Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – Combining of plural signals
Reexamination Certificate
1997-10-10
2003-04-15
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
Combining of plural signals
C327S094000, C327S360000
Reexamination Certificate
active
06549058
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a signal processing circuit and method for generating signals representing the division or multiplication of two analog signals. The signal processing circuit and method of the present invention has particular application in the field of optical triangulation distance measurement. More particularly, the present invention has application to photoelectric optical distance measurement utilizing a photoreceiver which generates two analog signals based upon the position of a light beam reflected from a target onto the photoreceiver and wherein the two analog signals contain information relating to the distance from the photoreceiver means to the target.
BACKGROUND OF THE INVENTION
There may be numerous signal processing applications where either the division or multiplication of two analog signals is desired. The signal processing circuits and methods of the present invention could be applicable in any one of such applications; however, they find particular application in the field of optical triangulation distance sensing.
An illustration of optical triangulation distance measurement system is shown diagrammatically in
FIG. 1. A
light source comprising a light emitting diode (LED)
10
emits a pulsed light beam that is collimated along its optical axis and directed toward a target or object T. With the target T at the position X
1
from LED
10
, a portion of the pulsed light beam is reflected back to a photoreceiver means such as a position sensitive detector (PSD)
12
, which is also referred to in the art as a lateral effect photodiode. The reflected light beam strikes the surface of the PSD
12
at the position Y
1
. PSD
12
converts the photon light energy striking its surface into two electrical current signals, I
1
and I
2
at two of its output terminals. The current signals, I
1
and I
2
, contain information relative to the position where the reflected light beam impinges upon the surface of PSD
12
. Accordingly, the current signals I
1
and I
2
contain information relating to the distance X
1
. When the position of the reflected light beam moves in a vertical direction, as illustrated in
FIG. 1
, the difference between the signals I
1
and I
2
changes. With the target at the position X
2
, the position of the reflected light beam on PSD
12
is shown at Y
2
. The displacement between Y
1
and Y
2
corresponds to the difference between X
1
and X
2
. It is known in the prior art to electronically process the change of the current signals I
1
and I
2
to generate distance measurement related signals. The position Y of the light beam on the surface of PSD
12
satisfies the following equation:
Y
=
I1
-
I2
I1
+
I2
In the prior art to accomplish the signal division required to determine the distance X, the most common processing circuitry includes logarithmic operational amplifiers. The current signals I
1
and I
2
are amplified and converted to voltages V
1
and V
2
, respectively. The division of the two voltages is accomplished with the use of logarithmic conversion according to the following formula
V2
V1
=
log
V2
-
log
V1
This implementation requires the use of bipolar transistors or diodes in the feedback path of amplifiers resulting in matching, stability and temperature compensation problems. Furthermore, since the relatively inexpensive CMOS processes do not include floating bipolar transistors or diodes, the integration of a log-based architecture would require a large number of external components resulting in a large pin count and consequently large PC board area. This results in a larger minimum package size for the sensor. In general, the integrated circuit (IC) area required to implement log-based architecture in the circuitry for the required signal processing is greater than that in the present invention. The signal processing system and method of the present invention addresses these shortcomings in the prior art. The circuit architecture of the present invention is fully compatible with inexpensive CMOS processes for IC integration. The number of components external to the IC is minimized, leading to smaller packaging requirements.
SUMMARY OF THE INVENTION
In one embodiment, the present invention is a signal processing system and method where first and second analog voltage signals are generated. The first analog voltage signal is then used to generate a current signal. A capacitor is charged with the current signal and the voltage on the capacitor is compared with the second analog voltage signal and a signal is then generated having a time interval that represents the division of the first and second analog voltage signals. In another embodiment, the signal processing circuit and method generates first and second analog voltage signals. The first analog voltage signal is used to generate a first current signal and the second analog voltage signal generates a second current signal. A first capacitor is charged with the first current signal and the voltage on that capacitor is compared with a predetermined reference voltage and an output signal having a time interval representing the time required to charge the first capacitor to a voltage exceeding the reference voltage is generated. That output signal controls the charging of a second capacitor with the second current signal in the time interval whereby the voltage on the second capacitor then represents the multiplication of the first and second analog voltage signals.
The present invention is based upon the following principle. The current I required to charge a capacitor C to a voltage &Dgr;V in a time &Dgr;T, is defined as:
I=C
(&Dgr;
V/&Dgr;T
)
This formula can be rewritten as:
T=C
(&Dgr;
V/I
)
With I=V
1
/R, where V
1
is the magnitude of a continuous input voltage V
1
sampled at time t
S
and with &Dgr;V=V
2
, where V
2
is the magnitude of a continuous input voltage V
2
sampled at time t
S
, then the following formula applies:
&Dgr;T=C×R×
(
V
2
/
V
1
)
Thus, &Dgr;T is the result of the division of V
2
/V
1
multiplied by a constant. This result is valid for any system where the maximum rate of change of V
1
and V
2
is less than the minimum &Dgr;T required to represent this change. The result, &Dgr;T, can easily be converted into an analog voltage level for standard analog signal processing, or it can be used in its current form for a wide range of digital signal processing. A similar calculation leads to the result that &Dgr;V=A(V
1
×V
2
) where &Dgr;V is the voltage to which the capacitor is charged in the interval &Dgr;T and represents the multiplication of the two voltages V
1
and V
2
with a constant multiplying factor A.
In the application of the signal processing system and method of the present invention to optical triangulation distance measurement, the two analog signals are voltage signals representing the currents I
1
and I
2
from the PSD. The two analog voltage signals are pulsed signals which are then converted to DC signals by sample and hold circuits which sample each voltage signal with the occurrence of each light pulse from the light emitting diode of the system. One of the two analog DC voltage signals is converted to a current signal which is used to charge a divider capacitor. A divider comparator has one input connected to the capacitor and a second input connected to the other of the DC analog voltage signals. The output of the comparator is a signal having a time interval that represents the division of the first and second analog voltage signals. The system has a range adjustment circuit that generates a signal representing the sensor range. A decoder has an input connected to the output of the divider comparator and a second input receiving the range signal from the range adjustment circuit. The decoder then generates an output signal that represents whether or not the target is within the preset range of the system. The divider capacitor is discharged with the occurrence of each light pulse of
Banner Engineering Corporation
Merchant & Gould P.C.
Wells Kenneth B.
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