Abstract-This paper presents the concept of IC and the distinguishing facts of Linear And Digital IC.

I. INTRODUCTION

An Integrated Circuit (IC) is a mini-scale electronic circuit consisting of active and passive components constructed on the surface of thin semiconductor wafer like material. The chip is mounted in a plastic or ceramic container and the connections are done with the help of gold wires to external pins, thus forming an integrated circuit. The number of pins varies from 14 (in a small IC) to 100 or more in a large IC package. ICs have revolutionized all the electronic devices present in today’s world.

The two main advantages of using IC, now used in almost every electronic circuit, are: cost and performance. Cost is low because the chips, with all their components, are printed as a unit by photolithography and not constructed one transistor at a time. Also, much less material is used to construct a circuit as a packaged IC than as a discrete circuit. Performance is high since the components switch quickly and consume little power (compared to their discrete counterparts) because the components are small and close together. As of 2009, chip areas range from a few square millimetres to around 350 mm2, with up to 1 million transistors per mm2. Modern devices like computers, mobiles, telecommunications, all rely on the ICs.

ICs are classified in mainly two types: (i) Linear, and (ii) Digital ICs.

Linear ICs are those who work by processing continuous signals, performing functions like amplification, demodulation, mixing, etc. Examples are sensors, power management systems and operational amplifiers.

Digital ICs are made up of one to millions of logic gates, flip-flops, multiplexers and other circuits. It works only at two states: (i) ‘on’ or ‘high’ state, and (ii) ‘off’ or ‘low’ state. Characteristics include high speed, low power dissipation,

Fig. 1. A simple Integrated Circuit (IC).

and significantly low cost of production. Examples are microprocessors, DSPs, and micro controllers.

There’s one more classification of IC, namely Mixed ICs. In this type, linear and digital ICs are mounted on a single chip to perform specific functions.

II. LINEAR INTEGRATED CIRCUITS

A linear integrated circuit (linear IC) is a solid-state analog device characterized by a theoretically infinite number of possible operating states. It operates over a continuous range of input levels. In contrast, a digital IC has a finite number of discrete input and output states.

Within a certain input range, the amplification curve of a linear IC is a straight line; the input and output voltages are directly proportional. The best known, and most common, linear IC is the operational amplifier or op amp , which consists of resistors, diodes, and transistors in a conventional analog circuit. There are two inputs, called inverting and non-inverting. A signal applied to the inverting input results in a signal of opposite phase at the output. A signal applied to the non-inverting input produces a signal of identical phase at the output. A connection, through a variable resistance , between the output and the inverting input is used to control the amplification factor .

Linear ICs are employed in audio amplifiers, A/D (analog-to-digital) converters, averaging amplifiers, differentiators, DC (direct-current) amplifiers, integrators, multivibrators, oscillators, audio filters, and sweep generators. Linear ICs are available in most large electronics stores. Some devices contain several amplifiers within a single housing.

We’ll be discussing two Linear ICs: (i) Operational Amplifier, and (ii) Fully Differential Amplifier.

A. Operational Amplifier

An operational amplifier, also termed as op-amp, where ‘op’ stands for various mathematical operations such as addition, subtraction, multiplication, differentiations, integration etc. And the word ‘amp’ is the one which will boost up the signal if a device will perform mathematical operation and also amplify a simple waveform (increase the gain).

It is IC 741 according to industrial standards but the designation of IC will depend upon various manufactures. Table I shows various manufactures and their op-amp IC designation.

Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume; however some integrated or hybrid operational amplifiers with special performance specifications may cost over $100 US in small quantities. Op-amps sometimes come in the form of macroscopic components, or as integrated circuit ‘cells’ or patterns that can be reprinted several times on one chip that is more complex, such as for a cell phone. Fig. 2. shows various op-amp chips.

TABLE I

OP-AMP MANUFACTURERS AND IC DESIGNATION

Fig. 2. Various Op-amps.

A.1. Circuit Notation

Circuit diagram symbol for an op-amp is shown in Fig. 3, where,

V₊: non-inverting input

V_-: inverting input

V_out: output

V_S+: positive power supply

V_S- negative power supply

Fig. 3. Circuit Diagram of an Op-amp

A.2. Applications Of An Op-Amp

1) Used In Electronics: Instead of using individual elements (resistors, transistors etc.) in a circuit, we can use an op-amp to reduce complexity of the system.

