Electronics Engineering

Satellites use Microwaves to send signals.

Tunnel diodes are usually fabricated from germanium, gallium or gallium arsenide. These all have small forbidden energy gaps and high ion motilities. Silicon is not used in the fabrication of tunnel diodes due to low (Ip,I v)value.

A small tin dot is soldered or alloyed to a heavily doped pellet of n-type Ge, GaSb or GaAs. The pellet is then soldered to anode which is also used for heat dissipation. The cathode contact is connected to the tin dot via a mesh screen used to reduce inductance. The diode has a ceramic body and a hermetically sealing lid on top.

Both reproduce analog waveforms by switching between 2 values at a much higher rate than the signal itself changes.

• Pulse duration modulation is a synonym for pulse-width modulation or PWM. The switching frequency is usually constant, and the width or duration of the "high" state determines the output. For instance, if the width is 100%, it is always high, and produces the highest analog value possible. If the width is 50%, it spends half of its time high and half low, producing a halfway voltage. If the width is 0%, it stays low all the time, producing the lowest possible voltage.
• Pulse density modulation uses a feedback loop to track the analog output voltage, switching low when the output is too high and high when the output is too low.

To produce a 50% voltage, with an equivalent resolution of 8-bits, a PWM waveform will turn on for 128 clock cycles and then off for 128 cycles. A PDM waveform with the same clock rate would alternate between on and off every other cycle. The average of both waveforms is 50%, but the PDM waveform switches more often. For 100% output or 0% output, they are identical.

No. Ohm's law is applicable in every case. That's why its called a "law". Its just that the calculation becomes more complex as parasitic effects creep in, such as at high frequency, voltage, or current.

ANOTHER ANSWER

Ohm's Law applies in so few circumstances that it hardy qualifies as a law at all! One can validly question whether Ohm's Law should be taught these days!

Ohm's Law is a law of constant proportionality. It ONLY applies to those conductors and other components whose ratio of voltage to current remains constant for variations in voltage. It does not apply to conductors or components whose ratio of voltage to current changes for variations in voltage. So Ohm's Law is not a universal law.

Conductors and other devices which obey Ohm's Law are termed 'linear' or 'ohmic'; those that do not (the majority, in fact!) are termed 'non-linear' or 'non-ohmic'. Some, but not all metals, are linear (e.g. tungsten is not) and most electronic components such as diodes, electrolytes, and gases are non-linear.

The ratio of voltage to current is, of course, resistance. And we can use this ratio to determine what the resistance of a device happens to be for that particular ratio, at any given voltage, even for devices that do not obey Ohm's Law. For non-linear devices, the ratio continuously changes for variations in voltage.

So, it's questionably whether Ohm's Law should be 'law' at all, and one might wonder why we even bother to teach it!

It is quite incorrect to define Ohm's Law as, "resistance equals voltage divided by current", as this equation is derived from the definition of the ohm, and NOT from Ohm's Law -which makes absolutely no reference to resistance.

To oversimplify it the "operational amplifier" was originally designed to perform mathematical operations in electronic analog computers. The designer set the mathematical operation of each amplifier by designing its feedback network. Some operations that could be done were: addition, subtraction, constant multiplication/division, logarithm, exponentiation, variable multiplication/division by combining logarithm-addition/subtraction-exponentiation, integration, differentiation, absolute value, clipping, etc.

A "normal" amplifier was just designed to produce a certain amount of voltage or current gain.

Most semiconductors are elements with 4 valence electrons:

1. carbon as either diamond or nanotubes, still has process problems
2. silicon, most preferred now
3. germanium

There are also binary semiconductors made of alloys of elements with 3 & 5 valence electrons:

• gallium arsenide is used in some very high speed electronics
• aluminum indium gallium phosphide is used in some LEDs and solid state LASERs
• etc.

There are also less commonly used semiconductors used in special purpose applications:

• copper oxide used to be used in high voltage rectifiers in low cost vacuum tube electronics
• selenium is used in light sensitive drum in photocopiers and laserprinters
• lead sulfide (galena) used in crystal radios
• etc.

Integrator : One application for this device would be to keep a "running total" of radiation exposure, or dosage, if the input voltage was a proportional signal supplied by an electronic radiation detector. Nuclear radiation can be just as damaging at low intensities for long periods of time as it is at high intensities for short periods of time. An integrator circuit would take both the intensity (input voltage magnitude) and time into account, generating an output voltage representing total radiation dosage.

Another application would be to integrate a signal representing water flow, producing a signal representing total quantity of water that has passed by the flowmeter. This application of an integrator is sometimes called a totalizer in the industrial instrumentation trade.

Differentiator: Applications for this, besides representing the derivative calculus function inside of an analog computer, include rate-of-change indicators for process instrumentation. One such rate-of-change signal application might be for monitoring (or controlling) the rate of temperature change in a furnace, where too high or too low of a temperature rise rate could be detrimental. The DC voltage produced by the differentiator circuit could be used to drive a comparator, which would signal an alarm or activate a control if the rate of change exceeded a pre-set level.

In process control, the derivative function is used to make control decisions for maintaining a process at setpoint, by monitoring the rate of process change over time and taking action to prevent excessive rates of change, which can lead to an unstable condition. Analog electronic controllers use variations of this circuitry to perform the derivative function.