Tamil Nadu HSE Second Year Basic Electronics Engineering cheat sheet

Intrinsic semiconductors have equal electron and hole concentrations (n = p = n_i); at room temperature n_i for silicon is about 1.5 × 10^16 /m^3, and conduction rises sharply with temperature because carrier density is thermally generated.

Mass-action law: n·p = n_i^2 in thermal equilibrium. Doping with donors (pentavalent, e.g. P, As) makes n-type material with electrons as majority carriers; acceptors (trivalent, e.g. B) make p-type with holes as majority carriers.

Built-in barrier potential of a PN junction: about 0.7 V for silicon and 0.3 V for germanium. Forward bias reduces the barrier and gives large diffusion current; reverse bias widens the depletion layer and leaves only a small leakage current.

Diode current equation: I = I_s (e^(V/(ηV_T)) − 1), where V_T ≈ 26 mV at 300 K and η ≈ 1 for germanium, ≈ 2 for silicon at low currents.

A PN junction is a depletion-region capacitor; junction capacitance falls as reverse voltage rises. Zener diodes operate in controlled reverse breakdown, with V_Z nearly constant, and are used as voltage references and shunt regulators.

Rectifier results: half-wave gives ripple frequency f, V_dc = V_m/π; full-wave and bridge give ripple frequency 2f, V_dc = 2V_m/π. Bridge needs four diodes; centre-tap full-wave needs two diodes and a centre-tapped transformer.

Ripple factor: half-wave 1.21, full-wave/bridge 0.48. Filtering with a shunt capacitor reduces ripple; larger C or larger R_L gives smaller ripple.

Avalanche breakdown is a collision-multiplication effect that occurs above about 6 V; Zener breakdown is a tunnelling effect that dominates below about 6 V. Both are non-destructive if the current is limited.

BJT relations: I_E = I_B + I_C, α = I_C/I_E, β = I_C/I_B, and β = α/(1 − α). Typical β is 50–300; α is slightly below 1.

For active-region operation, the emitter-base junction is forward biased and the collector-base junction is reverse biased. In saturation both junctions are forward biased (V_CE ≈ 0.2 V); in cutoff both are reverse biased.

Transistor configurations: common emitter gives voltage and current gain with 180° phase inversion; common base gives voltage gain with current gain below 1; common collector (emitter follower) gives voltage gain near 1 with high input impedance.

DC load line drawn on the output characteristic joins V_CE = V_CC (cutoff) to I_C = V_CC/R_C (saturation); the Q point is the intersection with the chosen base current.

Fixed bias: I_B = (V_CC − V_BE)/R_B, I_C = βI_B. It is simple but β-dependent and thermally unstable.

Voltage-divider bias sets V_B ≈ V_CC·R2/(R1 + R2) when the divider current is much larger than I_B; I_C ≈ (V_B − V_BE)/R_E, so the Q point is almost independent of β.

Stability factor S = ∂I_C/∂I_CO; smaller S means better thermal stability. Emitter resistance and collector-to-base feedback bias reduce S compared with fixed bias.

Transistor as a switch: drive it into saturation for ON (low V_CE, low dissipation) and cutoff for OFF. The base resistor is chosen so I_B ≥ I_C(sat)/β_min.

A JFET is a voltage-controlled device: the gate-source voltage V_GS controls drain current, and the gate draws almost no DC current because the gate-channel junction is reverse biased.

JFET drain current in saturation: I_D = I_DSS (1 − V_GS/V_P)^2, where V_P is pinch-off voltage. I_D = 0 when V_GS = V_P and I_D = I_DSS when V_GS = 0.

Transconductance g_m = ΔI_D/ΔV_GS = 2I_DSS/|V_P| · (1 − V_GS/V_P); voltage gain of a common-source amplifier is A_v = −g_m·R_D.

A MOSFET has an insulated gate (SiO2), so input resistance is very high (10^12 Ω or more). Enhancement MOSFETs need V_GS above the threshold V_th to conduct; depletion MOSFETs conduct at V_GS = 0.

JFET bias: self-bias uses a source resistor so V_GS = −I_D·R_S; the operating point is where this line meets the transfer characteristic.

Amplifier classes: Class A conducts over the full cycle (low distortion, efficiency ≤ 25% with resistive load); Class B over half a cycle (efficiency ≤ 78.5%, crossover distortion); Class AB reduces crossover distortion; Class C is used in tuned RF power stages.

Gain in decibels: A_dB = 20 log10(V_out/V_in) for voltage, 10 log10(P_out/P_in) for power. A cascade of stages adds gains in dB.

