Karnataka II PUC Electronics (KSEAB) flashcards

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

Intrinsic carrier concentration

Number of free electrons (equal to holes) per unit volume in pure semiconductor at thermal equilibrium; about 1.5×10¹⁶ m⁻³ for silicon at 300 K.

Barrier potential of diode

Forward voltage at which the depletion region is overcome and current rises sharply; about 0.7 V for silicon and 0.3 V for germanium junctions.

Ripple factor

Ratio of RMS value of AC component to DC component of rectifier output; 1.21 for half-wave and 0.48 for full-wave and bridge rectifiers.

Zener breakdown

Reverse breakdown in a heavily doped junction where a strong field frees carriers; voltage is nearly constant, making the Zener useful as a voltage regulator.

Transistor current gain beta

Ratio of collector current to base current in a BJT, β = I_C/I_B; related to α by β = α/(1 − α) and typically 50 to 300.

Pinch-off voltage

Drain-source voltage at which the JFET channel just closes at the drain end, so drain current saturates; equals V_GS − V_P.

Transconductance

Ratio of change in drain (or collector) current to change in controlling voltage; for a BJT g_m = I_C/V_T, about 38.5 mS per mA.

Cut-off region

BJT operating state where both junctions are reverse biased; base current is essentially zero and collector current is only leakage, so the device acts as an open switch.

Negative feedback

Portion of output returned to input with opposite phase; reduces gain to A/(1 + Aβ) but improves stability, bandwidth, distortion and input/output impedance.

Emitter follower

Common-collector amplifier with voltage gain near unity, no phase inversion, very high input impedance and low output impedance; used as a buffer stage.

Class B efficiency

Maximum theoretical efficiency of a push-pull Class B amplifier is 78.5%, since each transistor conducts for 180° and quiescent dissipation is nearly zero.

Slew rate

Maximum rate of change of op-amp output voltage, usually quoted in V/µs; it limits full-power bandwidth according to SR = 2πfV_m.

Barkhausen criterion

Condition for sustained oscillation: loop gain magnitude must equal one and total phase shift around the feedback loop must be zero or 360 degrees.

Wien bridge oscillator

RC oscillator using a lead-lag network giving zero phase shift at f = 1/(2πRC); amplifier gain must be exactly three for stable sine output.

Monostable multivibrator

One-shot circuit with a single stable state; a trigger produces one output pulse whose width is set by the RC timing network, then it returns to rest.

Crystal oscillator

Piezoelectric quartz crystal used as a high-Q resonant element; its very stable series and parallel resonant frequencies give excellent frequency stability.

Virtual short

In a linear negative-feedback op-amp circuit, the differential input voltage is nearly zero, so the inverting and non-inverting input nodes are at almost the same potential.

Inverting amplifier gain

Closed-loop voltage gain of an op-amp with input through R_in and feedback through R_f: A_v = −R_f/R_in; the negative sign means 180° phase inversion.

Common-mode rejection ratio

Ratio of differential gain to common-mode gain of an op-amp, usually in decibels; high CMRR rejects noise appearing equally on both inputs.

Active filter

Filter built from op-amps with resistors and capacitors, avoiding inductors; first-order low-pass cutoff is f_c = 1/(2πRC) with 20 dB/decade roll-off.

Universal gates

NAND and NOR gates, because any Boolean function can be implemented using only NAND gates or only NOR gates.

Full adder

Combinational circuit adding three bits; Sum = A⊕B⊕C_in and Carry out = AB + C_in(A⊕B), built from two half adders and an OR gate.

JK flip-flop

Bistable device like an SR flip-flop but with J = K = 1 producing toggling instead of an invalid state; widely used in counters and registers.

De Morgan's theorem

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

Modulation index of AM

Ratio m = V_m/V_c of modulating amplitude to carrier amplitude; values above one cause overmodulation, envelope distortion and sideband splatter.

Sampling theorem

A signal band-limited to f_max can be reconstructed exactly if sampled at f_s at least 2f_max; lower rates cause aliasing.

Carson's rule

Approximate bandwidth of an FM signal: BW ≈ 2(Δf + f_m), where Δf is peak frequency deviation and f_m is the highest modulating frequency.

Pulse code modulation

Digital modulation that samples an analog signal, quantises each sample to discrete levels, then encodes levels as binary words for transmission.

SCR latching

Once a silicon controlled rectifier is gate-triggered and anode current exceeds latching current, the gate loses control; it turns off only below holding current.

Triac

Bidirectional thyristor that conducts in both halves of an AC cycle, allowing phase-angle control of AC power in lamp dimmers and fan regulators.

LED colour

Colour of light from a forward-biased LED is set by the semiconductor band gap, since photon energy E_g ≈ hc/λ; wider gap gives bluer light.

PMMC instrument

Moving-coil meter whose deflection is proportional to average current; it measures DC directly and needs a rectifier for AC measurement.

Cathode ray oscilloscope

Instrument displaying voltage versus time on a phosphor screen; vertical sensitivity in V/div and time base in s/div allow amplitude and frequency measurement.