U.S. patent number RE31,207 [Application Number 06/058,198] was granted by the patent office on 1983-04-12 for leak current suppressing printed circuit board.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Tetsuya Taguchi, Tokuichi Tsunekawa.
United States Patent |
RE31,207 |
Tsunekawa , et al. |
April 12, 1983 |
Leak current suppressing printed circuit board
Abstract
A leak current suppressing printed circuit board in which the
input circuit is so designed that between the input terminals a
light sensing photoelectric converting element operating in the
current mode is connected. The input is guarded by means of the
circuit net, whose potential is same as that at the input terminal
of the inverting input circuit or the non-inverting input circuit
of the high input impedance operation amplifier.
Inventors: |
Tsunekawa; Tokuichi (Yokohama,
JP), Taguchi; Tetsuya (Tokyo, JP) |
Assignee: |
Canon Kabushiki Kaisha
(JP)
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Family
ID: |
14001040 |
Appl.
No.: |
06/058,198 |
Filed: |
July 17, 1979 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
703962 |
Jul 9, 1976 |
04114036 |
Sep 12, 1978 |
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Foreign Application Priority Data
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Jul 24, 1975 [JP] |
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50-90533 |
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Current U.S.
Class: |
250/214R;
361/816; 396/542 |
Current CPC
Class: |
G03B
7/083 (20130101); H05K 1/0254 (20130101); H01J
40/14 (20130101); H05K 2201/09781 (20130101) |
Current International
Class: |
G03B
7/083 (20060101); G03B 7/08 (20060101); H01J
40/14 (20060101); H01J 40/00 (20060101); H05K
1/02 (20060101); H01J 040/14 () |
Field of
Search: |
;250/214R,214A,214C,214P,211J ;317/11B,11C ;354/6R
;361/424,397,404 |
References Cited
[Referenced By]
U.S. Patent Documents
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3770968 |
November 1973 |
Hession et al. |
3786264 |
January 1974 |
Ferro et al. |
3852644 |
December 1974 |
Seidler et al. |
3983023 |
September 1976 |
Baker et al. |
|
Primary Examiner: Nelms; David C.
Attorney, Agent or Firm: Toren, McGeady & Stanger
Claims
What is claimed is:
1. A leak current suppressing light measuring circuit for a camera
comprising:
(a) a printed circuit board;
(b) a high impedance operational amplifier having inverting and
non-inverting terminals, off-set voltage adjusting means and an
output terminal;
(c) a first signal transfer path printed on said printed circuit
board for supplying an electrical signal to one of the input
terminals of said operational amplifier;
(d) a second signal transfer path printed on said printed circuit
board and connected to the other input terminal of said operational
amplifier to form a portion of a feedback circuit for the
operational amplifier;
(e) a photoelectric converting element connected between said input
terminals of the operational amplifier;
(f) a logarithmic suppression element connected between one end of
said second signal transfer path and the output terminal of said
operational amplifier; and
(g) guard lines which are arranged on both sides of the second
signal transfer path between the point at which the logarithmic
suppression element is connected to the second signal transfer path
and a point at which the input terminal of the operational
amplifier is connected to the second signal transfer path, one end
of each guard line being connected to said first signal transfer
path to make these guard lines have virtually the same potential as
the first signal transfer path.
2. A light measuring circuit according to claim 1, wherein a signal
terminal of said photoelectric converting element is connected to
said first and second signal transfer paths.
3. A leak current suppressing light measuring circuit for a camera
comprising:
(a) a calculating portion provided with a high impedance
operational amplifier having inverting and non-inverting input
terminals, off-set voltage adjusting means and an output terminal,
one of said input terminals being electrically connected to one end
of a first signal transfer path printed on a printed circuit board,
and the other end of the first signal transfer path being arranged
to receive a power supply signal from a power supply circuit; the
other input terminal being electrically connected to one end of a
second signal transfer path to form a portion of a feedback circuit
of the operational amplifier printed on said printed circuit board,
and the other end of the feedback circuit being connected to the
output terminal of the operational amplifier through a logarithmic
suppression element;
(b) a light receiving part provided with a photoelectric converting
element disposed in a position to receive a light coming from an
object to be photographed, a signal terminal of said light
receiving part being electrically connected between said first and
second signal transfer paths; and
(c) a leak current suppressing part provided with guard lines
printed on said printed circuit board and disposed on both sides of
said second signal transfer path in parallel therewith, the guard
lines being connected to said first signal transfer path.