2) Audio- and video-frequency pre-amplifiers and buffers.

3) Voltage comparators.

4) Differential amplifiers.

5) Differentiators and integrators.

6) Filters.

7) Precision rectifiers.

Precision peak detectors.

9) Voltage and current regulators.

10) Analog calculators.

11) Analog-to-digital converters.

12) Digital-to-analog converter.

13) Voltage clamps.

14) Oscillators and waveform generators.

A.3. Limitations Of Real Op-Amp

Real op-amp has all the limiting characteristics of an ideal op-amp:

1) Finite gain.

2) Finite input impedence.

3) Non-zero output impedence.

4) Mismatch of input current and input offset voltages.

5) Common mode gain.

6) Effect of temperature.

7) Power-Supply Rejection.

Occurrence of Drift.

9) Input Capacitance.

10) Finite Bandwidth.

11) Slewing.

12) Non-Linear Transfer Function.

13) Limited output current.

14) Limited power dissipation.

B. Fully Differential Amplifier

A Fully Differential Amplifier or FDA is a DC-coupled, high-gain electronic voltage amplifier with differential inputs and differential outputs. Unlike op-amp, FDA has two feedback paths, therefore determination of output voltage can be done at any given input. We can see FDA in Fig. 4.

B.1. DC Behaviour

In practical, the open-loop gain of FDA is assumed to be infinite, but in real it is not zero. Devices range 100,00 to over 1 million of open loop DC gain. If AC aspects are neglected in a DC FDA, it may cause implications in the design.

B.2. AC Behaviour

The FDA gain at Dc does not apply for high frequency ranges and gain is inversely proportional to the frequency. The process of frequency compensation is used to prevent any instability.

B.3. Limitations of a real FDA

Limitations are almost same as in the case of op-amp, because both are a type of amplifier only, no matter they are different in functioning.

1) Finite gain.

2) Finite Input Resistance.

3) Nonzero output resistance.

4) Input Biasing Current.

5) Input Offset Voltage.

6) Common Mode gain.

7) Temperature effects.

Finite Bandwidth.

9) Input capacitance.

10) Noise.

11) Saturation.

12) Slewing.

13) Non-linear transfer Function.

14) Limited Output Power.

15) Limited Output Current.

Fig. 4. A Fully Differential Amplifier

III. DIGITAL INTEGRATED CIRCUITS

Digital ICs operate at only a few defined levels or states, rather than over a continuous range of signal amplitudes. These devices are used in computers, computer networks, modems, and frequency counters. The fundamental building blocks of digital ICs are logic gates, which work with binary data, that is, signals that have only two different states, called low (logic 0) and high (logic 1). Examples are already been given.

We’ll be discussing three digital ICs: (i) Microprocessors,   (ii) Digital Signal Processors, and (iii) Counter.

A. Microprocessors

A microprocessor incorporates most or all of the functions of a central processing unit (CPU) on a single integrated circuit (IC). The first microprocessors emerged in the early 1970s and were used for electronic calculators, using binary-coded decimal (BCD) arithmetic on 4-bit words. Other embedded uses of 4- and 8-bit microprocessors, such as terminals, printers, various kinds of automation etc, followed rather quickly. Affordable 8-bit microprocessors with 16-bit addressing also led to the first general purpose microcomputers in the mid-1970s.

Computer processors were for a long period constructed out of small and medium-scale ICs containing the equivalent of a few to a few hundred transistors. The integration of the whole CPU onto a single chip therefore greatly reduced the cost of processing capacity. From their humble beginnings, continued increases in microprocessor capacity have rendered other forms of computers almost completely obsolete (see history of computing hardware), with one or more microprocessor as processing element in everything from the smallest embedded systems and handheld devices to the largest mainframes and supercomputers.

Since the early 1970s, the increase in capacity of microprocessors has been known to generally follow Moore’s Law, which suggests that the complexity of an integrated circuit, with respect to minimum component cost, doubles every two years. In the late 1990s, and in the high-performance microprocessor segment, heat generation (TDP), due to switching losses, static current leakage, and other factors, emerged as a leading developmental constraint.

Fig.5. shows a microprocessor chip.

Fig.5. A Microprocessor

A.2.Applications

Its biggest application is in the computer industry. Every computer is made up of CPU, which is a microprocessor itself. Whether it’s a server or a desktop or a laptop, all have a microprocessor embedded in them.

