Patent Application
20070278382
In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
Multiple sensor unit 100 utilizes trans-impedance amplifiers for achieving low noise and also allows to control the characteristics of each single sensing diode, by virtually connecting each sensing diode to a adjustable voltage source, instead of being virtually grounded.
For simplicity of explanation only output circuit 199 that is connected to sensing diode DN 59 is shown, although each sensing diode (out of D1-DN 51-59) is connected to such an output circuit.
Output circuit 199 includes capacitor 119, resistor 129, adjustable voltage source 139 and operational amplifier 79′ that includes a positive input 79′-1, a negative input 79′-2 and an output 79′-3.
The cathode of sensing diode DN 59 is connected to a positive input 79′-1 of operational amplifier 79′. The DC voltage level at positive input 79′-1 is virtually the same as the voltage at negative input 79′-2 of operational amplifier 79′. This voltage level is determined by an adjustable voltage source 139 that can be controlled by digital an/or analog means. For example this adjustable voltage source 139 can include a digital to analog converter.
Negative input 79′-2 of operational amplifier 79′ is connected to one end of capacitor CN 119 and to one end of resistor RN1129. The other end of resistor RN1129 is connected to the adjustable voltage source 139. The other end of capacitor 119 is grounded.
When a certain voltage VrefN is provided by adjustable voltage source 139 a negative voltage drop of Vrb-VrefN developes over sensing diode DN 59.
By altering the voltage supplied by adjustable voltage source 139 the inverse voltage over sensing diode DN 59 can be altered. Thus, if the sensing diode is an avalanche photo diode and its gain it lower than expected then the adjustable voltage source 139 can be adjusted to increase the inverse voltage over that sensing diode.
The circuit outputs an output signal VoutN (from output 79′-3) that is responsive to the current that flows through DN 59 and to the voltage supplied by the adjustable voltage source 139.
The controller can evaluate the non-uniformity of sensing diodes D1-DN 51-59 based upon the relationship between the expected sensed light intensities and the output signals provided to controller 201. An in response adjust the voltage provided by the adjustable voltage sources such as to compensate for non-uniformities.
Multiple sensor unit 100′ differs from multiple sensor unit 100 by providing an output signal VoutN 189 that is responsive to the current that flows through DN 59 and is not responsive to the voltage supplied by the adjustable voltage source 139. This is achieved by having (within output circuit 199′) an additional operational amplifier stage that reduces the voltage supplied by the adjustable voltage source 139 from a sensing voltage that is responsive to the current flowing via sensing diode DN 59.
The additional operational amplifier stage includes resistors 149, 159, 99 and 109 and operational amplifier 169.
The output 79′-3 of operational amplifier 79′ is connected to a first end of resistor 99. The other end of resistor 99 is connected to a first end of resistor 109 and to a positive input 169-1 of operational amplifier 169. The other end of resistor 109 is grounded.
The other end of resistor RN1129 is connected to the adjustable voltage source 139 and to one end of resistor 149. The other end of resistor 149 is connected to a negative input 169-2 of operational amplifier 169 and to a first end of resistor 159. The other end of resistor 169 is connected to an output 169-3 of operational amplifier 169 and forms an output of the circuit. It outputs a signal Vout 189 that is proportional to the current that flows through sensing diode DN 59.
According to other embodiments of the invention instead of connecting an output circuit to each sensing diode then some sensing diodes can share a single output circuit. This can reduce the ability to compensate sensing diode non-uniformity but can be more size efficient and less expensive.
Method 200 starts by stage 210 of providing multiple sensing diodes adapted to convert light to current. Each sensing diode is coupled to an output circuit that includes a trans-impedance amplifier connected to an adjustable voltage source.
Stage 210 is followed by stage 220 of determining a voltage signal provided by each of the adjustable voltages sources such as to affect a sensing diode characteristic.
Conveniently, stage 220 includes determining the voltage signals provided by the adjustable voltages sources such as to compensate for non-uniformities between the sensing diodes.
Conveniently, stage 220 includes measuring the sensing diodes non-uniformities.
Stage 220 is followed by stage 230 of adjusting the adjustable voltage sources according to the determination.
Conveniently, stage 230 is followed by stages 240 or 250. These stages depend upon the configuration of the output circuits connected to the sensing diodes. If the output circuit resembles output circuit 199 then stage 230 is followed by stage 250. If the output circuit resembles output circuit 199′ than stage 230 is followed by stage 250.
Stage 240 includes illuminating a wafer or a reticle and providing multiple output signals, whereas each output signal is responsive to a current that flows through a sensing diode and to a voltage signal provided by an adjustable voltage source coupled to that sensing diode.
Stage 250 includes illuminating a wafer or a reticle and providing multiple output signals, wherein each output signal is responsive to a current that flows through a sensing diode.
The present invention can be practiced by employing conventional tools, methodology and components. Accordingly, the details of such tools, component and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details are set forth, such as shapes of cross sections of typical lines, amount of deflection units, etc., in order to provide a thorough understanding of the present invention. However, it should be recognized that the present invention might be practiced without resorting to the details specifically set forth.
Only exemplary embodiments of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.
