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LINEAR_DAC_WITH_NONLINEAR_OUTPUT

2017-03-21 01:41  
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LINEAR_DAC_WITH_NONLINEAR_OUTPUT
When controlling a nonlinear device, such as an incandescent lamp, it is desirable to have fine resolution at the high end, where a small change in current can cause a large change in brightness.At the low end, coarser resolution is quite adequate. Using the circuit shown, any desired compression can be produced using just about any multiplying DAC. A negative 10-V reference is fed through R1 to inverting amplifier A1, which has an initial gain set to unity by R2. A1's output supplies a positive variable reference to the DAC. The DAC output provides additional feedback through R3, reducing the amplifier's gain as the DAC data increase. The variable reference is gradually reduced so that each step is progressively smaller than the one before. With the values shown, as the DAC data approaches full-scale; the reference approaches 1/4 of its original value. This produces output with four times as much resolution at the high end as at the low end. By decreasing the value of R3, greater compression and higher resolution can be achieved. The variable-reference output also can be useful in some applications.