B. Digital Signal Processor (DSP)

A digital signal processor (DSP) is a specialized microprocessor with an optimized architecture for the fast operational needs of digital signal processing.

B.1. Characteristics

DSP processes large no. Of mathematical operations on a set of data. Signals are first converted from analog to digital, then are processed and at the end are converted again into analog form. We can see it’s working in Fig.6.

Fig.6. A Simple Digital Signal Processing

B.2. Applications

DSPs are used for communication purposes, encoding and decoding of large amount of database. Hybrid processors are manufactured with the characteristics of simple processor and a DSP to improve its functions.

C. Counter

Counters can be implemented using register type circuits like flip flops. It stores the count of various processes. Counters come in various designs:

1)       Asynchronous (ripple) counter – changing state bits are used as clocks to subsequent state flip-flops.

2)       Synchronous counter – all state bits change under control of a single clock.

3)       Decade counter – counts through ten states per stage.

4)       Up–down counter – counts both up and down, under command of a control input.

5)       Ring counter – formed by a shift register with feedback connection in a ring.

6)       Johnson counter – a twisted ring counter.

7)       Cascaded counter.

Each design has its own specific application. We’ll be discussing few of them. Counter circuits are digital in nature and the count is always binary. Counting sequences are used in binary operations like binary coded decimal counter, a linear feedback shift register counter, or a Gray-code counter.

C.1  Asynchronous (Ripple) Counter

It can be constructed using J-K flip flops like in Fig. 7. or with the D-flip flop. Well D-flip flop is the basic and simplest circuit.

Fig. 7. Asynchronous Counter Using J-K Flip Flops

TABLE II

ASYNCHRONOUS COUNTER I/O TABLE

D flip-flop counter circuit can store one bit, and hence can count from zero to one before it overflows (starts over from 0). This counter will increment once for every clock cycle and takes two clock cycles to overflow, so every cycle it will alternate between a transition from 0 to 1 and a transition from 1 to 0. Notice that this creates a new clock with a 50% duty cycle at exactly half the frequency of the input clock. If this output is then used as the clock signal for a similarly arranged D flip-flop (remembering to invert the output to the input), we will get another 1 bit counter that counts half as fast. Putting them together yields a two bit counter whose table is shown as table II.

C.2. Synchronous Counter

A simple way of implementing the logic for each bit of an ascending counter  is for each bit to toggle when all of the less significant bits are at a logic high state. For example, bit 1 toggles when bit 0 is logic high; bit 2 toggles when both bit 1 and bit 0 are logic high; bit 3 toggles when bit 2, bit 1 and bit 0 are all high; and so on.

Synchronous counters can also be implemented with hardware finite state machines, which are more complex but allow for smoother, more stable transitions.

C.3. Ring Counter

A ring counter is a shift register (a cascade connection of flip-flops) with the output of the last one connected to the input of the first, that is, in a ring. Typically a pattern consisting of a single 1 bit is circulated, so the state repeats every N clock cycles if N flip-flops are used. It can be used as a cycle counter of N states. Fig. 8. Shows a Ring Counter.

Fig.8. A 4-bit Ring Counter

C.4 Johnson Counter

A Johnson counter (or switchtail ring counter, twisted-ring counter, walking-ring counter, or Moebius counter) is a modified ring counter, where the output from the last stage is inverted and fed back as input to the first stage.  A pattern of bits equal in length to twice the length of the shift register thus circulates indefinitely. These counters find specialist applications, including those similar to the decade counter, digital to analog conversion, etc.

C.5 Decade Counter

A decade counter is one that counts in decimal digits, rather than binary. A decimal counter may have each digit binary encoded (that is, it may count in binary-coded decimal, as the 7490 integrated circuit did) or other binary encodings (such as the bi-quinary encoding of the 7490 integrated circuit). Alternatively, it may have a “fully decoded” or one-hot output code in which each output goes high in turn; the 4017 was such a circuit. The latter type of circuit finds applications in multiplexers and demultiplexers, or wherever a scanning type of behaviour is useful. Similar counters with different numbers of outputs are also common.

The decade counter is also known as a mod-10 counter.

C.6 Up-Down Counter

A counter that can change state in either direction, under control an up–down selector input, is known as an up–down counter. When the selector is in the up state, the counter increments its value; when the selector is in the down state, the counter decrements the count. It is shown in Fig. 9.