Analog Electronic Circuits: Field Effect Transistors, Feedback Amplifiers, and Oscillators

Comprehensive vocabulary flashcards covering field effect transistors (JFET, DE-MOSFET, E-MOSFET, CMOS), small-signal models, amplifier frequency responses, feedback topologies, and oscillator circuits.

Field Effect Transistor (FET)

A voltage-controlled, unipolar semiconductor device in which current conduction is carried out exclusively by majority charge carriers through a conduction channel controlled by an electric field without direct contact between controlling and controlled quantities.

Shockley's Equation

The mathematical relationship describing the parabolic transfer characteristics of a JFET or depletion-type MOSFET, expressed as $I_D = I_{DSS}\left(1 - \frac{V_{GS}}{V_p}\right)^2$, where $I_{DSS}$ is the maximum drain saturation current and $V_p$ is the pinch-off voltage.

Depletion-Type MOSFET (DE-MOSFET)

A field effect transistor constructed with a pre-existing physical channel between the source and drain, capable of operating in both depletion mode (when negative $V_{GS}$ reduces channel carriers) and enhancement mode (when positive $V_{GS}$ attracts additional electrons to increase conductivity).

Enhancement-Type MOSFET (E-MOSFET)

A field effect transistor fabricated without a pre-existing channel between the heavily doped regions, requiring an applied gate voltage greater than the threshold voltage ($V_{GS} > V_T$) to induce an inversion layer and allow drain current to flow according to $I_D = k(V_{GS} - V_T)^2$.

Threshold Voltage ($V_T$)

The minimum gate-to-source voltage level required to induce a conductive inversion channel beneath the $\text{SiO}_2$ insulating layer, causing drain current in an enhancement-type MOSFET to rise from zero to a significant value.

CMOS Inverter

A complementary logic circuit consisting of a p-channel enhancement MOSFET (connected to $V_{SS}$) and an n-channel enhancement MOSFET (connected to ground) whose gates share the input and whose drains share the output, ensuring one transistor is off while the other is on.

Transconductance ($g_m$)

The control factor of a FET representing the slope of the transfer characteristic curve at a given Q-point, defined mathematically as the derivative of drain current with respect to gate-to-source voltage: $g_m = \left.\frac{d I_D}{d V_{GS}}\right|_{Q\text{-point}} = \frac{\Delta I_D}{\Delta V_{GS}}$.

Zero-Bias Transconductance ($g_{m0}$)

The maximum transconductance of a JFET occurring when the gate-to-source voltage $V_{GS} = 0\,\text{V}$, calculated using the formula $g_{m0} = \frac{2 I_{DSS}}{|V_p|}$.

Small-Signal Drain Resistance ($r_d$)

The dynamic output impedance of a FET amplifier, defined as the reciprocal of the slope of the drain characteristic curve in the saturation region: $r_d = \left.\frac{\Delta V_{DS}}{\Delta I_D}\right|_{V_{GS} = \text{constant}} = \frac{1}{y_{os}}$.

Source Follower (Common Drain Configuration)

A JFET amplifier configuration where the output is taken from the source terminal with the drain placed at AC ground; it exhibits high input impedance ($Z_i = R_G$), low output impedance ($Z_o \approx R_S \parallel \frac{1}{g_m}$), and an in-phase voltage gain slightly less than unity ($A_v < 1$).

Miller Input Capacitance ($C_{Mi}$)

The effective capacitance appearing across the input terminals of an inverting amplifier due to feedback capacitance $C_f$ between input and output, defined as $C_{Mi} = (1 - A_v) C_f$, which significantly lowers the high-frequency cutoff.

Negative Feedback

The circuit configuration in which a fraction of the output signal is fed back out of phase ($180^\circ$) to subtract from the applied input signal ($X_i = X_s - X_f$), reducing closed-loop gain ($A_f = \frac{A}{1 + \beta A}$) while enhancing gain stability and reducing distortion.

