RRB JE CBT 2 - Electronics flashcards

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

Mass-action law

In thermal equilibrium the product of electron and hole concentrations equals the square of intrinsic carrier concentration: n·p = n_i^2. Doping one type reduces the other.

Zener breakdown

Reverse breakdown in heavily doped diodes at low voltages (below about 6 V), caused by tunnelling of electrons across a narrow depletion region. Voltage is nearly constant.

Transconductance g_m

Ratio of small change in collector or drain current to small change in controlling voltage. For a BJT, g_m = I_C/V_T, about 38 mS per mA at room temperature.

Emitter follower

Common-collector amplifier with voltage gain near unity, no phase inversion, high input resistance and low output resistance. Used for impedance buffering between stages.

Barkhausen criterion

Condition for sustained oscillation: loop gain magnitude |Aβ| must equal one and total loop phase shift must be 0° or 360° at the oscillation frequency.

Class B efficiency

Maximum theoretical efficiency of a push-pull Class B amplifier is 78.5 percent. Conduction angle is 180°, and crossover distortion appears without biasing.

Slew rate

Maximum rate of change of an op-amp output voltage, expressed in volts per microsecond. It limits large-signal high-frequency response and causes output distortion.

De Morgan's theorems

Complement of a product equals the sum of complements, and complement of a sum equals the product of complements: (A·B)' = A' + B' and (A + B)' = A'·B'.

Universal gates

NAND and NOR gates are called universal because each can implement AND, OR and NOT alone, so any Boolean function can be built from one type.

Setup and hold time

Setup time is the interval data must be stable before the clock edge; hold time is the interval after it. Violation causes metastability in flip-flops.

Modulation index AM

Ratio m = V_m/V_c of modulating amplitude to carrier amplitude. It must not exceed one; values above one cause overmodulation and envelope distortion.

Carson's rule

Approximate FM bandwidth equals twice the sum of peak frequency deviation and highest modulating frequency: B ≈ 2(Δf + f_m). Reduces to 2Δf for large deviation.

Nyquist criterion

To reconstruct a bandlimited signal without aliasing, the sampling rate must be at least twice the highest signal frequency present in the input.

Quantization noise

Error introduced when a continuous sample is rounded to the nearest discrete level. For n-bit uniform PCM of a full-scale sinusoid, SNR is about 6.02n + 1.76 dB.

8085 flags

Five flags in the 8085: Sign, Zero, Auxiliary Carry, Parity and Carry. They are set or reset by arithmetic and logical instructions and stored in the flag register.

8086 segmentation

Memory is divided into 64 KB segments addressed by CS, DS, SS and ES. Physical address equals segment register times 16 plus offset, giving a 20-bit address.

8051 machine cycle

With a 12 MHz crystal the 8051 machine cycle is 1 microsecond, because each machine cycle takes twelve oscillator periods. Most instructions take one or two cycles.

DMA transfer

Direct memory access moves data between memory and peripherals without CPU involvement. The CPU releases the bus through HOLD and HLDA handshake signals.

Thevenin theorem

Any linear two-terminal network can be replaced by one voltage source V_th in series with one resistance R_th. V_th is open-circuit voltage, R_th is V_oc divided by I_sc.

Maximum power transfer

A source delivers maximum power to a load when load resistance equals source resistance. At that point efficiency is 50 percent, half the power lost internally.

Series resonance

At f = 1/(2π√(LC)) the inductive and capacitive reactances cancel, impedance is minimum and purely resistive, current is maximum and power factor is unity.

Wheatstone bridge

Four-arm resistive bridge balanced when R1/R2 = R3/R4, giving zero galvanometer current. Suited to medium resistance measurement; Kelvin bridge handles low resistance.

Voltmeter multiplier

High series resistance added to a PMMC movement to extend range. Its value is R_s = (V/V_m − 1)R_m, where V is the new full-scale voltage.

CRO deflection sensitivity

Vertical deflection per unit input, usually stated in volts per division. Time base is set in seconds per division; bandwidth limits accurate high-frequency amplitude display.

SCR latching

A thyristor conducts when gate current flows and anode is positive, then remains on even after gate current stops. It turns off below holding current.

Buck converter

Switching DC-DC converter that steps voltage down. Ideal output equals duty cycle times input, V_o = D·V_in, with high efficiency and pulsed input current.

TRIAC and DIAC

TRIAC is a bidirectional thyristor for AC phase control; DIAC is a bidirectional trigger diode that fires symmetrically. Together they form a simple AC dimmer.

Two's complement

Method of representing signed binary numbers: invert all bits of the magnitude and add one. An n-bit word then ranges from −2^(n−1) to 2^(n−1) − 1.

Compiler versus interpreter

A compiler translates the entire source program into machine code before execution; an interpreter translates and executes line by line, easing debugging but slowing execution.

Kavach system

Indigenous automatic train protection system developed by RDSO for Indian Railways. It prevents signal passing at danger and enforces speed limits through onboard and trackside equipment.

Syllogism validity

A conclusion is valid only if it follows in every possible Venn diagram consistent with the premises. A single counterexample diagram makes it invalid.

Quadratic formula

Roots of ax^2 + bx + c = 0 are x = (−b ± √(b^2 − 4ac))/2a. The discriminant b^2 − 4ac decides real, equal or complex roots.