Glossary Terms and Definitions Beginning with the Letter C

Maxim offers both regulated and non-regulated charge pumps, as well as ICs with on-board charge pumps to boost internal voltages.

See: DC-DC Converter Tutorial

2. Encoding element, in Direct-Sequence Spread Spectrum systems.

This is achieved by biasing both transistors so they conduct when the signal is close to zero (the point where class B amplifiers introduce non-linearities). The transistors transition to class B operation for large excursions.

So, for small signals both transistors are active, acting like a class A amplifier. For large signal excursions, only one transistor is active for each half of the waveform, acting like a class B amplifier.

Class B amplifiers are much more efficient than class A amplifiers, but have high distortion due to the crossover point when the two transistors transition from on to off.

Class C amps are very efficient because the transistors are off most of the time and when they are on, they are in full conduction. They deliver high distortion and are often used in RF circuits, where tuning circuits restore some of the original signal and reduce distortion. They are also used in low-fidelity applications where the distortion is not important, such as a siren speaker driver.

Class D amplifiers are highly efficient (often up to 90% or higher) since the output transistors are either fully turned on or off during operation. This completely eliminates the use of the linear region of the transistor which is responsible for the inefficiency of other amplifier types. Modern Class D amplifiers achieve fidelity comparable to class AB.

Class G amplifiers are more efficient than class AB amplifiers since they use the maximum supply voltage only when required, while a class AB amplifier always uses the maximum supply voltage.

Class H amplifiers are generally more complex than other designs, with extra control circuitry required to predict and control the supply voltage.

• powered up (power applied)
• powered down (power removed)
• brought out of shutdown (power applied previously)
• forced into shutdown (power still applied)

For more information and illustrations, see:

• "Jitter Overview" in HFAN-04.3.0: Jitter Specifications Made Easy; and
• An Introduction to Jitter in Communications Systems.

See the tutorial, Understanding Common-Mode Signals.

Examples: In NTSC television, a 3.579545MHz color subcarrier is quadrature-modulated by two color-difference signals and added to the luminance signal. The PAL television standard uses a subcarrier frequency of 4.43362MHz.

See: Video Basics

In an ideal differential amp, the common-mode element is cancelled out, since the differential (+ and -) inputs should subtract out the identical components. A measurement of the actual ability to do this is called the Common Mode Rejection Ratio, or CMRR.

See the tutorial, Understanding Common-Mode Signals.

A signal is passed through a non-linear transformation prior to transmission. A reverse of this transformation occurs at reception. The transformation is such that quiet portions are boosted and loud portions reduced. Noise is reduced because the quiet signals are louder, compared to the noise in the transmission channel.

Used in digital, PCM, transmissions as well as analog applications. Dolby is a common example of a compander-based noise reduction system.

When described that way, the comparator resembles a 1-bit ADC.

A simple comparator can be achieved using an op amp without negative feedback. Its high voltage gain enables it to resolve very small differences in input voltage. But op amps used this way are generally slower than comparators and lack special features, such as hysteresis and internal references.

Application Note 886: Selecting the Right Comparator goes into more details on how comparators work, their specifications, common comparator features, and how to select a comparator that best fits your needs.

It is usually achieved by an SCR or other silicon device, or by a mechanical shorting device.

Probably named for the concept of using a big metal bar to mechanically provide the short circuit, as might be used done in a high-current application; or from the appearance of a crowbar circuit's I-V curve.

See: Protection and Isolation products.