Patent ID: 6930532

Claim:
An exponential conversion circuit comprising: a first voltage conversion circuit for converting first and second reference voltages to first and second differential output voltages, respectively, on the basis of a first gain control signal; a first exponential conversion device for creating a first output current which changes exponentially with respect to the first differential output voltage; a second exponential conversion device for creating a second output current which changes exponentially with respect to the second differential output voltage; a first current comparison circuit for changing the first gain control signal in accordance with the ratio of the first and second output currents; a second voltage conversion circuit for converting a third reference input voltage and the first reference input voltage to third and fourth differential output voltages, respectively, on the basis of a second gain control signal; a third exponential conversion device for creating a third output current which changes exponentially with respect to the third differential output voltage; a fourth exponential conversion device for creating a fourth output current which changes exponentially with respect to the fourth differential output voltage; a second current comparison circuit for changing the second gain control signal in accordance with the ratio of the third and fourth output currents; a third voltage conversion circuit for converting the second reference input voltage and the third reference input voltage to fifth and sixth differential output voltages, respectively, on the basis of a third gain control signal; a voltage comparison circuit for creating the third gain control signal in accordance with the ratio of the fifth or sixth differential output voltage as against the second gain control signal; a fourth voltage conversion circuit for converting a control input voltage and the first reference input voltage to seventh and eighth differential output voltages, respectively, on the basis of the third gain control signal; a fifth voltage conversion circuit for converting the control input voltage and the first reference input voltage to a ninth differential output voltage on the basis of a fourth gain control signal; and a fifth exponential conversion device for creating a fifth output current which changes exponentially with respect to the ninth differential output voltage; wherein one of the seventh and eighth differential output voltages becomes the fourth gain control signal to change the fifth output current exponentially with respect to the control input voltage.