Glossary of EE Terms

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  • Acceleration

    Acceleration is the change in linear velocity.

  • Accelerometer

    An accelerometer is a sensor that measures acceleration.

  • Acquisition Time

    This term relates to sampling A/Ds, which use a track/hold amplifier on the input to acquire and hold (to a specific tolerance) the analog input signal. Acquisition time is the time required by the T/H amplifier to settle to its final value after it is placed in the track mode.

  • Active Filter

    An active filter is one that uses active devices such as operational amplifiers to synthesize the filter response function. This technique has an advantage at high speeds because the need for inductors (with their poor high-frequency characteristics) is eliminated.

  • ADC Architecture

    Pipeline – An architecture consisting of a series of conversion stages that provide sufficient resolution overlap to correct for flash errors in the preceding stage. The quantized outputs from each stage are combined into a final N-bit result in digital correction logic. The pipelined architecture permits the first stage to operate with a new input sample while the remaining stages operate with preceding samples.

    SAR – An architecture whereby an input sample-and-hold is placed in the hold mode, and an internal N-bit DAC is set to midscale. A comparator determines whether the SHA output is above or below the DAC output, and the result (bit 1, the most significant bit of the conversion) is stored in the successive approximation register (SAR). The SAR then sets the DAC to either ¼ scale or ¾ scale (depending on the value of bit 1), and the comparator makes the decision for bit 2 of the conversion. The result is stored in the register, and the process continues until the desired N-bits of conversion resolution are obtained.

    Sigma-Delta – An oversampling architecture consisting of a SHA, a subtracter stage, low-pass filter, a 1-bit DAC, and a sigma-delta modulator. When the analog input is sampled and held by to a SHA, the held output is subtracted from the output of the 1-bit DAC, which is set by filtering the difference signal, in turn feeding that to the comparator whose output sets the DAC. The duty cycle of the resulting digital pulse train contains highly precise conversion information. An oversampling digital filter (DSP) retrieves the digital output word.

  • ADC Gain Error

    The deviation of the last code transition, for example (111…110) to (111.111) from the ideal (VREF - 1 LSB) after the offset error is adjusted out. Gain error for an ADC does not include the reference error and is typically expressed as a percentage of full scale, or in LSBs.

  • ADIsimADC™

    The ADIsimADC tool is an aid to help in the selection of Analog to Digital Converters(ADCs, A/D Converters), perform evaluations and assist with troubleshooting. The tool uses typical data values to mathematically model the general behavior of the selected ADC. It allows a user to apply input signals, set encode (sample) rates and simulate FFT's on a selected a/d converter. It is useful for checking the SNR, SFDR, SINAD, THD, ENOB etc. of a selected ADC. Note: This tool does not fully model all aspects of an A to D and should not be used in place of actual hardware testing. Additional functions can be found using the full featured downloadable version of this tool. (For more information, please see the application note, AN-737 pdf.)

  • Adjacent Channel Leakage Ratio (ACLR)

    A ratio in dBc between the measured power within a channel relative to an adjacent channel.

  • Adjacent Channel Power Ratio (ACPR)

    See Adjacent Channel Leakage Ratio (ACLR).

  • Aliased Imaging

    This is a technique, commonly applied to Direct Digital Synthesis (DDS), for using intentional aliasing as a source of high-frequency signals.

  • Aliasing

    In a sampled data system, the analog input must be sampled at a rate of FS>2FA in order to avoid loss of data (Nyquist Theorem). Adhering to the Nyquist Theorem prevents in-band "alias" signals, which are beat frequencies between the analog signal and the sampling clock that inherently occur at FS± FA. As the Nyquist limit is exceeded, the aliased signals move within the band of the analog input (DC - FS/2) and create distortion. Likewise, high-frequency noise can also be aliased into the input signal range, which mandates low-pass filtering, or anti-alias filtering, on the input of a sampled system. See also Aliased Imaging.

  • Amplifier

    An amplifier is an electronic device which produces a larger replica of its analog input (in voltage and/or current) at the output. There are several amplifier types, the most common being the operational amplifier.

