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Circuit Types Flashcards

1
Q

What’s a “latch” circuit?

A

Essentially a memory unit, used to temporarily store binary data.

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2
Q

How do you build a simple latch circuit?

A

Cross-couple 2 inverters, 2 nands, or 2 nors.

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3
Q

What’s a sequential circuit?

A

A time-dependent circuit, with a close relationship with the clock signal. A “clocked” circuit.

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4
Q

What’s a flip-flop, or “flop”?

A

“Sample and hold” circuit. Basic cell of a sequential circuit.

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5
Q

What are common examples of sequential circuits?

A

Counters, timers, SerDes (serializer/deserializer), state machines, shift registers, USB controllers

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6
Q

What are three common flavors of flip-flops?

A

D flip-flop or dff, toggle flip-flop, JK flip-flop

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7
Q

What’s a shift register?

A

Transfers data serially in a FIFO fashion.

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8
Q

What’s a longer name for the most common SRAM cell?

A

Six transistor single-port Static RAM cell

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9
Q

What does the equalization circuitry do?

A

Equalizes (calibrates) the bit lines while the word lines are off before the read cycle.

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10
Q

What are the two main types of memory modules? Describe them and give examples.

A
  1. Volatile memories. Require power supply to store data. SRAM and DRAM.
  2. Non-volatile memories. No power supply required to store. ROM, E2PROM and Flash memories.
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11
Q

What does E2PROM stand for?

A

Electrically erasable programmable read-only memory

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12
Q

What are three things that exclusive circuits are used for?

A
  1. Comparators
  2. Error correction circuits
  3. Adders
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13
Q

What does ECC stand for?

A

Error correction circuits

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14
Q

What are two ways that sequential circuits are triggered?

A
  1. Edge triggered

2. Level triggered

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15
Q

Draw a truth table for JK flip flop

A 
J = 0 K = 1, Q = 0
J = 1 K = 0, Q = 1
J = 1 K = 1, Q toggles
J = 0, K = 0, store previous
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16
Q

What does OD stand for?

A

Oxide definition layer, ndiff + pdiff

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17
Q

What does PLDD stand for?

A

Positive lightly doped diffusion

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18
Q

What’s the usual logic threshold (Vt)?

A

vdd / 2

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19
Q

When is an SRAM in “storage mode”?

A

When wl is off

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20
Q

What’s analogous to “complementary” in analogue circuits?

A

“differential pair”

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21
Q

What’s a “sense amplifier” or “sensamp”?

A

Reads SRAM via differentials. High-speed circuit.

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22
Q

What’s the difference between “static logic” and “dynamic logic”?

A

Static logic output comes from vdd or vss through solid path (transistors and wires).
Dynamic logic output comes from residual charges from previous operation. Sometimes requires a refresh circuit.

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23
Q

What’s “embedded memory”?

A

Memory inside a larger circuit.

24
Q

What’s the difference between “dummys” and “redundancy”?

A

Dummys solve edge effect (proximity effect), redundancy are spares.

25
Q

What’s “SDRAM” stand for?

A

Synchronous dynamic RAM.

26
Q

What’s “CAM” stand for?

A

Content addressable memory

27
Q

What makes up the ROM core?

A

Dynamic NORs

28
Q

What are the six steps of reverse engineering?

A
  1. Get to know basic layer combos that make up various devices.
  2. Differentiate PMOS from NMOS – look for nwell (or pwell), vdd and vss.
  3. Recognize shared diffusions,
  4. Identify finger-gates.
  5. Identify AND and OR configurations,
  6. Convert layout to device-level schematic first, then logic form if it exists.
29
Q

What are three ways to describe the function of a logic gate?

A
  1. Truth table
  2. Boolean equation
  3. Timing diagram
30
Q

What are the four common boolean operators?

A
  1. Bar means “not”
  2. Dot means “and”
  3. Plus means “or”
  4. Circle around plus means “xor”
31
Q
  1. What does PLL stand for?
  2. What does PDT stand for?
  3. What does VCO stand for?
A
  1. Phase Locked Loop
  2. Phase Detector
  3. Voltage Controlled Oscillator
32
Q

What does a PLL do?