Loop Gain

The factor by which a signal is multiplied as it completes one complete transmission around the feedback loop, equal to $-\beta A$ for negative feedback and $+\beta A$ for positive feedback.

Voltage Series Feedback

A feedback topology where output voltage is sampled in parallel and the feedback voltage signal is connected in series with the input voltage source, resulting in increased input impedance ($Z_{if} = Z_i(1 + \beta A)$) and decreased output impedance ($Z_{of} = \frac{Z_o}{1 + \beta A}$).

Current Series Feedback

A feedback topology where output load current is sampled in series and the feedback signal is mixed in series with the input signal, resulting in an increase of both input impedance ($Z_{if} = Z_i(1 + \beta A)$) and output impedance ($Z_{of} = Z_o(1 + \beta A)$).

Barkhausen Criterion

The two mandatory conditions required for an amplifier circuit to maintain sustained sinusoidal oscillations without an external input: the magnitude of the loop gain must equal unity ($|A\beta| = 1$), and the net phase shift around the feedback loop must be $0^\circ$, $360^\circ$, or an integer multiple of $2\pi$.

RC Phase Shift Oscillator

An audio-frequency oscillator comprising an inverting op-amp providing a $180^\circ$ phase shift cascaded with a three-stage RC ladder feedback network (each stage providing $60^\circ$, totaling $180^\circ$), oscillating at a frequency of $f_o = \frac{1}{2\pi R C \sqrt{6}}$.

Wien Bridge Oscillator

An oscillator employing a non-inverting amplifier and an RC lead-lag bridge network that provides zero phase shift at its resonant frequency, with frequency of oscillation given by $f_o = \frac{1}{2\pi \sqrt{R_1 R_2 C_1 C_2}}$ and requiring an amplifier gain of $A \ge 3$ to sustain oscillations.

Hartley Oscillator

An LC radio-frequency oscillator whose frequency-selective feedback tank network consists of two tapped inductors ($L_1$ and $L_2$) and a single parallel capacitor ($C$), producing a resonant frequency of $f_o = \frac{1}{2\pi \sqrt{(L_1 + L_2) C}}$.

Colpitts Oscillator

An LC radio-frequency oscillator that utilizes a tank circuit consisting of an inductor ($L$) and a split capacitive voltage divider ($C_1$ and $C_2$), with an oscillation frequency defined by $f_o = \frac{1}{2\pi \sqrt{L \left(\frac{C_1 C_2}{C_1 + C_2}\right)}}$.

Clapp Oscillator

A modified Colpitts oscillator that incorporates an additional small capacitor $C_3$ in series with the tank inductor $L$, making the oscillation frequency $f_o \approx \frac{1}{2\pi \sqrt{L C_3}}$ independent of the transistor internal capacitances ($C_{in}$ and $C_{out}$).

Crystal Oscillator

A highly stable tuned oscillator in which a piezoelectric quartz crystal replaces the inductor in an LC tank circuit, exploiting electromechanical resonance to eliminate drift caused by temperature and aging.

Series-Fed Class A Power Amplifier

A power amplifier configuration where the active device conducts for the full $360^\circ$ of the input cycle, possessing a maximum theoretical conversion efficiency of $25\%$ in direct series-fed form and $50\%$ when transformer-coupled.

Class B Push-Pull Amplifier

An amplifier topology utilizing two complementary active devices that conduct alternately for exactly $180^\circ$ (half-cycle) each, achieving a theoretical maximum power conversion efficiency of $78.5\%$.

Crossover Distortion

Non-linear distortion occurring in complementary class B push-pull amplifiers during the zero-crossing transition of the input signal when both transistors remain momentarily turned off due to their base-emitter cut-in voltages.

Voltage Shunt Feedback FET Circuit

A field effect transistor amplifier configuration where a feedback resistor $R_F$ connects the drain output back to the gate input, sampling output voltage and feeding back current in parallel with the source resistance to stabilize gain.