4. A leak current suppressing light measuring circuit according to
claim 3, wherein said photoelectric converting element is disposed
on a printed circuit board which is extended from the printed
circuit board of said calculating part and is arranged in a light
receiving position of the camera to receive the light of the object
to be photographed; one end of the signal terminal of the
photoelectric converting element being connected to said second
signal transfer path printed on the extended printed circuit board;
and the other end of the signal terminal being connected to said
guide lines printed on the extended printed circuit board.
5. A leak current suppressing light measuring circuit for a camera
comprising:
(a) a printed circuit board provided with printed circuit wiring
which is electrically connected to an electrical circuit element
and is disposed on a nonfunctional face of a pentagonal prism;
(b) a high impedance operational amplifier which is disposed on
said printed circuit board and is provided with inverting and
non-inverting input terminals, off-set voltage adjusting means and
an output terminal;
(c) a first signal transfer path which is printed on said printed
circuit board and is electrically connected to one of the input
terminals of said operational amplifier to permit power supply
thereto;
(d) a feedback circuit of said operational amplifier provided with
a logarithmic suppression element disposed between the other input
terminal and the output terminal of the operational amplifier;
(e) a photoelectric converting element which is electrically
connected between the inverting and noninverting input terminals of
said operational amplifier and which is disposed in a light
receiving position on the pentagonal prism for receiving a light
coming from an object to be photographed; and
(f) guard lines provided to three-dimensionally cover a signal path
between a connecting point of the input terminal of said
operational amplifier and a connecting point of said logarithmic
suppression element in said feedback circuit, said guard lines
being electrically connected to said first signal transfer path to
have the same potential as said first signal transfer path for
suppressing a leak current. .Iadd.
6. A device for preventing leakage current in a light responsive
circuit of a camera comprising:
(a) a photoelectric element in the light responsive circuit for
receiving light from an object; and
(b) a guard line surrounding at least a part of said light
responsive circuit, said guard line having applied thereto a
potential equal to the potential of the light responsive circuit
for preventing leakage current in a light responsive circuit.
.Iaddend. .Iadd.7. A device for preventing leakage current in a
light responsive circuit of a camera comprising:
(a) a photoelectric element for receiving light from an object;
(b) a connecting line for connecting said photoelectric element to
an input of said light responsive circuit; and
(c) a guard line for surrounding at least a part of said light
responsive circuit in co-operation with said connecting line, said
guard line having applied thereto a potential equal to the
potential of said connecting line. .Iaddend. .Iadd.8. A device
according to claim 7, in which said
guard line is connected to said connecting line. .Iaddend. .Iadd.9.
A device for preventing leakage current in a light responsive
circuit of a camera comprising:
(a) a photoelectric element for receiving light from an object;
and
(b) a connecting line for connecting said photoelectric element to
an input part of said light responsive circuit for operating said
photoelectric element in a current mode, at least a part of said
connecting line being arranged so as to surround at least a part of
said input part of said light responsive circuit to prevent leakage
current in said light responsive circuit, said connecting line
having applied thereto a potential substantially the same as the
potential of said input part of the light responsive circuit.
.Iaddend. .Iadd.10. A device for preventing leakage current in a
light responsive circuit of a camera, said circuit including an
amplifier, said device comprising:
(a) a photoelectric element coupled to said amplifier, said element
operating in a current mode; and
(b) a guard line which is arranged around an input part of said
amplifier, said guard line havng applied thereto a potential equal
to the potential
of said input part of said amplifier. .Iaddend. .Iadd.11. A device
for preventing leakage current in a light responsive circuit of a
camera comprising:
(a) a photoelectric element for receiving light from an object;
(b) an operational amplifier having a first and second input
terminals, said photoelectric element being connected to said input
terminals of said amplifier with first and second connecting lines
for operating said photoelectric element in a current mode; and
(c) a guard line arranged along the second connecting line, said
guard line having applied thereto a potential substantially the
same as the potential applied to the first connecting line.
.Iaddend. .Iadd.12. A device according to claim 11, in which the
guard line is connected to the first connecting line. .Iaddend.
