Category: linear Integrated Circuits Applications

Digital to Analog Converters A Digital to Analog Converter (DAC) converts a digital input signal into an analog output signal. The digital signal is represented with a binary code, which is a combination of bits 0 and 1. This chapter deals with Digital to Analog Converters in detail. The block diagram of DAC is shown in the following figure − A Digital to Analog Converter (DAC) consists of a number of binary inputs and a single output. In general, the number of binary inputs of a DAC will be a power of two. Types of DACs There are two types of DACs Weighted Resistor DAC R-2R Ladder DAC This section discusses about these two types of DACs in detail − Weighted Resistor DAC A weighted resistor DAC produces an analog output, which is almost equal to the digital (binary) input by using binary weighted resistors in the inverting adder circuit. In short, a binary weighted resistor DAC is called as weighted resistor DAC. The circuit diagram of a 3-bit binary weighted resistor DAC is shown in the following figure − Recall that the bits of a binary number can have only one of the two values. i.e., either 0 or 1. Let the 3-bit binary input is $b_{2}b_{1}b_{0}$. Here, the bits $b_{2}$ and $b_{0}$ denote the Most Significant Bit (MSB) and Least Significant Bit (LSB) respectively. The digital switches shown in the above figure will be connected to ground, when the corresponding input bits are equal to ‘0’. Similarly, the digital switches shown in the above figure will be connected to the negative reference voltage, $-V_{R}$ when the corresponding input bits are equal to ‘1’. In the above circuit, the non-inverting input terminal of an op-amp is connected to ground. That means zero volts is applied at the non-inverting input terminal of op-amp. According to the virtual short concept, the voltage at the inverting input terminal of opamp is same as that of the voltage present at its non-inverting input terminal. So, the voltage at the inverting input terminal’s node will be zero volts. The nodal equation at the inverting input terminal’s node is: $$frac{0+V_{R}b_{2}}{2^{0}R}+frac{0+V_{R}b_{1}}{2^{1}R}+frac{0+V_{R}b_{0}}{2^{2}R}+frac{0-V_{0}}{R_{f}}=0$$ $$=>frac{V_{0}}{R_{f}}=frac{V_{R}b_{2}}{2^{0}R}+frac{V_{R}b_{1}}{2^{1}R}+frac{V_{R}b_{0}}{2^{2}R}$$ $$=>V_{0}=frac{V_{R}R_{f}}{R}left {frac{b_{2}}{2^{0}}+frac{b_{1}}{2^{1}}+frac{b_{0}}{2^{2}}right }$$ Substituting, $R=2R_{f}$𝑓 in above equation. $$=>V_{0}=frac{V_{R}R_{f}}{2R_{f}}left {frac{b_{2}}{2^{0}}+frac{b_{1}}{2^{1}}+frac{b_{0}}{2^{2}}right }$$ $$=>V_{0}=frac{V_{R}}{2}left {frac{b_{2}}{2^{0}}+frac{b_{1}}{2^{1}}+frac{b_{0}}{2^{2}}right }$$ The above equation represents the output voltage equation of a 3-bit binary weighted resistor DAC. Since the number of bits are three in the binary (digital) input, we will get seven possible values of output voltage by varying the binary input from 000 to 111 for a fixed reference voltage, $V_{R}$. We can write the generalized output voltage equation of an N-bit binary weighted resistor DAC as shown below based on the output voltage equation of a 3-bit binary weighted resistor DAC. $$=>V_{0}=frac{V_{R}}{2}left { frac{b_{N-1}}{2^{0}}+ frac{b_{N-2}}{2^{1}}+….+frac{b_{0}}{2^{N-1}} right }$$ The disadvantages of a binary weighted resistor DAC are as follows − The difference between the resistance values corresponding to LSB & MSB will increase as the number of bits present in the digital input increases. It is difficult to design more accurate resistors as the number of bits present in the digital input increases. R-2R Ladder DAC The R-2R Ladder DAC overcomes the disadvantages of a binary weighted resistor DAC. As the name suggests, R-2R Ladder DAC produces an analog output, which is almost equal to the digital (binary) input by using a R-2R ladder network in the inverting adder circuit. Thecircuit diagramof a 3-bit R-2R Ladder DAC is shown in the following figure − Recall that the bits of a binary number can have only one of the two values. i.e., either 0 or 1. Let the 3-bit binary input is $b_{2}b_{1}b_{0}$. Here, the bits $b_{2}$ and $b_{0}$ denote the Most Significant Bit (MSB) and Least Significant Bit (LSB) respectively. The digital switches shown in the above figure will be connected to ground, when the corresponding input bits are equal to ‘0’. Similarly, the digital switches shown in above figure will be connected to the negative reference voltage, $-V_{R}$ when the corresponding input bits are equal to ‘1’. It is difficult to get the generalized output voltage equation of a R-2R Ladder DAC. But, we can find the analog output voltage values of R-2R Ladder DAC for individual binary input combinations easily. The advantages of a R-2R Ladder DAC are as follows − R-2R Ladder DAC contains only two values of resistor: R and 2R. So, it is easy to select and design more accurate resistors. If more number of bits are present in the digital input, then we have to include required number of R-2R sections additionally. Due to the above advantages, R-2R Ladder DAC is preferable over binary weighted resistor DAC. Learning working make money