Negative feedback: gain falls by the factor (1 + Aβ), but bandwidth, input impedance, linearity and stability improve, and distortion falls by the same factor. Barkhoff criterion for oscillation: loop gain Aβ = 1 with 180° phase shift.

Ideal op-amp assumptions: infinite open-loop gain, infinite input impedance, zero output impedance, infinite bandwidth and zero offset; the summing-point rule gives V+ = V− and I+ = I− = 0 in linear negative-feedback circuits.

Inverting amplifier: A_v = −R_f/R_in, input impedance R_in. Non-inverting amplifier: A_v = 1 + R_f/R_in, input impedance very high.

Voltage follower (A_v = 1) buffers high-impedance sources. Summing amplifier output is the weighted sum of inputs: V_o = −R_f(V1/R1 + V2/R2 + …).

Op-amp parameters: input offset voltage, input bias current, CMRR (typically 80–100 dB), slew rate (V/µs) and gain-bandwidth product. Slew rate limits large-signal high-frequency response: SR = 2πf·V_m.

Comparator: with no feedback the op-amp saturates at ±V_sat, so it converts an analog level into a two-state output. Schmitt trigger uses positive feedback for hysteresis and noise immunity.

Integrator (capacitor in feedback) gives V_o = −(1/RC)∫V_in dt; differentiator (capacitor at input) gives V_o = −RC·dV_in/dt.

Active filters replace inductors with op-amp RC networks; a first-order low-pass has cut-off f = 1/(2πRC) and roll-off of −20 dB/decade.

Instrumentation amplifier uses three op-amps for high CMRR and high input impedance, and is used with bridge transducers. 555 timer in astable mode gives f = 1.44/((R1 + 2R2)C).

Number systems: binary, octal and hexadecimal to decimal by positional weights; decimal to binary by repeated division by 2. BCD encodes each decimal digit in 4 bits; Gray code changes one bit between successive values.

Boolean identities: A + A' = 1, A·A' = 0, A + AB = A, A + A'B = A + B, and De Morgan: (A + B)' = A'·B', (A·B)' = A' + B'.

Universal gates NAND and NOR can realise any logic function; XOR gives A⊕B = A'B + AB', and is used for parity and adders.

TTL logic levels: nominal V_CC = 5 V, logic 0 near 0.2 V, logic 1 near 3.4 V; fan-out typically 10, propagation delay about 10 ns per gate.

CMOS uses complementary NMOS/PMOS pairs, draws negligible static current, has very high noise margin and low power, but is sensitive to static discharge.

Standard gate count and function: half adder gives Sum = A⊕B, Carry = AB; full adder adds three bits and is built from two half adders plus an OR gate.

Open-collector outputs need a pull-up resistor and allow wired-AND connection; tri-state outputs allow bus sharing.

Combinational circuits have outputs determined only by present inputs (adders, multiplexers, decoders, encoders); sequential circuits also depend on stored state (flip-flops, counters, registers).

A 2^n-to-1 multiplexer needs n select lines; a 1-to-2^n decoder needs n inputs. A 4-variable Karnaugh map has 16 cells and groups of 1, 2, 4, 8 give terms of 4, 3, 2, 1 literals.

SR latch using NOR gates: S = 1 sets, R = 1 resets; S = R = 1 is the forbidden state. A clocked JK flip-flop removes this by toggling when J = K = 1.

D flip-flop output follows input at the clock edge (Q = D); T flip-flop toggles when T = 1. Flip-flops are edge-triggered; latches are level-sensitive.

An n-bit ripple counter has n flip-flops and modulus 2^n; a modulus-M counter needs at least ceil(log2 M) flip-flops and a reset or decoding network to skip unused states.

Shift register modes: serial-in serial-out, serial-in parallel-out, parallel-in serial-out, parallel-in parallel-out; a ring counter is a shift register with feedback giving one-hot states.

Setup time is the interval before the clock edge during which data must be stable; hold time is the interval after it. Violations cause metastability.

A memory with n address lines has 2^n locations; ROM is non-volatile and programmed at manufacture, while RAM is volatile and read/write.

Modulation places a baseband signal on a carrier so it can be radiated efficiently; antenna length is about λ/4 and λ = c/f.

AM: carrier amplitude varies with the message. Modulation index m = V_m/V_c; m ≤ 1 avoids overmodulation. Bandwidth = 2f_m, and total power P_t = P_c(1 + m^2/2).

FM: carrier frequency varies with the message. Modulation index β = Δf/f_m; bandwidth by Carson's rule is B ≈ 2(Δf + f_m). FM has better noise immunity than AM but needs more bandwidth.

Sidebands: AM with a single tone gives carrier plus upper and lower sidebands (f_c ± f_m). SSB transmits one sideband only, saving power and bandwidth.

