电子工程术语表.doc

Glossary of EE termsAccelerationAcceleration is the change in linear velocity.AccelerometerAn accelerometer is a sensor that measures acceleration.Acquisition TimeThis 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 FilterAn 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.ADIsimADCThe 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 FFTs 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 ImagingThis is a technique, commonly applied to Direct Digital Synthesis (DDS), for using intentional aliasing as a source of high-frequency signals.AliasingIn a sampled data system, the analog input must be sampled at a rate of FS2FA 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.AmplifierAn 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 ModulationAmplitude 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 BandwidthThe 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 - CTAThis 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 GroundIn 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 SensorAn analog output sensor provides a voltage that is proportional to its input stimulus.Analog SignalsAnalog 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 AccelerationAngular acceleration is the rate of change of angular velocity over time.Angular DisplacementAngular displacement is the relative change in angular position.Angular VelocityAngular velocity is the rate of change of angular displacement with respect to time.Aperture DelayThe delay between the 50% point of the rising edge of the ENCODE command and the instant at which the analog input is sampled.Aperture JitterUncertainty, 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 UnitArithmetic Logic Unit (ALU) is the core of a digital processor. AsynchronousA 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 UnionAudio Engineering Society/European Broadcast Union (AES/EBU) is a standard for digital audio signal transmission. It is officially known as AES3.AutocorrelationMultiplication of a signal with a time-delayed replica of itself.Automatic Frequency SweepAn implementation of DDS where the output frequency is automatically swept across a band of frequencies. This is particularly useful in radar applications.Automatic Gain ControlAutomatic 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 ControlAutomatic Level Control is similar to automatic gain control. It is more commonly applied to audio systems and is often for speaker protection. A-WeightingA-weighting is a special noise weighting filter applied to noise measurements to better approximate human perception of low-level noise. Back ChamberThe back chamber is the enclosed air volume behind the microphone element.BackplateThe backplate is the stationary part of the condenser.Bandwidth1 - BWFrequency at which the output falls to 2/2 of the maximum value.Base StationThe central transmitter in a communications system that acts as the cell hub for communicating with handsets and/or mobile units.BasebandThe frequency bandwidth of the fundamental signal of interest, i.e., the voice, audio, or video signal bandwidth within a communication system.Baud RateThe speed at which data is transmitted measured in symbols-per-second.Bias Voltage, VbiasThis is the voltage supplied to the microphone backplate.Bit RateThe rate of transfer of information necessary to insure satisfactory reproduction of the information at the receiver.Cable TelephonyThis is the idea of using digital communications techniques to provide enhanced home telephone service via the exisiting home cable-TV connections. The bandwidth of cable is high enough to simultaneously support interactive cable-TV, telephone communications, and on-line data services. In this scenario, the cable connection becomes the primary link to the information highway vs. twisted pair telephone wire or a wireless connection.Carrier to Noise Ratio (CNR)SNR measured relative to a modulated carrier; may be defined in a specific frequency band depending on the transmission standard.ChipA single frequency output from a frequency hopping signal source. Chip RateIn spread spectrum systems, this is the rate at which the pseudo-random noise code is applied. In frequency hopping systems, chip rate is the inverse of the dwell time which the output frequency occupies a single carrier frequency. Also called chipping rate. ChirpPulsed frequency modulation scheme in which a carrier is swept over a wide frequency band during a given pulse interval. Clock Pulse Width (Latch Pulse Width)Clock Pulse Width is the minimum amount of time that the Clock pulse should be left in the logic 1 state to achieve rated performance. ComparatorOn chip comparator allows square wave generation for clocking purposes. Complex Image RejectionIn a traditional two-part upconversion, two images are created around the second IF frequency. These images are redundant and have the effect of wasting transmitter power and system bandwidth. By placing the real part of a second complex modulator in series with the first complex modulator, either the upper or lower frequency image near the second IF can be rejected. Complex ModulationThe process of passing the real and imaginary components of a signal through a complex modulator (transfer function = ejt = cos t + jsin t) and realizing real and imaginary components on the modulator output. Conversion Speed (Rate)The number of repetitive conversions per second for a full-scale change to specified resolution and linearity. Coriolis ForceWhen an object is moving in a periodic fashion (either oscillating or rotating), rotating the object in an orthogonal plane to its periodic motion causes a translational force in the other orthogonal direction. Gyroscopes measure angular rate by measuring the Coriolis Force generated when an internal vibrating mass is rotated.Cross-correlationThe degree of agreement between two unlike signals.D/A Converter (also D/A or DAC)Short for digital-to-analog converter, this is a device that changes a digitally-coded word into its equivalent quantized analog voltage or current. Just like the A/D device, there are very high-speed D/As available, capable of converting at data rates up to 1 GHz.dB FSThese are decibels relative to full scale amplitude (digital microphones)dB SPLSound pressure level in decibel, relative to 20 Pa (20 Pa = 0 dB SPL, 1 Pa = 94 dB SPL).dBAdBA are decibels A-weighted.dBVA decibel relative 1V reference (1V = 0dBV)Dead ReckoningDead Reckoning is a method of determining position using a combination of previous position, direction, and acceleration. A