Clippers Wave shaping circuits are the electronic circuits, which produce the desired shape at the output from the applied input wave form. These circuits perform two functions − Attenuate the applied wave Alter the dc level of the applied wave. There are two types of wave shaping circuits: Clippers and Clampers. In this chapter, you will learn in detail about clippers. Op-amp based Clippers A clipper is an electronic circuit that produces an output by removing a part of the input above or below a reference value. That means, the output of a clipper will be same as that of the input for other than the clipped part. Due to this, the peak to peak amplitude of the output of a clipper will be always less than that of the input. The main advantage of clippers is that they eliminate the unwanted noise present in the amplitude of an ac signal. Clippers can be classified into the following two types based on the clipping portion of the input. Positive Clipper Negative Clipper These are discussed in detail as given below − Positive Clipper A positive clipper is a clipper that clips only the positive portion(s) of the input signal. The circuit diagramof positive clipper is shown in the following figure − In the circuit shown above, a sinusoidal voltage signal $V_{t}$ is applied to the non-inverting terminal of the op-amp. The value of the reference voltage $V_{ref}$ can be chosen by varying the resistor $R_{2}$. The operation of the circuit shown above is explained below − If the value of the input voltage $V_i$ is less than the value of the reference voltage $V_{ref}$, then the diode D1 conducts. Then, the circuit given above behaves as a voltage follower. Therefore, the output voltage $V_{0}$ of the above circuit will be same as that of the input voltage $V_{i}$, for $V_{i}$ < $V_{ref}$. If the value of the input voltage $V_{i}$ is greater than the value of reference voltage $V_{ref}$, then the diode D1 will be off. Now, the op-amp operates in an open loop since the feedback path was open. Therefore, the output voltage $V_{0}$ of the above circuit will be equal to the value of the reference voltage $V_{ref}$, for $V_{i}$ > $V_{ref}$. The input wave form and the corresponding output wave form of a positive clipper for a positive reference voltage $V_{ref}$, are shown in the following figure − Negative Clipper A negative clipper is a clipper that clips only the negative portion(s) of the input signal. You can obtain the circuit of the negative clipper just by reversing the diode and taking the reverse polarity of the reference voltage, in the circuit that you have seen for a positive clipper. The circuit diagram of a negative clipper is shown in the following figure − In the above circuit, a sinusoidal voltage signal $V_{i}$ is applied to the non-inverting terminal of the op-amp. The value of the reference voltage $V_{ref}$ can be chosen by varying the resistor $R_{2}$. The operation of a negative clipper circuit is explained below − If the value of the input voltage $V_{t}$ is greater than the value of reference voltage $V_{ref}$, then the diode D1 conducts. Then, the above circuit behaves as a voltage follower. Therefore, the output voltage $V_{0}$ of the above circuit will be same as that of the input voltage $V_{i}$ for $V_{i}$> $V_{ref}$. If the value of the input voltage $V_{i}$ is less than the value of reference voltage , then the diode D1 will be off. Now, the op-amp operates in an open loop since the feedback path is open. Therefore, the output voltage $V_{0}$ of the above circuit will be equal to the value of reference voltage ,$V_{ref}$ for $V_{i}$ < $V_{ref}$. The input wave form and the corresponding output wave form of a negative clipper, for a negative reference voltage $V_{ref}$, are shown in the following figure − Learning working make money

