Glossary of EE Terms

Acceleration is the change in linear velocity.

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.

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.

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.)

See Adjacent Channel Leakage Ratio (ACLR).

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.

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.

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.

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 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.

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

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

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.

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

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

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

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