Modulation types: PAM, PWM and PPM are analog pulse modulations; PCM samples, quantises and encodes, with bit rate = n·f_s and minimum sampling f_s ≥ 2f_m (Nyquist).

Superheterodyne receiver: RF amplifier, mixer with local oscillator to produce intermediate frequency (455 kHz for AM), IF amplifier, detector and audio amplifier.

Digital modulation: ASK, FSK, PSK and QAM; QPSK carries 2 bits per symbol. Shannon capacity C = B log2(1 + S/N) sets the maximum error-free data rate.

Transmission lines: characteristic impedance Z0 = √(L/C); a line terminated in Z0 has no reflection, and VSWR = (1 + |Γ|)/(1 − |Γ|).

A thyristor (SCR) is a four-layer PNPN device: it conducts when anode is positive and a gate pulse is applied, then latches ON; it turns off only when anode current falls below holding current.

SCR conduction angle is controlled by the firing angle α. Half-wave phase control gives V_dc = (V_m/2π)(1 + cos α) for a resistive load.

TRIAC is a bidirectional thyristor for AC control (fan regulators, lamp dimmers); DIAC is a bidirectional trigger diode used to fire a TRIAC.

A diode rectifier conducts uncontrolled; a fully controlled bridge with firing angle α gives V_dc = (2V_m/π)cos α, which becomes negative for α > 90° (inverter mode).

Power devices: MOSFET for high-frequency low-voltage switching, IGBT for high-voltage high-current switching, BJT for medium power; all are turned on/off by gate or base drive.

Switching losses rise with frequency; snubber circuits (RC across the device) limit dv/dt and suppress transients. Freewheeling diodes protect inductive loads.

Choppers convert fixed DC to variable DC; step-down (buck) chopper gives V_o = D·V_in where D is duty cycle. Inverters convert DC to AC.

UJT relaxation oscillator provides a pulse train for SCR gate triggering; the intrinsic stand-off ratio η = R_B1/(R_B1 + R_B2) sets the peak voltage V_P = ηV_BB + V_D.

A PMMC (D'Arsonval) meter responds to average DC and has a linear scale; it cannot measure AC directly. An electrodynamometer responds to rms and works on AC and DC.

Ammeter is connected in series and should have low resistance; voltmeter is in parallel and should have high resistance. A shunt extends ammeter range; a series multiplier extends voltmeter range.

Cathode ray oscilloscope: the electron beam is deflected by horizontal and vertical plates; the time base gives sweep. Measurements: V_pp = (vertical divisions) × (volts/div), T = (horizontal divisions) × (time/div).

Digital multimeter measures V, I, R and often continuity and diode test; accuracy is quoted as ±(% reading + counts).

Wheatstone bridge balances when R1/R2 = R3/R4; it is used for resistance measurement. Maxwell bridge measures inductance, Schering bridge capacitance and dissipation factor.

Transducers: thermistor and thermocouple for temperature, LVDT for displacement (linear, high resolution), strain gauge for force (gauge factor ≈ 2), piezoelectric for pressure and vibration, photodiode/LDR for light.

Strain gauge bridge output ΔV = V·(ΔR/R)/4 for a single active arm; a full bridge gives four times the sensitivity.

Signal conditioning: amplification, filtering and linearisation convert a small transducer output into a usable voltage or 4–20 mA current loop.

8051 architecture: 8-bit CPU, 4 KB on-chip ROM, 128 bytes RAM, 4 register banks, 4 parallel ports (P0–P3), two 16-bit timers, one full-duplex UART and five interrupt sources.

8051 has a 16-bit address bus, so it can address 64 KB of external program and 64 KB of external data memory. P0 provides the multiplexed low address and data bus.

Special function registers: accumulator ACC, B, PSW (with carry and parity flags), SP, DPTR, TMOD, TCON, SCON, IE and IP.

Timer mode 1 is 16-bit; machine cycle = 12 oscillator periods, so a 12 MHz crystal gives 1 µs per machine cycle. Timer delay = (65536 − count) × machine cycle.

Serial mode 1 is 8-bit UART with baud rate set by Timer 1 overflow: baud = (2^SMOD/32) × (f_osc/(12(256 − TH1))).

Interrupts in 8051: external INT0/INT1, Timer 0/1, serial. The ISR jumps to a fixed vector address; the RETI instruction restores the interrupted program.

Embedded system components: processor, memory, input/output and power supply, with firmware in ROM/flash. Common applications: traffic light control, temperature controller, washing machine, digital clock and stepper motor drive.