Voltage Regulators The function of a voltage regulator is to maintain a constant DC voltage at the output irrespective of voltage fluctuations at the input and (or) variations in the load current. In other words, voltage regulator produces a regulated DC output voltage. Voltage regulators are also available in Integrated Circuits (IC) forms. These are called as voltage regulator ICs. Types of Voltage Regulators There are two types of voltage regulators − Fixed voltage regulator Adjustable voltage regulator This chapter discusses about these two types of voltage regulators one by one. Fixed voltage regulator A fixed voltage regulator produces a fixed DC output voltage, which is either positive or negative. In other words, some fixed voltage regulators produce positive fixed DC voltage values, while others produce negative fixed DC voltage values. 78xx voltage regulator ICs produce positive fixed DC voltage values, whereas, 79xx voltage regulator ICs produce negative fixed DC voltage values. The following points are to be noted while working with 78xx and 79xx voltage regulator ICs − “xx” corresponds to a two-digit number and represents the amount (magnitude) of voltage that voltage regulator IC produces. Both 78xx and 79xx voltage regulator ICs have 3 pins each and the third pin is used for collecting the output from them. The purpose of the first and second pins of these two types of ICs is different − The first and second pins of 78xx voltage regulator ICs are used for connecting the input and ground respectively. The first and second pins of 79xx voltage regulator ICs are used for connecting the ground and input respectively. Examples 7805 voltage regulator IC produces a DC voltage of +5 volts. 7905 voltage regulator IC produces a DC voltage of -5 volts. The following figure shows how to produce a fixed positive voltage at the output by using a fixed positive voltage regulator with necessary connections. In the above figure that shows a fixed positive voltage regulator, the input capacitor Ci is used to prevent unwanted oscillations and the output capacitor, C0 acts as a line filter to improve transient response. Note − an get a fixed negative voltage at the output by using a fixed negative voltage regulator with suitable connections. Adjustable voltage regulator An adjustable voltage regulator produces a DC output voltage, which can be adjusted to any other value of certain voltage range. Hence, adjustable voltage regulator is also called as a variable voltage regulator. The DC output voltage value of an adjustable voltage regulator can be either positive or negative. LM317 voltage regulator IC LM317 voltage regulator IC can be used for producing a desired positive fixed DC voltage value of the available voltage range. LM317 voltage regulator IC has 3 pins. The first pin is used for adjusting the output voltage, second pin is used for collecting the output and third pin is used for connecting the input. The adjustable pin (terminal) is provided with a variable resistor which lets the output to vary between a wide range. The above figure shows an unregulated power supply driving a LM 317 voltage regulator IC, which is commonly used. This IC can supply a load current of 1.5A over an adjustable output range of 1.25 V to 37 V. Learning working make money

Indirect Type ADC In the previous chapter, we discussed about what an ADC is and the examples of a Direct type ADC. This chapter discusses about the Indirect type ADC. If an ADC performs the analog to digital conversion by an indirect method, then it is called an Indirect type ADC. In general, first it converts the analog input into a linear function of time (or frequency) and then it will produce the digital (binary) output. Dual slope ADC is the best example of an Indirect type ADC. This chapter discusses about it in detail. Dual Slope ADC As the name suggests, a dual slope ADC produces an equivalent digital output for a corresponding analog input by using two (dual) slope technique. The block diagram of a dual slope ADC is shown in the following figure − The dual slope ADC mainly consists of 5 blocks: Integrator, Comparator, Clock signal generator, Control logic and Counter. The working of a dual slope ADC is as follows − The control logic resets the counter and enables the clock signal generator in order to send the clock pulses to the counter, when it is received the start commanding signal. Control logic pushes the switch sw to connect to the external analog input voltage $V_{i}$, when it is received the start commanding signal. This input voltage is applied to an integrator. The output of the integrator is connected to one of the two inputs of the comparator and the other input of comparator is connected to ground. Comparator compares the output of the integrator with zero volts (ground) and produces an output, which is applied to the control logic. The counter gets incremented by one for every clock pulse and its value will be in binary (digital) format. It produces an overflow signal to the control logic, when it is incremented after reaching the maximum count value. At this instant, all the bits of counter will be having zeros only. Now, the control logic pushes the switch sw to connect to the negative reference voltage $-V_{ref}$. This negative reference voltage is applied to an integrator. It removes the charge stored in the capacitor until it becomes zero. At this instant, both the inputs of a comparator are having zero volts. So, comparator sends a signal to the control logic. Now, the control logic disables the clock signal generator and retains (holds) the counter value. The counter value is proportional to the external analog input voltage. At this instant, the output of the counter will be displayed as the digital output. It is almost equivalent to the corresponding external analog input value $V_{i}$. The dual slope ADC is used in the applications, where accuracy is more important while converting analog input into its equivalent digital (binary) data. Learning working make money

