Title: InkPhysics / Electronics
On every note of this deck, unless a note says otherwise:
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Front: DEFINITION
Define: D-type flip-flop.
Back: A one-bit memory: on each rising clock edge it copies D to Q, then holds Q unchanged, ignoring D, until the next edge.

Front: EQUATION · NOT ON THE DATA SHEET
Cut-off frequency of an RC filter:
f_c = ?\(f_{c} = \, ?\)f_c = ?
Back: f_c = 12πRC\(f_{c} = \frac{1}{2\pi RC}\)f_c = 1/2πRC

Front: DEFINITION
Define: Modulation.
Back: Printing a signal onto a higher-frequency carrier wave by varying the carrier amplitude or frequency, so that aerials can be a practical length and each station can be given a frequency of its own.

Front: SPOT THE ERROR
Say what is wrong with this claim: FM radio sounds cleaner than AM because it is broadcast at higher power.
Back: The advantage lies in what the receiver reads. Noise adds to a wave's amplitude; an FM receiver clips the amplitude flat and detects only the frequency, so nearly all of that noise is removed, and the wide FM channel also carries audio to 15 kHz.

Front: DEFINITION
Define: Ideal operational amplifier.
Back: An amplifier of the difference between its two inputs, taken to have infinite open-loop gain, infinite input resistance, zero output resistance and infinite bandwidth.

Front: RECALL
State the summing amplifier equation.
Back: V_out = −R_f(V_1/R_1 + V_2/R_2 + ...): each input is amplified by R_f divided by its own input resistor, and the weighted total is inverted.

Front: RECALL
State the sampling rule.
Back: The sampling rate must be greater than twice the highest frequency present in the signal; sampled more slowly, a high frequency is recorded as a lower one and cannot be recovered.

Front: SPOT THE ERROR
Say what is wrong with this claim: Switching a heavy load needs a heavy current into the transistor's control terminal.
Back: A MOSFET is controlled by a voltage, not a current. Its gate sits on an insulating oxide layer, so only a negligible leakage current enters it: the driver supplies the brief charge the gate capacitance needs, and a logic pin rated at a milliamp can switch amps.

Front: EQUATION · NOT ON THE DATA SHEET
Current in a zener regulator's series resistor:
I = ?\(I = \, ?\)I = ?
Back: I = V_S - V_ZR_S\(I = \frac{V_{S} - V_{Z}}{R_{S}}\)I = (V_S - V_Z)/R_S

Front: DEFINITION
Define: Q factor.
Back: The resonant frequency divided by the bandwidth. A high Q means a narrow, sharp peak and little energy lost from the circuit each cycle.

Front: DEFINITION
Define: Zener diode.
Back: A diode built to break down at a chosen reverse voltage without damage, holding its pd nearly constant while the current through it varies widely.

Front: DEFINITION
Define: Virtual earth.
Back: The inverting input of an inverting amplifier, held within microvolts of 0 V by negative feedback although it carries no connection to earth.

Front: RECALL
Explain what regeneration does that amplification cannot.
Back: A regenerator decides whether each incoming pulse is 0 or 1 and issues a brand-new, full-height, noise-free pulse, so the noise collected so far is discarded. An amplifier raises the signal and the accumulated noise together.

Front: DEFINITION
Define: Sideband.
Back: One of the two frequencies produced either side of the carrier by amplitude modulation, at f_c + f_M and f_c − f_M; they carry the information, the carrier itself carries none.

Front: DEFINITION
Define: Resonance in an LC circuit.
Back: The condition in which the inductive and capacitive reactances are equal and opposite, so they cancel, the impedance falls to a minimum and the current is a maximum.

Front: DEFINITION
Define: Threshold voltage.
Back: The gate-source voltage at which a MOSFET first forms a conducting channel. Below it no channel exists and the drain current is zero, however large the drain voltage.

Front: SPOT THE ERROR
Say what is wrong with this claim: A summing amplifier simply adds up its input voltages.
Back: It adds weighted voltages, and inverts the total. Each input reaches the virtual earth through its own resistor, so it arrives with its own gain R_f/R_in: equal weights happen only if you choose equal resistors.

