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CACD Group updated 2000.03.30 Author Janez Puhan |
Logarithmic DC AmplifierThe circuitIn initial simulation stages, it is preferable to use idealized components in order to get the simulation going. Higher order nonlinearities and more realistic models can then be added as the simulation is refined. Also, by partitioning a complete system into several subsystems, localization of possible errors or problem areas can be made much easier. These factors lead us to the creation of an ideal op-amp. The idealized operational amplifier is a voltage controlled voltage source with infinite gain, infinite bandwidth, and an infinite input and output voltage swing. In the following example, a logarithmic transfer function is approximated by six piece-wise linear sections and an ideal op-amp. The input file (logarithmic_dc_amplifier.cir)logarithmic dc amplifier * v(3) = 6 + 4 log(v(1)) * y = 12.75 x ********* 0 < x < 0.3125 * y = 4 x + 2.7 ******* 0.3125 < x < 0.625 * y = 2 x + 3.91 ****** 0.625 < x < 1.25 * y = x + 5.16 ******** 1.25 < x < 2.5 * y = 0.5 x + 6.41 **** 2.5 < x < 5 * y = 0.219 x + 7.81 ** 5 < x < 10 * v(1) / r1 = v(3) / r7 + (v(3) - vd5) / r6 + (v(3) - vd4) / r5 + ************* (v(3) - vd3) / r4 + (v(3) - vd2) / r3 + (v(3) - vd1) / r2 .control dc v1 0 10V 0.05V plot v(3) xlabel v1[V] ylabel output[V] title 'DC analysis' .endc v1 0 1 dc 0 r1 1 2 10k r2 4 3 3.865k r3 5 3 10k r4 6 3 20.56k r5 7 3 39.35k r6 8 3 55.26k r7 3 2 127.5k eopamp 3 0 0 2 1meg d1 2 4 zener1 d2 2 5 zener2 d3 2 6 zener3 d4 2 7 zener4 d5 2 8 zener5 .model zener1 d bv=8.91V .model zener2 d bv=7.66V .model zener3 d bv=6.41V .model zener4 d bv=5.16V .model zener5 d bv=3.98V .end The results |
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