555 Timer The 555 Timer IC got its name from the three $5KOmega$ resistors that are used in its voltage divider network. This IC is useful for generating accurate time delays and oscillations. This chapter explains about 555 Timer in detail. Pin Diagram and Functional Diagram In this section, first let us discuss about the pin diagram of 555 Timer IC and then its functional diagram. Pin Diagram The 555 Timer IC is an 8 pin mini Dual-Inline Package (DIP). The pin diagram of a 555 Timer IC is shown in the following figure − The significance of each pin is self-explanatory from the above diagram. This 555 Timer IC can be operated with a DC supply of +5V to +18V. It is mainly useful for generating non-sinusoidal wave forms like square, ramp, pulse & etc Functional Diagram The pictorial representation showing the internal details of a 555 Timer is known as functional diagram. The functional diagram of 555 Timer IC is shown in the following figure − Observe that the functional diagram of 555 Timer contains a voltage divider network, two comparators, one SR flip-flop, two transistors and an inverter. This section discusses about the purpose of each block or component in detail − Voltage Divider Network The voltage divider network consists of a three $5KOmega$ resistors that are connected in series between the supply voltage $V_{cc}$ and ground. This network provides a voltage of $frac{V_{cc} }{3}$ between a point and ground, if there exists only one $5KOmega$ resistor. Similarly, it provides a voltage of $frac{2V_{cc} }{3}$ between a point and ground, if there exists only two $5KOmega$ resistors. Comparator The functional diagram of a 555 Timer IC consists of two comparators: an Upper Comparator (UC) and a Lower Comparator (LC). Recall that a comparator compares the two inputs that are applied to it and produces an output. If the voltage present at the non-inverting terminal of an op-amp is greater than the voltage present at its inverting terminal, then the output of comparator will be $+V_{sat}$. This can be considered as Logic High (”1”) in digital representation. If the voltage present at the non-inverting terminal of op-amp is less than or equal to the voltage at its inverting terminal, then the output of comparator will be $-V_{sat}$. This can be considered as Logic Low (”0”) in digital representation. SR Flip-Flop Recall that a SR flip-flop operates with either positive clock transitions or negative clock transitions. It has two inputs: S and R, and two outputs: Q(t) and Q(t)’. The outputs, Q(t) & Q(t)’ are complement to each other. The following table shows the state table of a SR flip-flop S R Q(t+1) 0 0 Q(t) 0 1 0 1 0 1 1 1 – Here, Q(t) & Q(t+1) are present state & next state respectively. So, SR flip-flop can be used for one of these three functions such as Hold, Reset & Set based on the input conditions, when positive (negative) transition of clock signal is applied. The outputs of Lower Comparator (LC) and Upper Comparator (UC) are applied as inputs of SR flip-flop as shown in the functional diagram of 555 Timer IC. Transistors and Inverter The functional diagram of a 555 Timer IC consists of one npn transistor $Q_{1}$ and one pnp transistor $Q_{2}$. The npn transistor $Q_{1}$ will be turned ON if its base to emitter voltage is positive and greater than cut-in voltage. Otherwise, it will be turned-OFF. The pnp transistor $Q_{2}$ is used as buffer in order to isolate the reset input from SR flip-flop and npn transistor $Q_{1}$. The inverter used in the functional diagram of a 555 Timer IC not only performs the inverting action but also amplifies the power level. The 555 Timer IC can be used in mono stable operation in order to produce a pulse at the output. Similarly, it can be used in astable operation in order to produce a square wave at the output. Learning working make money

