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Subelement E6
Section E6E
Analog ICs: MMICs, CCDs, Device packages
Which of the following is true of a charge-coupled device (CCD)?
  • Its phase shift changes rapidly with frequency
  • It is a CMOS analog-to-digital converter
  • Correct Answer
    It samples an analog signal and passes it in stages from the input to the output
  • It is used in a battery charger circuit

A charge-coupled device (CCD) samples an analog signal and passes it in stages from the input to the output.

A CCD is a chain of capacitors separated by MOSFET transistors. Both the capacitors and the MOSFETs are made in metal-oxide semiconductor material itself. The MOSFETs are used to transfer the voltage from one capacitor to another in the chain until it reaches the output, where it can be converted to digital.

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Which of the following device packages is a through-hole type?
  • Correct Answer
  • PLCC
  • Ball grid array
  • SOT

DIP stands for Dual In-line Package, referring to the two rows of pins. It is a common type of through-hole integrated circuit and is frequently used in prototyping because it fits neatly into a solderless breadboard.

Tip: You take a DIP in a swimming HOLE.

"D" for device, "D" for DIP

The stereotypical cartoon image of a "computer chip" is actually a DIP.

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Which of the following materials is likely to provide the highest frequency of operation when used in MMICs?
  • Silicon
  • Silicon nitride
  • Silicon dioxide
  • Correct Answer
    Gallium nitride

From Wikipedia:

Gallium nitride (GaN) is a binary III/V direct bandgap semiconductor commonly used in bright light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV affords it special properties for applications in optoelectronic[4][5], high-power and high-frequency devices. For example, GaN is the substrate which makes violet (405 nm) laser diodes possible, without use of nonlinear optical frequency-doubling.

Its sensitivity to ionizing radiation is low (like other group III nitrides), making it a suitable material for solar cell arrays for satellites. Military and space applications could also benefit as devices have shown stability in radiation environments.[6] Because GaN transistors can operate at much hotter temperatures and work at much higher voltages than gallium arsenide (GaAs) transistors, they make ideal power amplifiers at microwave frequencies. (Emphasis added)

An easy way to remember this one is it is the only non-Silicon answer.

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Which is the most common input and output impedance of circuits that use MMICs?
  • Correct Answer
    50 ohms
  • 300 ohms
  • 450 ohms
  • 10 ohms

MMICs (or "mimics") are Monolithic Microwave Integrated Circuits designed for use in the 300 MHz to 300 GHz frequency range. They are typically designed to have a characteristic impedance of 50 ohms at both the input and output. This allows them to be cascaded in a circuit without the need for additional impedance matching components. This impedance also matches most up with most microwave test equipment allowing for easier connections.

Hint: MMIC's "mimic" the common impedance of your transmission line

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Which of the following noise figure values is typical of a low-noise UHF preamplifier?
  • Correct Answer
    2 dB
  • -10 dB
  • 44 dBm
  • -20 dBm

Noise figure (NF) is the ratio between the noise the receiver produces and the theoretical minimum noise for a perfect receiver:

\[\text{noise figure}=\frac{\text{receiver noise}}{\text{theoretical minimum noise}}\]

Since it is a ratio, it is measured in dB. We can thus eliminate both values given in dBm.

Real-world receivers can never be as good as a perfect receiver, so the noise figure ratio will always be greater than unity. If this ratio is strictly positive, we cannot have negative values.

The only remaining answer is 2 dB.

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What characteristics of the MMIC make it a popular choice for VHF through microwave circuits?
  • The ability to retrieve information from a single signal even in the presence of other strong signals
  • Plate current that is controlled by a control grid
  • Nearly infinite gain, very high input impedance, and very low output impedance
  • Correct Answer
    Controlled gain, low noise figure, and constant input and output impedance over the specified frequency range

Monolithic Microwave Integrated Circuit (MMIC) is a type of "black box" amplifier that makes design simpler because its characteristics are well-known and it has input and output ports with a 50 ohm impedance. It is essentially a "LEGO brick" that can be plugged into a circuit to get a fixed quantity of gain without any additional design work (in theory, anyway).