gyroscope can be used to measure rate of rotation, which is integrated once to obtain heading information. An accelerometer can be used to measure acceleration, which is integrated twice to obtain distance traveled.Degrees of FreedomDegrees of freedom (DoF) are the set of displacements and rotations along which an object can move. 6 degrees of freedom (x, y, z translational; pitch, roll, yaw rotational) are sufficient to fully define motion in free space.DiaphragmA diaphragm is the same as a membrane. It is the moving part of the condenser.Differential Analog Input Voltage RangeThe peak to peak differential voltage that must be applied to the converter to generate a full scale response. Peak differential voltage is computed by observing the voltage on a single pin and subtracting the voltage from the other pin, which is 180 degrees out of phase. Peak to peak differential is computed by rotating the inputs phase 180 degrees and taking the peak measurement again. Then the difference is computed between both peak measurements. Digital Downconversion (also direct-IF-to-digital conversion)This refers to a demodulation technique for sampling an intermediate frequency (IF) signal with a wide-bandwidth A/D whose sampling rate is equivalent to the local oscillator frequency ( IF frequency). In this super-Nyquist application, the A/D serves as the mixer stage and its digital output data is a beat frequency; the modulation data can be recovered with a DSP stage. Digital FilteringThe process of smoothing, spectrally shaping, or removing noise from a signal has traditionally been accomplished with analog components. With the advent of high-speed DSP products, now filtering can effectively and economically be accomplished in the digital domain. Digital filters are basically mathematical functions that are performed on the digital data stream and their characteristics can be altered under software control, which adds to their overall flexibility. Finite Impulse Response (FIR) and Infinite Inpulse Response (IIR) are examples of digital filter functions. Digital Output SensorA digital output sensor provides a discrete binary code that is proportional to its input stimulus.Digital Potentiometer - DigiPOT, VR, Variable ResistorThe Digital Potentiometer is an integrated circuit that performs the same resistance adjustment as a mechanical trimmer or Rheostat. In addition, it can be configured to perform the three-terminal mechanical potentiometer voltage divider function. Digital Potentiometers are known by several abbreviated names: E2POT, DACPOT, VR, variable resistor, RDAC, Rheostat, etc. Digital to Analog Converter (DAC, D/A Converter)An digital to analog converter is a device that changes a digitally coded word into its equivalent quantized analog voltage or current. Direct Digital Synthesis (DDS)A process by which you can digitally generate a frequency-agile, highly-pure sinewave, or arbitrary waveform, from an accurate reference clock. The digital output waveform is typically tuned by a 32-bit digital word that allows sub-Hz frequency agility. The DDSs frequency output is normally reconstructed with a high-speed, high- performance D/A to generate an analog output signal. The ability to add internal functions such as phase modulation, amplitude modulation, digital filtering, and I&Q outputs, are making DDS devices attractive for digital communication applications. They serve in capacities such as modulators, local oscillators, and clock detect/recovery circuits. DirectionalityDirectionality is the way a microphone responds to sounds coming from different directions. There are three basic types of microphones by directionality: Omnidirectional, or Omni responds equally to sounds coming from all directions Unidirectional responds primarily to sounds coming from one direction. Most common unidirectional microphones are cardioid microphones. Bi-directional, or Figure-eight responds to sounds coming from two opposite directions, with a null in between. Note: all ADI microphone models are Omnidirectional.DitherThe technique of adding controlled amounts of noise to a signal to improve overall system loop control, or to smear quantizing error in an A/D converter application. Double TapA double tap refers to two taps in close succession.Effective Number of Bits (ENOB)The effective number of bits (ENOB) is calculated from the measured SNR based on the equation:EINEIN stands for Equivalent Input Noise, the noise created by the microphone expressed as an external noise source placed at the microphones input.Encode Pulse Width (Duty Cycle)Pulse width high is the minimum amount of time that the ENCODE pulse should be left in logic 1 state to achieve rated performance; pulse width low is the minimum time ENCODE pulse should be left in low state. At a give clock rate, these specs define an acceptable Encode duty cycle. Fast Fourier Transform (FFT)Fast Fourier Transform is a computationally efficient mathematical technique that converts digital information from the time domain to the frequency domain for rapid spectral analysis. FFTs generally use a time weighting function to compensate for data records with a non-integer number of samples; some popular weighting functions are Hanning Window and 4-term Blackman-Harris.FIFOFIFO refers to a First-In, First-Out memory stack. Data points are processed in the same order in which they are stored. Having a FIFO built in to a sensor provides a data storage buffer that can be used to reduce the resources required by the host processor.Flash ConverterFlash A/D Converters are the fastest type of ADC and use large numbers of comparators. An N-bit flash ADC consists of 2N resistors and 2N-1 comparators. Free-FallFree-fall is the state of motion with no acceleration other than acceleration due to gravity.Frequency Hopping SystemCarrier frequency shifting in discrete increments in a pattern dictated by a code sequence. The transmitter jumps from frequency-to-frequency within some predetermined set: the order of frequency hops is determined by a code sequence, which, in turn, is detected and followed by the receiver. Frequency Shift KeyingA modulation scheme that shifts between two frequencies to represent a 1 or 0 state of data transmission. Full Scale Error - VWFSEIn the voltage divider mode, this is the error in the RDAC output voltage with all 1s loaded to the RDAC. Ideally the output voltage, with all 1s loaded to the RDAC registers, should be VA. The error is expressed in LSBs. Full Scale Input PowerFull Scale Power is expressed in dBm. It is computed using the followin