Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1998-06-02
2001-03-13
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S214100, C250S551000, C250S2140AG
Reexamination Certificate
active
06201234
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to an operational amplifier based on a voltage-phase optoelectronic switch (referred to as an “opsistor”). More specifically, this invention relates to an operational amplifier which has a pair of current based sensors such as photodiodes arranged in opposite orientation and an impedance device in parallel with the sensors to control amplifier gain.
BACKGROUND OF THE INVENTION
A well known building block for digital and analog electronic circuits is the operational amplifier or differential amplifier. A basic operational amplifier configuration may be used to make comparisons between the voltage level of two input signals. An operational amplifier may have multiple uses in different circuit configurations such as amplifying an input signal to a desired level using different circuit components, performing mathematical functions such as addition or multiplication, and signal modulation.
However, present operational amplifiers have several problems. Present operational amplifiers are analog circuits having components which add electrical noise to the basic sensor signal and are sensitive to signal saturation. Each of the two input sensor signals on a conventional operational amplifier must first be preamplified before they can be differentially processed. This preamplification is commonly done using transimpedance amplifiers that “sample” the sensor current with a summing junction node. The output of the transimpedance amplifier produces a voltage which forces a current (via a feedback resistor) back into the node to offset the current produced by the sensor. The resultant output voltage is therefore a “transform” of the sensor current. Use of the transimpedance amplifier functions well except the sensor current is easily contaminated by amplifier noise.
Signal and amplifier noise may be reduced by the use of optical switch sensors which are impervious to stray electronic noise. Previously, optosensors included a single photodiode, phototransistor, photodarlington, and the like are two-state, current-driven devices that have an “on” or “off” current state. For applications such as optocouplers and optoisolators, these devices responded to an “on” or “off” pre-couple signal with a corresponding “on” or “off” post-couple current signal. The inherent speed of such devices was limited by the rate at which they could switch their currents “on” and “off,” the limiting factor often being the passive return-to-ground period. Also for an “on” current state to be recognized, the current had to be at a significantly greater amplitude than background noise. However, the higher the signal current that was needed to generate this recognition, the longer time required by the switch device to generate that current level, and an even longer period was required before the switch device would return to the ground level. These characteristics of previous optoelectronic switches resulted in relatively slow switching speeds of usually less than 1 MHZ for a standard photodiode, and even slower speeds for more complicated devices such as phototransistors.
An improved faster optoelectronic switch, termed an opsistor, has been proposed in our co-pending application, Ser. No. 08/755,729, now U.S. Pat. No. 5,837,995, to the same inventors. However, although such optoelectronic switches can be designed to respond with faster switch frequencies by using special circuitry, the additional components of such circuitry increase the complexity and cost of such devices. Further, the transmitter and receiving elements of fast optoelectronic switches have to be in close proximity, usually in a single package, for efficient function and to minimize extraneous light interference.
Ideally, the sensor current should be sensed by FET high impedance probes that do not contaminate the signal purity. The sensor current itself must flow in a circuit free of contamination currents. To achieve this, the sensor current has to be confined in an “electrical loop” where it can flow with high purity. This property, however, has no utility if the sensor current magnitude cannot be “read.” Therefore, this ideal circuit must also produce a detectable voltage change proportional to its sensor current. In addition, the operating point DC bias across this sensor must be at a fixed voltage (usually 0 volts) to achieve sensor linearity. The transimpedance amplifier satisfies some of these conditions but suffers from the fact the feedback resistor must be in contact with the actual sensor input, thus injecting amplifier noise that is also amplified along with the sensor signal. These requirements of a closed loop current path and a pure input signal cannot be simultaneously met with teachings from current art.
Thus, there is a need for an operational amplifier which may minimize input signal noise. There is a further need for a simple optical operational amplifier which may use presently known circuit components. There is also a need for a simple optical operational amplifier which allows an adjustment of output gain. There is a need for an optical operational amplifier which includes passive components to shape an input waveform.
SUMMARY OF THE INVENTION
One aspect of the present invention is an electrical switch which has a first current producing sensor having a source current terminal and a sink current terminal. A first sensor input is operatively coupled to the first current producing sensor and emits an input signal. A second current producing sensor has a source current terminal coupled to the sink current terminal of the first current producing sensor and a sink current terminal coupled to the source current terminal of the first current producing sensor. A second sensor input is operatively coupled to the second current producing sensor and emits an input signal. The voltage phase of the first current sensor and the second current sensor is proportional to the sensor input levels received by the first and second current producing sensors.
The invention is also embodied in an optoelectronic operational amplifier having a first photodiode with an anode and a cathode. A second photodiode has an anode coupled to the cathode of the first photodiode and an anode coupled to the cathode of the first photodiode, to form an output terminal. A resistor is coupled in parallel with the first and second photodiodes.
The invention also includes an optical ruler system for determining the position of an object. The object has a light source emitting a light beam having an impact area with a specific length. A first photodiode element having a photo sensitive surface, with a length shorter than that of the impact are of the light beam, is provided. A second photodiode element is coupled with the first photodiode element. The second photodiode element has a photo sensitive surface with a length shorter than that of the impact area of the light beam. The impact area of the light beam impacts the photo sensitive surfaces of the first and second photodiode element depending on the position of the object. A processing circuit reads an output signal from the first and second photodiode elements and determines the position of the object based on the value of the combined signal from the first and second photodiode elements and a known position.
The invention is also embodied in a method for determining the position of an object. The object has a light source emitting a light beam having an impact area with a specific length. A position measurement sensor is placed in the plane of the light beam. The position measurement sensor has a first photodiode element having a photo sensitive surface with a length shorter than that of the impact area of the light beam and a second photodiode element coupled with the first photodiode element. The second photodiode element has a photo sensitive surface having a length shorter than that of the impact area of the light beam. The impact area of the light beam impacts the photo sensitive surfaces of the first and second photodiode element depending on the position
Chow Alan Y
Chow Vincent Y.
Chow Alan Y
Lee John R.
Mayer Brown & Platt
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