Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2002-09-12
2004-07-13
Han, Jessica (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
C330S260000
Reexamination Certificate
active
06762596
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a constant voltage circuit which is preferably used in an infrared remote control receiver, a low-frequency highly sensitive sensor circuit and the like, and to an infrared remote control receiver equipped with the same, and especially relates to countermeasures against power source noise thereof.
2. Description of the Related Art
FIG. 9
is a block diagram which entirely shows an example of a reception system of an infrared remote control receiver
1
, and
FIGS. 10A
to
10
D are waveform diagrams of individual portions thereof. This receiver
1
converts infrared transmission code signals to photocurrent signals Iin shown in
FIG. 10A
in an external photodiode
2
to input the signals into a reception chip
3
which is configured as an integrated circuit, and outputs output signals OUT shown in
FIG. 10D
demodulated in the reception chip
3
to a microcomputer which controls electronics and the like. The infrared signals are ASK signals which are modulated by a predetermined carrier from 30 kHz to 60 kHz approximately.
Within the reception chip
3
, the photocurrent signals Iin shown in
FIG. 10A
are amplified sequentially in a first amplifier (HA)
4
, a second amplifier (2nd AMP)
5
and a third amplifier (3rd AMP)
6
, and a carrier component as shown by a reference numeral &agr;l in
FIG. 10B
is taken out in a band pass filter (BPF)
7
which is matched with the frequency of the carrier. Then, the carrier component is detected at a carrier detection level Det denoted by a reference numeral &agr;
2
in a detector circuit
8
of the following stage, a time when the carrier exists is integrated in an integration circuit
9
as shown by a reference numeral &agr;
11
in
FIG. 10C
, and an integration output Int obtained thereby is compared with a predetermined discrimination level denoted by a reference numeral &agr;
12
in a hysteresis comparator
10
, whereby the presence or absence of the carrier is recognized, and the signals are digitally outputted as output signals OUT shown in FIG.
10
D.
A low pass filter
11
is placed on the output side of the first amplifier
4
, by which a direct current level by a fluorescent lamp and sunlight is detected, and in the second amplifier
5
of the following stage, the part of the direct current level is eliminated from a direct output of the first amplifier
4
and the output is amplified, whereby the influence of noise of the fluorescent lamp, sunlight and so on is removed at a certain level. Moreover, a ABCC (Auto Bias Current Control) circuit
12
is placed with reference to the first amplifier
4
, and by this ABCC circuit
12
, a direct current bias of the first amplifier
4
is controlled in response to an output of the low pass filter
11
.
It has been mainstream up to now that a power supply voltage of the infrared remote control receiver
1
configured in the above manner and a highly sensitive sensor circuit is a 5 V system. However, in recent years, a power supply voltage of a peripheral LSI has been decreased to, for example, 3 V, and power consumption thereof has been decreased, and also regarding the infrared remote control receiver
1
and a highly sensitive sensor circuit, voltage decrease has been strongly desired. On the other hand, a request of a device supplier for a power supply voltage has a broad range. For example, a guarantee of a minimum operating voltage of 3.3 V±0.3 V is required in one system, and 2.4 V or 1.8 V is required in another system using a battery. In this manner, regarding voltage decrease, a response to a broad range of power supply voltage is often required in one device.
With reference to such a response as described above, power source noise is one of the design problems to take countermeasures. The power source noise enters from a power source in most cases and enters from a load side in some cases, thereby causing jitters in a power supply voltage. In the infrared remote control receiver
1
and a highly sensitive sensor circuit, an amplifier (denoted by reference numerals
4
,
5
in
FIG. 9
) amplifies infrared signals and sensor signals at a very high gain, and therefore the amplifier is very apt to be affected by power source noise. In a case where power source noise influences the operation of the amplifier in the circuit, it is amplified to cause malfunction throughout.
Although, for this reason, it has been historically recommended to insert and mount a noise filter in a power supply line of a sensor circuit and the like, states of power source noise are different depending on used sets, and trouble is often caused. Furthermore, because of downsizing of a package in recent years, it becomes difficult to mount such a power source filter resistor and a capacitor in a package, so that there is no other choice to build a constant voltage circuit for countermeasures against power source noise in an integrated circuit.
FIG. 11
is a view for describing countermeasures against power source noise of a typical prior art. In this prior art, by inserting a constant voltage circuit
22
in a power supply bias of an amplifier
21
, power source noise is decreased. The constant voltage circuit
22
is a so-called three-terminal regulator. A direct current output voltage Vs from the constant voltage circuit
22
is fixed, and by preventing variation of a power supply voltage Vcc, that is, preventing the power source noise from transmitting to the output voltage Vs, the influence of the power source noise on the amplifier
21
is prevented or decreased.
Here, in a case where the voltage range of the power supply voltage Vcc required to be responded is broad as described before, it is necessary to set the value of the output voltage Vs of the constant voltage circuit
22
in relation to the minimum voltage that guarantees the operation. As a result, the operation range of the amplifier
21
is also restricted by the voltage. In other words, even in a case where the amplifier is used in a state that the power supply voltage Vcc is not the minimum voltage that guarantees the operation, for example, even in a case where the amplifier is used at 3.3 V while the minimum operation voltage thereof is 2.4 V, the output voltage Vs of the constant voltage circuit
22
remains set to less than 2.4 V, so that the maximum output amplitude from the amplifier
21
does not become 3.3 V but remains 2.4 V.
As a general example of countermeasures against such a problem, a configuration shown in
FIG. 12
which is another prior art may be cited. In this prior art, the power supply voltage Vcc is supplied to the amplifier
21
via a NPN transistor q, and the power supply voltage Vcc is supplied to a base of the transistor q via a low pass filter constituted by a resistor r and a capacitor c. Therefore, power source noise is decreased in the low pass filter, and a current capacity is ensured in the transistor q to become a bias voltage (Vs) of the amplifier
21
, whereby the countermeasures against the power source noise are taken. Since the bias voltage (Vs) varies in conjunction with the power supply voltage Vcc, the operation range of the amplifier
21
can be enlarged when the power supply voltage Vcc is high.
However, according to the prior art described above, there is a problem that, since the infrared remote control receiver
1
and a sensor circuit that handle low-frequency signals of tens of kHz or so require that a time constant of RC is set to a large value, it is impossible to achieve integration with ease. For example, a capacity value which allows integration is normally 100 pF or less. Furthermore, a practical capacity value for decreasing the influence on a chip area is 20 pF or so. In order to achieve a capability of removing power source noise to some extent while using this capacity value, a large time constant by an enormously large resistance component is needed. For example, in a case where it is required to set a power source noise removing rate PSRR at 40 kHz to −40 dB (1/100), assuming th
Inoue Takahiro
Yokogawa Naruichi
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