Chapter 4- Information and energy control systems 4.1 Information systems 4.1.1 block diagram representation of a typical information system (eg audio-communication, instrumentation, process monitoring) 4.1.2 qualitative description of how electrical signals convey system information 4.1.3 function, operation and interfacing of information system components (eg transducers, transducer output and accuracy, amplifier types, typical gain, resolution of analogue to digital and digital to analogue converters, types of oscillators and operating frequencies) 4.1.4 effect of noise on a system 4.1.5 determination of system output for a given input
Typical information systems BS Base Station (BS) UE UE UE User Equipment (UE)
• Communication System – The purpose of a Communication System is to transport an information bearing signal from a source to a user destination via a communication channel Source Destination• Source: -discrete events (from an alphabet) -waveforms (speech, sound, images, video)• Transmission media: -radio frequency ”on the air” -satellite channel -copper wire -optical fiber
Block diagram representation of atypical information system
Transducer converts the output of a source into an electrical signal. The heart of the communication system consists of three basic parts, the transmitter the channel, and the receiver. The transmitter converts the electrical signal into a format that is suitable for transmission - modulation. Example of modulation: amplitude modulation (AM), frequency modulation (FM). Receiver: The receiver performs carrier demodulation to extract the message signal contained in the received signal
Amplitude and frequency modulation• In AM broadcast, the information signal that is transmitted is contained in the amplitude variations of the sinusoidal carrier.• In an FM broadcast, the information signal that is transmitted is contained in the frequency variations of the sinusoidal carrier.• The choice of the type of modulation is based on several factors, such as the amount of bandwidth allocated, the types of noise and interference that the signal encounters in transmission over the channel, and the electronic devices that are available for signal amplification prior to transmission.
Analog vs digital communication • Analog signal - continuous signal, e.g., speech signal. • Analog signal can be transmitted directly via carrier modulation over the communication channel and demodulated at the receiver (Analog communications). • An analog source can be converted into a digital form and the digital form can be transmitted via digital modulation and demodulated as a digital signal (Digital communications). • Advantages of digital communications – Signal fidelity is better controlled. – Regeneration of the digital signal can be performed without noise enhancement.
Digital Communication Systems Basic elements of digital communication system
• Digital Source, e.g., English text, computer data.• Fundamental elements of digital communication systems – Information source: analog or digital – Source encoder: converts the information source to binary form and removes the redundancy. (source encoding for data compression) – Channel encoder: adds redundancy to overcome the effects of noise and interference introduced by the channel. – Digital modulator: maps the binary information sequence into signal waveforms. – Digital demodulator: convert the received waveform to binary information sequence. – Channel decoder: corrects the demodulated errors based on the redundancy added by the channel encoder. – Source decoder: recover the original information source.
Digital systems• Advantages – More resilient to interference and imperfections – Can be mathematically processed allowing compression or enhancement of data – Information can be stored as numerical data: data storage cheap – Longevity: data can be stored over very long periods of time.• Disadvantage – Digital signal will not be an exact copy of the original analogue signal: sampling error – Complex processing involved – Takes time to do – The transmitter and receiver have to be synchronized
Advantages of digital signals • The most important advantage of digital communications is noise immunity. • Receiver circuitry can distinguish between a binary 0 and 1 with a significant amount of noise. • Digital signals can be stripped of any noise in a process called signal regeneration 1 0 1 1 0 1Voltage (V) Time (sec) analog signal with noise digital signal with noise
Analog DigitalAmplified regeneratedNoise added no noise added original analog signal original analog signal signal at repeater 1 signal at repeater 1 signal at repeater 2 signal at repeater 2 signal at repeater 3 signal at repeater 3
Conversion from analog to digital• Translating an analog signal into a digital signal is called analog-to-digital (A/D) conversion, digitizing a signal, or encoding. – The device used to perform this translation is known as an analog-to-digital converter or ADC.
• An analog signal is a smooth or continuous voltage or current variation. – Through A/D conversion these continuously variable signals are changed into a series of binary numbers.Voltage (V) 01101010100111001101010101111 Time (sec)
Step 1- sampling• The first step in A/D conversion is a process of sampling the analog signal at regular time intervals. sample points Voltage (V) sampling frequency 1 f = T Time (sec) sampling period (T)
• How often do we need to sample the signal? – How large does our sampling frequency f need to be in order to accurately represent the signal?o ae V o ae VVt g ( ) Vt g ( ) l l T e sc i m( e ) T e sc i m( e ) high sampling rateo ae V o ae VVt g ( ) Vt g ( ) l l T e sc i m( e ) T e sc i m( e ) low sampling rate
Minimum sampling frequency• The minimum sampling rate required in order to accurately reconstruct the analog input is given by the Nyquist sampling rate fN given f N ≥ 2 fm where fm is the highest frequency of the analog input. – The Nyquist rate is a theoretical minimum. – In practice, sampling rates are typically 2.5 to 3 times the Nyquist rate fN.
