A photodiode is a type of photo detector capable of converting light into either current or voltage, depending upon the mode of operation.Photo diodes are similar to regular semiconductor diodes except that they may be either exposed or packaged with a window or optical fiber connection to allow light to reach the sensitive part of the device. Many diodes designed for use specifically as a photo diode will also use a PIN junction rather than the typical PN junction.
Working:-
A photodiode is a PN junction or PIN structure. When a photon of sufficient energy strikes the diode, it excites an electron, thereby creating a free electron and a (positively charged electron hole). This mechanism is also known as the photoelectric effect. If the absorption occurs in the junction's depletion region, or one diffusion length away from it, these carriers are swept from the junction by the built-in field of the depletion region. Thus holes move toward the anode, and electrons toward the cathode, and a photo current is produced. This photocurrent is the sum of both the dark current (without light) and the light current, so the dark current must be minimised to enhance the sensitivity of the device.
1)P-N photodiodes are used in similar applications to other photo detectors.
2)Photo diodes are used in consumer electronics devices such as compact disc players, smoke detectors, and
4)PIN diodes are much faster and more sensitive than ordinary p-n junction diodes, and hence are often used
5)P-N photodiodes are not used to measure extremely low light intensities. Instead, if high sensitivity is
Applications:
2)Photo diodes are used in consumer electronics devices such as compact disc players, smoke detectors, and
the receivers for remote controls in VCR's and televisions.
3)In other consumer items such as camera light meters, clock radios (the ones that dim the display when it's
3)In other consumer items such as camera light meters, clock radios (the ones that dim the display when it's
dark).
4)PIN diodes are much faster and more sensitive than ordinary p-n junction diodes, and hence are often used
for optical communications and in lighting regulation.
5)P-N photodiodes are not used to measure extremely low light intensities. Instead, if high sensitivity is
needed, avalanche photo diodes,intensified charge-coupled devices or photomultiplier tubes are used for
applications such as astronomy, spectroscopy, night vision equipment and laser rangefinding.
"Logic circuit is an electric circuit whose output depends upon the input in a way that can be expressed as a function in symbolic logic; it has one or more binary inputs (capable of assuming either of two states, e.x:- "on" or "off") and a single binary output".
Electronic circuits which process information encoded as one of a limited set of voltage or current levels. Logic circuits are the basic building blocks used to realize consumer and industrial products that incorporate digital electronics. Such products include digital computers, video games, voice synthesizers, pocket calculators, and robot controls. All logic circuits may be described in terms of three fundamental elements..
Logic circuits can be built from any binary electric or electronic devices, including switches, relays, electron tubes, solid-state diodes, and transistors; the choice depends upon the application and design requirements..
Logic circuits are classified into two categories.They are:-
1.Combinational Logic circuit.
2.Sequential Logic circuit.
1.Combinational Logic Circuits:-
These are the circuits whose output depends on the function of input only at that instant..The Combinational circuit does not have the memory to store the output..
Ex:- Adders,Subtractors etc.,.
A combinational circuit consists of input variables, logic gates, and output variables. The logic gates accept signals from inputs and output signals are generated according to the logic circuits employed in it. Binary information from the given data transforms to desired output data in this process. Both input and output are obviously the binary signals, i.e., both the input and output signals are of two possible states, logic 1 and logic 0.There are 'n' number of input variables coming from an electric source and 'm' number of output signals go to an external destination. The source and/or destination may consist of memory elements or sequential logic circuit or shift registers, located either in the vicinity of the combinational logic circuit or in a remote external location. But the external circuit does not interfere in the behavior of the combinational circuit.
Combination Logic Circuits are made up from basic logic NAND, NOR or NOT gates that are "combined" or connected together to produce more complicated switching circuits. These logic gates are the building blocks of combinational logic circuits. An example of a combinational circuit is a decoder, which converts the binary code data present at its input into a number of different output lines, one at a time producing an equivalent decimal code at its output.
Combinational logic circuits can be very simple or very complicated and any combinational circuit can be implemented with only NAND and NOR gates as these are classed as "universal" gates. The three main ways of specifying the function of a combinational logic circuit are:
As combination logic circuits are made up from individual logic gates only, they can also be considered as "decision making circuits" and combinational logic is about combining logic gates together to process two or more signals in order to produce at least one output signal according to the logical function of each logic gate. Common combinational circuits made up from individual logic gates that carry out a desired application include Multiplexers, De-multiplexers, Encoders, Decoders,etc.
Multiplexer(mux) :- Multiplexer is a device that allows the digital information from several sources to be routed on to a single line from transmitter to the reciever..The basic multiplexer has several data input lines and a single output line..It also has the select input which permits the digital data or any one of the input to be switched to the output line..Multiplexers are also called as "DATA SELECTORS".
De-Multiplexer(de-mux) :- De-multiplexer is a device which performs the reverse function of Multiplexer.It takes the digital information from a single line and distributes to a given number of output lines..
Encoders :- Encoder is a combinational circuit which converts the decimal or octal to the coded form such as BCD.
2.Sequential circuits:-
These are the circuits whose output depends on the present input as well as the past output..The sequential Logic circuits have memory to store the output..Ex:-Flipflops,Registers,Counters,Shift Registers etc.,.