Data Converters All the real world quantities are analog in nature. We can represent these quantities electrically as analog signals. An analog signal is a time varying signal that has any number of values (variations) for a given time slot. In contrast to this, a digital signal varies suddenly from one level to another level and will have only finite number of values (variations) for a given time slot. This chapter discusses about the types of data converters and their specifications. Types of Data Converters The electronic circuits, which can be operated with analog signals are called as analog circuits. Similarly, the electronic circuits, which can be operated with digital signals are called as digital circuits. A data converter is an electronic circuit that converts data of one form to another. There are two types of data converters − Analog to Digital Converter Digital to Analog Converter If we want to connect the output of an analog circuit as an input of a digital circuit, then we have to place an interfacing circuit between them. This interfacing circuit that converts the analog signal into digital signal is called as Analog to Digital Converter. Similarly, if we want to connect the output of a digital circuit as an input of an analog circuit, then we have to place an interfacing circuit between them. This interfacing circuit that converts the digital signal into an analog signal is called as Digital to Analog Converter. Note that some Analog to Digital Converters may require Digital to Analog Converter as an internal block for their operation. Specifications The following are the specifications that are related to data conversions − Resolution Conversion Time Resolution Resolution is the minimum amount of change needed in an analog input voltage for it to be represented in binary (digital) output. It depends on the number of bits that are used in the digital output. Mathematically, resolution can be represented as $$Resolution=frac{1}{2^{N}}$$ where, ‘N’ is the number of bits that are present in the digital output. From the above formula, we can observe that there exists an inverse relationship between the resolution and number of bits. Therefore, resolution decreases as the number of bits increases and vice-versa. Resolution can also be defined as the ratio of maximum analog input voltage that can be represented in binary and the equivalent binary number. Mathematically, resolution can be represented as $$Resolution=frac{V_{FS}}{2^{N}-1}$$ where, $V_{FS}$ is the full scale input voltage or maximum analog input voltage, ‘N’ is the number of bits that are present in the digital output. Conversion Time The amount of time required for a data converter in order to convert the data (information) of one form into its equivalent data in other form is called as conversion time. Since we have two types of data converters, there are two types of conversion times as follows Analog to Digital Conversion time Digital to Analog Conversion time The amount of time required for an Analog to Digital Converter (ADC) to convert the analog input voltage into its equivalent binary (digital) output is called as Analog to Digital conversion time. It depends on the number of bits that are used in the digital output. The amount of time required for a Digital to Analog Converter (DAC) to convert the binary (digital) input into its equivalent analog output voltage is called as Digital to Analog conversion time. It depends on the number of bits that are present in the binary (digital) input. Learning working make money

Active Filters Filters are electronic circuits that allow certain frequency components and / or reject some other. You might have come across filters in network theory tutorial. They are passive and are the electric circuits or networks that consist of passive elements like resistor, capacitor, and (or) an inductor. This chapter discusses about active filters in detail. Types of Active Filters Active filters are the electronic circuits, which consist of active element like op-amp(s) along with passive elements like resistor(s) and capacitor(s). Active filters are mainly classified into the following four types based on the band of frequencies that they are allowing and / or rejecting − Active Low Pass Filter Active High Pass Filter Active Band Pass Filter Active Band Stop Filter Active Low Pass Filter If an active filter allows (passes) only low frequency components and rejects (blocks) all other high frequency components, then it is called as an active low pass filter. The circuit diagram of an active low pass filter is shown in the following figure − We know that the electric network, which is connected to the non-inverting terminal of an op-amp is a passive low pass filter. So, the input of a non-inverting terminal of an opamp is the output of a passive low pass filter. Observe that the above circuit resembles a non-inverting amplifier. It is having the output of a passive low pass filter as an input to