Thursday, October 18, 2012

Electronics Interview questions with answer

Ideal voltage source is a circuit element where the voltage across it is independent of the current through it. It only exists in mathematical models of circuits. If the voltage across an ideal voltage source can be specified independently of any other variable in a circuit, it is called an independent voltage source.

Impulse response of a system is its output when presented with a very brief input signal, an impulse. A system in the class known as LTI systems (linear, time-invariant systems) is completely characterized by its impulse response. The Laplace transform of the impulse response function is known as the transfer function. It is usually easier to analyze systems using transfer functions as opposed to impulse response functions. The Laplace transform of a system's output may be determined by the multiplication of the transfer function with the input function in the complex plane, also known as the frequency domain. An inverse Laplace transform of this result will yield the output function in the time domain. To determine an output function directly in the time domain requires the convolution of the input function with the impulse response function. 

Finite impulse response (FIR) filter is a type of a digital filter. The impulse response, the filter's response to a Kronecker delta input, is 'finite' because it settles to zero in a finite number of sample intervals. This is in contrast to infinite impulse response filters which have internal feedback and may continue to respond indefinitely.
A FIR filter has a number of useful properties which sometimes make it preferable to an infinite impulse response filter. FIR filters:
* Are inherently stable. This is due to the fact that all the poles are located at the origin and thus are located within the unit circle.
* Require no feedback. This means that any rounding errors are not compounded by summed iterations. The same relative error occurs in each calculation.
* They can be designed to be linear phase, which means the phase change is proportional to the frequency.

Infinite impulse response (IIR) is a property of signal processing systems. They have an impulse response function which is non-zero over an infinite length of time. The simplest analog IIR filter is an RC filter made up of a single resistor (R) feeding into a node shared with a single capacitor (C). This filter has an exponential impulse response characterized by an RC time constant

Common-mode rejection ratio (CMRR) of a differential amplifier (or other device) measures the tendency of the device to reject input signals common to both input leads. A high CMRR is important in applications where the signal of interest is represented by a small voltage fluctuation superimposed on a (possibly large) voltage offset, or when relevant information is contained in the voltage difference between two signals.

Signal-to-noise ratio (often abbreviated SNR or S/N) defined as the ratio of a signal power to the noise power corrupting the signal. In less technical terms, signal-to-noise ratio compares the level of a desired signal (such as music) to the level of background noise. The higher the ratio, the less obtrusive the background noise is. 

Asynchronous transmission uses start and stop bits to signify the beginning bit ASCII character would actually be transmitted using 10 bits e.g.: A "0100 0001" would become "1 0100 0001 0". The extra one (or zero depending on parity bit) at the start and end of the transmission tells the receiver first that a character is coming and secondly that the character has ended. This method of transmission is used when data is sent intermittently as opposed to in a solid stream. In the previous example the start and stop bits are in bold. The start and stop bits must be of opposite polarity. This allows the receiver to recognize when the second packet of information is being sent.

Synchronous transmission uses no start and stop bits but instead synchronizes transmission speeds at both the receiving and sending end of the transmission using clock signals built into each component. A continual stream of data is then sent between the two nodes. Due to there being no start and stop bits the data transfer rate is quicker although more errors will occur, as the clocks will eventually get out of sync, and the receiving device would have the wrong time that had been agreed in protocol (computing) for sending/receiving data, so some bytes could become corrupted (by losing bits). Ways to get around this problem include re-synchronization of the clocks and use of check digits to ensure the byte is correctly interpreted and received.

Difference between real ground and virtual ground
Virtual ground (sometimes called virtual earth) is an important concept found in electronic circuit designs. It identifies a point in a circuit as being held close to the circuit's ground or reference level electric potential. It is called virtual since this point does not have any real electrical connection to ground. The reference may or may not be the same as the local utility ground or earth

Real ground: Voltage is a differential quantity, which appears between two points. In order to deal only with a voltage (an electrical potential) of a single point, the second point has to be connected to a reference point (ground) having usually zero voltage. This point has to have steady potential, which does not vary when the electrical sources "attack" the ground by "injecting" or "sucking" a current to/from it. Usually, the power supply terminals serve as grounds; when the internal points of compound power sources are accessible, they can also serve as real grounds

BUS: In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers. Unlike a point-to-point connection, a bus can logically connect several peripherals over the same set of wires. Each bus defines its set of connectors to physically plug devices, cards or cables together. Early computer buses were literally parallel electrical buses with multiple connections, but the term is now used for any physical arrangement that provides the same logical functionality as a parallel electrical bus.

Pull-up resistors are resistors used in the design of electronic logic circuits to ensure that inputs to logic systems settle at expected logic levels if external devices are disconnected. Pull-up resistors may also be used at the interface between two different types of logic devices, possibly operating at different power supply voltages.
The idea of a pullup resistor is that it weakly "pulls" the voltage of the wire it's connected to towards 5V (or whatever voltage represents a logic "high"). However, the resistor is intentionally weak (high-resistance) enough that, if something else strongly pulls the wire toward 0V, the wire will go to 0V.

Transponder: An automatic device that receives, amplifies, and retransmits a signal on a different frequency (see also broadcast translator).

Superconductivity is a phenomenon occurring in certain materials at extremely low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field. The electrical resistivity of a metallic conductor decreases gradually as the temperature is lowered. However, in ordinary conductors such as copper and silver, impurities and other defects impose a lower limit. Even near absolute zero a real sample of copper shows a non-zero resistance. The resistance of a superconductor, on the other hand, drops abruptly to zero when the material is cooled below its "critical temperature". An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source.

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1 comment:

  1. Nice stuff really an informative one!Thanks for taking time to share your great experience here with us..