Detecting device of an encoder

Computer graphics processing and selective visual display system – Display peripheral interface input device – Cursor mark position control device

Reexamination Certificate

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Reexamination Certificate

active

06252584

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a detecting device of an encoder, especially to an optomechanical encoder used in a computer mouse or in a related pointing device.
2. Background of the Invention
The conventional mouse uses a detecting circuit with a conventional optomechanical encoder, as shown in FIG.
1
. The detecting circuit is formed by a photodetector
11
and a detection circuit
12
. The photodetector
11
is of the type of a phototransistor with two active areas P
1
and P
2
(as shown in
FIG. 2
) for receiving the optical signals from the working light beam through a code wheel
3
, transferring the optical signals into electric signals, and then outputting the electric signals to a detection circuit
12
. The detection circuit
12
is installed with two comparators OP
1
and OP
2
. The input positive end (+) of the first comparator OP
1
is connected with the output of the first active area P
1
and further connected with a resistor R
1
and the negative end (−) thereof is connected with resistors R
2
and R
3
. The other end of the resistor R
2
is connected with the other end of the resistor R
1
. The other end of the resistor R
3
is connected with a power source VDD.
The input positive end of the second comparator OP
2
is connected with the output of the second active area P
2
and further connected with a resistor R
4
and the negative end (−) thereof is connected with resistors R
5
and R
6
. The other end of the resistor R
5
is connected with another end of the resistor R
4
. The other end of the resistor R
6
is connected with a power source VDD.
By the above connection, each of the input negative ends (−) of the comparators OP
1
and OP
2
may connect with a fixed reference voltage Vref
1
and Vref
2
, wherein
Vref
1
=
VDD×R
2
/
R
2
+
R
3
)
Vref
2
=
VDD×R
5
/(
R
5
+
R
6
)
The active area P
1
and P
2
(as shown in
FIG. 2
) for receiving the optical signals from the working light beam through a code wheel
3
are easily affected by the sensitivity of the photodetector
11
and the light intensity of the light emitting source LED, and thus the output encoding signal is also affected, as shown in FIG
3
. After comparing the level of the encoding signals with the fixed reference voltages Vref
1
and Vref
2
by the comparators OP
1
and OP
2
, respectively, digital waveforms with different phase periods and pulse width are obtained, as shown in FIG.
4
.
The aforementioned circuit has the following drawbacks in applications:
1) Since a fixed reference voltage (Vref) is used as a bigger voltage in the detecting circuit for digital wave shaping, the magnitude of the encoding signal could be too strong or too weak, depending on the sensivities of the photodetectors and the light intensity of the light source LED. Therefore, it is necessary to classify and match different LEDs and photodetector
Since the reference voltage in the detecting circuit is performed by a fixed voltage, it is difficult to control the the duty cycle of the output signals (A, B) and the phase differences are difficult to be controlled. Therefore, the vector data can not be provided correctly. If this occurs in a mouse, the mouse will lose counts and become motionless.
2) The manufacture of the photodetectors and LEDs must classify and match the photodetectors and LEDs correctly in order to satisfy the requirement of the manufacturer of mice. Thus troubles in inventory and assembling are induced.
3) For the manufacture of mice, the produced mice are probably not good and the quality thereof is difficult to be controlled because of the assembly tolerance and decay of the LEDs in a mouse and the variation of the IC comparing voltage.
SUMMARY OF THE MENTION
Accordingly, the object of the present invention is to provide a detecting device of an encoder, wherein the detecting device comprises a photodetector and a detection circuit. The photodetector has three active areas, and the detection circuit compares each two of the electric signals outputted from the three active areas to output digital waveforms with suitable phase and suitable duty cycle. Thus, the digital signal may be correctly decoded into vector information by a digital circuit in next stage (such as a decoding and processing circuit
5
, as shown in FIG.
5
).
A further object of the present invention is to provide a detecting device of an encoder, by which the trouble induced from the matching and classification of the opto components is solved.
Another object of the present invention is to provide a detecting device encoder, by which the decay problem of a LED may be overcome, the design margin increased, the yield ratio is increased and the quality of products are improved.
A further object of the present invention is to provide a detecting device of an encoder, in which the photodetector and the detection circuit are integrated as a single component.
A further object of the present invention is to provide a detecting device of an encoder, in which the detection circuit may be incorporated into the control IC of a computer pointing device (foe example, a computer mouse).
A further object of the present invention is to provide a computer mouse having said photodetector.
A further object of the present invention is to provide a computer pointing device with said photodetector.
The shift of signal level induced from the decay of LEDs may be dispelled and the defect of a prior art optomechanical encoder is avoided, in which a fixed voltage is used as a comparing voltage and thus makes the signal too strong or too weak to output a correct encoding signal due to the differences in the sensitivities of different photodetectors and the variations of the intensities of the LEDs.
The present invention will be better understood and its numerous objects and advantages will become apparent to those skilled in the art by referencing to the following drawings in which:


REFERENCES:
patent: 5680157 (1997-10-01), Bidiville et al.
patent: 5703356 (1997-12-01), Bidiville et al.
patent: 5777605 (1998-07-01), Yoshinobu et al.

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