.Iadd.13. A device for preventing leakage current in a light
responsive circuit of a camera comprising:
(a) a photoelectric element for receiving light from an object;
(b) an operational amplifier having first and second input
terminals, said photoelectric element being connected to said input
terminals of said amplifier in a current mode with first and second
connecting lines; and
(c) a guard line connected to said first connecting line, said
first connecting line and said guard line being arranged so as to
surround the second line. .Iaddend. .Iadd.14. A device according to
claim 6, in which the light responsive circuit and the guard line
are arranged on a printed circuit board. .Iaddend. .Iadd.15. A
device according to claim 7, in which the connecting line and the
guard line are arranged on a printed circuit board. .Iaddend.
.Iadd.16. A device according to claim 10, in which the input part
of the amplifier and the guard line are arranged on a printed
circuit board. .Iaddend. .Iadd.17. A device according to claim 11,
in which the connecting line and the guard line are arranged on a
printed circuit board. .Iaddend. .Iadd.18. A device according to
claim 13, in which the connecting line and the guard line are
arranged on a printed
circuit board. .Iaddend. .Iadd.19. A device for preventing leakage
current in a light responsive circuit of a camera comprising:
(a) a photoelectric element for receiving light from an object;
(b) an input circuit including an input line for connecting a
photoelectric element to the input part of said light responsive
circuit; and
(c) a guard line arranged close to the input circuit, said guard
line having applied thereto a potential substantially the same as
the potential applied to the input part of the light responsive
circuit to prevent leakage current in the input circuit. .Iaddend.
.Iadd.20. A device according to claim 19, in which the guard line
is connected to the input line. .Iaddend. .Iadd.21. A device
according to claim 19, in which the guard line is arranged so as to
surround at least a part of the input circuit. .Iaddend. .Iadd.22.
A device according to claim 20, in which the guard line is arranged
so as to surround at least a part of the input circuit. .Iaddend.
.Iadd.23. A device for preventing leakage current in a light
responsive circuit of a camera comprising:
(a) a photoelectric element for receiving light from an object;
and
(b) an input circuit including an input line for connecting a
photoelectric element to an input part of said light responsive
circuit, said input line having applied thereto a potential
substantially the same as the potential applied to the input part
of the light responsive circuit, at least a part of said input line
being arranged so as to surround at least a part of the input
circuit to prevent leakage in the input circuit.
Description
BACKGROUND OF THE INVENTION
Generally, in the case of the light measuring circuit of a camera
or the like, the input and the output circuit of the associated
operation amplifier are composed as printed circuits, by providing
or wiring the circuit elements on the insulated base plate. In the
case of such a light measuring circuit, a photovoltaic converting
element such as a silicon photo cell is connected, as a light
sensing photoelectric converting element, between the inverting and
the non-inverting input terminal of the high input impedance
operation amplifier. Further, a circuit arrangement having a diode
connected to it is used as the impedance element for Log.
compression.
When in such circuit, the light amount incident on the light
sensing element is very low, the photoelectric current produced in
the photovoltaic element is very small. Accordingly, the light
measurement error due to the influence of the leak current in the
input circuit becomes large and therefore it is difficult to
enlarge the practical light measurement range.
SUMMARY OF THE INVENTION
A purpose of the present invention is to provide a leak current
suppressing printed circuit board for preventing the deterioration
of the characteristics due to the leak current in the input circuit
of the high input impedance operation amplifier.
Another purpose of the present invention is to provide a leak
current suppressing printed circuit board for suppressing the leak
current in the printed circuit board composing the input circuit so
as to enlarge the operation range of the light measuring circuit on
the low brightness end.
The above mentioned and other purposes as well as the novel merits
of the present invention will be disclosed and the following
detailed explanations are made in accordance with the accompanying
drawings.
The accompanying drawings are mainly intended as an exemplary
explanation of the present invention and therefore the present
invention is not limited thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a circuit diagram of a conventional light measuring
circuit.
FIG. 2 shows a diagram for showing the deterioration of the
characteristics of the light measuring circuit due to the leak
current.
FIG. 3 shows an embodiment of the leak current suppressing circuit
in accordance with the present invention.