Stepper motor control: a 4-step sequence energises one phase at a time (full step); 8-step half-stepping doubles resolution. Each step rotates the rotor by the step angle.

Semiconductor doping concentration is typically 1 in 10^6 to 10^8 host atoms; heavily doped regions are marked n+ and p+.

The depletion region contains uncompensated fixed ions and no mobile carriers; its width shrinks under forward bias and grows under reverse bias.

Reverse saturation current I_s roughly doubles for every 10 °C rise in temperature; forward voltage drop falls about 2 mV/°C.

LED forward drop is 1.8–2.2 V for red and about 3.2 V for blue/white; photodiode is reverse biased and its reverse current increases with illumination.

Varactor diode works as a voltage-variable capacitor in tuning circuits; Schottky diode has a metal-semiconductor junction with low forward drop and fast switching.

Early effect: increasing V_CE narrows the effective base width, so I_C rises slightly with V_CE and output curves are not perfectly flat.

Hybrid parameters: h_ie (input impedance), h_fe (current gain), h_re (reverse voltage feedback) and h_oe (output admittance) describe the BJT as a two-port network.

Common-emitter voltage gain A_v = −h_fe·R_L/h_ie; input impedance is h_ie and output impedance approximately 1/h_oe.

Thermal runaway occurs when I_CO rises with temperature and raises dissipation; emitter degeneration (R_E) and heat sinking prevent it.

Darlington pair gives β_total ≈ β1·β2 and is used for high-current switching and high input impedance buffers.

FET input impedance is far higher than a BJT, making FETs suitable for the input stage of electrometers and amplifiers.

MOSFET handling precautions: keep gate-source shorted during storage, use grounded wrist straps, avoid exceeding V_GS(max).

Common-drain (source follower) gives voltage gain below 1 with high input impedance; common-gate gives low input impedance.

FET as a voltage-variable resistor: in the ohmic region, drain-source resistance varies with V_GS, used in AGC and gain control.

Miller effect: gate-drain capacitance is multiplied by (1 + A_v) and limits high-frequency response of common-source stages.

Op-amp 741: open-loop gain about 2 × 10^5, input impedance about 2 MΩ, slew rate 0.5 V/µs, unity-gain bandwidth about 1 MHz.

Precision rectifier uses an op-amp inside the diode loop to remove the 0.7 V diode drop for small signals.

Log and antilog amplifiers use a diode or transistor in the feedback path; their output follows the exponential I-V relation.

Peak detector, sample-and-hold and voltage-to-current converter are standard op-amp applications in instrumentation.

Virtual ground at the inverting input holds the node near 0 V because of negative feedback and very high open-loop gain.

Noise margin = V_IH − V_OH (high) and V_IL − V_OL (low); larger margin means better noise immunity.

Figure of merit = propagation delay × power dissipation; lower is better. CMOS is far better than TTL on this measure.

TTL unused inputs must not float; tie them high through a resistor or to V_CC, because floating TTL inputs behave as logic 1 and pick up noise.

ECL is the fastest family but has high power consumption; it uses current steering and non-saturating transistors.

Karnaugh map grouping must be in powers of two and can wrap around edges; don't-care conditions can be used to enlarge groups.

State diagram and state table describe sequential behaviour; the number of states determines the number of flip-flops needed.

Asynchronous (ripple) counters have cumulative propagation delay; synchronous counters clock all flip-flops together and are faster.

Johnson counter (twisted-ring) with n flip-flops has 2n states; a ring counter has n states.

A shift register with parallel load can convert serial data to parallel and back, used in serial communication interfaces.

Flip-flop excitation tables: for JK, J = K = 1 toggles; for D, D equals the next state; for T, T = 1 toggles.

Noise figure F = (S/N)_in / (S/N)_out; in dB it is 10 log10 F, and a low-noise first stage dominates receiver performance.

AM envelope detector uses a diode, resistor and capacitor; the RC time constant must be short compared with the modulating period.

Frequency mixer produces sum and difference frequencies; the difference is the IF, and image frequency rejection needs a preselector filter.

Quantisation noise in PCM decreases by about 6 dB per additional bit; companding (µ-law or A-law) equalises S/N over the speech range.

Optical fibre communication uses total internal reflection; attenuation is quoted in dB/km and is lowest near 1550 nm.

SCR ratings: latching current is the minimum anode current needed to stay ON after the gate pulse is removed; holding current is the minimum to remain ON.

dv/dt and di/dt ratings limit false triggering and device damage; snubbers and series inductors protect the device.

Phase-controlled rectifier with R-L load needs a freewheeling diode to maintain continuous current and improve the power factor.

Buck-boost chopper gives V_o = −V_in·D/(1 − D); boost chopper gives V_o = V_in/(1 − D).

