Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-08-12
2002-11-12
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C327S122000
Reexamination Certificate
active
06480311
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a peak-hold circuit and an infrared communication device provided with such a circuit. It further relates to the prevention of malfunction resulting from variations in the input-signal level.
BACKGROUND OF THE INVENTION
FIG. 8
is a block diagram showing an electrical construction of a commonly-used infrared receiver
1
. Infrared light from a transmitting device is photoelectrically transferred by a photodiode d, and inputted to amplifier a
2
capable of variably gaining an ac component through pre-amplifier al and coupling capacitor c
0
. The output of amplifier a
2
is voltage-divided by resistors r
1
and r
2
, and then inputted to peak-hold circuit ph
1
. Peak-hold circuit ph
1
, which has a comparatively short time constant, holds the peak value of the input signal by using hold capacitor c
1
.
The holding value of peak-hold circuit ph
1
is voltage-divided by dividing resistors r
3
and r
4
, and inputted to the inversion input terminal of comparator cmp
1
. The output of amplifier a
2
is applied to the non-inversion input terminal of comparator cmp
1
through dividing resistors r
1
and r
2
. The output of comparator cmp
1
is applied to the base of output transistor q
1
. The collector of output transistor q
1
is connected to a power line with “high level” Vcc through resistor r
5
, and is also connected to an output terminal p
0
, while the emitter thereof is grounded.
Moreover, the output of amplifier a
2
is inputted to peak-hold circuit ph
2
having a comparatively long time constant, and the holding value of hold capacitor c
2
is inputted to the non-inversion input terminal of comparator cmp
2
. A predetermined reference voltage vref
1
is applied to the inversion input terminal of the above-mentioned comparator cmp
2
so that comparator cmp
2
outputs an AGC signal. This increases the gain of amplifier a
2
when the holding value of peak-hold circuit ph
2
is lower than the reference voltage vref
1
and decreases it when the holding value thereof is higher than the reference voltage vref
1
. Therefore, the peak level of noise of externally-applied light is captured by peak-hold circuit ph
2
. When the level becomes greater than the reference voltage vref
1
, an AGC operation for reducing the gain of amplifier a
2
is carried out.
In the infrared receiver
1
having the above-mentioned construction, the photoelectrically-transferred output of the photodiode d, as shown in FIG.
9
(
a
), is amplified by amplifiers a
1
and a
2
as is indicated by reference symbol &agr;
1
in FIG.
9
(
b
). The holding value of peak-hold circuit ph
1
is indicated by reference symbol &agr;
2
while the discrimination level of comparator cmp
1
, which is determined by divided-voltage outputs of resistors r
3
and r
4
, is indicated by reference symbol &agr;
3
. Therefore, comparator cmp
1
level-discriminates the output of amplifier a
2
by using the divided voltage values of the holding value of peak-hold circuit ph
1
. The results of the discrimination is inverted by output transistor q
1
and resistor r
5
. Thus, a low-active receiving signal waveform, as shown in FIG.
9
(
c
), is outputted to the output terminal p
0
.
In another situation, multiples of infrared communication devices, each of which uses the infrared receiver
1
having the above-mentioned construction, are connected in a time-sharing manner. That is, a common host device
2
and multiples of subordinate devices
3
communicate with each other, for example, as shown in FIG.
10
. Supposing that the host device
2
is a receiver and one of the subordinate devices
3
is a transmitter, the light-receiving level of the host device
2
varies greatly depending on the distance and directional angle between the respective subordinate devices
3
and the host device
2
.
Therefore, in the case when infrared light from a subordinate device located in a comparatively short range or on the front side of the photodiode d is switched to infrared light, from another subordinate device located in a comparatively long range or on the non-front side of the photodiode d, in response to the level variation of the receiving signal as indicated by reference symbol &agr;
1
, the peak hold level merely follows in a manner as indicated by reference symbol &agr;
2
, as shown in FIG.
11
(
a
). As such, the detection level is merely allowed to follow in a manner as indicated by reference symbol &agr;
3
. In other words, upon receiving a signal from a subordinate device whose signal level is small and which is located in a long range or on the non-front side, the detection level, which still remains great after having followed the signal level of the subordinate device located in a short range or on the front side, fails to return to a predetermined initial level L
1
. This results in a problem in which a discrimination error occurs in comparator cmp
1
, thereby causing a malfunction in the output waveform as shown in FIG.
11
(
b
).
FIG. 12
is a block diagram which shows an electrical construction of typical prior-art peak-hold circuit ph
11
which can solve the above-mentioned problem. An input signal, which has been inputted to the input terminal p
1
, is inputted to the non-inversion input terminal of comparator cmp
11
through input resistor r
11
. To the inversion input terminal of this comparator cmp
11
is inputted the output from the output terminal p
2
of comparator cmp
12
which will be described later, through feed-back resistor r
12
. Comparator cmp
11
supplies hold capacitor c
11
with a charging current through resistor r
13
and diode d
11
when the input signal is higher than the output signal. Discharging constant current source f
11
, which has a current value smaller than the charging current from comparator cmp
11
, is parallel-connected to hold capacitor c
11
. The terminal voltage of hold capacitor c
11
is outputted to the output terminal p
2
through the above-mentioned comparator cmp
12
that functions as a buffer.
The output of the above-mentioned comparator cmp
11
is also supplied to the inversion input terminal of comparator cmp
13
through resistor r
14
, and the non-inversion input terminal of comparator cmp
13
is grounded through resistor r
15
. Comparator cmp
13
outputs “low level” to capacitor c
12
from its output terminal when the output of comparator cmp
11
goes high. Further, the input terminal of capacitor c
12
is pulled up to “high level” Vs through resistor r
16
. Therefore, when comparator cmp
13
outputs “low level”, capacitor c
12
makes a discharge instantaneously, and when the output of comparator cmp
13
is opened, charging is carried out in accordance with the time constant of c
12
·r
16
.
The terminal voltage of capacitor c
12
is inputted to the non-inversion input terminal of comparator cmp
14
, and if the terminal voltage of capacitor c
12
is higher than the reference voltage vref
11
inputted to the inversion input terminal, comparator cmp
14
outputs “high level”. If the terminal voltage is not higher, it outputs a “low level”. The output from the above-mentioned comparator cmp
14
is voltage-divided by resistors r
17
and r
18
, and supplied to the base of transistor q
11
. The collector of transistor q
11
is connected to the input terminal of the aforementioned hold capacitor c
11
through resistor r
19
, and the emitter is grounded.
Therefore, during the period in which the output from comparator cmp
14
is maintained at a “high level”, transistor q
11
is parallel-connected to constant current source f
11
so as to allow hold capacitor c
11
to discharge, and maintained at the aforementioned initial level L
1
.
In the peak-hold circuit ph
11
having the above-mentioned construction, in response to the input signal waveform as shown in FIG.
13
(
a
), the output signal waveform of comparator cmp
11
has a shape as indicated in FIG.
13
(
b
), and the output signal waveform of comparator cmp
13
has a shape as indicated in FIG.
13
(
c
). Therefore, in comparator cmp
14
, by adjusting the time constant c
12
&square
Okuda Takanori
Yokogawa Naruichi
Pascal Leslie
Sharp Kabushiki Kaisha
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