*Asynchronous Counter
*Synchronous Counter
* Asynchronous Counter :-In Asynchronous Counter the first flipflop is clocked by an external clock pulse and then each successive flipflop is clocked by the output of the previous Flipflop.Therefore in this counterthe flipflops are not clocked simultaneously..Asynchronous Counter is also called as Ripple Counter..
*Synchronous Counter :-In Synchronous Counter the clock input is connected to all the flipflops and thus they are clocked simultaneously..
Shift Register :-Group of flipflops used where the data is stored and shifted from one Flipflop to the another Flipflop is called as Shift Register..
Electronic circuits which process information encoded as one of a limited set of voltage or current levels. Logic circuits are the basic building blocks used to realize consumer and industrial products that incorporate digital electronics. Such products include digital computers, video games, voice synthesizers, pocket calculators, and robot controls. All logic circuits may be described in terms of three fundamental elements..
Logic circuits can be built from any binary electric or electronic devices, including switches, relays, electron tubes, solid-state diodes, and transistors; the choice depends upon the application and design requirements..
Logic circuits are classified into two categories.They are:-
1.Combinational Logic circuit.
2.Sequential Logic circuit.
1.Combinational Logic Circuits:-
These are the circuits whose output depends on the function of input only at that instant..The Combinational circuit does not have the memory to store the output..
Ex:- Adders,Subtractors etc.,.
A combinational circuit consists of input variables, logic gates, and output variables. The logic gates accept signals from inputs and output signals are generated according to the logic circuits employed in it. Binary information from the given data transforms to desired output data in this process. Both input and output are obviously the binary signals, i.e., both the input and output signals are of two possible states, logic 1 and logic 0.There are 'n' number of input variables coming from an electric source and 'm' number of output signals go to an external destination. The source and/or destination may consist of memory elements or sequential logic circuit or shift registers, located either in the vicinity of the combinational logic circuit or in a remote external location. But the external circuit does not interfere in the behavior of the combinational circuit.
Combination Logic Circuits are made up from basic logic NAND, NOR or NOT gates that are "combined" or connected together to produce more complicated switching circuits. These logic gates are the building blocks of combinational logic circuits. An example of a combinational circuit is a decoder, which converts the binary code data present at its input into a number of different output lines, one at a time producing an equivalent decimal code at its output.
Combinational logic circuits can be very simple or very complicated and any combinational circuit can be implemented with only NAND and NOR gates as these are classed as "universal" gates. The three main ways of specifying the function of a combinational logic circuit are:
As combination logic circuits are made up from individual logic gates only, they can also be considered as "decision making circuits" and combinational logic is about combining logic gates together to process two or more signals in order to produce at least one output signal according to the logical function of each logic gate. Common combinational circuits made up from individual logic gates that carry out a desired application include Multiplexers, De-multiplexers, Encoders, Decoders,etc.
Multiplexer(mux) :- Multiplexer is a device that allows the digital information from several sources to be routed on to a single line from transmitter to the reciever..The basic multiplexer has several data input lines and a single output line..It also has the select input which permits the digital data or any one of the input to be switched to the output line..Multiplexers are also called as "DATA SELECTORS".
De-Multiplexer(de-mux) :- De-multiplexer is a device which performs the reverse function of Multiplexer.It takes the digital information from a single line and distributes to a given number of output lines..
De-Multiplexers are also called as "DATA DISTRIBUTER"
Encoders :- Encoder is a combinational circuit which converts the decimal or octal to the coded form such as BCD.
Decoder :-Decoder is a device which converts the coded data into uncoded form..An AND gate is used as a decoding element because it produces the high output and all inputs are high..
2.Sequential circuits:-
These are the circuits whose output depends on the present input as well as the past output..The sequential Logic circuits have memory to store the output..
Flip-flops:-Flipflop is a bistable device that can reside in either of two states by the feedback arrangement.it is used to store one bit of data ..Hence flipflops are used in counters,registers,memories & shift registers..
Group of flipflops used for data storage is called as Register..
Applications of Flipflops:-
*Used in data storage devices
*Counters
*Registers and shift-registers
*Frequency devices..
Counters:-Flipflops which are connected together to perform the counting operations is called as counters..The njumber of Flip-flops deetermine the number of states and is called as modulus..
*Counters
*Registers and shift-registers
*Frequency devices..
Counters:-Flipflops which are connected together to perform the counting operations is called as counters..The njumber of Flip-flops deetermine the number of states and is called as modulus..
Counters are clissified into two categories, they are:-
*Asynchronous Counter
*Synchronous Counter
* Asynchronous Counter :-In Asynchronous Counter the first flipflop is clocked by an external clock pulse and then each successive flipflop is clocked by the output of the previous Flipflop.Therefore in this counterthe flipflops are not clocked simultaneously..Asynchronous Counter is also called as Ripple Counter..
*Synchronous Counter :-In Synchronous Counter the clock input is connected to all the flipflops and thus they are clocked simultaneously..
Shift Register :-Group of flipflops used where the data is stored and shifted from one Flipflop to the another Flipflop is called as Shift Register..
