Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-01-27
2002-07-02
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S214100
Reexamination Certificate
active
06414776
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an infrared signal receiver.
2. Description of the Related Art
FIG. 1
of the accompanying drawings shows in block form a conventional infrared signal receiver. A pulse-position-modulated (PPM) signal which is generated when a carrier having a certain frequency is turned on and off is applied to energize an infrared LED to generate a modulated infrared radiation signal. As shown in
FIG. 1
, such a modulated infrared radiation signal is received by an infrared radiation sensor
1
, and then amplified by an amplifier
2
. The amplified signal is a passed through a band-pass filter (BPF)
3
that is tuned to the carrier of the PPM signal, so that unwanted signal components and noise are removed from the signal from the amplifier
2
. The BPF
3
supplies an output signal to a detector
4
which detects low and high levels of the PPM signal. An output signal from the detector
4
is shaped in waveform by a waveform shaper
5
, which outputs pulses depending on the carrier of the PPM signal from an output terminal
6
.
The infrared radiation sensor
1
generally comprises a Pin photodiode.
The BPF
3
, the detector
4
, and the waveform shaper
5
will be described in detail with reference to
FIG. 2
of the accompanying drawings. As shown in
FIG. 2
, in the BPF
3
, a capacitor C
1
has a terminal connected to the output terminal of the amplifier
2
and another terminal connected to an input terminal of a buffer
12
and an output terminal of a variable-transconductance amplifier
11
which has a noninverting input terminal and an inverting input terminal. The buffer
12
has an output terminal connected to a noninverting input terminal of a variable-transconductance amplifier
13
. The variable-transconductance amplifier
13
has an output terminal connected to an input terminal of a buffer
14
and a terminal of a capacitor C
2
. The capacitor C
2
has another terminal connected to ground. The buffer
14
has an output terminal connected to the inverting input terminal of the variable-transconductance amplifier
11
and a terminal of a resistor R
2
. The noninverting input terminal of the variable-transconductance amplifier
11
is connected to a positive terminal of a voltage source and a terminal of a resistor R
1
. The other terminal of the resistor R
1
is connected to the other terminal of the resistor R
2
and an inverting input terminal of the variable-transconductance amplifier
13
. The capacitors C
1
, C
2
, the variable-transconductance amplifiers
11
,
13
, the buffers
12
,
14
, and the resistors R
1
, R
2
thus connected jointly make up the BPF
3
whose input terminal is provided by the terminal of the capacitor C
1
which is connected to the amplifier
2
and whose output terminal is provided by the output terminal of the buffer
14
.
The BPF
3
has a tuned frequency f
0
expressed by the following equation (1):
f0
=
1
2
π
C1
×
C2
gm1
×
gm2
(
1
)
where C
1
, C
2
represent the respective capacitances of the capacitors C
1
, C
2
, and gm
1
, gm
2
represent the respective transconductances of the variable-transconductance amplifiers
11
,
13
.
The BPF
3
thus amplifies only a signal whose frequency is tuned with the tuned frequency f
0
depending on the amount of feedback that is established by the resistors R
1
, R
2
.
The output terminal of the BPF
3
is connected to an input terminal of a DC level shifter
15
of the detector
4
. The DC level shifter
15
has a pair of NPN transistors Q
100
, Q
101
having respective bases connected to each other. The NPN transistor Q
100
has an emitter connected to a constant-current supply
25
and serving as a first output terminal of the DC level shifter
15
. The NPN transistor Q
101
has an emitter connected to a constant-current supply
26
and serving as a second output terminal of the DC level shifter
15
. The first output terminal of the DC level shifter
15
is connected to the base of an NPN transistor Q
102
of a differential amplifier. The second output terminal of the DC level shifter
15
is connected to an input terminal of a low-pass filter
16
. The low-pass filter
16
comprises a resistor R
4
having a terminal which serves as the input terminal of the low-pass filter
16
and another terminal connected to a terminal of a capacitor C
3
whose other terminal is grounded. The junction between the resistor R
4
and the capacitor C
3
serves as an output terminal of the low-pass filter
16
. The output terminal of the low-pass filter
16
is coupled to the base of an NPN transistor Q
103
of the differential amplifier. The differential amplifier has an output terminal connected to an input terminal
17
.
1
of a current mirror
17
whose output terminal
17
.
2
is connected to an output terminal
23
.
3
of a current mirror
23
and a terminal of a capacitor C
4
whose other terminal is grounded. The NPN transistors Q
102
, Q
103
have respective emitters connected to an output terminal
23
.
2
of the current mirror
23
. The current mirror
23
has an input terminal
23
.
1
connected through a resistor R
5
to a voltage supply.
Operation of the detector
4
will be described below with reference to
FIGS. 3A
though
3
D of the accompanying drawings.
FIG. 3A
shows the waveform of a PPM signal by way of example. As shown in
FIG. 3A
, the PPM signal comprises on periods where the carrier exists and off periods where only a DC signal exists. The PPM signal is supplied from the output terminal of the BPF
3
to the DC level shifter
15
of the detector
4
, and applied to the NPN transistors Q
100
, Q
101
. The PPM signal applied to the NPN transistor Q
100
is transmitted through the NPN transistor Q
100
as an emitter follower to the base of the NPN transistor Q
102
. The PPM signal applied to the NPN transistor Q
101
is transmitted through the NPN transistor Q
101
as an emitter follower to the low-pass filter
16
where the carrier of the PPM signal is removed. The PPM signal from the low-pass filter
16
is applied to the base of the NPN transistor Q
103
. The NPN transistors Q
102
, Q
103
operate as a differential switch. When the base potential of the NPN transistor Q
102
is lower than the base potential of the NPN transistor Q
103
, the NPN transistor Q
103
is turned on, allowing a current to flow through the current mirror
17
to the output terminal
17
.
2
thereof. When the base potential of the NPN transistor Q
102
is higher than the base potential of the NPN transistor Q
103
, the NPN transistor Q
103
is turned off, preventing a current from flowing to the output terminal
17
.
2
of the current mirror
17
.
A current I
4
which flows from the current mirror
17
when the NPN transistor Q
103
is turned on is selected to be larger than a current I
3
which flows through the output terminal
23
.
3
of the current mirror
23
. Therefore, when the NPN transistor Q
103
is turned on, the capacitor C
4
is charged with the difference between the currents I
4
, I
3
. When the NPN transistor Q
103
is turned off, the capacitor C
4
is discharged with the current I
3
. In each of the on periods of the PPM signal, the capacitor C
4
is repeatedly charged with the difference between the currents I
4
, I
3
and discharged with the current I
3
according to a sawtooth pattern and becomes high in level. In each of the off periods of the PPM signal, the capacitor C
4
becomes low in level as it is only discharged with the current I
3
. The charging and discharging voltages of the capacitor C
4
are expressed as follows:
Charging
voltage
=
I
4
-
I
3
C4
×
1
2
f
IN
(
2
)
Discharging
voltage
=
I
3
C4
×
1
2
f
IN
(
3
)
where f
IN
represents the carrier frequency of the PPM signal and C
4
represents the capacitance of the capacitor C
4
.
The charging and discharging signal from the capacitor C
4
is applied to the waveform shaper
5
. The waveform shaper
5
has a hysteresis comparator
Chan Jason
NEC Corporation
Payne David C.
Sughrue & Mion, PLLC
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