"Nearly infinite gain" is a characteristic of op-amps, which require supporting circuitry to control that infinite gain and do something meaningful with it. Plates and grids are parts of a vacuum tube, which also needs supporting circuitry to bias it into a useful mode of operation. The remaining answer is non-technical and doesn't make much sense.


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Which of the following is typically used to construct a MMIC-based microwave amplifier?
  • Ground-plane construction
  • Correct Answer
    Microstrip construction
  • Point-to-point construction
  • Wave-soldering construction

Microstrip transmission lines consist of a conductive strip of width "W" and thickness "t" and a wider ground plane, separated by a dielectric layer (a.k.a. the "substrate") of thickness "H" as shown in the figure below. Microstrip is by far the most popular microwave transmission line, especially for microwave integrated circuits and MMICs. The major advantage of microstrip over stripline is that all active components can be mounted on top of the board.

TIP: MICROwave = MICROstrip


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How is voltage from a power supply normally furnished to the most common type of monolithic microwave integrated circuit (MMIC)?
  • Correct Answer
    Through a resistor and/or RF choke connected to the amplifier output lead
  • MMICs require no operating bias
  • Through a capacitor and RF choke connected to the amplifier input lead
  • Directly to the bias voltage (VCC IN) lead

An RF choke allows the DC current to pass from the supply into the amplifier while blocking the RF from escaping the other direction. This is a common configuration due to the types of circuitry inside the MMIC (Monolithic microwave integrated circuit), while a separate "VCC IN" is very uncommon.

All amplifiers require bias -- you can't make more power from less power without that power coming from somewhere. And you can't supply DC power through a capacitor because capacitors block DC.

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Which of the following component package types would be most suitable for use at frequencies above the HF range?
  • TO-220
  • Axial lead
  • Radial lead
  • Correct Answer
    Surface mount

Each lead or pin of an electronic device adds a parallel capacitance and a series inductance to that connection.

Surface Mount Devices (SMD) generally have shorter pins or no leads at all, which helps reduce both the capacitance and inductance associated with connections to the device. At VHF and above, these capacitive and inductive reactances may become significant, so it helps to minimize them.

Hint: stove 'range' as a surface

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What is the packaging technique in which leadless components are soldered directly to circuit boards?
  • Direct soldering
  • Virtual lead mounting
  • Stripped lead
  • Correct Answer
    Surface mount

Surface mount components don't have leads attached - they don't install on a circuit board by putting leads through holes or running leads from a component to another component or connection point. Instead, surface mount components are soldered flat against the circuit board, without leads.

The name for this type of component, is, "Surface mount" and it found in virtually all modern miniaturized circuit boards.

The surface mount component has no leads - it is soldered directly to the circuit board.

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What is a characteristic of DIP packaging used for integrated circuits?
  • Package mounts in a direct inverted position
  • Low leakage doubly insulated package
  • Two chips in each package (Dual In Package)
  • Correct Answer
    A total of two rows of connecting pins placed on opposite sides of the package (Dual In-line Package)

The abbreviation "DIP" stands for Dual In-line Package. DIP is a common package type for a variety of electronic components. The package is rectangular in shape with two parallel rows of pins along opposite sides of the package. The pins extend downwards from the edge of the package so they can be soldered into a through-hole PC board or inserted into a socket. The package material for DIP components is usually plastic, but ceramic packaging is sometimes used for high-power components. Surface mount technology (SMT) is rapidly replacing DIP and other through-hole technologies due to its smaller footprint and higher pin densities.

The easiest way to remember what a DIP is is to recall the usual stereotypical "computer chip" depiction of a little black box with two rows of pins.

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Why are high-power RF amplifier ICs and transistors sometimes mounted in ceramic packages?
  • High-voltage insulating ability
  • Correct Answer
    Better dissipation of heat
  • Enhanced sensitivity to light
  • To provide a low-pass frequency response

The "better" in this answer is as compared to a plastic or epoxy package, neither of which conduct heat as well as ceramic packages. Metal would be be better, but it would conduct electricity as well as heat, so it would short out the RF amplifier IC or transistor. Plastic, epoxy and ceramic packages can be built to not conduct electricity, but of those choices, ceramic has the best dissipation of heat.

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