ECE006 Engineering College Quiz

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Fundamentals of Electronics

• Gain refers to amplification, and the ratio of output to input voltage is called voltage gain (Av)
• Voltage gain (Av) is expressed as: Av = Vout / Vin
• Power gain (AP) is calculated as: AP = Pout / Pin
• When cascading amplifiers, the overall gain is the product of individual gains

Attenuation

• Attenuation refers to a loss introduced by a circuit or component
• Attenuation (A) is expressed as: A = Vout / Vin
• Circuits with attenuation have a gain less than 1
• Total attenuation is the product of individual attenuations of each cascaded circuit

Decibels

• Decibel (dB) is a unit of measurement that expresses the ratio of two values
• Decibel is one-tenth of a bel
• Decibel calculations: gain/attenuation in dB = 10 * log10 (output/input)
• dBm: a decibel value referenced to 1 mW

Tuned Circuits

• Tuned circuits consist of inductive and capacitive elements that resonate at specific frequencies
• Inductive and capacitive elements offer an opposition to alternating current flow known as reactance

Reactive Components

• Capacitors:
  • Oppose voltage changes across them
  • Capacitive reactance (XC) is inversely proportional to capacitance (C) and frequency (f)
  • XC = 1 / (2 * π * f * C)
• Inductors:
  • Produce a magnetic field when current passes through them
  • Inductance opposes current changes in the coil
  • The basic unit of inductance is the henry (H)

Let me know if you'd like me to make any changes!### Inductance and Inductors

• Inductance is affected by physical characteristics of the coil, including the number of turns, spacing, length, diameter, and magnetic core material
• In a dc circuit, an inductor has little or no effect, only ohmic resistance of the wire affects current flow
• In an ac circuit, the inductor opposes changes in current, known as inductive reactance (XL)
• XL is expressed in ohms and is calculated using the expression XL = 2πfL
• Stray capacitance between turns of the coil is like a small capacitor connected in parallel with the coil
• At high frequencies, lead lengths should be kept short to minimize inductive reactance

Types of Inductors

• Heavy self-supporting wire coils
• Inductors made as copper patterns
• Insulating forms
• Toroidal inductors
• Ferrite bead inductors
• Chip inductors

Resistors

• At low frequencies, a standard low-wattage color-coded resistor offers nearly pure resistance
• At high frequencies, the leads have considerable inductance, and stray capacitance between leads causes the resistor to act as a complex RLC circuit
• To minimize inductive and capacitive effects, leads are kept very short in radio applications
• Tiny resistor chips used in surface-mount construction have virtually no leads and little stray capacitance

Skin Effect

• The resistance of a wire conductor is primarily determined by the ohmic resistance of the wire
• Skin effect is the tendency of electrons flowing in a conductor to flow near and on the outer surface of the conductor at high frequencies
• Skin effect decreases the total cross-sectional area of the conductor, increasing its resistance and affecting circuit performance
• Copper tubing and thin conductors are used to minimize skin effect

Tuned Circuits

• A tuned circuit is made up of inductance and capacitance and resonates at a specific frequency
• Tuned circuits are frequency-selective, responding best at the resonant frequency and a narrow range of frequencies around it
• A series resonant circuit is made up of inductance, capacitance, and resistance, and resonates when the inductive and capacitive reactances are equal
• The resonant frequency can be expressed in terms of inductance and capacitance: fr = 1/2π√LC

Series Resonant Circuits

• The total impedance of the circuit is given by the expression Z = √R² + (XL - XC)²

• At resonance, the total circuit impedance is simply the value of all series resistances in the circuit

• The resonant frequency can be expressed in terms of inductance and capacitance: fr = 1/2π√LC

• The bandwidth of a series resonant circuit is determined by the Q of the circuit: BW = fr/Q

• The upper and lower boundaries of the bandwidth are defined by two cutoff frequencies, f1 and f2### Resonance and Impedance

• When the reactances, resistances, and current are known, the voltage drops across each component can be computed.

• At resonance, the voltage drops across the inductor and capacitor are significantly higher than the applied voltage, known as the resonant step-up voltage.

• The voltage across the inductor leads the current by 90° and the voltage across the capacitor lags the current by 90°.

• The inductive and reactive voltages are equal but 180° out of phase, resulting in a total reactive voltage of 0.

Resonant Circuits

• Series resonant circuits: the voltage across the inductor and capacitor are in series with the source voltage.
• Parallel resonant circuits: the inductor and capacitor are connected in parallel with the applied voltage.
• At resonance, a parallel tuned circuit appears to have infinite resistance, draws no current from the source, and has infinite impedance.
• The equivalent inductance (Leq) and resistance (Req) are calculated using the formulas: Leq = L/(Q² + 1) and Req = R(Q² + 1).

Quality Factor (Q)

• Q is determined by the formula: Q = XL/R or Q = RP/XL.
• A high Q indicates a high energy storage capacity and a narrow bandwidth.
• Q is a measure of the circuit's ability to selectively respond to a particular frequency.

Filters

• A filter is a frequency-selective circuit that passes some frequencies and rejects others.
• There are four kinds of filters: low-pass, high-pass, bandpass, and band-reject filters.
• Each type of filter has a specific frequency response and is used to achieve a particular filtering action.

Passive Filters

• Passive filters use resistors, capacitors, and inductors to achieve the desired frequency response.
• RC filters are widely used due to their simplicity and low cost.
• RL filters are not as widely used due to the larger size and higher cost of inductors.

RC Filters

• Low-pass filters: introduce no attenuation at frequencies below the cutoff frequency and completely eliminate all signals with frequencies above the cutoff.
• High-pass filters: pass frequencies above the cutoff frequency and reject frequencies below the cutoff.
• Band-reject filters: reject or stop frequencies over a narrow range but allow frequencies above and below to pass.
• Notch filters: used to greatly attenuate a narrow range of frequencies around a center point.

LC Filters

• LC filters are commonly used at radio frequencies due to their better selectivity.
• Low-pass, high-pass, and band-pass filters can be implemented using LC filters.
• The major types of LC filters are named after the person who discovered and developed the analysis and design method for each filter.

Types of LC Filters

• Butterworth filters: have maximum flatness in response in the passband and a uniform attenuation with frequency.
• Chebyshev filters: have extremely good selectivity and a high attenuation rate outside the passband.
• Cauer (Elliptical) filters: produce an even greater attenuation or roll-off rate than Chebyshev filters and greater attenuation out of the passband.
• Bessel filters: have a flat group delay, meaning that the phase shift or time delay introduced by the filter is constant across the passband.

Ripple

• Ripple is the amplitude variation with frequency in the passband, or the repetitive rise and fall of the signal level in the passband of some types of filters.
• Ripple is usually stated in decibels and can be present in the passband and stopband of some filters.