Tamil Nadu HSE Second Year Basic Electronics Engineering flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Depletion region

The region around a PN junction where mobile carriers have diffused away, leaving fixed charged ions. It acts as a barrier to current and widens under reverse bias.

Zener breakdown

A controlled reverse breakdown in heavily doped junctions below about 6 V, caused by tunnelling. The voltage stays nearly constant, so the diode works as a voltage reference.

Ripple factor

The ratio of AC ripple to DC output of a rectifier. It is 1.21 for a half-wave rectifier and 0.48 for full-wave or bridge rectifiers.

Transistor current gain beta

Beta equals collector current divided by base current in the active region. It typically ranges from 50 to 300 and relates to alpha by beta = alpha/(1 − alpha).

DC load line

A straight line on the output characteristic joining cutoff (V_CE = V_CC) and saturation (I_C = V_CC/R_C). The quiescent point lies on this line.

Voltage-divider bias

A bias method where two resistors set the base voltage and an emitter resistor stabilises the operating point. The quiescent current becomes almost independent of transistor beta.

Pinch-off voltage

The gate-source voltage at which a JFET channel is fully depleted and drain current falls to nearly zero. It is denoted V_P and is a negative value for an n-channel device.

Transconductance

The change in drain current divided by the change in gate-source voltage at constant drain-source voltage. It is measured in siemens and sets the voltage gain of a FET amplifier.

Class B amplifier

An amplifier in which each transistor conducts for half the input cycle. Efficiency can reach 78.5 percent, but crossover distortion appears near the zero crossing.

Virtual ground

A node at the inverting input of an op-amp held near zero volts by negative feedback. It carries almost no current because input impedance is very high.

Slew rate

The maximum rate of change of an op-amp output voltage, usually quoted in volts per microsecond. It limits full-power bandwidth and causes triangular output at high frequencies.

CMRR

Common-mode rejection ratio is the ratio of differential gain to common-mode gain, usually expressed in decibels. A high value is needed for accurate bridge measurements.

De Morgan's theorems

Two Boolean identities: the complement of a sum equals the product of the complements, and the complement of a product equals the sum of the complements.

Fan-out

The maximum number of gate inputs that one logic gate output can drive while keeping voltage levels within specified logic limits. It is typically ten for standard TTL.

Universal gate

A gate from which any Boolean function can be built. NAND and NOR gates are universal because each can implement NOT, AND and OR functions.

Multiplexer

A combinational circuit that selects one of several data inputs and routes it to a single output. A device with 2^n inputs requires n select lines.

JK flip-flop

A clocked bistable element whose output sets when J is high, resets when K is high, and toggles when both are high. It avoids the forbidden state of the SR latch.

Modulus of a counter

The number of distinct states a counter passes through before repeating. A modulus-M counter needs at least ceil(log2 M) flip-flops in its chain.

Modulation index of AM

The ratio of modulating signal amplitude to carrier amplitude. It must not exceed one, otherwise overmodulation causes envelope distortion and loss of the message.

Carson's rule

An approximation of FM bandwidth: twice the sum of peak frequency deviation and the highest modulating frequency. It gives the practical channel width needed for FM.

Nyquist sampling rate

The minimum sampling frequency needed to reconstruct a band-limited signal without aliasing. It equals twice the highest frequency present in the signal.

Firing angle

The delay angle measured from the start of the positive half cycle until a thyristor is triggered. Increasing it reduces the average output voltage of a controlled rectifier.

Holding current

The minimum anode current that keeps a thyristor conducting after the gate pulse is removed. Below this value the device returns to its blocking state.

Buck chopper

A DC-to-DC converter that steps down the input voltage. Its average output equals the input multiplied by the duty cycle of the switching device.

Wheatstone bridge

A four-arm resistance bridge that balances when the ratio of two arms equals the ratio of the other two. It is used for accurate resistance measurement and strain gauges.

LVDT

A linear variable differential transformer that converts displacement into an AC voltage. It has a primary winding and two secondary windings whose outputs are compared.

Strain gauge

A sensor whose resistance changes when it is stretched or compressed. Its gauge factor is about two, and it is usually connected in a bridge circuit.

8051 special function registers

Registers that control the microcontroller peripherals, including the accumulator, PSW, stack pointer, timers, serial port and interrupt enable registers. They are addressed directly.

Machine cycle

The basic timing unit of the 8051, equal to twelve oscillator periods. With a 12 MHz crystal, one machine cycle lasts one microsecond.

Interrupt vector

A fixed memory address to which the processor jumps when a particular interrupt occurs. The 8051 assigns separate vector addresses to external, timer and serial interrupts.

PWM control

Pulse-width modulation varies the duty cycle of a square wave to control average power. It is used for motor speed, LED brightness and heater control.

Darlington pair

Two transistors connected so that the emitter of the first drives the base of the second. Total current gain is approximately the product of the individual gains.