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ICL7134BKCJI Datasheet(PDF) 9 Page - Intersil Corporation |
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ICL7134BKCJI Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 16 page 9 Definition of Terms Nonlinearity - Error contributed by deviation of the DAC transfer function from a straight line through the end points of the actual plot of transfer function. Normally expressed as a percentage of full scale range or in (sub)multiples of 1 LSB. Resolution - It is addressing the smallest distinct analog out- put change that a D/A converter can produce. It is commonly expressed as the number of converter bits. A converter with resolution of n bits can resolve output changes of 2-n of the full-scale range, e.g. 2-n VREF for a unipolar conversion. Res- olution by no means implies linearity. Settling Time - Time required for the output of a DAC to settle to within specified error band around its final value (e.g. 1/2 LSB) for a given digital input change, i.e. all digital inputs LOW to HIGH and HIGH to LOW. Gain Error - The difference between actual and ideal analog output values at full-scale range, i.e., all digital inputs at HIGH state. It is expressed as a percentage of full-scale range or in (sub)multiples of 1 LSB. Feedthrough Error - Error caused by capacitive coupling from VREF to IOUT with all digital inputs LOW. Output Capacitance - Capacitance from IOUT terminal to ground. Output Leakage Current - Current which appears on IOUT terminal when all DAC register outputs are LOW. Detailed Description The ICL7134 consists of 14-bit primary DAC, two PROM controlled correction DACs, input buffer registers, and microprocessor interface logic (See Functional Block Diagram). The 14-bit primary DAC is an R-2R thin film resistor ladder with N-channel MOS SPDT current steering switches. Precise balancing of the switch resistances, and all other resistances in the ladder, results in excellent temperature stability. True 14-bit linearity is achieved by programming a floating poly- silicon gate PROM array which controls two correction DAC cir- cuits. A 6-bit gain correction DAC, or G-DAC, diverts up to 2% of the feedback resistor’s current to Analog GND and reduces the gain error to less than 1 LSB, or 0.006%. The 5 most significant outputs of the DAC register address a 31-word PROM array that controls a 12-bit linearity correction DAC, or C-DAC. For every combination of the primary DAC’s 5 most significant bits, a different C-DAC code is selected. This allows correction of superposition errors, caused by bit interaction on the primary resistor ladder’s current output bus and by voltage non-linearity in the feedback resistor. Superposition errors can- not be corrected by any method which corrects individual bits only, such as laser trimming. Since the PROM programming occurs in packaged form, it corrects for resistor shifts caused by the thermal stresses of packaging. These packaging shifts limit the accuracy that can be achieved using wafer level correction methods such as laser trimming, which has also been found to degrade the time stability of thin film resistors at the 14-bit level. Analog Section The ICL7134 inherently provides both unipolar and bipolar operation. The bipolar application circuit (Figure 6) requires one additional op-amp but no external resistors. The two on- chip resistors, RINV1 and RINV2, together with the op-amp, form a voltage inverter which drives the MSG reference ter- minal, VRFM, to -VREF, where VREF is the voltage applied at the less significant bits’ reference terminal, VRFL. Notice the values of 1.95R and 2R for the RINV1 and RINV2. The VRFM absolute value is about 2.5% higher than the VRFL. This is necessary so that the gain error can be corrected. This reverses the weight of the MSG, and gives the DAC a 2’s complement transfer function. The op-amp and reference connection to VRFM and VRFL can be reversed, without affecting linearity, but a small gain error will be introduced. For unipolar operation the VRFM and VRFL terminals are both tied to VREF, and the RINV pin is left unconnected. Since the PROM correction codes required are different for bipolar and unipolar operation, the ICL7134 is available in two different versions; the ICL7134U, which is corrected for unipolar operation, and the ICL7134B, which is programmed for bipolar application. The feedback resistance is also differ- ent in the two versions, and is switched under PROM control from ‘R’ in the unipolar device to ‘2R’ in the bipolar part. These feedback resistors have a dummy (always ON) switch in series to compensate for the effect of the ladder switches. This greatly improves the gain temperature coefficient and the power supply rejection of the device. FIGURE 6. BIPOLAR OPERATION WITH INVERTED VREF TO MSB ICL7134 |
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