  • Amplitude Modulation

    Amplitude Modulation (AM) is when a signal with information to be transmitted varies the strength of a carrier signal (typically much higher frequency) to allow the information to be sent over a medium such as radio waves.

  • Analog Bandwidth

    The analog input frequency at which the spectral power of the fundamental frequency (as determined by the FFT analysis) is reduced by 3 dB.

  • Analog Crosstalk - CTA

    This is the ratio of the amplitude of the signal at the wiper of one RDAC to a sine wave applied to terminal A of another RDAC. It is measured in dBs.

  • Analog Frequency

    The analog frequency is the frequency of oscillation of the analog waveform for a given ADC or DAC. For an ADC, this is the input signal; for a DAC, this is the output signal.

  • Analog Ground

    In high-speed data acquisition applications, system ground is generally physically separated into "analog" and "digital" grounds in an attempt to supress digital switching noise and minimize its effect on noise-sensitive analog signal processing circuitry. Input signal conditioners, amplifiers, references, and A/D converters are usually connected to analog ground.

  • Analog Output Sensor

    An analog output sensor provides a voltage that is proportional to its input stimulus.

  • Analog Signals

    Analog Signals are continuously varying electrical signals (current or voltage) that represent measurable quantities in the real world. Signals that humans can see, hear, or feel, including, sound, light, temperature, pressure, current or voltage, are called ‘analog signals.’ In electronic circuits: analog voltages and currents are analogous (similar to) to the real-world signals that they represent. For example, a temperature transducer provides an analog output signal that varies in direct proportion to the temperature it is exposed to; a higher temperature gives a higher voltage.

  • Analog to Digital Converter (ADC, A/D Converter)

    This device converts real world analog signals into a digital format that can be processed by a computer.

  • Angular Acceleration

    Angular acceleration is the rate of change of angular velocity over time.

  • Angular Displacement

    Angular displacement is the relative change in angular position.

  • Angular Velocity

    Angular velocity is the rate of change of angular displacement with respect to time.

  • Aperture Delay

    The delay between the 50% point of the rising edge of the ENCODE command and the instant at which the analog input is sampled.

  • Aperture Jitter

    Uncertainty, or sample-to-sample of variation, in the aperture delay time. Aperture jitter is a source of error in a sampling system, and it determines the maximum slew rate limitation of the sampled analog input signal for a given system resolution. A digital communications application that allows for up to 7 MBPS of Subscriber Line data transmission capacity over conventional twisted pair telephone lines. ADSL is a contender for a major piece of the "information highway" pie and it promises to deliver telephone, TV, and data services to your home over the existing telephone line.

  • Aperture Uncertainty (Jitter)

    The sample-to-sample variation in aperture delay.

  • Arithmetic Logic Unit

    Arithmetic Logic Unit (ALU) is the core of a digital processor.

  • Asynchronous

    A multiplexing and switching technique that organizes information Transfer Mode into fixed-length cells consisting of an identification header field and an information field. The transfer rate is asynchronous in that the recurrence of cells depends on the instantaneously required bit rate.

  • Audio Engineering Society/European Broadcast Union

    Audio Engineering Society/European Broadcast Union (AES/EBU) is a standard for digital audio signal transmission. It is officially known as AES3.

  • Autocorrelation

    Multiplication of a signal with a time-delayed replica of itself.

  • Automatic Frequency Sweep

    An implementation of DDS where the output frequency is automatically swept across a band of frequencies. This is particularly useful in radar applications.

  • Automatic Gain Control

    Automatic gain control employs the use of feedback to maintain the output level of an amplifier within a min/max bounded range even when the input signal can extend over a very wide dynamic range. ACG is commonly used in RF, radar, audio, and ultrasound systems.

  • Automatic Level Control

    Automatic Level Control is similar to automatic gain control. It is more commonly applied to audio systems and is often for speaker protection.

  • A-Weighting

    A-weighting is a special noise weighting filter applied to noise measurements to better approximate human perception of low-level noise.


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