Step 2-quantization• The actual analog signal is smooth and continuous and represents an infinite number of actual voltage values. – It is not possible to convert all analog samples to a precise binary number. – Therefore, samples are converted to a binary number whose value is close to the actual sample value.• The A/D converter can represent only a finite number of voltage values over a specific range.• An A/D converter divides a voltage range into discrete increments, each of which is represented by a binary number.
A/D conversion• The process of mapping the sampled analog voltage levels to these discrete, binary values is called quantization.• Quantizers are characterized by their number of output levels.• An N-bit quantizer has 2N levels and outputs binary numbers of length N. – Telephones use 8-bit encoding → 28 = 256 levels – CD audio use 16-bit encoding → 216 = 65,536 levels
TransducersDefinition: A transducer is a device, which converts one type of physical property, quantity or condition into another easily usable formAdvantages of transducers If the output signal from the transducer is in electrical form then it is convenient to handle and has many advantages. – Ease of amplification – Ease of integration and differentiation – Ease of convertibility from analog to digital and vise versa – Remote controllability and easy data transmission capability – Compatibility with microprocessors and computers
Categorization of transducers• Input (sensors) and output (actuators and displays)• Active (where external excitation source is needed) and passive• Analog (continuous in time domain) /digital (discrete in time domain and may quantized in amplitude) and carrier• Primary and secondary
Input and output transducers• Input Transducers convert a quantity to an electrical signal (voltage) or to resistance (which can be converted to voltage). Input transducers are also called sensors. Examples: – LDR converts brightness (of light) to resistance. – Thermister converts temperature to resistance. – Microphone converts sound to voltage.• Output Transducers convert an electrical signal to another quantity Output transducers can be either an actuator or a display Examples: – Lamp converts electricity to light. – LED converts electricity to light. – Loudspeaker converts electricity to sound. – Motor converts electricity to motion. – Heater converts electricity to heat
Signal conditioning• Amplification – To strengthen the signal – Before transmission, repeater stations and before usage• Level shifting – To make bipolar signal to uni-polar signal• Filtering – To remove noise – Limit bandwidth for sampling• Linearising – To convert nonlinear quantities into linearly varying quantities – Eg: use of exponential amplifier if the transducer response is logarithmic• Isolation – To amplify only the ac component of the electrical signal – To avoid distortions of signals
Amplification• Amplifier types – By construction • IC amplifiers (eg:-operational amplifiers) • Transistor/FET amplifiers (VMOS) • Valve amplifiers – By application • Pre-amplifier • Power amplifier (eg:-push pull amplifiers) • Intermediate stage amplifiers • Low noise amplifiers
Noise• Any electrical signal transmitted from one point to another point is classified as having two parts, the desirable part and undesirable part, which is noise• There are three types of noise: (a) External noise (b) Internal noise. (c) Cross talk• External Noise External noise is noise that is generated outside the device or circuit. Below are the primary sources of external noise: – Lightning – Solar noise – Cosmic Noise – Man-made noise
• Internal Noise Internal noise is caused by electrical interference generated within the device or circuit. Below are the primary sources of internal noise: – Shot noise The name originates from the sound that it produces at the audio output of a receiver. The sound is similar to that leaf shot falling on top of a tin roof. This noise is caused by the random arrival of carriers (holes and electrons) at the output element of electronic devices, such as diode and transistor. – Thermal noise It is caused by rapid and random movement of electrons within a conductor due to thermal agitation. Since particles such as free electrons are in movement, they posses kinetic energy that is directly related to the temperature of the resistive body. Below is the equation shows the mathematical relationship that was developed by Johnson
• Cross Talk Many of us have experienced listening to other telephone conversations. This type of noise called cross talk occurs as a result of inductive and capacitive coupling from adjacent channels. Subscriber loops and trunk circuits commonly multiplexed together to form bundled cables often have severe cross talk, particularly in long lengths of cable.Noise measurements Several mathematical tools have been developed to evaluate the effects of noise based on its magnitude. There are two types of measurements: (a) Signal-to-Noise Ratio The ratio of signal power to noise power.
(b) Noise Figure and Noise– Noise factor is a measure of how noisy a device is. It is the ratio of signal-to-noise power at the input of a device to the signal-to-noise power at its output. Expressed in decibels, noise factor is called noise figure.