the non-inverting terminal of op-amp. Hence, it produces an output, which is $left(1+frac{R_f}{R_1}right)$ times the input present at the non-inverting terminal. We can choose the values of $R_{f}$ and $R_{1}$ suitably in order to obtain the desired gain at the output. Suppose, if we consider the resistance values of $R_{f}$ and $R_{1}$ as zero ohms and infinity ohms, then the above circuit will produce a unity gain low pass filter output. Active High Pass Filter If an active filter allows (passes) only high frequency components and rejects (blocks) all other low frequency components, then it is called an active high pass filter. The circuit diagram of an active high pass filter is shown in the following figure − We know that the electric network, which is connected to the non-inverting terminal of an op-amp is a passive high pass filter. So, the input of a non-inverting terminal of opamp is the output of passive high pass filter. Now, the above circuit resembles a non-inverting amplifier. It is having the output of a passive high pass filter as an input to non-inverting terminal of op-amp. Hence, it produces an output, which is $left(1+frac{R_f}{R_1}right)$ times the input present at its non-inverting terminal. We can choose the values of $R_f$ and $R_1$ suitably in order to obtain the desired gain at the output. Suppose, if we consider the resistance values of $R_{f}$ and $R_{1}$ as zero ohms and infinity ohms, then the above circuit will produce a unity gain high pass filter output. Active Band Pass Filter If an active filter allows (passes) only one band of frequencies, then it is called as an active band pass filter. In general, this frequency band lies between low frequency range and high frequency range. So, active band pass filter rejects (blocks) both low and high frequency components. The circuit diagram of an active band pass filter is shown in the following figure Observe that there are two parts in the circuit diagram of active band pass filter: The first part is an active high pass filter, while the second part is an active low pass filter. The output of the active high pass filter is applied as an input of the active low pass filter.That means, both active high pass filter and active low pass filter are cascaded in order to obtain the output in such a way that it contains only a particular band of frequencies. The active high pass filter, which is present at the first stage allows the frequencies that are greater than the lower cut-off frequency of the active band pass filter. So, we have to choose the values of $R_{B}$ and $C_{B}$ suitably, to obtain the desired lower cut-off frequency of the active band pass filter. Similarly, the active low pass filter, which is present at the second stage allows the frequencies that are smaller than the higher cut-off frequency of the active band pass filter. So, we have to choose the values of $R_{A}$ and $C_{A}$ suitably in order to obtain the desired higher cut-off frequency of the active band pass filter. Hence, the circuit in the diagram discussed above will produce an active band pass filter output. Active Band Stop Filter If an active filter rejects (blocks) a particular band of frequencies, then it is called as an active band stop filter. In general, this frequency band lies between low frequency range and high frequency range. So, active band stop filter allows (passes) both low and high frequency components. The block diagram of an active band stop filter is shown in the following figure − Observe that the block diagram of an active band stop filter consists of two blocks in its first stage: an active low pass filter and an active high pass filter. The outputs of these two blocks are applied as inputs to the block that is present in the second stage. So, the summing amplifier produces an output, which is the amplified version of sum of the outputs of the active low pass filter and the active high pass filter. Therefore, the output of the above block diagram will be the output of an active band stop , when we choose the cut-off frequency of low pass filter to be smaller than cut-off frequency of a high pass filter. The circuit diagram of an active band stop filter is shown in the following figure − We have already seen the circuit diagrams of an active low pass filter, an active high pass filter and a summing amplifier. Observe that we got the above circuit diagram of active

Discuss Linear Integrated Circuits Applications Linear Integrated Circuits are solid state analog devices that can operate over a continuous range of input signals. Theoretically, they are characterized by an infinite number of operating states. Linear Integrated Circuits are widely used in amplifier circuits. Learning working make money

