UGC NET Electronic Science flashcards

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

De Morgan's theorems

They state that the complement of a product equals the sum of the complements, and the complement of a sum equals the product of the complements, enabling NAND-only or NOR-only implementation.

Two's complement subtraction

To compute A − B in n bits, add A to the two's complement of B and discard the final carry, which yields the correct signed result when no overflow occurs.

Karnaugh map grouping rule

Adjacent cells differing in one variable are grouped in powers of two, and each group yields one product term containing only the variables that stay constant across the group.

Static-1 hazard

A glitch that can appear when two product terms differ in one variable during a transition; adding the consensus term that covers both eliminates the hazard in combinational output.

Modulo-m counter flip-flops

The minimum number of flip-flops needed to count through m distinct states equals the ceiling of log base two of m, since n flip-flops provide at most two to the n states.

Ring counter

A shift register whose serial output feeds back to the serial input with a single one circulating; an n-bit ring counter has n states and requires no decoding logic.

Johnson counter states

A twisted-ring counter feeding back the complemented output has 2n states for n flip-flops, doubling the ring counter's count while keeping one-hot decoding.

Memory capacity computation

Capacity in bits equals the number of addressable words multiplied by the word width; the number of chips required equals total required capacity divided by per-chip capacity.

8051 machine cycle

One machine cycle spans twelve oscillator periods; therefore a 12 MHz crystal gives one microsecond per machine cycle, and most instructions take one or two cycles.

CMOS power dissipation

Dynamic power equals capacitance times supply voltage squared times frequency, dominated by charging node capacitances; static power is only leakage current, unlike bipolar TTL logic.

Noise margin definition

High-state noise margin is the minimum output high voltage minus the minimum input high voltage; low-state noise margin is the maximum input low voltage minus the maximum output low voltage.

DAC resolution

For an n-bit converter with full-scale voltage V, the step size or least significant bit equals V divided by two to the n minus one, setting the smallest representable output change.

Successive approximation ADC timing

An n-bit successive-approximation converter completes a conversion in n comparison cycles, so conversion time equals n clock periods plus acquisition and settling overhead.

Ideal op-amp assumptions

Infinite open-loop gain, infinite input impedance, zero output impedance and infinite bandwidth; with negative feedback these force zero input current and equal input terminal voltages.

Inverting amplifier gain

Closed-loop voltage gain equals negative feedback resistance divided by input resistance; the inverting input is a virtual ground, so input impedance equals the input resistor.

Slew rate limit

Slew rate is the maximum output voltage change per unit time; it caps undistorted sinusoidal output at a frequency equal to slew rate divided by two pi times peak voltage.

Gain-bandwidth product

For a compensated op-amp the product of closed-loop gain and closed-loop bandwidth is constant, so higher gain reduces usable bandwidth proportionally and vice versa.

Zener diode regulation

Operated in reverse breakdown, it holds a nearly constant voltage; a series resistor drops the excess supply voltage, and regulation holds while current stays above the knee.

BJT active region

The base-emitter junction is forward biased and the collector-base junction reverse biased; collector current equals beta times base current and the device behaves as a current-controlled source.

MOSFET saturation condition

The transistor is in saturation when drain-source voltage exceeds the overdrive, gate-source voltage minus threshold; drain current then follows a square law largely independent of drain voltage.

Transistor Q-point

The quiescent operating point is the DC collector current and collector-emitter voltage at zero input signal, set by the bias network and bounded by the load line.

Negative feedback effects

Feedback reduces gain by the factor one plus loop gain, extends bandwidth by the same factor, reduces distortion, and modifies input and output impedance depending on sampling and mixing type.

Nyquist sampling criterion

A band-limited signal must be sampled at more than twice its highest frequency component to allow exact reconstruction and to avoid aliasing of high-frequency content into the baseband.

Aliasing

When sampling is too slow, a frequency above half the sampling rate appears as a false lower frequency equal to the difference from the nearest multiple of the sampling rate.

RMS of sinusoid

The root-mean-square value of a sine wave equals peak value divided by the square root of two, giving the equivalent heating value used for power calculations.

Fourier series of square wave

A square wave contains only odd harmonics with amplitudes inversely proportional to harmonic order; the fundamental peak equals four times the amplitude divided by pi.

Characteristic impedance

For a lossless line it equals the square root of inductance per unit length divided by capacitance per unit length, and determines reflection behavior at terminations.

Reflection coefficient

Defined as load impedance minus characteristic impedance divided by their sum; it is zero for a matched load, minus one for a short, and plus one for an open circuit.

Quarter-wave transformer

A line one quarter wavelength long transforms a load impedance to characteristic impedance squared divided by the load, giving matching when the line equals the geometric mean.

AM modulation index

Ratio of modulating amplitude to carrier amplitude; total transmitted power equals carrier power times one plus half the square of the index, and overmodulation causes envelope distortion.

Carson's rule

Approximate FM bandwidth equals twice the sum of peak frequency deviation and highest modulating frequency, valid when deviation greatly exceeds the modulating frequency.

Shannon channel capacity

Maximum error-free data rate equals bandwidth times the base-two logarithm of one plus signal-to-noise ratio, giving the theoretical ceiling for a noisy channel.