FIGS. 4 to 8 show respectively further embodiments in accordance
with the present invention; whereby the members or elements with
same figures or numbers are same or similar members in the above
drawings.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In FIGS. 1 to 8; 100 is a high input impedance operation amplifier,
101 is a photoelectric converting element such as a silicon
photocell. 102 is a diode with log. compression characteristics,
103 is a resistance for adjusting the off-set voltage of the
operation amplifier. 104 is an exposure value display instrument
such as a meter. 105 is a resistance for adjusting an exposure
value display instrument such as a meter. 106 is the constant
voltage source for setting the level of the light measuring
circuit, giving a bias to the non-inverted input to the operation
amplifier 100. Thus, the constant voltage source 106 is temperature
compensated with the negative temperature coefficient versus the
change of the ambient temperature. 107 is a resistance for
adjusting the constant voltage source for setting the level of the
light measuring circuit. 108 is the current source. 109 is the
current source switch. 110 and 111 are respectively the equivalent
resistances for the leak current. 112 and 112' are respectively the
guard lines for guarding the inverted or the non-inverted input
terminal of the operation amplifier 100. 113 shows a printed
circuit plate composing the light measuring circuit. 114 shows a
time integrating condenser. 115 shows a count switch. 116 shows a
Schmitt trigger circuit for level detecting 117 shows a shutter
controlling magnet, and 118 shows a pentagonal prism in camera and
the like.
In FIG. 2, the abscissa shows as APEX value (Bv) of the brightness
of the object to be photographed, while the ordinate shows an
output voltage (Eo) of the light measuring circuit.
The curve Q.sub.1 in the drawing is that for the ideal
characteristics without the leak current, while the curve Q.sub.2
shows that for the characteristics in the presence of a leak
current from the inverting input (-) of the operation amplifier 100
to the circuit (such as an earth circuit) whose potential is lower
than that of the non-inverting input (+). The curve Q.sub.3 shows
that for the characteristics in presence of a leak current from the
inverting input (-) of the operation amplifier 100 to the circuit
(such as a positive terminal circuit of the current source) whose
potential is higher than that of the non-inverting input (+).
In FIG. 1, in the light measuring circuit of a camera, a
communication device, a measuring instrument, a photovoltaic
element 101 such as silicon photocell is connected between the
inverting input (-) terminal and the non-inverting input (+)
terminal of the high input impedance operation amplifier 100 as the
light sensing photoelectric converting element.
In the feedback circuit of the high input impedance operation
amplifier 100, the diode 102 or the like is inserted as an
impedance element for log. compression. The output signal of the
operation amplifier 100 is applied to the exposure value display
device 104 such as meter through the adjusting resistance 105.
In the case of the printed circuit board for such a light measuring
circuit, when the light amount incident on the photoelectric
converting element 101 is small small, the photoelectric current
produced in the photovoltaic element 101 is very small. Further a
leak current takes place between the input circuit of the operation
amplifier 100 and the earth or the current source wiring so that
the light measurement error due to this influence becomes large.
When there takes place a leak current from the non-inverting input
circuit of the operation amplifier 100 to the earth circuit, i.e.,
if the resistance 110 in FIG. 1 assumes a limited value, the
photoelectric current (i) produced in the photoelectric converting
element 101 in accordance with the brightness of the object to be
photographed flows dividedly to the log. compression element 102
and to the leak resistance 110.
In consequence, the current flowing to the log. compression element
102 is represented by (iP-iL), whereby iP is the photoelectric
current while iL is the leak current. Thus the output voltage (Eo)
of the operation amplifier 100 increases in the range in which the
APEX value (Bv) of the brightness of the object to be photographed
is low, as is shown by the curve Q.sub.2 in FIG. 2.
When, on the other hand, there takes place a leak current from the
non-inverting input circuit to the positive terminal circuit of the
current source, the resistance 111 in FIG. 1 assumes a limited
value, whereby the sum of the photoelectric current (iP) and the
leak current (iL') flowing through the leak resistance 111, namely
(iP+iL') flows to the log. compression element 102. In consequence
the output voltage (Eo) of the operation amplifier 100 decreases in
the range in which the APEX value (Bv) of the brightness of the
object to be photographed is low as is shown by the curve Q.sub.3
in FIG. 2.
FIG. 3 shows the leak current suppressing printed circuit board in
accordance with the present invention, whereby the guard lines
shown by 112 and 112' are provided.
In accordance with the present invention, along the wiring of the
signal input circuit for the one input terminal of the operation
amplifier 100, the guard lines whose potential is substantially
equal to the other input terminal are provided in the neighborhood
of the above mentioned signal input circuit.
