric..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gain-adjustable photoreceiver circuit with photoelectric... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2581622