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AD7876CR データシート(PDF) 8 Page - Analog Devices |
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AD7876CR データシート(HTML) 8 Page - Analog Devices |
8 / 20 page REV. B AD7870/AD7875/AD7876 –8– straight binary with 1 LSB = FS/4096 = 5 V/4096 = 1.22 mV. The ideal input/output transfer function is shown in Figure 7. Figure 5c. AD7875 Analog Input Figure 6. AD7870/AD7876 Transfer Function Figure 7. AD7875 Transfer Function OFFSET AND FULL-SCALE ADJUSTMENT—AD7870 In most digital signal processing (DSP) applications, offset and full-scale errors have little or no effect on system performance. Offset error can always be eliminated in the analog domain by ac coupling. Full-scale error effect is linear and does not cause problems as long as the input signal is within the full dynamic range of the ADC. Some applications will require that the input signal span the full analog input dynamic range. In such applica- tions, offset and full-scale error will have to be adjusted to zero. Where adjustment is required, offset error must be adjusted be- fore full-scale error. This is achieved by trimming the offset of the op amp driving the analog input of the AD7870 while the input voltage is 1/2 LSB below ground. The trim procedure is as follows: apply a voltage of –0.73 mV(–1/2 LSB) at V1 in Figure 8 and adjust the op amp offset voltage until the ADC output code flickers between 1111 1111 1111 and 0000 0000 0000. Gain error can be adjusted at either the first code transition (ADC negative full-scale) or the last code transition (ADC posi- tive full scale). The trim procedures for both cases are as follows (see Figure 8). Figure 8. Offset and Full-Scale Adjust Circuit Positive Full-Scale Adjust Apply a voltage of 2.9978 V (FS/2 – 3/2 LSBs) at V1. Adjust R2 until the ADC output code flickers between 0111 1111 1110 and 0111 1111 1111. Negative Full-Scale Adjust Apply a voltage of –2.9993 V (–FS/2 + 1/2 LSB) at V1 and ad- just R2 until the ADC output code flickers between 1000 0000 0000 and 1000 0000 0001. OFFSET AND FULL-SCALE ADJUSTMENT—AD7876 The offset and full-scale adjustment for the AD7876 is similar to that just outlined for the AD7870. The trim procedure, for those applications that do require adjustment, is as follows: apply a voltage of –2.44 mV (–1/2 LSB) at V1 and adjust the op amp offset voltage until the ADC output code flickers between 1111 1111 1111 and 0000 0000 0000. Full-scale error can be adjusted at either the first code transition (ADC negative full scale) or the last code transition (ADC positive full scale). The trim procedure for both case is as follows (see Figure 8): Positive Full-Scale Adjust Apply a voltage of 9.9927 V (FS/2 –3/2 LSBs) at V1. Adjust R2 until the ADC output code flickers between 0111 1111 1110 and 0111 1111 1111. Negative Full-Scale Adjust Apply a voltage of –9.9976 V (FS/2 + 1/2 LSB) at V1 and adjust R2 until the ADC output code flickers between 1000 0000 0000 and 1000 0000 0001. |
同様の部品番号 - AD7876CR |
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同様の説明 - AD7876CR |
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