Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-06-24
2001-05-22
Pascal, Leslie (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06236484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an infrared remote control circuit, and in particular, to an infrared remote control circuit that can effectively remove noise.
2. Description of the Related Art
Infrared remote control circuits are commonly used to operate remote electronic or electric equipment by means of infrared rays. For example, they are used to switch the channels of a television receiver.
Referencing
FIG. 4
, a conventional general reception circuit having an infrared remote control circuit is described. This figure is a block diagram showing a conventional general infrared remote control reception circuit.
An infrared remote control system for remote-controlling the switching over the channels of a television receiver is composed of a transmission section (not shown) having an oscillation circuit and an infrared light emitting diode; and a reception section including an infrared remote control reception circuit such as that shown in FIG.
4
.
The transmission section oscillates a pulse position modulation (hereafter simply referred to as “PPM”) signal provided by discontinuing a carrier of a specific frequency in order to operate the infrared LED to transmit the PPM signal to the reception section as an infrared modulation wave that uses infrared rays as a medium.
The reception section normally comprises an infrared sensing element
1
consisting of a Pin photodiode; an amplifying circuit
2
; a band pass filter (hereafter simply referred to as a “BPF”)
3
that tunes with a carrier for the PPM signal; a wave detection circuit
4
, a waveform shaping circuit
5
including a hysteresis comparator; and an output terminal
6
in order to output a pulse signal depending on whether the carrier for the PPM signal is interrupted.
The PPM signal, which is transmitted as the infrared modulation wave, is received by the infrared sensing element
1
and amplified by the amplifying circuit
2
using an appropriate gain. The BPF
3
removes unwanted signal or noise from the amplified signal, and the wave detection circuit
4
detects a low or a high level depending on whether the carrier for the PPM signal is interrupted. The hysteresis comparator in the waveform shaping circuit
5
shapes an output signal from the wave detection circuit
4
, which is then output from the output terminal
6
as a pulse signal that is output depending on whether the carrier for the PPM signal is interrupted.
Referencing
FIG. 3
, the configuration of a part of the conventional infrared remote control circuit that is located after the BPF
3
is described in detail.
In the BPF
3
, a first capacitor C
1
·
7
is connected at one end to an output terminal of the amplifying circuit
2
and at the other end to an input terminal of a first buffer circuit
12
and an output terminal of a first variable transconductance amplifier
11
. The first variable transconductance amplifier
11
has a non-inverted and an inverted input terminals.
The output of the first buffer circuit
12
is connected to a non-inverted input terminal of a second variable transconductance amplifier
13
having a non-inverted and an inverted input terminals. An output terminal of the second variable transconductance amplifier
13
is connected to an input terminal of a second buffer circuit
14
and is grounded via a second capacitor C
2
·
8
.
An output terminal of the second buffer circuit
14
is connected to an input terminal of the wave detection circuit
4
and to the inverted input terminals of the first and second variable transconductance amplifiers
11
and
13
. The non-inverted input terminal of the first variable transconductance amplifier
11
is connected to a positive terminal of a voltage source
113
. An output terminal of a current mirror circuit
19
is connected to the first and second variable transconductance amplifiers
11
and
13
to allow currents I
1
and I
2
to flow as control signals.
The above circuit constitutes the BPF
3
having one end of the first capacitor C·
17
as a signal input terminal and the output terminal of the buffer
14
as a signal output terminal.
gm (transconductance) of the first and second variable transconductance amplifiers
11
and
13
used for the BPF
3
is expressed by the following Equation (1).
[Equation 1]
gm
=
I2
4
×
KT
/
q
+
2
×
RE
×
I1
[
Equation
1
]
K=Boltzmann's constant
T=Absolute temperature
q=Amount of charges in electrons
RE=Value of resistors R
1
and R
2
I
1
=Current value of an control signal from the first variable transconductance amplifier
11
I=Current value of an control signal from the second variable transconductance amplifier
13
gm decreases with increasing I
1
(or decreasing I
2
) while it increases with decreasing I
1
(or increasing I
2
). Hereafter, a lead-in terminal of I
1
is referred to as a negative control terminal and a lead-in terminal of I
2
is referred to as a positive control terminal of the variable transconductance amplifier.
gm of the variable transconductance amplifiers
11
and
13
can be varied by setting the voltage from the voltage source
113
to fix I
1
to an appropriate value while varying the value of the variable resistor R
3
to vary the value of I
2
.
When the capacity values of the first and second capacitors C
1
·
7
and C
2
·
8
are designated as C
1
and C
2
, respectively, and gm of the variable transconductance amplifiers
11
and
13
are indicated as gm
1
and gm
2
, respectively, the tuning frequency f
0
(hereafter referred to as f
0
) of the BPF
3
shown in
FIG. 3
can be expressed by Equation (2).
[Equation 2]
f
0
=
1
2
π
C1
×
C2
gm1
×
gm2
=
1
2
π
C1
×
C2
×
I2
4
KT
/
q
+
2
×
RE
×
I1
[
Equation
2
]
The tuning frequency f
0
of the BPF
3
can be adjusted by using the variable resistor R
3
to control the lead-in current I
2
at the positive control terminal of the second variable transconductance amplifier
13
.
Conventional infrared remote control reception circuits are generally composed of semiconductor integrated circuits. During an impurity diffusion step in a semiconductor integrated circuit fabrication process, the diffusion of impurities more or less varies, resulting in differences in the values of resistors and capacitors in the semiconductor integrated circuit constituting the infrared remote control circuit. As a result, the tuning frequency f
0
of the BPF
3
varies.
As the resistance value varies, the value of I
1
on the circuit varies. Since, however, I
1
contributes as a product with RE, which is the resistance value of the resistors R
1
and R
2
, as shown in Equation (2) defining f
0
, it does not substantially vary the value of f
0
. On the other hand, the variation of the value of I
2
directly noticeably varies the value of f
0
.
Thus, the variable resistor R
3
that determines I
2
is not provided on the semiconductor integrated circuit but outside it, or if it is provided on the semiconductor integrated circuit, trimming is carried out so that f
0
remains unchanged despite the difference in the values of the internal resistors of the semiconductor integrated circuit.
In addition, f
0
directly varies if the capacities of the capacitors C
1
·
7
and C
2
·
8
differ. To deal with this problem, the resistor R
3
has a variable resistance so that the variation of f
0
is compensated for by adjusting the resistance value of the resistor R
3
after the diffusion of impurities.
Next, the configuration of the wave detection circuit
4
is described. The output terminal of the BFP circuit
3
is connected to a base of an NPN transistor Q
100
and an input terminal of a DC level shift circuit
15
. The output of the DC level shift circuit
15
is connected to an input terminal of a low pass filter
16
, and an output terminal of the low pass filter
16
is then connected to a base of an NPN transistor Q
101
.
Emitters of t
Bello Agustin
NEC Corporation
Pascal Leslie
LandOfFree
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