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AD669BR Folha de dados(PDF) 5 Page - Analog Devices |
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AD669BR Folha de dados(HTML) 5 Page - Analog Devices |
5 / 12 page AD669 REV. A –5– DEFINITIONS OF SPECIFICATIONS INTEGRAL NONLINEARITY: Analog Devices defines inte- gral nonlinearity as the maximum deviation of the actual, ad- justed DAC output from the ideal analog output (a straight line drawn from 0 to FS–1 LSB) for any bit combination. This is also referred to as relative accuracy. DIFFERENTIAL NONLINEARITY: Differential nonlinearity is the measure of the change in the analog output, normalized to full scale, associated with a 1 LSB change in the digital input code. Monotonic behavior requires that the differential linearity error be within ±1 LSB over the temperature range of interest. MONOTONICITY: A DAC is monotonic if the output either increases or remains constant for increasing digital inputs with the result that the output will always be a single-valued function of the input. GAIN ERROR: Gain error is a measure of the output error be- tween an ideal DAC and the actual device output with all 1s loaded after offset error has been adjusted out. OFFSET ERROR: Offset error is a combination of the offset errors of the voltage-mode DAC and the output amplifier and is measured with all 0s loaded in the DAC. BIPOLAR ZERO ERROR: When the AD669 is connected for bipolar output and 10 . . . 000 is loaded in the DAC, the devia- tion of the analog output from the ideal midscale value of 0 V is called the bipolar zero error. DRIFT: Drift is the change in a parameter (such as gain, offset and bipolar zero) over a specified temperature range. The drift temperature coefficient, specified in ppm/ °C, is calculated by measuring the parameter at TMIN, 25 °C and T MAX and dividing the change in the parameter by the corresponding temperature change. TOTAL HARMONIC DISTORTION + NOISE: Total har- monic distortion + noise (THD+N) is defined as the ratio of the square root of the sum of the squares of the values of the har- monics and noise to the value of the fundamental input fre- quency. It is usually expressed in percent (%). THD+N is a measure of the magnitude and distribution of lin- earity error, differential linearity error, quantization error and noise. The distribution of these errors may be different, depend- ing upon the amplitude of the output signal. Therefore, to be the most useful, THD+N should be specified for both large and small signal amplitudes. SIGNAL-TO-NOISE RATIO: The signal-to-noise ratio is de- fined as the ratio of the amplitude of the output when a full- scale signal is present to the output with no signal present. This is measured in dB. DIGITAL-TO-ANALOG GLITCH IMPULSE: This is the amount of charge injected from the digital inputs to the analog output when the inputs change state. This is measured at half scale when the DAC switches around the MSB and as many as possible switches change state, i.e., from 011 . . . 111 to 100 . . . 000. DIGITAL FEEDTHROUGH: When the DAC is not selected (i.e., CS is held high), high frequency logic activity on the digi- tal inputs is capacitively coupled through the device to show up as noise on the VOUT pin. This noise is digital feedthrough. THEORY OF OPERATION The AD669 uses an array of bipolar current sources with MOS current steering switches to develop a current proportional to the applied digital word, ranging from 0 mA to 2 mA. A seg- mented architecture is used, where the most significant four data bits are thermometer decoded to drive 15 equal current sources. The lesser bits are scaled using a R-2R ladder, then ap- plied together with the segmented sources to the summing node of the output amplifier. The internal span/bipolar offset resistor can be connected to the DAC output to provide a 0 V to +10 V span, or it can be connected to the reference input to provide a –10 V to +10 V span. SPAN/ BIP OFF AGND DGND REF IN REF OUT VOUT LDAC DB15 (MSB) (LSB) DB0 CS L1 –VEE +VCC +VLL 16-BIT LATCH 10k AMP AD669 22 7 6 5 23 27 28 10V REF 2 14 3 26 24 10k 10.05k 16-BIT LATCH 16-BIT DAC 25 Figure 2. AD669 Functional Block Diagram ANALOG CIRCUIT CONNECTIONS Internal scaling resistors provided in the AD669 may be con- nected to produce a unipolar output range of 0 V to +10 V or a bipolar output range of –10 V to +10 V. Gain and offset drift are minimized in the AD669 because of the thermal tracking of the scaling resistors with other device components. UNIPOLAR CONFIGURATION The configuration shown in Figure 3a will provide a unipolar 0 V to +10 V output range. In this mode, 50 Ω resistors are tied between the span/bipolar offset terminal (Pin 26) and VOUT (Pin 25), and between REF OUT (Pin 28) and REF IN (Pin 27). It is possible to use the AD669 without any external components by tying Pin 28 directly to Pin 27 and Pin 26 directly to Pin 25. Eliminating these resistors will increase the gain error by 0.25% of FSR. OUTPUT GND LDAC DB15 (MSB) (LSB) DB0 CS L1 –V EE +V CC +V LL 16-BIT LATCH 10k AMP AD669 22 7 6 5 23 27 28 10V REF 2 1 4 3 10k 10.05k 16-BIT LATCH 16-BIT DAC 26 25 24 R1 50 Ω R2 50 Ω Figure 3a. 0 V to +10 V Unipolar Voltage Output |
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Descrição semelhante - AD669BR |
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