UPS systems use an inverter with battery backup; SMPS uses high-frequency switching for compact, efficient DC supplies.

Loading effect: a low-resistance voltmeter across a high-resistance circuit reads low; a high-resistance voltmeter reduces error.

A multimeter's input impedance is typically 10 MΩ on voltage ranges; the oscilloscope probe is usually 10× with 10 MΩ input.

Lissajous figures on an oscilloscope compare two frequencies: the ratio of tangent counts gives the frequency ratio.

Thermocouple produces a small emf (µV/°C) by the Seebeck effect; cold-junction compensation is required.

Piezoelectric transducer output is proportional to applied force and needs a charge amplifier with very high input impedance.

Port 0 in 8051 has no internal pull-up and needs external pull-up resistors for output; ports 1, 2 and 3 have internal pull-ups.

TMOD sets timer mode and gate control; TCON holds run control (TR0, TR1) and interrupt flags (TF0, TF1).

MOVX accesses external data memory; MOVC reads program memory (lookup tables).

Serial SCON register: SM0, SM1 select mode, REN enables reception, TI and RI are transmit and receive interrupt flags.

Watchdog timer resets the processor if firmware hangs; brown-out detection holds the CPU in reset when supply voltage is low.

Diode testing with a multimeter: forward resistance is low (a few hundred ohms), reverse resistance is very high; a shorted diode reads low in both directions.

Zener regulator design: R_S = (V_in − V_Z)/(I_Z + I_L), and the Zener must dissipate at least V_Z·I_Z(max).

Bridge rectifier PIV per diode is V_m, while centre-tap full-wave PIV is 2V_m; this matters when selecting diodes.

Photovoltaic cell converts light to emf; photoconductive cell (LDR) changes resistance with light.

Thermistor has a large negative temperature coefficient and is used for temperature sensing and inrush current limiting.

A transistor can be tested as two back-to-back diodes: base-emitter and base-collector junctions should conduct in one direction only.

Cut-off region: I_C ≈ 0, V_CE ≈ V_CC; saturation region: V_CE ≈ 0.2 V, I_C limited by R_C.

The emitter follower is used for impedance matching because of its high input impedance and low output impedance.

Power dissipation of a BJT is P_D = V_CE·I_C; the maximum rating must not be exceeded without a heat sink.

In a common-base amplifier, input is at the emitter and output at the collector; the base is common to both.

The transfer characteristic of a JFET is a parabola; the output characteristic has ohmic, saturation and breakdown regions.

Pinch-off occurs when the depletion regions meet and the channel narrows; drain current then becomes almost constant.

MOSFET symbols: enhancement mode has a broken channel line, depletion mode has a solid channel line.

FET switching speed is high because there are no minority-carrier storage effects, unlike a BJT.

CMOS inverter uses a PMOS pull-up and NMOS pull-down; it draws current only during switching.

Open-loop comparator with hysteresis: the upper and lower trigger levels are set by the feedback divider and the saturation voltage.

Difference amplifier output V_o = (R_f/R_in)(V2 − V1) when resistor ratios are matched.

Active low-pass filter: above cut-off the gain falls at 20 dB/decade per pole; a second-order filter gives 40 dB/decade.

Current-to-voltage converter (transimpedance amplifier) is used with photodiodes; gain is set by the feedback resistor.

Op-amp output cannot exceed the supply rails; rail-to-rail types come close, and the output saturates otherwise.

A logic gate's truth table lists all input combinations; for n inputs there are 2^n rows.

SOP form is implemented with AND gates feeding an OR gate; POS form uses OR gates feeding an AND gate.

A half subtractor gives Difference = A⊕B and Borrow = A'B.

A decoder with enable input can be used as a demultiplexer; a multiplexer can implement any Boolean function of its select lines.

Static RAM stores a bit in a bistable latch (6 transistors); dynamic RAM stores charge in a capacitor and needs refresh.

A master-slave JK flip-flop avoids race-around by latching on one clock level and updating on the other.

Preset and clear inputs set or reset a flip-flop asynchronously, independent of the clock.

A counter with modulus 10 (decade counter) is built from four flip-flops with reset at count 10.

A register stores n bits with n flip-flops; a shift register moves data one position per clock.

Finite state machine design steps: state diagram, state table, state assignment, flip-flop selection, excitation and output equations.

FM capture effect: the stronger of two co-channel signals suppresses the weaker, so FM needs capture ratio control.

Pre-emphasis and de-emphasis in FM boost and cut high frequencies to improve the signal-to-noise ratio.

AM broadcast band is 535–1605 kHz with 10 kHz channel spacing; FM broadcast is 88–108 MHz.

