Logarithmic resistor ladder


Posted on Feb 6, 2014

A logarithmic resistor ladder is an electronic circuit composed of a series of resistors and switches, designed to create an attenuation from an input to an output signal, where the logarithm of the attenuation ratio is proportional to a digital code word that represents the state of the switches. The logarithmic behavior of the circuit is its ma


Logarithmic resistor ladder
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in differentiator in comparison with digital-to-analog converters in general, and traditional R-2R Ladder networks specifically. Logarithmic attenuation is desired in situations where a large dynamic range needs to be handled. The circuit described in this article is applied in audio devices, since human perception of sound level is properly expressed on a logarithmic scale. As in digital-to-analog converters, a binary word is applied to the ladder network, whose N bits are treated to represent an integer value according the relation: This example circuit is composed of 4 stages, numbered 1 to 4, and an additional leading Rsource and trailing Rload. Each stage i, has a designed input-to-output voltage attenuation ratioi as: The different stages 1. N should function independently of each other, as to obtain 2N different states with a composable behavior. To achieve an attenuation of each stage that is independent of its surrounding stages, either one of two design choices is to be implemented: constant input resistance or constant output resistance. The circuit as depicted above, can also be applied in reverse direction. That correspondingly reverses the role of constant-input and constant-output resistance equations. Since the stages do not influence each other`s attenuation, the stage order can be chosen arbitrarily. Such reordering can have a significant effect on the input resistance of the constant output resistance...




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