Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
2002-11-14
2004-02-17
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S077000
Reexamination Certificate
active
06693466
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a comparator circuit for discriminating input voltages and giving out a logic output indicating the discrimination results, and an infrared signal receiving apparatus that can be realized with such a comparator circuit.
2. Description of the Related Art
Conventionally, a comparator circuit
1
as shown in
FIG. 8
has been used, for example, to discriminate integrated output voltages with a receiver of an infrared remote control apparatus or to discriminate outputs of a highly sensitive sensor or the like. The comparator circuit
1
employs a hysteresis comparator circuit
2
that has the hysteresis characteristics at the discrimination level. The hysteresis comparator circuit
2
compares an input voltage with the discrimination level, and when the input voltage becomes higher than the discrimination level, an output Vout is turned on. At the same time, the discrimination level is dropped so as to prevent the output Vout from being turned off, even if the input voltage is slightly varied and dropped. When the input voltage is further dropped to be lower than the dropped discrimination level, the output Vout of the hysteresis comparator circuit
2
is turned off, and the discrimination level is increased. Thus, the hysteresis threshold voltage Vth, which is the discrimination level of the hysteresis comparator circuit
2
, is changed with the operational state.
Since in the hysteresis comparator circuit
2
, the discrimination level has the hysteresis characteristics, malfunction that might occur inherently in circuits can be prevented, such as chattering in which an output is fluctuated between ON and OFF because the input voltage is fluctuated in the vicinity of the discrimination level when the discrimination level is fixed. In an infrared remote control receiver, for example, a photodiode which is an infrared receiving device receives an infrared signal that is modulated in an ASK (Amplitude Shift Keying) system, and a carrier frequency component is retrieved and detected, the hysteresis comparator circuit
2
determines whether or not a carrier is present while the detected output is integrated in an integrating circuit, and a digital output indicating determination results is given out. The determination results as to whether or not a carrier is present are processed in a logic circuit and thus are converted to digital signals. Since the input voltage for determining the presence of a carrier is an output from the integrating circuit, small fluctuations can readily occur because noise or the like superimposes, although a change is comparatively slow. It is possible to determine the presence of a carrier stably by using the hysteresis comparator circuit
2
.
Conventionally, for power voltage for infrared remote control receiver, highly sensitive sensor circuits and the like, 5 V, which is a general power voltage for digital circuits, has been mainly used. In recent years, low power consumption and use of low voltage have been promoted for large-scale semiconductor integrated circuits (LSIs), so that there is a strong demand for use of a low power voltage of 3 V or less for infrared remote control receivers or highly sensitive sensor circuits as well. In particular, in a system employing batteries, there is a demand for ensuring operation at 2.4 V or 1.8 V as the lowest operation voltage. Although the hysteresis comparator circuit
2
serves to prevent malfunction that might occur inherently in circuits such as chattering, in order to permit stable operation at a low voltage, a sufficient hysteresis voltage width with respect to the discrimination level and a limiting circuit
3
for preventing saturation at an input portion are necessary. In addition, in order to reduce costs, it is necessary to configure a circuit having a simple and small circuit configuration that can be realized easily as a semiconductor integrated circuit.
The limiting circuit
3
limits an input voltage Vsig so as not to exceed a limit voltage Vlimit. When an integrating capacitor
5
with a capacitance C is charged with a signal current
4
denoted by Isig, the charging voltage constitutes the input voltage Vsig. The sum of a bias voltage supplied from a bias circuit
7
to the base of a PNP type transistor
6
of the limiting circuit
3
and a pn junction forward voltage between the base and the emitter of the transistor
6
constitutes the limit voltage Vlimit. When the input voltage Vsig exceeds the limit voltage Vlimit, conductivity occurs between the emitter and the collector of the transistor
6
, and the impedance becomes low, so that the signal current
4
for charging the integrating capacitor
5
is absorbed to suppress the input voltage Vsig from increasing. The input voltage Vsig that is limited by the limiting circuit
3
is input to a hysteresis comparator
8
in the hysteresis comparator circuit
2
and is compared with a hysteresis threshold voltage Vth.
FIG. 9
shows signal processing waveforms in a principal portion of the comparator circuit
1
of FIG.
8
. As shown by the solid lines, even if the input voltage Vsig is changed with variations, when the input voltage exceeds the hysteresis threshold voltage Vth, the output voltage Vout is changed from the high level to the low level. Here, the hysteresis comparator
8
operates in a negative logic in which when an output is off, the level is high, and when it is on, the level is low. With a transition of an output from OFF to ON, the hysteresis threshold voltage Vth is dropped by a hysteresis voltage width Vhis, so that even if the input voltage Vsig is fluctuated, chattering in which small fluctuations of an output occurs.
When the input voltage Vsig is increased and reaches the limit voltage Vlimit, the input voltage is limited by the limiting circuit
3
and does not exceed the limit voltage Vlimit. When the input voltage Vsig is started to drop and reaches the hysteresis threshold voltage Vth that is dropped from the original discrimination level by the hysteresis voltage width Vhis or becomes lower than that, then the output voltage Vout transits from the low level of being an ON state to the high level of being in an OFF state, and the hysteresis threshold voltage Vth is increased by the hysteresis voltage width Vhis. As the output voltage Vout, a pulse output corresponding to an overall change in which small fluctuations of the input voltage Vsig are ignored can be obtained. However, the pulse width in the ON state becomes longer by a period during which the input voltage Vsig is dropped from the limit voltage Vlimit to the hysteresis threshold voltage Vth that has been dropped. When the limiting circuit
3
is not provided, as shown in the broken line, the input voltage Vsig is increased further than the level shown by the limit voltage Vlimit, so that a period of time required for the input voltage to be dropped again becomes longer so that the pulse width is further increased.
A conventional technique related to a comparator with an integrator used for an infrared remote control receiver is disclosed in Japanese Unexamined Patent Publication JP-A 10-187862 (1998) by the present applicant. This conventional technique aims at reducing an influence of the temperature characteristics of a semiconductor on a reference voltage, which serves as the discrimination level, when a comparator circuit with an integrator is realized as a semiconductor integrated circuit.
The comparator circuit
1
shown in
FIG. 8
is configured on the assumption that it is implemented in a semiconductor integrated circuit (IC). In semiconductor integrated circuits, various reference voltages such as the hysteresis threshold voltage Vth, the hysteresis voltage width Vhis, the limit voltage Vlimit and the like are generated in internal circuits in many cases. Therefore, the reference voltages are affected significantly by variations in parameters in IC production processes or changes in the ambient temperature during operation.
In the comparator circuit
1
shown in
Inoue Takahiro
Nishino Takeshi
Yokogawa Naruichi
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