By means of operating the off-set voltage adjusting resistance 103
of the operation amplifier 100, so as to off set the circuit at
zero, the potential difference between the inverting input terminal
(-) and the non-inverting input terminal (+) of the operation
amplifier 100 is brought to zero, whereby by guarding the
non-inverting input circuit with the inverting input potential for
level setting, the leak current can be suppressed.
FIG. 4 shows a plane view of an embodiment in which the leak
current suppressing printed circuit board in accordance with the
present invention is actually applied as the printed circuit
board.
In the drawing, the parts shown in thick lines are the printed
circuit provided on the circuit board 113.
In the case of the light measuring circuit, as is shown in FIG. 3,
in which the photovoltaic photoelectric converting element 101 is
used in the current mode, along the wiring of the signal input
circuit for the one input terminal of the operation amplifier 100,
the guard lines 112 and 112' whose potential is substantially equal
to that of the other input terminal are provided in the
neighborhood of the signal input circuit in such a manner that the
leak current can be completely suppressed so that the light
measuring accuracy especially in the range of the low brightness
can be remarkably improved.
FIGS. 5 and 6 show another embodiment of the leak current
suppressing printed circuit board in accordance with the present
invention.
In the case of the embodiment shown in FIG. 5, in the light
measuring operation amplifier circuit composed of a printed circuit
nets on a printed circuit board together with the current supply
circuit and the bias circuit connected to the one input terminal of
the operation amplifier 100, whereby a photovoltaic photoelectric
converting element such as silicon photocell is connected, as a
light sensing photoelectric converting element which operates at
the current mode, between both input terminals of the high input
impedance operation amplifier 100 which includes a diode 102 as
impedance element in the feedback circuit, along the wiring of the
signal input circuit of the one input terminal of the operation
amplifier 100 the guard lines 112 and 112' are provided in the
neighborhood of the signal input circuit.
By operating the off-set voltage adjusting resistance 103 of the
operation amplifier 100, so as to off-set the circuit at zero, the
potential difference between the inverting input terminal (-) and
the non-inverting input terminal (+) of the operation amplifier 100
is brought to zero, whereby by guarding the inverting input circuit
by the non-inverting input potential for level setting the leak
current is suppressed. Namely, even if in the neighborhood of the
guard lines 112 and 112' the positive terminal circuit of the
current source or the earth circuit or the like is provided, there
takes place no leak current from the inverting input circuit of the
operation amplifier 100 to those circuits because the guard lines
are on the same potential as the inverting input terminal.
FIG. 6 shows the leak current suppressing printed circuit board for
the circuit diagram shown in FIG. 5.
FIG. 7 shows a circuit diagram in which the present invention is
applied to the electronic shutter circuit of the external light
measuring system.
Nearly at the same time, when in FIG. 7 the shutter of the camera
not shown in the drawing is opened the count switch 115 is opened
in such a manner that the time integrating condenser 114 is charged
with the photoelectric current produced by the photoelectric
converting element 101.
When the output of the operation amplifier 100 has reached a
certain determined level, the Schmitt trigger circuit 116 is
inverted whereby the shutter control magnet 117 is switched off so
as to terminate the exposure. In the printed circuit board of this
circuit, along the wiring of the signal input circuit of the one
input terminal of the operation amplifier 100 the guard lines 112
and 112' whose potential is substantially equal to that of the
other input terminal are provided in the neighborhood of the wiring
of the signal input circuit so as to suppress the leak current.
Hereby it goes without saying that in the case of the printed
circuit boards shown in FIGS. 3-7 in accordance to which the
present invention has so far been explained the guard for the
inverting input circuit or the non-inverting input circuit of the
operation amplifier 100 used not to be the guard lines fixed on the
printed circuit board, whereby the three dimensional guard lines
provided on the printed circuit boards also meet the purpose of the
present invention.
FIG. 8 shows a further embodiment of the leak current suppressing
printed circuit boards in accordance with the present invention. In
FIG. 8, the leak current suppressing printed circuit board on which
the guard lines 112 and 112' are composed in a three dimensional
way is provided on the upper surface of the pentagonal prism 118.
Hereby the dotted line shows the input circuit wiring of the high
input impedance operation amplifier 100, being guarded by the
coaxial lines 112 and 112' on the same potential .
* * * * *