A duplexer allows one antenna to serve both transmitter and receiver in a radar or repeater.

Satellite link budget: EIRP, free-space path loss and receiver G/T determine the carrier-to-noise ratio.

A cycloconverter converts AC of one frequency directly to AC of another frequency without a DC link.

A matrix converter is a direct AC-AC converter using bidirectional switches.

Thermal design: junction temperature T_j = T_a + P·R_th, where R_th is the total thermal resistance.

Gate drive for an SCR needs isolation (pulse transformer or optocoupler) to protect the control circuit.

Solid-state relay uses a TRIAC or back-to-back SCRs with an optocoupler for isolated AC switching.

A true-rms meter measures the heating effect of the waveform; an average-responding meter is calibrated for sine waves only.

Frequency counter counts cycles in a gate time; resolution improves with a longer gate time.

A signal generator produces sine, square and triangular waves; a function generator adds sweep and modulation.

A spectrum analyser displays amplitude against frequency; an oscilloscope displays amplitude against time.

Calibration traceability links an instrument to national standards through a chain of comparisons.

A/D conversion in a microcontroller uses successive approximation; resolution is V_ref/2^n per LSB.

PWM output from a timer controls motor speed and LED brightness by varying duty cycle.

The 8051 uses bit-addressable RAM from 20H to 2FH for flags and single-bit control.

Assembly instructions: MOV, ADD, SUBB, MUL, DIV, ANL, ORL, XRL, JMP, CALL, RET, DJNZ.

Embedded C uses volatile for hardware registers and bit masking to set or clear individual port pins.

Junction capacitance C_T = εA/W, so it decreases as the depletion width W increases with reverse bias.

Diffusion capacitance dominates under forward bias because of stored minority charge; it rises with forward current.

The depletion region has a contact potential that cannot be measured directly by an external voltmeter.

Breakdown voltage rises with lighter doping; heavily doped junctions have low breakdown voltage.

A varactor's capacitance varies with reverse voltage, giving electronic tuning in radio receivers.

Collector-to-base bias feeds base current from the collector, giving negative feedback that stabilises the Q point.

Two-supply emitter bias uses a negative supply at the emitter resistor to set a stable emitter current.

The Q point should be near the middle of the load line for maximum symmetrical swing.

Gain-bandwidth product limits the usable frequency range of a transistor amplifier stage.

Coupling capacitors block DC between stages while passing the AC signal.

The common-source amplifier inverts the signal; the source follower does not invert.

Miller capacitance at the gate-drain node lowers the upper cut-off frequency of a common-source stage.

Class B push-pull uses complementary transistors; bias diodes reduce crossover distortion in Class AB.

Transformer coupling in Class A gives higher efficiency than resistive coupling because there is no DC drop across the load.

Total harmonic distortion measures amplifier nonlinearity; negative feedback reduces it.

A window comparator uses two comparators to indicate when a signal lies between two reference levels.

A voltage-controlled oscillator produces a frequency proportional to input voltage, used in PLL circuits.

A phase-locked loop consists of a phase detector, low-pass filter and voltage-controlled oscillator.

A precision current source built with an op-amp and a pass transistor delivers a load current set by a reference resistor.

A peak-hold circuit stores the maximum input voltage on a capacitor buffered by an op-amp.

NAND and NOR are called universal gates because any other gate can be built from them alone.

Exclusive-NOR gives 1 when inputs are equal; it is used in equality comparators.

A buffer has gain greater than 1 and isolates stages; its logic function is identity.

Fan-out is the number of gate inputs a single output can drive without violating logic levels.

Propagation delay is measured between 50% points of input and output waveforms.

A modulo-16 counter needs four flip-flops; a modulo-12 counter resets after twelve states.

A BCD counter counts 0000 to 1001 and resets on the next clock.

Synchronous counter design uses excitation tables to derive flip-flop input equations.

A shift register can multiply by 2 (left shift) or divide by 2 (right shift) in binary.

Debouncing a mechanical switch uses an RC filter or a Schmitt trigger to remove contact bounce.

AM power in sidebands is m^2/(2 + m^2) of total power; at m = 1 sidebands carry one-third of total power.

FM deviation ratio is Δf/f_m(max); wideband FM has a deviation ratio much greater than 1.

Frequency-division multiplexing assigns separate carrier frequencies; time-division multiplexing assigns time slots.

Pulse code modulation uses sampling, quantisation and encoding; companding improves small-signal resolution.

A repeater regenerates a digital signal, removing noise accumulated over a long link.

A single-phase full bridge inverter uses four switches and produces a square wave; PWM shapes the output toward a sine wave.