A

Permits an external reference signal to control the frequency and the phase of an oscillator in the loop. The loop oscillator can be the same as, or a multiple of, the reference frequency.

33
Q

What are some applications of a PLL?

A
  1. Tracking filters
  2. FSK decoders
  3. FM stereo decoders
  4. Frequency synthesizers
  5. Frequency multipliers
  6. Clocking circuits
    Used in ICs for generation of local-oscillator frequencies in TV, FM tuners and various wireless circuits.
34
Q

What does a bias do?

A

Generates one or more constant very stable current and / or voltage points (outputs), under different operating and manufacturing variations. A quiet circuit.

35
Q

What are some common IO devices (circuits)?

A
  1. Bond(ing) pads
  2. Electro-Static Discharge devices
  3. Various buffers
  4. Level shifters
  5. Schmitt Triggers
  6. Oscillators
36
Q

What’s a bond pad?

A

Provides a place for soldering a wire between the die and the lead-frame on a die package.

37
Q

What connects a die to its package? What are they made of? How big are they?

A

Bond(ing) wires, made of aluminum or gold, diameters of 1 mil down to a few microns

38
Q

What are the wide metal traces leading away from a bond pad called?

A

Fillets

39
Q

What does ESD stand for?

A

Electro-static discharge

40
Q

What do ESD devices do?

A

Provide ESD charges with low resistance paths to vss and or vdd, which remove the charges before they reach CMOS input terminals.

41
Q

Why is the basic ESD device made of two diodes instead of just one?

A

One diode is better at handling excessively high voltages, the other excessively low ones. (More explanation needed here.)

42
Q

What’s another name for a buffer? What do buffers do?

A

“Large driver”. Designed to “source” and / or “sink” a large amount of current to handle heavy off-chip loads (large capacitance).

43
Q

What are some typical buffer types?

A
  1. Inverting or non-inverting buffer
  2. Open-source buffer
  3. Open-drain buffer
  4. Tri-state buffer (inverting or non-inverting)
  5. Bi-directional buffer (inverting or non-inverting)
44
Q

What are common ESD layout techniques?

A
  1. Double guard-rings for transistors.
  2. Recommended width for ESD power and ground
  3. More (recommended) distance between drain contact to poly spacing. Remove silicide.
  4. Drain diffusion corners must be chamfered if on the outside
45
Q

What do level shifter circuits do?

A

Solve voltage compatibility issues. Adjust (or compensate) for the voltage level (swing) of incoming foreign signals which have voltages lower than the threshold voltages (Vt) of receivers. Necessary when chips are operating from different power suppose and / or have different natures, such as analog vs. digital.

46
Q

What is a Schmitt Trigger circuit?

A

Reshapes noisy and / or slow rising or falling incoming signals. Uses hysteresis, a circuit design technique that splits the threshold of a logic gate into 2 levels of operating thresholds.

47
Q

What is a clock generator?

A

Consists of a precision oscillator which generates clock signals (continuous pulses). These pulses are used as a Time Base for most operations in a chip. Most operations are Timed and Synchronized by the clock circuit. High frequency and very noisy.

48
Q

What is a ring oscillator?

A

An odd number of inverters in a loop. Less precise clock pulse generation.

49
Q

What’s another name for an ESD circuit?

A

Input protection circuit

50
Q

What’s another name for a probe pad?

A

Test pad

51
Q

What’s a trim pad?

A

A pad used to burn out fuses.

52
Q

What’s a micromanipulator?

A

Used to adjust the position of a probe

53
Q

Do you need to remove passivation from probe pads? Why or why not?

A

No, because layer will not exist yet at time of probe.

54
Q

What’s a 3D chip? What kind of connections does it use?

A

Multiple dies stacked on top of each other. Uses “z-via” or “Through Silicon Via” TSV to connect them.

55
Q

What are common applications of two poly technology?

A

E2PROM and Flash

Layout (24 decks)

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