Waveform Generators A waveform generator is an electronic circuit, which generates a standard wave. There are two types of op-amp based waveform generators − Square wave generator Triangular wave generator This chapter discusses each of these op-amp based waveform generators in detail. Square Wave Generator A square wave generator is an electronic circuit which generates square wave. This section discusses about op-amp based square wave generators. The circuit diagram of a op-amp based square wave generator is shown in the following figure Observe that in the circuit diagram shown above, the resistor $R_{1}$ is connected between the inverting input terminal of the op-amp and its output of op-amp. So, the resistor $R_{1}$ is used in the negative feedback. Similarly, the resistor $R_{2}$ is connected between the noninverting input terminal of the op-amp and its output. So, the resistor $R_{2}$ is used in the positive feedback path. A capacitor C is connected between the inverting input terminal of the op-amp and ground. So, the voltage across capacitor C will be the input voltage at this inverting terminal of op-amp. Similarly, a resistor $R_{3}$ is connected between the non-inverting input terminal of the op-amp and ground. So, the voltage across resistor $R_{3}$ will be the input voltage at this non-inverting terminal of the op-amp. The operation of a square wave generator is explained below − Assume, there is no charge stored in the capacitor initially. Then, the voltage present at the inverting terminal of the op-amp is zero volts. But, there is some offset voltage at non-inverting terminal of op-amp. Due to this, the value present at the output of above circuit will be $+V_{sat}$. Now, the capacitor C starts charging through a resistor $R_{1}$. The value present at the output of the above circuit will change to $-V_{sat}$, when the voltage across the capacitor C reaches just greater than the voltage (positive value) across resistor $R_{3}$. The capacitor C starts discharging through a resistor $R_{1}$, when the output of above circuit is $-V_{sat}$. The value present at the output of above circuit will change to $+V_{sat}$,when the voltage across capacitor C reaches just less than (more negative) the voltage (negative value) across resistor $R_{3}$. Thus, the circuit shown in the above diagram will produce a square wave at the output as shown in the following figure − From the above figure we can observe that the output of square wave generator will have one of the two values: $+V_{sat}$ and $-V_{sat}$. So, the output remains at one value for some duration and then transitions to another value and remains there for some duration. In this way, it continues. Triangular Wave Generator A triangular wave generator is an electronic circuit, which generates a triangular wave. The block diagram of a triangular wave generator is shown in the following figure − The block diagram of a triangular wave generator contains mainly two blocks: a square wave generator and an integrator. These two blocks are cascaded. That means, the output of square wave generator is applied as an input of integrator. Note that the integration of a square wave is nothing but a triangular wave. The circuit diagram of an op-amp based triangular wave generator is shown in the following figure − We have already seen the circuit diagrams of a square wave generator and an integrator. Observe that we got the above circuit diagram of an op-amp based triangular wave generator by replacing the blocks with the respective circuit diagrams in the block diagram of a triangular wave generator. Learning working make money

Direct Type ADCs An Analog to Digital Converter (ADC) converts an analog signal into a digital signal. The digital signal is represented with a binary code, which is a combination of bits 0 and 1. The block diagram of an ADC is shown in the following figure − Observe that in the figure shown above, an Analog to Digital Converter (ADC) consists of a single analog input and many binary outputs. In general, the number of binary outputs of ADC will be a power of two. There are two types of ADCs: Direct type ADCs and Indirect type ADC. This chapter discusses about the Direct type ADCs in detail. If the ADC performs the analog to digital conversion directly by utilizing the internally generated equivalent digital (binary) code for comparing with the analog input, then it is called as Direct type ADC. The following are the examples of Direct type ADCs − Counter type ADC Successive Approximation ADC Flash type ADC This section discusses about these Direct type ADCs in detail. Counter type ADC A counter type ADC produces a digital output, which is approximately equal to the analog input by using counter operation internally. The block diagram