A three-phase inverter needs six switches and produces 120° displaced outputs.

A cycloconverter is used for low-speed high-torque AC motor drives.

A resonant converter switches at zero voltage or zero current to reduce switching losses.

Battery charging in a UPS uses a controlled rectifier in the forward direction and an inverter in backup mode.

An RTD (platinum) has a positive, nearly linear temperature coefficient and is more linear than a thermistor.

An LVDT has a primary winding and two secondary windings; output is the difference of the secondary voltages.

A Hall-effect sensor detects magnetic field and is used for speed and position sensing.

An ultrasonic sensor measures distance by time of flight of a sound pulse.

An IR sensor detects obstacles by reflected infrared light and is common in robots.

A traffic light controller uses timer interrupts and a state machine to sequence red, yellow and green.

A temperature controller reads an ADC channel, compares with a setpoint and drives a relay or PWM output.

A stepper motor driver uses a transistor array (e.g. ULN2003) because the microcontroller pin cannot source motor current.

An LCD display in 4-bit mode uses four data lines plus RS, RW and E control lines.

Firmware debugging uses breakpoints, single-stepping and serial output; in-circuit debuggers program flash memory.

Energy gap at 0 K: silicon 1.12 eV, germanium 0.67 eV; germanium is more temperature-sensitive.

Drift current is due to the electric field; diffusion current is due to the carrier concentration gradient.

Fermi level lies near the middle of the gap in intrinsic material; doping shifts it toward the conduction or valence band.

Recombination of electron-hole pairs releases energy as light (LED) or heat.

Hall effect measures carrier type and concentration in a semiconductor.

A transistor in the active region behaves as a current-controlled current source: I_C = βI_B.

Small-signal model uses r_e = 26 mV/I_E for the emitter resistance; gain of a common-emitter stage is −R_C/r_e.

The hybrid-pi model uses r_π = βr_e and g_m = I_C/V_T.

Input and output impedance of each configuration determine its use as a buffer or amplifier.

The transistor as a variable resistor in the ohmic region is used in automatic gain control.

JFET is used as a buffer in electrometers and as a voltage-variable resistor in AGC circuits.

MOSFET is used in power switching because of low on-resistance and fast switching.

CMOS logic uses complementary MOSFETs; power is consumed mainly during transitions.

A MOSFET's gate oxide can be damaged by static electricity; handle with grounded tools.

The body diode of a power MOSFET conducts in the reverse direction and is used as a freewheeling diode.

Offset nulling uses a potentiometer on the offset null pins to zero the output for zero input.

Input bias current causes an error voltage across the source resistance; a compensating resistor at the non-inverting input reduces it.

Slew rate limits the maximum frequency of a full-scale sine output; exceeding it causes a triangular output.

CMRR measures rejection of common-mode signals; a high value is needed for bridge measurement.

Power-supply decoupling capacitors near the op-amp suppress high-frequency noise.

Signed binary uses two's complement: invert bits and add 1 to negate.

Overflow in two's-complement addition occurs when the carry into and out of the sign bit differ.

A parity bit detects single-bit errors; even parity makes the total number of 1s even.

Hamming code adds multiple check bits to correct single-bit errors.

ASCII uses 7 bits; extended ASCII uses 8 bits.

Mealy output depends on state and input; Moore output depends only on state.

A state diagram with n states needs ceil(log2 n) flip-flops.

Race conditions in asynchronous circuits occur when two state variables change simultaneously.

Clock skew between flip-flops reduces the timing margin and can cause hold violations.

Reset can be synchronous (applied at the clock edge) or asynchronous (immediate).

Antenna gain is quoted in dBi relative to an isotropic radiator; a dipole has 2.15 dBi.

Free-space path loss in dB is 32.44 + 20 log10(f in MHz) + 20 log10(d in km).

Frequency reuse in cellular systems increases capacity; co-channel interference limits reuse.

Spread spectrum (DSSS and FHSS) improves interference rejection and security.

Bluetooth and Wi-Fi use 2.4 GHz ISM band; 5 GHz Wi-Fi offers more channels and less interference.

DC motor speed is proportional to armature voltage; torque is proportional to armature current.

A DC chopper drive controls motor speed by varying the duty cycle of the armature voltage.

An AC induction motor's speed is set by synchronous speed N_s = 120f/P, where P is the number of poles.

A variable-frequency drive (VFD) controls induction motor speed by changing supply frequency.

A stepper motor is driven by a sequence of pulses; the speed depends on the pulse rate.

Systematic errors are reproducible and can be corrected by calibration; random errors are reduced by averaging.

Accuracy is closeness to the true value; precision is repeatability of the reading.