Front: DEFINITION
Define: Common-mode signal.
Back: A signal appearing identically on both inputs, such as mains hum induced equally on both leads of a cable. It appears in both terms of (V_+ − V_−) and so cancels before the gain is applied.

Front: DEFINITION
Define: Time-division multiplexing.
Back: Sharing one channel by giving each user the whole channel for a brief repeating time slot, which suits digital signals because their samples are short pulses with gaps between them.

Front: SPOT THE ERROR
Say what is wrong with this claim: An op-amp with an open-loop gain of 100 000 multiplies any input by 100 000.
Back: Only for inputs under about 130 μV. An open-loop gain of 100 000 multiplied by more than that asks for an output beyond the supply rails, so the amplifier saturates. Useful gain comes from negative feedback, and then the resistors set it, not the chip.

Front: RECALL
Explain what happens when an amplifier saturates.
Back: The output cannot pass the supply rails, so once the equation demands more than the rail voltage the output sticks about a volt inside that rail and the waveform is clipped.

Front: DEFINITION
Define: Saturation.
Back: The state in which the output demanded by the gain would pass the supply rails, so the output sticks just inside a rail and no longer follows the input.

Front: DEFINITION
Define: EOR gate.
Back: A two-input gate whose output is 1 when the inputs differ and 0 when they are the same.

Front: EQUATION · NOT ON THE DATA SHEET
Gain-bandwidth product:
gain × bandwidth = ?\(\text{gain} \times \text{bandwidth} = \, ?\)gain × bandwidth = ?
Back: gain × bandwidth = constant\(\text{gain} \times \text{bandwidth} = \text{constant}\)gain × bandwidth = constant

Front: DEFINITION
Define: Photodiode.
Back: A diode used in reverse bias, in which absorbed photons free electron-hole pairs so that the reverse current, the photocurrent, is proportional to the intensity of the light.

Front: SPOT THE ERROR
Say what is wrong with this claim: Digital signals survive long distances because they are transmitted at higher power.
Back: Transmitted power is beside the point, and digital links usually use less of it. Two levels with a threshold between them leave a margin for noise, and a repeater regenerates each pulse as a new clean one, throwing the accumulated noise away.

Front: SPOT THE ERROR
Say what is wrong with this claim: A tuned circuit responds at one frequency and rejects everything else.
Back: It passes a band, not a line. The response falls to 1/√2\(1/\sqrt{2}\)1/√(2) of the peak a half bandwidth either side of f_0, and f_B = f_0/Q\(f_{B} = f_{0}/Q\)f_B = f_0/Q, so a real signal with its own spread of frequencies needs the band wide enough to carry it.

Front: DEFINITION
Define: Cut-off frequency of an RC filter.
Back: The frequency at which the reactance equals the resistance, so the output has fallen to 1/√2\(1/\sqrt{2}\)1/√(2), about 0.71, of its full value.

Front: DEFINITION
Define: Half-adder.
Back: A circuit that adds two bits: an EOR gate on the two inputs gives the sum and an AND gate on the same two inputs gives the carry.

Front: DEFINITION
Define: Gain-bandwidth product.
Back: The constant product of closed-loop gain and bandwidth for a given op-amp, so a gain raised by a factor of ten cuts the bandwidth by the same factor.

Front: RECALL
Explain why the currents add at the virtual earth.
Back: The inverting input sits at 0 V, so each input resistor carries V/R regardless of the others, and since the op-amp inputs draw no current every one of those currents flows on through the feedback resistor.

Front: DEFINITION
Define: Hall voltage.
Back: The steady pd produced across a current-carrying slab, at right angles to both the current and an applied magnetic field, and proportional to the flux density at constant current.

Front: DEFINITION
Define: Bandwidth of a resonant circuit.
Back: The width in frequency between the two points either side of the peak at which the current has fallen to 1/√2\(1/\sqrt{2}\)1/√(2) of its maximum, where the power delivered is half its peak.

Front: EQUATION · NOT ON THE DATA SHEET
Frequency after n dividing stages:
f_out = ?\(f_{out} = \, ?\)f_out = ?
Back: f_out = f_in2^n\(f_{out} = \frac{f_{in}}{2^{n}}\)f_out = f_in/2^n