of a counter type ADC is shown in the following figure − The counter type ADC mainly consists of 5 blocks: Clock signal generator, Counter, DAC, Comparator and Control logic. The working of a counter type ADC is as follows − The control logic resets the counter and enables the clock signal generator in order to send the clock pulses to the counter, when it received the start commanding signal. The counter gets incremented by one for every clock pulse and its value will be in binary (digital) format. This output of the counter is applied as an input of DAC. DAC converts the received binary (digital) input, which is the output of counter, into an analog output. Comparator compares this analog value,$V_{a}$ with the external analog input value $V_{i}$. The output of comparator will be ‘1’ as long as 𝑉𝑖 is greater than. The operations mentioned in above two steps will be continued as long as the control logic receives ‘1’ from the output of comparator. The output of comparator will be ‘0’ when $V_{i}$ is less than or equal to $V_{a}$. So, the control logic receives ‘0’ from the output of comparator. Then, the control logic disables the clock signal generator so that it doesn’t send any clock pulse to the counter. At this instant, the output of the counter will be displayed as the digital output. It is almost equivalent to the corresponding external analog input value $V_{i}$. Successive Approximation ADC A successive approximation type ADC produces a digital output, which is approximately equal to the analog input by using successive approximation technique internally. The block diagram of a successive approximation ADC is shown in the following figure The successive approximation ADC mainly consists of 5 blocks− Clock signal generator, Successive Approximation Register (SAR), DAC, comparator and Control logic. The working of a successive approximation ADC is as follows − The control logic resets all the bits of SAR and enables the clock signal generator in order to send the clock pulses to SAR, when it received the start commanding signal. The binary (digital) data present in SAR will be updated for every clock pulse based on the output of comparator. The output of SAR is applied as an input of DAC. DAC converts the received digital input, which is the output of SAR, into an analog output. The comparator compares this analog value $V_{a}$ with the external analog input value $V_{i}$. The output of a comparator will be ‘1’ as long as $V_{i}$ is greater than $V_{a}$. Similarly, the output of comparator will be ‘0’, when $V_{i}$ is less than or equal to $V_{a}$. The operations mentioned in above steps will be continued until the digital output is a valid one. The digital output will be a valid one, when it is almost equivalent to the corresponding external analog input value $V_{i}$. Flash type ADC A flash type ADC produces an equivalent digital output for a corresponding analog input in no time. Hence, flash type ADC is the fastest ADC. The circuit diagram of a 3-bit flash type ADC is shown in the following figure − The 3-bit flash type ADC consists of a voltage divider network, 7 comparators and a priority encoder. The working of a 3-bit flash type ADC is as follows. The voltage divider networkcontains 8 equal resistors. A reference voltage $V_{R}$ is applied across that entire network with respect to the ground. The voltage drop across each resistor from bottom to top with respect to ground will be the integer multiples (from 1 to 8) of $frac{V_{R}}{8}$. The external input voltage $V_{i}$ is applied to the non-inverting terminal of all comparators. The voltage drop across each resistor from bottom to top with respect to ground is applied to the inverting terminal of comparators from bottom to top. At a time, all the comparators compare the external input voltage with the voltage drops present at the respective other input terminal. That means, the comparison operations take place by each comparator parallelly. The output of the comparator will be ‘1’ as long as $V_{i}$ is greater than the voltage drop present at the respective other input terminal. Similarly, the output of comparator will be ‘0’, when, $V_{i}$ is less than or equal to the voltage drop present at the respective other input terminal. All the outputs of comparators are connected as the inputs of priority encoder.This priority encoder produces a binary code (digital output), which is corresponding to the high priority input that has ‘1’. Therefore, the output of priority encoder is nothing but the binary equivalent (digital output) of external analog input voltage, $V_{i}$. The flash type ADC is used in the applications where the conversion speed of analog input into digital data should be very high. Learning working make money