Resolution is the smallest change an instrument can display; sensitivity is output per unit input.

A bridge circuit converts a small resistance change into a voltage, enabling precise measurement.

A data acquisition system consists of sensors, signal conditioning, an ADC and a processor.

An ADC channel is selected by a multiplexer; conversion time depends on the clock and resolution.

A DAC converts a digital value to an analog voltage; resolution is V_ref/2^n.

A UART frame consists of a start bit, data bits, an optional parity bit and stop bits.

I2C uses two wires (SDA and SCL) with device addresses; SPI uses four wires with a chip-select line.

An interrupt service routine should be short; long processing is deferred to the main loop.

A clipper limits the signal amplitude; a clamper shifts the DC level without changing the peak-to-peak value.

A voltage doubler uses two diodes and two capacitors to produce about twice the peak input voltage.

A freewheeling diode protects a switching transistor from inductive kickback.

A varactor-tuned circuit uses reverse bias to change the resonant frequency.

A photodiode in reverse bias produces a photocurrent proportional to illumination.

Common emitter: high voltage gain, medium input impedance, output inverted.

Common collector: voltage gain about 1, high input impedance, low output impedance, used as a buffer.

Common base: low input impedance, high output impedance, no current gain, used at high frequencies.

Cascode connection combines common emitter and common base for high gain and wide bandwidth.

Darlington pair gives very high current gain and is used in power switching.

Drain resistance r_d = ΔV_DS/ΔI_D in the saturation region; it is high for a good current source.

Amplification factor µ = g_m·r_d relates the three small-signal parameters.

Gate-source cut-off voltage is the value at which drain current becomes negligible.

MOSFET on-resistance R_DS(on) determines conduction loss in power switching.

Gate charge Q_g determines the drive energy and switching speed of a power MOSFET.

Voltage regulator using an op-amp and a series pass transistor maintains a constant output against load changes.

A Wien-bridge oscillator uses an op-amp with RC networks to produce a sine wave at f = 1/(2πRC).

A square-wave generator uses an op-amp Schmitt trigger with an RC feedback network.

A triangular-wave generator integrates the square wave from a Schmitt trigger.

A phase-locked loop can be used for FM demodulation and frequency synthesis.

Standard TTL propagation delay is about 10 ns; Schottky TTL is faster because it prevents saturation.

CMOS propagation delay rises with supply voltage reduction but power falls sharply.

TTL output can sink more current than it sources; this affects LED driving.

Interfacing TTL to CMOS requires a pull-up because TTL high level may be below the CMOS threshold.

Unused CMOS inputs must be tied to V_DD or ground to prevent oscillation and excess current.

ROM types: mask ROM, PROM (one-time programmable), EPROM (UV erasable), EEPROM (electrically erasable) and flash.

A memory chip's capacity is (number of words) × (bits per word); address lines = log2(number of words).

A FIFO buffers data between systems with different rates; a LIFO (stack) reverses order.

A multiplexer-based bus selects one of several sources onto a common line.

A shift register with feedback can generate pseudo-random bit sequences for testing.

Half-wave dipole length ≈ 0.95 × λ/2 in free space, shortened by the velocity factor of the wire.

Yagi-Uda antenna uses a driven element, reflector and directors for directional gain.

Ground-wave propagation follows the earth's surface; sky-wave uses ionospheric reflection.

Line-of-sight propagation requires antenna height for a given distance; radio horizon extends beyond the geometric horizon.

Fading in mobile radio is caused by multipath interference and can be mitigated by diversity reception.

The IGBT combines MOS gate drive with the low saturation voltage of a BJT.

A power MOSFET has an intrinsic body diode and is used in high-frequency switching supplies.

The TRIAC conducts in both directions and is triggered by a gate pulse of either polarity.

The DIAC triggers the TRIAC when the voltage across it reaches the breakover voltage.

A snubber RC network across a thyristor limits dv/dt and prevents false triggering.

A transducer converts a physical quantity into an electrical signal; a sensor is the sensing element.

Signal conditioning amplifies, filters and linearises the transducer output.

An isolation amplifier protects the measurement system from high common-mode voltages.

A 4–20 mA current loop is immune to voltage drops along long cables.

A data logger records measurements over time for later analysis.

The 8051 reset circuit holds RST high for at least two machine cycles to initialise the CPU.

The 8051 crystal oscillator typically uses 11.0592 MHz for accurate UART baud rates.

A watchdog timer resets the CPU if the firmware fails to clear it periodically.

Memory-mapped I/O assigns addresses to peripherals in the same address space as memory.

Firmware is stored in non-volatile memory and copied to RAM at startup for execution.