|
2.4.2 Operational Amplifier
An operational amplifier (often op-amp or opamp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op-amp produces an output potential (relative to circuit ground) that is typically hundreds of thousands of times larger than the potential difference between its input terminals. Operational amplifiers had their origins in analog computers, where they were used to do mathematical operations in many linear, non-linear and frequency-dependent circuits. The popularity of the op-amp as a building block in analog circuits is due to its versatility. Due to negative feedback, the characteristics of an op-amp circuit, its gain, input and output impedance, bandwidth etc. Are determined by external components and have little dependence on temperature coefficients or manufacturing variations in the op-amp itself.
Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Op-amps may be packaged as components, or used as elements of more complex integrated circuits. The op-amp is one type of differential amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op-amp, but with two outputs), the instrumentation amplifier (usually built from three op-amps), the isolation amplifier (similar to the instrumentation amplifier, but with tolerance to common mode voltages that would destroy an ordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps and a resistive feedback network) (Stout D.F 1976).
2.4.3 Microcontroller
Microcontrollers must contain at least two primary components – random access memory (RAM), and an instruction set. RAM is a type of internal logic unit that stores information temporarily. RAM contents disappear when the power is turned off. While RAM is used to hold any kind of data, some RAM is specialized, referred to as registers. The instruction set is a list of all commands and their corresponding functions. During operation, the microcontroller will step through a program (the firmware). Each valid instruction set and the matching internal hardware that differentiate one microcontroller from another.
Most microcontrollers also contain read-only memory (ROM), programmable read-only memory (PROM), or erasable programmable read-only memory (EPROM). Al1 of these memories are permanent: they retain what is programmed into them even during loss of power. They are used to store the firmware that tells the microcontroller how to operate. They are also used to store permanent lookup tables. Often these memories do not reside in the microcontroller; instead, they are contained in external ICs, and the instructions are fetched as the microcontroller runs. This enables quick and low-cost updates to the firmware by replacing the ROM.
Where would a microcontroller be without some way of communicating with the outside world? This job is left to input/output (I/O) port pins. The number of I/O pins per controllers varies greatly, plus each I/O pin can be programmed as an input or output (or even switch during the running of a program). The load (current draw) that each pin can drive is usually low. If the output is expected to be a heavy load, then it is essential to use a driver chip or transistor buffer. Most microcontrollers contain circuitry to generate the system clock. This square wave is the heartbeat of the microcontroller and all operations are synchronized to it. Obviously, it controls the speed at which the microcontroller functions. All that needed to complete the clock circuit would be the crystal or RC11 components. We can, therefore precisely select the operating speed critical to many applications.
To summarize, a microcontroller contains (in one chip) two or more of the following elements in order of importance: Instruction set, SRAM, ROM, PROM or EPROM, I/O ports, Clock generator, Reset function, Watchdog timer, Serial port, Interrupts, Timers, Analog-to- digital converters and Digital-to-analog converters
The architecture of the microcontroller is the same thing as that of the Harvard Architecture; here the process is built with a separate memory for program and data. As a result, while an instruction is been executed by the CPU of the chip, program can be pre-fetched (Filipovic D.Miomir 2003).
ADC converts analog input signals to digital output signals.
• Watchdog Timer: Watchdog clock is available with inner oscillator.
• Interrupts: Microcontroller has 21 interrupt sources. Four of which are designed to serve external interrupt while the rest are meant to take care of internal interrupt which provide support for peripherals such as USART, Timers etc.
• Memory: Microcontroller has three separate memory areas:
1. Flash EEPROM: Flash EEPROM is used to store programs burnt by the programmer into the microcontroller.
2. SRAM: Static Random Access Memory, this an unstable memory embedded inside the microcontroller. Once power supply is cut off, information is lost. Atmega16 is furnished with 1kb of inside SRAM.
3. Byte Addressable EEPROM: This is an additional non volatile memory used to store information when the programmer makes estimations of specific variables.
Do'stlaringiz bilan baham: |
